IPTEL Working Group J. Rosenberg, dynamicsoft
Internet Draft H. Salama, Cisco Systems
draft-ietf-iptel-trip-04.txt M. Squire, WindWire
November, 2000
Expires May 2001
Telephony Routing over IP (TRIP)
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Abstract
This document presents the Telephony Routing over IP (TRIP). TRIP is
a policy driven inter-administrative domain protocol for advertising
the reachability of telephony destinations between location servers,
and for advertising attributes of the routes to those destinations.
TRIP's operation is independent of any signaling protocol, hence
TRIP can serve as the telephony routing protocol for any signaling
protocol.
The Border Gateway Protocol (BGP-4) is used to distribute routing
information between administrative domains. TRIP is used to
distribute telephony routing information between telephony
administrative domains. The similarity between the two protocols is
obvious, and hence TRIP is modeled after BGP-4.
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Internet Draft Telephony Routing over IP November 2000
Table of Contents
Status of this Memo 1
Abstract 1
Table of Contents 2
1. Terminology 6
2. Introduction 6
3. Summary of Operation 8
3.1 Peering Session Establishment and Maintenance 8
3.2 Database Exchanges 8
3.3 Internal Versus External Synchronization 9
3.4 Advertising TRIP Routes 9
3.5 Telephony Routing Information Bases 10
4. Message Formats 12
4.1 Message Header Format 12
4.2 OPEN Message Format 13
4.2.1 Open Message Optional Parameters 15
4.2.1.1 Capability Information 15
4.2.1.1.1 Route Types Supported 16
4.2.1.1.2 Send Receive Capability 16
4.3 UPDATE Message Format 18
4.3.1 Routing Attributes 18
4.3.2 Attribute Flags 19
4.3.2.1 Attribute Flags and Route Selection 20
4.3.2.2 Attribute Flags and Route Dissemination 20
4.3.2.3 Attribute Flags and Route Aggregation 21
4.3.2.4 Attribute Flags and Encapsulation 22
4.3.3 Mandatory Attributes 22
4.3.4 TRIP UPDATE Attributes 22
4.3.4.1 WithdrawnRoutes 22
4.3.4.2 ReachableRoutes 23
4.3.4.3 NextHopServer 23
4.3.4.4 AdvertisementPath 23
4.3.4.5 RoutedPath 23
4.3.4.6 AtomicAggregate 23
4.3.4.7 LocalPreference 24
4.3.4.8 MultiExitDisc 24
4.3.4.9 Communities 24
4.3.4.10 ITAD Topology 24
4.3.4.11 ConvertedRoute 24
4.4 KEEPALIVE Message Format 24
4.5 NOTIFICATION Message Format 25
5. TRIP Attributes 26
5.1 WithdrawnRoutes 26
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5.1.1 Syntax of WithdrawnRoutes 27
5.1.1.1 Generic TRIP Route Format 27
5.1.1.2 Decimal Routing Numbers 28
5.1.1.3 HexaDecimal Routing Numbers 29
5.2 ReachableRoutes 29
5.2.1 Syntax of ReachableRoutes 30
5.2.2 Route Origination and ReachableRoutes 30
5.2.3 Route Selection and ReachableRoutes 30
5.2.4 Aggregation and ReachableRoutes 30
5.2.5 Route Dissemination and ReachableRoutes 30
5.2.6 Aggregation Specifics for Decimal Routing
Numbers and HexaDecimal Routing Numbers 31
5.3 NextHopServer 31
5.3.1 NextHopServer Syntax 31
5.3.2 Route Origination and NextHopServer 32
5.3.3 Route Selection and NextHopServer 32
5.3.4 Aggregation and NextHopServer 32
5.3.5 Route Dissemination and NextHopServer 32
5.4 AdvertisementPath 33
5.4.1 AdvertisementPath Syntax 33
5.4.2 Route Origination and AdvertisementPath 33
5.4.3 Route Selection and AdvertisementPath 34
5.4.4 Aggregation and AdvertisementPath 34
5.4.4.1 Aggregating Routes with Identical Paths 34
5.4.4.2 Aggregating Routes with Different Paths 34
5.4.4.3 Example Path Aggregation Algorithm 35
5.4.5 Route Dissemination and AdvertisementPath 36
5.5 RoutedPath 36
5.5.1 RoutedPath Syntax 37
5.5.2 Route Origination and RoutedPath 37
5.5.3 Route Selection and RoutedPath 37
5.5.4 Aggregation and RoutedPath 37
5.5.5 Route Dissemination and RoutedPath 37
5.6 AtomicAggregate 38
5.6.1 AtomicAggregate Syntax 38
5.6.2 Route Origination and AtomicAggregate 38
5.6.3 Route Selection and AtomicAggregate 38
5.6.4 Aggregation and AtomicAggregate 38
5.6.5 Route Dissemination and AtomicAggregate 39
5.7 LocalPreference 39
5.7.1 LocalPreference Syntax 39
5.7.2 Route Origination and LocalPreference 39
5.7.3 Route Selection and LocalPreference 39
5.7.4 Aggregation and LocalPreference 39
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5.7.5 Route Dissemination and LocalPreference 40
5.8 MultiExitDisc 40
5.8.1 MultiExitDisc Syntax 40
5.8.2 Route Origination and MultiExitDisc 40
5.8.3 Route Selection and MultiExitDisc 40
5.8.4 Aggregation and MultiExitDisc 40
5.8.5 Route Dissemination and MultiExitDisc 41
5.9 Communities 41
5.9.1 Syntax of Communities 42
5.9.2 Route Origination and Communities 43
5.9.3 Route Selection and Communities 43
5.9.4 Aggregation and Communities 43
5.9.5 Route Dissemination and Communities 43
5.10 ITAD Topology 43
5.10.1 ITAD Topology Syntax 44
5.10.2 Route Origination and ITAD Topology 44
5.10.3 Route Selection and ITAD Topology 44
5.10.4 Aggregation and ITAD Topology 45
5.10.5 Route Dissemination and ITAD Topology 45
5.11 ConvertedRoute 45
5.11.1 ConvertedRoute Syntax 45
5.11.2 Route Origination and ConvertedRoute 45
5.11.3 Route Selection and ConvertedRoute 45
5.11.4 Aggregation and ConvertedRoute 45
5.11.5 Route Dissemination and ConvertedRoute 45
5.12 Considerations for Defining New TRIP Attributes 46
6. TRIP Error Detection and Handling 46
6.1 Message Header Error Detection and Handling 46
6.2 OPEN Message Error Detection and Handling 47
6.3 UPDATE Message Error Detection and Handling 48
6.4 NOTIFICATION Message Error Detection and Handling 49
6.5 Hold Timer Expired Error Handling 50
6.6 Finite State Machine Error Handling 50
6.7 Cease 50
6.8 Connection Collision Detection 50
7. TRIP Version Negotiation 51
8. TRIP Capability Negotiation 51
9. TRIP Finite State Machine 52
10. UPDATE Message Handling 57
10.1 Flooding Process 58
10.1.1 Database Information 58
10.1.2 Determining Newness 58
10.1.3 Flooding 59
10.1.4 Sequence Number Considerations 59
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10.1.5 Purging a Route Within the ITAD 60
10.1.6 Receiving Self-Originated Routes 60
10.1.7 Removing Withdrawn Routes 60
10.2 Decision Process 61
10.2.1 Phase 1: Calculation of Degree of Preference 62
10.2.2 Phase 2: Route Selection 62
10.2.2.1 Breaking Ties (Phase 2) 63
10.2.3 Phase 3: Route Dissemination 64
10.2.4 Overlapping Routes 64
10.3 Update-Send Process 65
10.3.1 Internal Updates 65
10.3.1.1 Breaking Ties (Internal Updates) 66
10.3.2 External Updates 67
10.3.3 Controlling Routing Traffic Overhead 67
10.3.3.1 Frequency of Route Advertisement 67
10.3.3.2 Frequency of Route Origination 68
10.3.3.3 Jitter 68
10.3.4 Efficient Organization of Routing Information 68
10.3.4.1 Information Reduction 68
10.3.4.2 Aggregating Routing Information 69
10.4 Route Selection Criteria 70
10.5 Originating TRIP routes 70
11. TRIP Transport 70
12. ITAD Topology 71
13. IANA Considerations 71
13.1 TRIP Capabilities 71
13.2 TRIP Attributes 71
13.3 Destination Address Families 71
13.4 TRIP Application Protocols 72
13.5 ITAD Numbers 72
14. Security Considerations 72
15. Changes Since the Last Revision 73
Appendix 1. TRIP FSM State Transitions and Actions 74
Appendix 2. Implementation Recommendations 77
A.2.1. Multiple Networks Per Message 77
A.2.2. Processing Messages on a Stream Protocol 77
A.2.4. TRIP Timers 78
A.2.5. AP_SET Sorting 78
Acknowledgments 78
References 79
Authors' Addresses 80
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1. Terminology
A framework for a Telephony Routing over IP (TRIP) is described in
[1]. We assume the reader is familiar with the framework and
terminology of [1]. We define and use the following terms in
addition to those defined in [1].
Telephony Routing Information Base (TRIB): The database of reachable
telephony destinations built and maintained at an LS as a result of
its participation in TRIP.
IP Telephony Administrative Domain (ITAD): The set of resources
(gateways, location servers, etc.) under the control of a single
administrative authority. End users are customers of an ITAD.
Less/More Specific Route: A route X is said to be less specific than
a route Y if every destination in Y is also a destination in X, and
X and Y are not equal. In this case, Y is also said to be more
specific than X.
Peers: Two LSs that share a logical association (a transport
connection). If the LSs are in the same ITAD, they are internal
peers. Otherwise, they are external peers. The logical association
between two peer LSs is called a peering session.
Telephony Routing Information Protocol (TRIP): The protocol defined
in this specification. The function of TRIP is to advertise the
reachability of telephony destinations, attributes associated with
the destinations, as well as the attributes of the path towards
those destinations.
TRIP destination: TRIP can be used to manage routing tables for
multiple protocols (SIP, H323, etc.). In TRIP, a destination is the
combination of (a) a set of addresses (given by an address family
and address prefix), and (b) an application protocol (SIP, H323,
etc).
2. Introduction
The gateway location and routing problem has been introduced in [1].
It is considered one of the more difficult problems in IP telephony.
The selection of an egress gateway for a telephony call, traversing
an IP network towards an ultimate destination in the PSTN, is driven
in large part by the policies of the various parties along the path,
and by the relationships established between these parties. As such,
a global directory of egress gateways in which users look up
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destination phone numbers is not a feasible solution. Rather,
information about the availability of egress gateways is exchanged
between providers, and subject to policy, made available locally and
then propagated to other providers in other ITADs, thus creating
routes towards these egress gateways. This would allow each provider
to create its own database of reachable phone numbers and the
associated routes - such a database could be very different for each
provider depending on policy.
TRIP is an inter-domain (i.e., inter-ITAD) gateway location and
routing protocol. The primary function of a TRIP speaker, called a
location server (LS), is to exchange information with other LSs.
This information includes the reachability of telephony
destinations, the routes towards these destinations, and information
about gateways towards those telephony destinations residing in the
PSTN. The TRIP requirements are set forth in [1].
LSs exchange sufficient routing information to construct a graph of
ITAD connectivity so that routing loops may be prevented. In
addition, TRIP can be used to exchange attributes necessary to
enforce policies and to select routes based on path or gateway
characteristics. This specification defines TRIP's transport and
synchronization mechanisms, its finite state machine, and the TRIP
data. This specification defines the basic attributes of TRIP. The
TRIP attribute set is extendible, so additional attributes may be
defined in future drafts.
TRIP is modeled after the Border Gateway Protocol 4 (BGP-4) [2] and
enhanced with some link state features as in the Open Shortest Path
First (OSPF) protocol [3], IS-IS [4], and the Server Cache
Synchronization Protocol (SCSP) [5]. TRIP uses BGP's inter-domain
transport mechanism, BGP's peer communication, BGP's finite state
machine, and similar formats and attributes as BGP. Unlike BGP
however, TRIP permits generic intra-domain LS topologies, which
simplifies configuration and increases scalability in contrast to
BGP's full mesh requirement of internal BGP speakers. TRIP uses an
intra-domain flooding mechanism similar to that used in OSPF [3],
IS-IS [4], and SCSP [5].
TRIP permits aggregation of routes as they are advertised through
the network. TRIP does not define a specific route selection
algorithm.
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TRIP runs over a reliable transport protocol. This eliminates the
need to implement explicit fragmentation, retransmission,
acknowledgment, and sequencing. The error notification mechanism
used in TRIP assumes that the transport protocol supports a graceful
close, i.e., that all outstanding data will be delivered before the
connection is closed.
TRIP's operation is independent of any particular telephony
signaling protocol. Therefore, TRIP can be used as the routing
protocol for any of these protocols, e.g., H.323 [6] and SIP [7].
The LS peering topology is independent of the physical topology of
the network. In addition, the boundaries of ITAD are independent of
the boundaries of the layer 3 routing autonomous systems. Neither
internal nor external TRIP peers need be physically adjacent.
3. Summary of Operation
This section summarizes the operation of TRIP. Details are provided
in later sections.
3.1 Peering Session Establishment and Maintenance
Two peer LSs form a transport protocol connection between one
another. They exchange messages to open and confirm the connection
parameters, and to negotiate the capabilities of each LS as well as
the type of information to be advertised over this connection.
KeepAlive messages are sent periodically to ensure adjacent peers
are operational. Notification messages are sent in response to
errors or special conditions. If a connection encounters an error
condition, a Notification message is sent and the connection is
closed.
3.2 Database Exchanges
Once the peer connection has been established, the initial data flow
is a dump of all routes relevant to the new peer (In case of an
external peer, all routes in the LS's Adj-TRIB-Out for that external
peer. In case of an internal peer, all routes in the Ext-TRIB and
all Adj-TRIBs-In). Note that the different TRIBs are defined in
Section 3.5.
Incremental updates are sent as the TRIP routing tables (TRIBs)
change. TRIP does not require periodic refresh of the routes.
Therefore, an LS must retain the current version of all routing
entries.
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If a particular ITAD has multiple LSs and is providing transit
service for other ITADs, then care must be taken to ensure a
consistent view of routing within the ITAD. When synchronized the
TRIP routing tables, i.e., the Loc-TRIBs, of all internal peers are
identical.
3.3 Internal Versus External Synchronization
As with BGP, TRIP distinguishes between internal and external peers.
Within an ITAD, internal TRIP uses link-state mechanisms to flood
database updates over an arbitrary topology. Externally, TRIP uses
point-to-point peering relationships to exchange database
information.
To achieve internal synchronization, internal peer connections are
configured between LSs of the same ITAD such that the resulting
intra-domain LS topology is connected and sufficiently redundant.
This is different from BGP's approach that requires all internal
peers to be connected in a full mesh topology, which may result in
scaling problems. When an update is received from an internal peer,
the routes in the update are checked to determine if they are newer
than the version already in the database. Newer routes are then
flooded to all other peers in the same domain.
3.4 Advertising TRIP Routes
In TRIP, a route is defined as the combination of (a) a set of
destination addresses (given by an address family indicator and an
address prefix), and (b) an application protocol (e.g. SIP, H323,
etc.). Generally, there are additional attributes associated with
each route (for example, the next-hop server).
TRIP routes are advertised between a pair of LSs in UPDATE messages.
The destination addresses are included in the ReachableRoutes
attribute of the UPDATE, while other attributes describe things like
the path or egress gateway.
If an LS chooses to advertise the TRIP route, it may add to or
modify the attributes of the route before advertising it to a peer.
TRIP provides mechanisms by which an LS can inform its peer that a
previously advertised route is no longer available for use. There
are three methods by which a given LS can indicate that a route has
been withdrawn from service:
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Include the route in the WithdrawnRoutes Attribute in an UPDATE
message, thus marking the associated destinations as being no longer
available for use.
Advertise a replacement route with the same set of destinations in
the ReachableRoutes Attribute.
For external peers where flooding is not in use, the LS-to-LS peer
connection can be closed, which implicitly removes from service all
routes which the pair of LSs had advertised to each other over that
peer session. Note that terminating an internal peering session does
not necessarily remove the routes advertised by the peer LS as the
same routes may have been received from multiple internal peers
because of flooding. If an LS determines that the another internal
LS is no longer active (from the ITAD Topology attributes of the
UPDATE messages from other internal peers), then it MUST remove all
routes originated into the LS by that LS and rerun its decision
process.
3.5 Telephony Routing Information Bases
A TRIP LS processes three types of routes:
- External routes: An external route is a route received from an
external peer LS.
- Internal routes: An internal route is a route received from an
internal LS in the same ITAD.
- Local routes: A local route is a route locally injected into
TRIP, e.g. by configuration or by route redistribution from
another routing protocol.
The Telephony Routing Information Base (TRIB) within an LS consists
of four distinct parts:
- Adj-TRIBs-In: The Adj-TRIBs-In store routing information that has
been learned from inbound UPDATE messages. Their contents
represent TRIP routes that are available as an input to the
Decision Process. These are the 'unprocessed' routes received.
The routes from each external peer LS and each internal LS are
maintained in this database independently, so that updates from
one peer do not affect the routes received from another LS. Note
that there is an Adj-TRIBs-In for every LS within the domain, even
those with which the LS is not directly peering.
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- Ext-TRIB: There is only one Ext-TRIB database per LS. The LS runs
the route selection algorithm on all external routes (stored in
the Adj-TRIBs-In of the external peers) and local routes (may be
stored in an Adj-TRIB-In representing the local LS) and selects
the best route for a given destination and stores it in the Ext-
TRIB. The use of Ext-TRIB will be explained further in Section
10.3.1.
- Loc-TRIB: The Loc-TRIB contains the local TRIP routing
information that the LS has selected by applying its local
policies to the routing information contained in its Adj-TRIBs-In
of internal LSs and the Ext-TRIB.
- Adj-TRIBs-Out: The Adj-TRIBs-Out store the information that the
local LS has selected for advertisement to its external peers. The
routing information stored in the Adj-TRIBs-Out will be carried in
the local LS's UPDATE messages and advertised to its peers.
Figure 1 illustrates the relationship between the three parts of the
routing information base.
Loc-TRIB
/\
|
Decision Process
/\ /\ |
| | |
Adj-TRIBs-In | \/
(Internal LSs) | Adj-TRIBs-Out
|
|
|
Ext-TRIB
/\ /\
| |
Adj-TRIB-In Local Routes
(External Peers)
Figure 1: TRIB Relationships
Although the conceptual model distinguishes between Adj-TRIBs-In,
Loc-TRIB, and Adj-TRIBs-Out, this neither implies nor requires that
an implementation must maintain three separate copies of the routing
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information. The choice of implementation (for example, 3 copies of
the information vs. 1 copy with pointers) is not constrained by the
protocol.
4. Message Formats
This section describes message formats used by TRIP. Messages are
sent over a reliable transport protocol connection. A message MUST
be processed only after it is entirely received. The maximum message
size is 4096 octets. All implementations MUST support this maximum
message size. The smallest message that MAY be sent consists of a
TRIP header without a data portion, or 3 octets.
4.1 Message Header Format
Each message has a fixed-size header. There may or may not be a data
portion following the header depending on the message type. The
layout of the header fields is shown in Figure 2.
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+--------------+----------------+---------------+
| Length | Type |
+--------------+----------------+---------------+
Figure 2: TRIP Header
Length:
This 2-octet unsigned integer indicates the total length of the
message, including the header, in octets. Thus, it allows one to
locate in the transport-level stream the beginning of the next
message. The value of the Length field must always be at least 3 and
no greater than 4096, and may be further constrained depending on
the message type. No padding of extra data after the message is
allowed, so the Length field must have the smallest value possible
given the rest of the message.
Type:
This 1-octet unsigned integer indicates the type code of the
message. The following type codes are defined
1 - OPEN
2 - UPDATE
3 - NOTIFICATION
4 - KEEPALIVE
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4.2 OPEN Message Format
After a transport protocol connection is established, the first
message sent by each side is an OPEN message. If the OPEN message is
acceptable, a KEEPALIVE message confirming the OPEN is sent back.
Once the OPEN is confirmed, UPDATE, KEEPALIVE, and NOTIFICATION
messages may be exchanged.
The minimum length of the OPEN message is 14 octets (including
message header). OPEN messages not meeting this minimum requirement
are handled as defined in Section 6.2.
In addition to the fixed-size TRIP header, the OPEN message contains
the following fields:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+--------------+----------------+
| Version | Reserved | Hold Time |
+---------------+---------------+--------------+----------------+
| My ITAD |
+---------------+---------------+--------------+----------------+
| TRIP Identifier |
+---------------+---------------+--------------+----------------+
| Optional Parameters Len |Optional Parameters (variable)...
+---------------+---------------+--------------+----------------+
Figure 3: TRIP OPEN Header
Version:
This 1-octet unsigned integer indicates the protocol version of the
message. The current TRIP version number is 1.
Hold Time:
This 2-octet unsigned integer indicates the number of seconds that
the sender proposes for the value of the Hold Timer. Upon receipt of
an OPEN message, an LS MUST calculate the value of the Hold Timer by
using the smaller of its configured Hold Time and the Hold Time
received in the OPEN message. The Hold Time MUST be either zero or
at least three seconds. An implementation MAY reject connections on
the basis of the Hold Time. The calculated value indicates the
maximum number of seconds that may elapse between the receipt of
successive KEEPALIVE and/or UPDATE messages by the sender.
My ITAD:
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This 4-octet unsigned integer indicates the ITAD number of the
sender. The ITAD number must be unique for this domain within this
confederation of cooperating LSs.
ITAD numbers are assigned by IANA as specified in Section 13. This
document reserves ITAD numbers 0 and 65535. ITAD numbers from 1 to
255 are designated for private use.
TRIP Identifier:
This 4-octet unsigned integer indicates the TRIP Identifier of the
sender. The TRIP Identifier MUST uniquely identify this LS within
its ITAD. A given LS MAY set the value of its TRIP Identifier to an
IPv4 address assigned to that LS. The value of the TRIP Identifier
is determined on startup and MUST be the same for all peer
connections. When comparing two TRIP identifiers, the TRIP
Identifier is interpreted as a numerical 4-octet unsigned integer.
Optional Parameters Length:
This 2-octet unsigned integer indicates the total length of the
Optional Parameters field in octets. If the value of this field is
zero, no Optional Parameters are present.
Optional Parameters:
This field may contain a list of optional parameters, where each
parameter is encoded as a <Parameter Type, Parameter Length,
Parameter Value> triplet.
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+--------------+----------------+
| Parameter Type | Parameter Length |
+---------------+---------------+--------------+----------------+
| Parameter Value (variable)...
+---------------+---------------+--------------+----------------+
Figure 4 Optional Parameter Encoding
Parameter Type is a 2-octet field that unambiguously identifies
individual parameters.
Parameter Length is a 2-octet field that contains the length of the
Parameter Value field in octets.
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Parameter Value is a variable length field that is interpreted
according to the value of the Parameter Type field.
4.2.1 Open Message Optional Parameters
This document defines the following Optional Parameters for the OPEN
message.
4.2.1.1 Capability Information
Capability Information uses Optional Parameter type 1. This is an
optional parameter used by an LS to convey to its peer the list of
capabilities supported by the LS. This permits an LS to learn of
the capabilities of its peer LSs. Capability negotiation is defined
in Section 8.
The parameter contains one or more triples <Capability Code,
Capability Length, Capability Value>, where each triple is encoded
as shown below:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+--------------+----------------+
| Capability Code | Capability Length |
+---------------+---------------+--------------+----------------+
| Capability Value (variable)...
+---------------+---------------+--------------+----------------+
Figure 5 Capability Optional Parameter
Capability Code:
Capability Code is a 2-octet field that unambiguously identifies
individual capabilities.
Capability Length:
Capability Length is a 2-octet field that contains the length of the
Capability Value field in octets.
Capability Value:
Capability Value is a variable length field that is interpreted
according to the value of the Capability Code field.
Any particular capability, as identified by its Capability Code, may
appear more than once within the Optional Parameter.
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This document reserves Capability Codes 32768-65536 for vendor-
specific applications (these are the codes with the first bit of the
code value equal to 1). This document reserves value 0. Capability
Codes (other than those reserved for vendor specific use) are
controlled by IANA. See Section 13 for IANA considerations.
The following Capability Codes are defined by this specification:
Code Capability
1 Route Types Supported
2 Send Receive Capability
4.2.1.1.1 Route Types Supported
The Route Types Supported Capability Code lists the route types
supported in this peering session by the transmitting LS. An LS
MUST NOT use route types that are not supported by the peer LS in
any particular peering session. If the route types supported by a
peer are not satisfactory, an LS SHOULD terminate the peering
session. The format for a Route Type is:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+--------------+----------------+
| Address Family | Application Protocol |
+---------------+---------------+--------------+----------------+
Figure 6 Route Types Supported Capability
The Address Family and Application Protocol are as defined in
Section 5.1.1. Address Family gives the address family being routed
(within the ReachableRoutes attribute). The application protocol
lists the application for which the routes apply. As an example, a
route type for TRIP could be <POTS, SIP>, indicating a set of POTS
destinations for the SIP protocol.
The Route Types Supported Capability MAY contain multiple route
types in the capability. The number of route types within the
capability is the maximum number that can fit given the capability
length. The Capability Code is 1 and the length is variable.
4.2.1.1.2 Send Receive Capability
This capability specifies the mode in which the LS will operate with
this particular peer. The possible modes are: Send Only mode,
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Internet Draft Telephony Routing over IP November 2000
Receive Only mode, or Send Receive mode. The default mode is Send
Receive mode.
In Send Only mode, an LS transmits UPDATE messages to its peer, but
the peer MUST NOT transmit UPDATE messages to that LS. If an LS in
Send Only mode receives an UPDATE message from its peer, it MUST
discard that message, but no further action should be taken.
The UPDATE messages sent by an LS in Send Only mode to its intra-
domain peer MUST include the ITAD Topology attribute whenever the
topology changes. A useful application of an LS in Send Only mode
with an external peer is to enable gateway termination services.
If a service provider terminates calls to a set of gateways it owns,
but never initiates calls, it can set its LSs to operate in Send
Only mode, since they only ever need to generate UPDATE messages,
not receive them.
If an LS in Send Receive mode has a peering session with a peer in
Send Only mode, that LS MUST set its route dissemination policy such
that it does not send any UPDATE messages to its peer.
In Receive Only mode, the LS acts as a passive TRIP listener. It
receives and processes UPDATE messages from its peer, but it MUST
NOT transmit any UPDATE messages to its peer. This is useful for
management stations that wish to collect topology information for
display purposes.
The behavior of an LS in Send Receive mode is the default TRIP
operation specified throughout this document.
The Send Receive capability is a 4-octet unsigned numeric value. It
can only take one of the following three values:
1 - Send Receive mode
2 - Send only mode
3 - Receive Only mode
A peering session MUST NOT be established between two LSs, both of
them in either Send Only mode or in Receive Only mode. If a peer LS
detects such a capability mismatch when processing an OPEN message,
it MUST respond with a NOTIFICATION message and close the peer
session. The error code in the NOTIFICATION message must be set to
'Capability Mismatch.'
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An LS MUST be configured in the same Send Receive mode for all
peers.
4.3 UPDATE Message Format
UPDATE messages are used to transfer routing information between
LSs. The information in the UPDATE packet can be used to construct
a graph describing the relationships between the various ITADs. By
applying rules to be discussed, routing information loops and some
other anomalies can be prevented.
An UPDATE message is used to both advertise and withdraw routes from
service. An UPDATE message may simultaneously advertise and
withdraw TRIP routes.
In addition to the TRIP header, the TRIP UPDATE contains a list of
routing attributes as shown in Figure 7. There is no padding
between routing attributes.
+------------------------------------------------+--...
| First Route Attribute | Second Route Attribute | ...
+------------------------------------------------+--...
Figure 7: TRIP UPDATE Format
The minimum length of an UPDATE message 11 octets (the TRIP header
plus at least the WithdrawnRoutes and ReachableRoutes attributes).
4.3.1 Routing Attributes
A variable length sequence of routing attributes is present in every
UPDATE message. Each attribute is a triple <attribute type,
attribute length, attribute value> of variable length.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+--------------+----------------+
| Attr. Flags |Attr. Type Code| Attr. Length |
+---------------+---------------+--------------+----------------+
| Attribute Value (variable) |
+---------------+---------------+--------------+----------------+
Figure 8: Routing Attribute Format
Attribute Type is a two-octet field that consists of the Attribute
Flags octet followed by the Attribute Type Code octet.
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The Attribute Type Code defines the type of attribute. The basic
TRIP-defined Attribute Type Codes are discussed later in this
section. Attributes MUST appear in the UPDATE message in numerical
order of the Attribute Type Code. An attribute MUST NOT be included
more than once in the same UPDATE message. Attribute Flags are used
to control attribute processing when the attribute type is unknown.
Attribute Flags are further defined in Section 4.3.2.
This document reserves Attribute Type Codes 224-255 for vendor-
specific applications (these are the codes with the first three bits
of the code equal to 1). This document reserves value 0. Attribute
Type Codes (other than those reserved for vendor specific use) are
controlled by IANA. See Section 13 for IANA considerations.
The third and the fourth octets of the route attribute contain the
length of the attribute value field in octets.
The remaining octets of the attribute represent the Attribute Value
and are interpreted according to the Attribute Flags and the
Attribute Type Code. The basic supported attribute types, their
values, and their uses are defined in this specification. These are
the attributes necessary for proper loop free operation of TRIP,
both inter-domain and intra-domain. Additional attributes may be
defined in a future documents.
4.3.2 Attribute Flags
It is clear that the set of attributes for TRIP will evolve over
time. Hence it is essential that mechanisms be provided to handle
attributes with unrecognized types. The handling of unrecognized
attributes is controlled via the flags field of the attribute.
Recognized attributes should be processed according to their
specific definition.
The following are the attribute flags defined by this specification:
Bit Flag
0 Optional Flag
1 Transitive Flag
2 Dependent Flag
3 Partial Flag
4 Link-state Encapsulated Flag
The high-order bit (bit 0) of the Attribute Flags octet is the
Optional Bit. It defines whether the attribute is optional (if set
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to 1) or well-known (if set to 0). Implementations are not required
support optional attributes, but MUST support well-known attributes.
The second high-order bit (bit 1) of the Attribute Flags octet is
the Transitive bit. It defines whether an optional attribute is
transitive (if set to 1) or non-transitive (if set to 0). For well-
known attributes, the Transitive bit MUST be zero on transmit and
MUST be ignored on receipt.
The third high-order bit (bit 2) of the Attribute Flags octet is the
Dependent bit. It defines whether a transitive attribute is
dependent (if set to 1) or independent (if set to 0). For well-known
attributes and for non-transitive attributes, the Dependent bit is
irrelevant, and MUST be set to zero on transmit and MUST be ignored
on receipt.
The fourth high-order bit (bit 3) of the Attribute Flags octet is
the Partial bit. It defines whether the information contained in the
optional transitive attribute is partial (if set to 1) or complete
(if set to 0). For well-known attributes and for non-transitive
attributes the Partial bit MUST be set to 0 on transmit and MUST be
ignored on receipt.
The fifth high-order bit (bit 4) of the Attribute Flags octet is the
Link-state Encapsulation bit. This bit is only applicable to
certain attributes (ReachableRoutes and WithdrawnRoutes) and
determines the encapsulation of the routes within those attributes.
If this bit is set, link-state encapsulation is used within the
attribute. Otherwise, standard encapsulation is used within the
attribute. The Link-state Encapsulation technique is described in
Section 4.3.2.4. This flag is only valid on the ReachableRoutes and
WithdrawnRoutes attributes. It MUST be cleared on transmit and MUST
be ignored on receipt for all other attributes.
The other bits of the Attribute Flags octet are unused. They MUST be
zeroed on transmit and ignored on receipt.
4.3.2.1 Attribute Flags and Route Selection
Any recognized attribute can be used as input to the route selection
process, although the utility of some attributes in route selection
is minimal.
4.3.2.2 Attribute Flags and Route Dissemination
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TRIP provides for two variations of transitivity due to the fact
that intermediate LSs need not modify the NextHopServer when
propagating routes. Attributes may be non-transitive, dependent
transitive, or independent transitive. An attribute cannot be both
dependent transitive and independent transitive.
Unrecognized independent transitive attributes may be propagated by
any intermediate LS. Unrecognized dependent transitive attributes
MAY only be propagated if the LS is NOT changing the next-hop
server. The transitivity variations permit some unrecognized
attributes to be carried end-to-end (independent transitive), some
to be carried between adjacent next-hop servers (dependent
transitive), and other to be restricted to peer LSs (non-
transitive).
An LS that passes an unrecognized transitive attribute to a peer
MUST set the Partial flag on that attribute. Any LS along a path
MAY insert a transitive attribute into a route. If any LS except
the originating LS inserts a new independent transitive attribute
into a route, then it MUST set the Partial flag on that attribute.
If any LS except an LS that modifies the NextHopServer inserts a new
dependent transitive attribute into a route, then it MUST set the
Partial flag on that attribute. The Partial flag indicates that not
every LS along the relevant path has processed and understood the
attribute. For independent transitive attributes, the 'relevant
path' is the path given in the AdvertisementPath attribute. For
dependent transitive attributes, the relevant path consists only of
those domains thru which this object has passed since the
NextHopServer was last modified. The Partial flag in an independent
transitive attribute MUST NOT be unset by any other LS along the
path. The Partial flag in a dependent transitive attribute MUST be
reset whenever the NextHopServer is changed, but MUST NOT be unset
by any LS that is not changing the NextHopServer.
The rules governing the addition of new non-transitive attributes
are defined independently for each non-transitive attribute.
Any attribute MAY be updated by an LS in the path.
4.3.2.3 Attribute Flags and Route Aggregation
Each attribute defines how it is to be handled during route
aggregation.
The rules governing the handling of unknown attributes are guided by
the Attribute Flags. Unrecognized transitive attributes are dropped
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during aggregation. There should be no unrecognized non-transitive
attributes during aggregation because non-transitive attributes must
be processed by the local LS in order to be propagated.
4.3.2.4 Attribute Flags and Encapsulation
Normally attributes have the simple format as described in Section
4.3.1. If the Link-state Encapsulation Flag is set, then the two
additional fields are added to the attribute header as shown in
Figure 9.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+--------------+----------------+
| Attr. Flags |Attr. Type Code| Attr. Length |
+---------------+---------------+--------------+----------------+
| Originator TRIP Identifier |
+---------------+---------------+--------------+----------------+
| Sequence Number |
+---------------+---------------+--------------+----------------+
| Attribute Value (variable) |
+---------------+---------------+--------------+----------------+
Figure 9: Link State Encapsulation
The Originator TRIP ID and Sequence Number are used to control the
flooding of routing updates within a collection of servers. These
fields are used to detect duplicate and old routes so that they are
not further propagated within the servers. The use of these fields
is defined in Section 10.1.
4.3.3 Mandatory Attributes
Certain attributes are mandatory; they must be in every UPDATE
message. Mandatory attributes are identified in their definition.
By definition, mandatory attributes are also well-known. UPDATE
messages that do not include all mandatory attributes are discarded.
4.3.4 TRIP UPDATE Attributes
This section summarizes the attributes that may be carried in an
UPDATE message. Attributes MUST appear in the UPDATE message in
increasing order of the Attribute Type Code. Additional details are
provided in Section 5.
4.3.4.1 WithdrawnRoutes
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This attribute lists a set of routes that are being withdrawn from
service. The transmitting LS has determined that these routes
should no longer be advertised, and is propagating this information
to its peers.
4.3.4.2 ReachableRoutes
This attribute lists set of routes that are being added to service.
These routes will the potential to be inserted into the Adj-TRIBs-In
of the receiving LS and the route selection process will be applied
to them.
4.3.4.3 NextHopServer
This attribute gives the identity of the entity to which messages
should be sent along this routed path. It specifies the identity of
the next hop server as either a host domain name or an IP address.
It MAY optionally specify the UDP/TCP port number for the next hop
signaling server. If not specified, then the default port SHOULD be
used. The NextHopServer is specific to the set of destinations and
application protocol defined in the ReachableRoutes attribute. Note
that this is NOT the address to which media (voice, video, etc.)
should be transmitted, it is only for the application protocol as
given in the ReachableRoutes attribute.
4.3.4.4 AdvertisementPath
The AdvertisementPath is analogous to the AS_PATH in BGP4 [2]. The
attribute records the sequence of domains through which this
advertisement has passed. The attribute is used to detect when the
routing advertisement is looping. This attribute does NOT reflect
the path through which messages following this route would traverse.
Since the next-hop need not be modified by each LS, the actual path
to the destination might not have to traverse every domain in the
AdvertisementPath.
4.3.4.5 RoutedPath
The RoutedPath attribute is analogous to the AdvertisementPath
attribute, except that it records the actual path (given by the list
of domains) *to* the destinations. Unlike AdvertisementPath, which
is modified each time the route is propagated, RoutedPath is only
modified when the NextHopServer attribute changes. Thus, it records
the subset of the AdvertisementPath over which messages following
this particular route would traverse.
4.3.4.6 AtomicAggregate
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The AtomicAggregate attribute indicates that a route may actually
include domains not listed in the RoutedPath. If an LS, when
presented with a set of overlapping routes from a peer LS, selects a
less specific route without selecting the more specific route, then
the LS MUST include the AtomicAggregate attribute with the route.
An LS receiving a route with an AtomicAggregate attribute MUST NOT
make the set of destinations more specific when advertising it to
other LSs.
4.3.4.7 LocalPreference
The LocalPreference attribute is an intra-domain attribute used to
inform other LSs of the local LSs preference for a given route. The
preference of a route is calculated at the ingress to a domain and
passed as an attribute with that route throughout the domain. Other
LSs within the same ITAD use this attribute in their route selection
process. This attribute has no significance between domains.
4.3.4.8 MultiExitDisc
There may be more than one LS peering relationship between
neighboring domains. The MultiExitDisc attribute is used by an LS
to express a preference for one link between the domains over
another link between the domains. The use of the MultiExitDisc
attribute is controlled by local policy.
4.3.4.9 Communities
The Communities attribute is optional attribute used to facilitate
and simplify the control of routing information by grouping
destinations into communities.
4.3.4.10 ITAD Topology
The ITAD topology attribute is an intra-domain attribute that is
used by LSs to indicate their intra-domain topology to other LSs in
the domain.
4.3.4.11 ConvertedRoute
The ConvertedRoute attribute indicates that an intermediate LS has
altered the route by changing the route's Application Protocol.
4.4 KEEPALIVE Message Format
TRIP does not use any transport-based keep-alive mechanism to
determine if peers are reachable. Instead, KEEPALIVE messages are
exchanged between peers often enough as not to cause the Hold Timer
to expire. A reasonable maximum time between KEEPALIVE messages
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would be one third of the Hold Time interval. KEEPALIVE messages
MUST NOT be sent more than once every 3 seconds. An implementation
SHOULD adjust the rate at which it sends KEEPALIVE messages as a
function of the negotiated Hold Time interval.
If the negotiated Hold Time interval is zero, then periodic
KEEPALIVE messages MUST NOT be sent.
KEEPALIVE message consists of only message header and has a length
of 3 octets.
4.5 NOTIFICATION Message Format
A NOTIFICATION message is sent when an error condition is detected.
The TRIP transport connection is closed immediately after sending a
NOTIFICATION message
In addition to the fixed-size TRIP header, the NOTIFICATION message
contains the following fields:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+--------------+----------------+
| Error Code | Error Subcode | Data... (variable)
+---------------+---------------+--------------+----------------+
Figure 10: TRIP NOTIFICATION Format
Error Code:
This 1-octet unsigned integer indicates the type of NOTIFICATION.
The following Error Codes have been defined:
Error Code Symbolic Name Reference
1 Message Header Error Section 6.1
2 OPEN Message Error Section 6.2
3 UPDATE Message Error Section 6.3
4 Hold Timer Expired Section 6.5
5 Finite State Machine Error Section 6.6
6 Cease Section 6.7
Error Subcode:
This 1-octet unsigned integer provides more specific information
about the nature of the reported error. Each Error Code may have one
or more Error Subcodes associated with it. If no appropriate Error
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Subcode is defined, then a zero (Unspecific) value is used for the
Error Subcode field.
Message Header Error Subcodes:
1 - Bad Message Length.
2 - Bad Message Type.
OPEN Message Error Subcodes:
1 - Unsupported Version Number.
2 - Bad Peer ITAD.
3 - Bad TRIP Identifier.
4 - Unsupported Optional Parameter.
5 - Unacceptable Hold Time.
6 - Unsupported Capability.
7 - Capability Mismatch.
UPDATE Message Error Subcodes:
1 - Malformed Attribute List.
2 - Unrecognized Well-known Attribute.
3 - Missing Well-known Mandatory Attribute.
4 - Attribute Flags Error.
5 - Attribute Length Error.
6 - Invalid Attribute.
Data:
This variable-length field is used to diagnose the reason for the
NOTIFICATION. The contents of the Data field depend upon the Error
Code and Error Subcode.
Note that the length of the data can be determined from
the message length field by the formula:
Data Length = Message Length - 5
The minimum length of the NOTIFICATION message is 5 octets
(including message header).
5. TRIP Attributes
This section provides details on the syntax and semantics of each
TRIP UPDATE attribute.
5.1 WithdrawnRoutes
Mandatory: TRUE.
Required Flags: Well-known.
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Potential Flags: Link-State Encapsulation (when flooding).
Trip Type Code: 1
The WithdrawnRoutes attribute MUST be included in every UPDATE
message. It specifies a set of routes that are to be removed from
service by the receiving LS(s). The set of routes MAY be empty,
indicated by a length field of zero.
5.1.1 Syntax of WithdrawnRoutes
The WithdrawnRoutes Attribute encodes a sequence of routes in its
value field. The format for individual routes is given in Section
5.1.1.1. The WithdrawnRoutes Attribute lists the individual routes
sequentially with no padding as shown in Figure 11. Each route
includes a length field so that the individual routes within the
attribute can be delineated.
+---------------------+---------------------+...
| WithdrawnRoute1... | WithdrawnRoute2... |...
+---------------------+---------------------+...
Figure 11: WithdrawnRoutes Format
5.1.1.1 Generic TRIP Route Format
The generic format for a TRIP route is given in Figure 12.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+--------------+----------------+
| Address Family | Application Protocol |
+---------------+---------------+--------------+----------------+
| Length | Address (variable) ...
+---------------+---------------+--------------+----------------+
Figure 12: Generic TRIP Route Format
Address Family:
The address family field gives the type of address for the route.
Two address families are defined in this Section:
Code Address Family
1 Decimal
Decimal Routing Numbers
2 HexaDecimal Routing
Numbers
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This document reserves address family code 0. Additional address
families may be defined in the future. Assignment of address family
codes is controlled by IANA. See Section 13 for IANA
considerations.
Application Protocol:
The application protocol gives the protocol for which this routing
table is maintained. The currently defined application protocols
are:
Code Protocol
1 SIP
2 H.323-H.225.0-Q.931
3 H.323-H.225.0-RAS
4 H.323-H.225.0-Annex-G
This document reserves application protocol code 0. Additional
application protocols may be defined in the future. Assignment of
application protocol codes is controlled by IANA. See Section 13
for IANA considerations.
Length:
The length of the address field, in bytes.
Address:
This is an address (prefix) of the family type given by Address
Family. The octet length of the address is variable and is
determined by the length field of the route.
5.1.1.2 Decimal Routing Numbers
The Decimal Routing Numbers address family is a super set of all
E.164 numbers, national numbers, local numbers, and private numbers.
It can also be used to represent the decimal routing numbers used in
conjunction with Number Portability in some countries/regions. A set
of telephone numbers is specified by a Decimal Routing Number
prefix. Decimal Routing Number prefixes are represented by a string
of digits, each digit encoded by its ASCII character representation.
This routing object covers all phone numbers starting with this
prefix. The syntax for the Decimal Routing Number prefix is:
Decimal-routing-number = *decimal-digit
decimal-digit = DECIMAL-DIGIT
DECIMAL-DIGIT = '0'|'1'|'2'|'3'|'4'|'5'|'6'|'7'|'8'|'9'
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This DECIMAL Routing Number prefix is not bound in length. This
format is similar to the format for a global telephone number as
defined in SIP [7] without visual separators and without the '+'
prefix for international numbers. This format facilitates efficient
comparison when using TRIP to route SIP or H323, both of which use
character based representations of phone numbers. The prefix length
is determined from the length field of the route. The type of
Decimal Routing Number (private, local, national, or international)
can be deduced from the first few digits of the prefix.
5.1.1.3 HexaDecimal Routing Numbers
This address family is used to represent hexadecimal Routing Numbers
used in conjunction with Number Portability in some
countries/regions. Routing Number prefixes are represented by a
string of digits, each digit encoded by its ASCII character
representation. This routing object covers all routing numbers
starting with this prefix. The syntax for the HexaDecimal Routing
Number prefix is:
Hexadecimal-routing-number = *hexadecimal-digit
hexadecimal-routing-digit = HEXADECIMAL-DIGIT
HEXADECIMAL-DIGIT = '0'|'1'|'2'|'3'|'4'|'5'|'6'|'7'|
'8'|'9'|'A'|'B'|'C'|'D'|'E'|'F'
Note the difference in alphabets between Decimal Routing Numbers and
HexaDecimal Routing Numbers. A HexaDecimal Routing Number prefix is
not bound in length.
Note that the address family, which suits the routing numbers of a
specific country/region depends on the alphabets used for routing
numbers in that country/region. For example, North American routing
numbers SHOULD use the Decimal Routing Numbers address family,
because their alphabet is limited to the digits '0' through '9'.
Another example, in most European countries routing numbers use the
alphabet '0' through '9' and 'A' through 'F', and hence these
countries SHOULD use the HexaDecimal Routing Numbers address family.
5.2 ReachableRoutes
Mandatory: TRUE.
Required Flags: Well-known.
Potential Flags: Link-State Encapsulation (when flooding).
Trip Type Code: 2
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The ReachableRoutes attribute MUST be included in every UPDATE
message. It specifies a set of routes that are to be added to
service by the receiving LS(s). The set of routes MAY be empty,
this is indicated by setting the length field to zero.
5.2.1 Syntax of ReachableRoutes
The ReachableRoutes Attribute has the same syntax as the
WithdrawnRoutes Attribute. See Section 5.1.1.
5.2.2 Route Origination and ReachableRoutes
Routes are injected into TRIP by a method outside the scope of this
specification. Possible methods include a front-end protocol, an
intra-domain routing protocol, or static configuration.
5.2.3 Route Selection and ReachableRoutes
The routes in ReachableRoutes are necessary for route selection.
5.2.4 Aggregation and ReachableRoutes
To aggregate multiple routes, the set of ReachableRoutes to be
aggregated MUST combine to form a less specific set.
There is no mechanism within TRIP to communicate that a particular
address prefix is not used and thus that these addresses could be
skipped during aggregation. LSs MAY use methods outside of TRIP to
learn of invalid prefixes that may be ignored during aggregation.
If an LS advertises an aggregated route, it MUST include the
AtomicAggregate attribute.
5.2.5 Route Dissemination and ReachableRoutes
The ReachableRoutes attribute is recomputed at each LS except where
flooding is being used (e.g., within a domain). It is therefore
possible for an LS to change Application Protocol field of a route
before advertising that route to an external peer.
If an LS changes the Application Protocol of a route it advertises,
it MUST include the ConvertedRoute attribute in the UPDATE message.
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5.2.6 Aggregation Specifics for Decimal Routing Numbers and
HexaDecimal Routing Numbers
An LS that has routes to all valid numbers in a specific prefix
SHOULD advertise that prefix as the ReachableRoutes, even if there
are more specific prefixes that do not actually exist on the PSTN.
Generally, it takes 10 Decimal Routing prefixes, or 16 HexaDecimal
Routing prefixes, of length n to aggregate into a prefix of length
n-1. However, if an LS is aware that a prefix is an invalid Decimal
Routing prefix, or Hexadecimal Routing prefix, then the LS MAY
aggregate by skipping this prefix. For example, if the Decimal
Routing prefix 19191 is known not to exist, then an LS can aggregate
to 1919 without 19191. A prefix representing an invalid set of PSTN
destinations is sometimes referred to as a 'black-hole.' The
method by which an LS is aware of black-holes is not within the
scope of TRIP, but if an LS has such knowledge, it can use the
knowledge when aggregating.
5.3 NextHopServer
Mandatory: True.
Required Flags: Well-known.
Potential Flags: None.
TRIP Type Code: 3.
Given a route with application protocol A and destinations D, the
NextHopServer indicates the next-hop that messages of protocol A
destined for D should be sent. This may or may not represent the
ultimate destination of those messages.
5.3.1 NextHopServer Syntax
For generality, the address of the next-hop server may be of various
types (domain name, IPv4, IPv6, etc). The NextHopServer attribute
includes the ITAD number of next-hop server, a length field , and a
next-hop name or address.
The syntax for the NextHopServer is given in Figure 13.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+--------------+----------------+
| Next Hop ITAD |
+---------------+---------------+--------------+----------------+
| Length | Server (variable) ...
+---------------+---------------+--------------+----------------+
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Figure 13: NextHopServer Syntax
The Next-Hop ITAD indicates the domain of the next-hop. Length field
gives the number of octets in the Server field, and the Server field
contains the name or address of the next-hop server. The server
field is represented as a string of ASCII characters. It is defined
as follows:
Server = host [':' port ]
host = < A legal Internet host domain name
or an IPv4 address using the textual representation
defined in Section 2.1 of RFC 1123 [8]
or an IPv6 address using the textual representation
defined in Section 2.2 of RFC 2373 [9]. The IPv6
address MUST be enclosed in '[' and ']'
characters.>
port = *DIGIT
If the port is empty or not given, the default port is assumed
(e.g., port 5060 if the application protocol is SIP).
5.3.2 Route Origination and NextHopServer
When an LS originates a routing object into TRIP, it MUST include a
NextHopServer within its domain. The NextHopServer could be an
address of the egress gateway or of a signaling proxy.
5.3.3 Route Selection and NextHopServer
LS policy may prefer certain next-hops or next-hop domains over
others.
5.3.4 Aggregation and NextHopServer
When aggregating multiple routing objects into a single routing
object, an LS MUST insert a new signaling server from within its
domain as the new NextHopServer unless all of the routes being
aggregated have the same next-hop.
5.3.5 Route Dissemination and NextHopServer
When propagating routing objects to peers, an LS may choose to
insert a signaling proxy within its domain as the new next-hop, or
it may leave the next-hop unchanged. Inserting a new next-hop will
cause the signaling messages to be sent to that address, and will
provide finer control over the signaling path. Leaving the next-hop
unchanged will yield a more efficient signaling path (fewer hops).
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It is a local policy decision of the LS to decide whether to
propagate or change the NextHopServer.
5.4 AdvertisementPath
Mandatory: TRUE.
Required Flags: Well-known.
Potential Flags: None.
TRIP Type Code: 4.
This attribute identifies the ITADs through which routing
information carried in an advertisement has passed. The
AdvertisementPath attribute is analogous to the AS_PATH attribute in
BGP. The attributes differ in that BGP's AS_PATH also reflects the
path to the destination. In TRIP, not every domain need modify the
next-hop, so the AdvertisementPath may include many more hops than
the actual path to the destination. The RoutedPath attribute
(Section 5.5) reflects the actual path to the destination.
5.4.1 AdvertisementPath Syntax
AdvertisementPath is a variable length attribute that is composed of
a sequence of ITAD path segments. Each ITAD path segment is
represented by a type-length-value triple.
The path segment type is a 1-octet long field with the following
values defined:
Value Segment Type
1 AP_SET: unordered set of ITADs a route in the
advertisement message has traversed
2 AP_SEQUENCE: ordered set of ITADs a route in
the advertisement message has traversed
The path segment length is a 1-octet long field containing the
number of ITADs in the path segment value field.
The path segment value field contains one or more ITAD numbers, each
encoded as a 4-octets long field. ITAD numbers uniquely identify an
Internet Telephony Administrative Domain, and must be obtained from
IANA. See Section 13 for procedures to obtain an ITAD number from
IANA.
5.4.2 Route Origination and AdvertisementPath
When an LS originates a route then:
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- The originating LS shall include its own ITAD number in the
AdvertisementPath attribute of all advertisements sent to LSs
located in neighboring ITADs. In this case, the ITAD number of
the originating LS's ITAD will be the only entry in the
AdvertisementPath attribute.
- The originating LS shall include an empty AdvertisementPath
attribute in all advertisements sent to LSs located in its own
ITAD. An empty AdvertisementPath attribute is one whose length
field contains the value zero.
5.4.3 Route Selection and AdvertisementPath
The AdvertisementPath may be used for route selection. Possible
criteria to be used are the number of hops on the path and the
presence or absence of particular ITADs on the path.
As discussed in Section 10, the AdvertisementPath is used to prevent
routing information from looping. If an LS receives a route with
its own ITAD already in the AdvertisementPath, the route MUST be
discarded.
5.4.4 Aggregation and AdvertisementPath
The rules for aggregating AdvertisementPath attributes are given in
the following sections, where the term 'path' used in Section
5.4.4.1 and 5.4.4.2 is understood to mean AdvertisementPath.
5.4.4.1 Aggregating Routes with Identical Paths
If all routes to be aggregated have identical path attributes, then
the aggregated route has the same path attribute as the individual
routes.
5.4.4.2 Aggregating Routes with Different Paths
For the purpose of aggregating path attributes we model each ITAD
within the path as a pair <type, value>, where 'type' identifies a
type of the path segment (AP_SEQUENCE or AP_SET), and 'value' is the
ITAD number. Two ITADs are said to be the same if their
corresponding <type, value> are the same.
If the routes to be aggregated have different path attributes, then
the aggregated path attribute shall satisfy all of the following
conditions:
- All pairs of the type AP_SEQUENCE in the aggregated path MUST
appear in all of the paths of routes to be aggregated.
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- All pairs of the type AP_SET in the aggregated path MUST appear in
at least one of the paths of the initial set (they may appear as
either AP_SET or AP_SEQUENCE types).
- For any pair X of the type AP_SEQUENCE that precedes pair Y in the
aggregated path, X precedes Y in each path of the initial set that
contains Y, regardless of the type of Y.
- No pair with the same value shall appear more than once in the
aggregated path, regardless of the pair's type.
An implementation may choose any algorithm that conforms to these
rules. At a minimum a conformant implementation MUST be able to
perform the following algorithm that meets all of the above
conditions:
- Determine the longest leading sequence of tuples (as defined
above) common to all the paths of the routes to be aggregated.
Make this sequence the leading sequence of the aggregated path.
- Set the type of the rest of the tuples from the paths of the
routes to be aggregated to AP_SET, and append them to the
aggregated path.
- If the aggregated path has more than one tuple with the same value
(regardless of tuple's type), eliminate all but one such tuple by
deleting tuples of the type AP_SET from the aggregated path.
An implementation that chooses to provide a path aggregation
algorithm that retains significant amounts of path information may
wish to use the procedure of Section 5.4.4.3.
5.4.4.3 Example Path Aggregation Algorithm
An example algorithm to aggregate two paths works as follows:
- Identify the ITADs (as defined in Section 5.4.1) within each path
attribute that are in the same relative order within both path
attributes. Two ITADs, X and Y, are said to be in the same order
if either X precedes Y in both paths, or if Y precedes X in both
paths.
- The aggregated path consists of ITADs identified in (a) in exactly
the same order as they appear in the paths to be aggregated. If
two consecutive ITADs identified in (a) do not immediately follow
each other in both of the paths to be aggregated, then the
intervening ITADs (ITADs that are between the two consecutive
ITADs that are the same) in both attributes are combined into an
AP_SET path segment that consists of the intervening ITADs from
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both paths; this segment is then placed in between the two
consecutive ITADs identified in (a) of the aggregated attribute.
If two consecutive ITADs identified in (a) immediately follow each
other in one attribute, but do not follow in another, then the
intervening ITADs of the latter are combined into an AP_SET path
segment; this segment is then placed in between the two
consecutive ITADs identified in (a) of the aggregated path.
If as a result of the above procedure a given ITAD number appears
more than once within the aggregated path, all, but the last
instance (rightmost occurrence) of that ITAD number should be
removed from the aggregated path.
5.4.5 Route Dissemination and AdvertisementPath
When an LS propagates a route which it has learned from another LS,
it shall modify the route's AdvertisementPath attribute based on the
location of the LS to which the route will be sent.
- When a LS advertises a route to another LS located in its own
ITAD, the advertising LS MUST NOT modify the AdvertisementPath
attribute associated with the route.
- When a LS advertises a route to an LS located in a neighboring
ITAD, then the advertising LS MUST update the AdvertisementPath
attribute as follows:
- If the first path segment of the AdvertisementPath is of
type AP_SEQUENCE, the local system shall prepend its own
ITAD number as the last element of the sequence (put it in
the leftmost position).
- If the first path segment of the AdvertisementPath is of
type AP_SET, the local system shall prepend a new path
segment of type AP_SEQUENCE to the AdvertisementPath,
including its own ITAD number in that segment.
5.5 RoutedPath
Mandatory: True.
Required Flags: Well-known.
Potential Flags: None.
TRIP Type Code: 5.
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This attribute identifies the ITADs through which messages sent
using this route would pass. The ITADs in this path are a subset of
those in the AdvertisementPath.
5.5.1 RoutedPath Syntax
The syntax of the RoutedPath attribute is the same as that of the
AdvertisementPath attribute. See Section 5.4.1.
5.5.2 Route Origination and RoutedPath
When an LS originates a route it MUST include the RoutedPath
attribute.
- The originating LS shall include its own ITAD number in the
RoutedPath attribute of all advertisements sent to LSs located in
neighboring ITADs. In this case, the ITAD number of the
originating LS's ITAD will be the only entry in the RoutedPath
attribute.
- The originating LS shall include an empty RoutedPath attribute in
all advertisements sent to LSs located in its own ITAD. An empty
RoutedPath attribute is one whose length field contains the value
zero.
5.5.3 Route Selection and RoutedPath
The RoutedPath MAY be used for route selection, and in most cases is
preferred over the AdvertisementPath for this role. Some possible
criteria to be used are the number of hops on the path and the
presence or absence of particular ITADs on the path.
5.5.4 Aggregation and RoutedPath
The rules for aggregating RoutedPath attributes are given in Section
5.4.4.1 and 5.4.4.2, where the term 'path' used in Section 5.4.4.1
and 5.4.4.2 is understood to mean RoutedPath.
5.5.5 Route Dissemination and RoutedPath
When an LS propagates a route that it learned from another LS, it
modifies the route's RoutedPath attribute based on the location of
the LS to which the route is sent.
- When a LS advertises a route to another LS located in its own
ITAD, the advertising LS MUST NOT modify the RoutedPath attribute
associated with the route.
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- If the LS has not changed the NextHopServer attribute, then the LS
MUST NOT change the RoutedPath attribute.
- Otherwise, the LS changed the NextHopServer and is advertising the
route to an LS in another ITAD. The advertising LS MUST update
the RoutedPath attribute as follows:
- If the first path segment of the RoutedPath is of type
AP_SEQUENCE, the local system shall prepend its own ITAD
number as the last element of the sequence (put it in the
leftmost position).
- If the first path segment of the RoutedPath is of type
AP_SET, the local system shall prepend a new path segment of
type AP_SEQUENCE to the RoutedPath, including its own ITAD
number in that segment.
5.6 AtomicAggregate
Mandatory: False.
Required Flags: Well-known.
Potential Flags: None.
TRIP Type Code: 6.
The AtomicAggregate attribute indicates that a route may traverse
domains not listed in the RoutedPath. If an LS, when presented with
a set of overlapping routes from a peer LS, selects the less
specific route without selecting the more specific route, then the
LS includes the AtomicAggregate attribute with the routing object.
5.6.1 AtomicAggregate Syntax
This attribute has length zero (0); the value field is empty.
5.6.2 Route Origination and AtomicAggregate
Routes are never originated with the AtomicAggregate attribute.
5.6.3 Route Selection and AtomicAggregate
The AtomicAggregate attribute may be used in route selection - it
indicates that the RoutedPath may be incomplete.
5.6.4 Aggregation and AtomicAggregate
If any of the routes to aggregate has the AtomicAggregate attribute,
then so MUST the resultant aggregate.
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5.6.5 Route Dissemination and AtomicAggregate
If an LS, when presented with a set of overlapping routes from a
peer LS, selects the less specific route (see Section 0) without
selecting the more specific route, then the LS MUST include the
AtomicAggregate attribute with the routing object (if it is not
already present).
An LS receiving a routing object with an AtomicAggregate attribute
MUST NOT make the set of destinations more specific when advertising
it to other LSs, and MUST NOT remove the attribute when propagating
this object to a peer LS.
5.7 LocalPreference
Mandatory: False.
Required Flags: Well-known.
Potential Flags: None.
TRIP Type Code: 7.
The LocalPreference attribute is only used intra-domain, it
indicates the local LS's preference for the routing object to other
LSs within the same domain. This attribute MUST NOT be included
when communicating to an LS in another domain, and MUST be included
over intra-domain links.
5.7.1 LocalPreference Syntax
The LocalPreference attribute is a 4-octet unsigned numeric value.
A higher value indicates a higher preference.
5.7.2 Route Origination and LocalPreference
Routes MUST NOT be originated with the LocalPreference attribute to
inter-domain peers. Routes to intra-domain peers MUST be originated
with the LocalPreference attribute.
5.7.3 Route Selection and LocalPreference
The LocalPreference attribute allows one LS in a domain to calculate
a preference for a route, and to communicate this preference to
other LSs within the domain.
5.7.4 Aggregation and LocalPreference
The LocalPreference attribute is not affected by aggregation.
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5.7.5 Route Dissemination and LocalPreference
An LS MUST include the LocalPreference attribute when communicating
with peer LSs within its own domain. An LS MUST NOT include the
LocalPreference attribute when communicating with LSs in other
domains. LocalPreference attributes received from inter-domain
peers MUST be ignored.
5.8 MultiExitDisc
Mandatory: False.
Required Flags: Well-known.
Potential Flags: None.
TRIP Type Code: 8.
When two ITADs are connected by more than one set of peers, the
MultiExitDisc attribute may be used to specify preferences for
routes received over one of those links versus routes received over
other links. The MultiExitDisc parameter is used only for route
selection.
5.8.1 MultiExitDisc Syntax
The MultiExitDisc attribute carries a 4-octet unsigned numeric
value. A higher value represents a more preferred routing object.
5.8.2 Route Origination and MultiExitDisc
Routes originated to intra-domain peers MUST NOT be originated with
the MultiExitDisc attribute. When originating a route to an inter-
domain peer, the MultiExitDisc attribute may be included.
5.8.3 Route Selection and MultiExitDisc
The MultiExitDisc attribute is used to express a preference when
there are multiple links between two domains. If all other factors
are equal, then a route with a higher MultiExitDisc attribute is
preferred over a route with a lower MultiExitDisc attribute.
5.8.4 Aggregation and MultiExitDisc
Routes with differing MultiExitDisc parameters MUST NOT be
aggregated. Routes with the same value in the MultiExitDisc
attribute MAY be aggregated and the same MultiExitDisc attribute
attached to the aggregated object.
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5.8.5 Route Dissemination and MultiExitDisc
If received from a peer LS in another domain, an LS MAY propagate
the MultiExitDisc to other LSs within its domain. The MultiExitDisc
attribute MUST NOT be propagated to LSs in other domains.
An LS may add the MultiExitDisc attribute when propagating routing
objects to an LS in another domain. The inclusion of the
MultiExitDisc attribute is a matter of policy, as is the value of
the attribute.
5.9 Communities
Mandatory: FALSE
Required Flags: Optional, Independent Transitive
Potential Flags: None
TRIP Type Code: 9.
A community is a group of destinations that share some common
property.
The Communities attribute is used to group destinations so that the
routing decision can be based on the identity of the group. Using
the Communities attribute should significantly simplify the
distribution of routing information by providing an administratively
defined aggregation unit.
Each ITAD administrator may define the communities to which a
particular route belongs. By default, all routes belong to the
general Internet Telephony community.
As an example, the Communities attribute could be used to define an
alliance between a group of Internet Telephony service providers for
a specific subset of routing information. In this case, members of
that alliance would accept only routes for destinations in this
group that are advertised by other members of the alliance. Other
destinations would be more freely accepted. To achieve this, a
member would tag each route with a designated Community attribute
value before disseminating it. This relieves the members of such an
alliance from the responsibility of keeping track of the identities
of all other members of that alliance.
Another example use of the Communities attribute is with
aggregation. It is often useful to advertise both the aggregate
route and the component more-specific routes that were used to form
the aggregate. These component information are only useful to the
neighboring TRIP peer, and perhaps the ITAD of the neighboring TRIP
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peer, so it is desirable to filter out the component routes. This
can be achieved by specifying a Community attribute value that the
neighboring peers will match and filter on. That way it can be
assured that the more specific routes will not propagate beyond
their desired scope.
5.9.1 Syntax of Communities
The Communities attribute is of variable length. It consists of set
of 8-octet values, each of which specifies a community. The first 4
octets of the Community value are the Community ITAD Number and the
next 4 octets are the Community ID.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+--------------+----------------+
| Community ITAD Number 1 |
+---------------+---------------+--------------+----------------+
| Community ID 1 |
+---------------+---------------+--------------+----------------+
| . . . . . . . . .
+---------------+---------------+--------------+----------------+
Figure 14: Communities Syntax
For administrative assignment, the following assumptions may be
made:
The Community attribute values starting with a Community ITAD Number
of 0x00000000 are hereby reserved.
The following communities have global significance and their
operation MUST be implemented in any Community attribute-aware TRIP
LS.
- NO_EXPORT (Community ITAD Number = 0x00000000 and
Community ID = 0xFFFFFF01). Any received route with a
community attribute containing this value MUST NOT be
advertised outside of the receiving TRIP ITAD.
Other community values MUST be encoded using an ITAD number in the
four most significant octets. The semantics of the final four octets
(the Community ID octets) may be defined by the ITAD (e.g., ITAD 690
may define research, educational, and commercial community IDs that
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may be used for policy routing as defined by the operators of that
ITAD).
5.9.2 Route Origination and Communities
The Communities attribute is optional. If a route has a Communities
attribute associated with it, the LS MUST include that attribute in
advertisement it originates.
5.9.3 Route Selection and Communities
The Communities attribute may be used for route selection. A route
that is a member of a certain community may be preferred over
another route that is not a member of that community. Likewise,
routes without a certain community value may be excluded from
consideration.
5.9.4 Aggregation and Communities
If a set of routes is to be aggregated and the resultant aggregate
does not carry an Atomic_Aggregate attribute, then the resulting
aggregate should have a Communities attribute that contains the
union of the Community attributes of the aggregated routes.
5.9.5 Route Dissemination and Communities
An LS may manipulate the Communities attribute before disseminating
a route to a peer. Community attribute manipulation may include
adding communities, removing communities, adding a Communities
attribute (if none exists), deleting the Communities attribute, etc.
5.10 ITAD Topology
Mandatory: False.
Required Flags: Well-known, Link-State encapsulated.
Potential Flags: None.
TRIP Type Code: 10.
Within an ITAD, each LS must know the status of other LSs so that LS
failure can be detected. To do this, each LS advertises its
internal topology to other LSs within the domain. When an LS
detects that another LS is no longer active, the information sourced
by that LS can be deleted (the Adj-TRIB-In for that peer may be
cleared). The ITAD Topology attribute is used to communicate this
information to other LSs within the domain.
An LS MUST send a topology update each time it detects a change in
its internal peer set. The topology update may be sent in an PDATE
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message by itself or it may be piggybacked on an UPDATE message
which includes ReachableRoutes and/or WithdrawnRoutes information.
When an LS receives a topology update from an internal LS, it MUST
recalculate to which LSs are active within their domain via a
connectivity algorithm on the topology.
5.10.1 ITAD Topology Syntax
The ITAD Topology attribute indicates the LSs with which the LS is
currently peering. The attribute consists of a list of the TRIP
Identifiers with which the LS is currently peering, the format is
given in
Figure 15. This attribute MUST use the link-state encapsulation as
defined in Section 4.3.2.4.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+--------------+----------------+
| TRIP Identifier 1 |
+---------------+---------------+--------------+----------------+
| TRIP Identifier 2 ... |
+---------------+---------------+--------------+----------------+
Figure 15: ITAD Topology Syntax
5.10.2 Route Origination and ITAD Topology
The ITAD Topology attribute is independent of any routes in the
UPDATE. Whenever the set of internal peers of a LS changes, it MUST
originate an UPDATE with the ITAD Topology Attribute included
listing the current set of internal peers. The LS MUST include
this attribute in the first UPDATE it sends to a peer after the
peering session is established.
5.10.3 Route Selection and ITAD Topology
This attribute is independent of any routing information in the
UPDATE. When an LS receives an UPDATE with an ITAD Topology
attribute, it MUST compute the set of LSs currently active in the
domain by performing a connectivity test on the ITAD topology as
given by the set of originated ITAD Topology attributes. The LS
MUST locally purge the Adj-TRIB-In for any LS that is no longer
active in the domain. The LS MUST NOT propagate this purging
information to other LSs as they will make a similar decision.
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5.10.4 Aggregation and ITAD Topology
This information is not aggregated.
5.10.5 Route Dissemination and ITAD Topology
An LS MUST ignore the attribute if received from a peer in another
domain. An LS MUST NOT send this attribute to an inter-domain peer.
5.11 ConvertedRoute
Mandatory: False.
Required Flags: Well-known.
Potential Flags: None.
TRIP Type Code: 12.
The ConvertedRoute attribute indicates that an intermediate LS has
altered the route by changing the route's Application Protocol. For
example, if an LS receives a route with Application Protocol X and
changes the Application Protocol to Y before advertising the route
to an external peer, the LS MUST include the ConvertedRoute
attribute. The attribute is an indication that the advertised
application protocol will not be used end-to-end, i.e., the
information advertised about this route is not complete.
5.11.1 ConvertedRoute Syntax
This attribute has length zero (0); the value field is empty.
5.11.2 Route Origination and ConvertedRoute
Routes are never originated with the ConvertedRoute attribute.
5.11.3 Route Selection and ConvertedRoute
The ConvertedRoute attribute may be used in route selection - it
indicates that advertised routing information is not complete.
5.11.4 Aggregation and ConvertedRoute
If any of the routes to aggregate has the ConvertedRoute attribute,
then so MUST the resultant aggregate.
5.11.5 Route Dissemination and ConvertedRoute
If an LS changes the Application Protocol of route before
advertising the route to an external peer, the LS MUST include the
ConvertedRoute attribute.
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5.12 Considerations for Defining New TRIP Attributes
Any proposal for defining new TRIP attributes should specify the
following:
- the use of this attribute,
- the attribute's flags,
- the attribute's syntax,
- how the attribute works with route origination,
- how the attribute works with route aggregation, and
- how the attribute works with route dissemination and the
attribute's scope (e.g., intra-domain only like LocalPreference)
IANA will manage the assignment of TRIP attribute type codes to new
attributes.
6. TRIP Error Detection and Handling
This section describes errors to be detected and the actions to be
taken while processing TRIP messages.
When any of the conditions described here are detected, a
NOTIFICATION message with the indicated Error Code, Error Subcode,
and Data fields MUST be sent, and the TRIP connection MUST be
closed. If no Error Subcode is specified, then a zero Subcode MUST
be used.
The phrase 'the TRIP connection is closed' means that the transport
protocol connection has been closed and that all resources for that
TRIP connection have been de-allocated. If the connection was
inter-domain, then routing table entries associated with the remote
peer MUST be marked as invalid. Routing table entries MUST NOT be
marked as invalid if an internal peering session is terminated. The
fact that the routes have been marked as invalid is passed to other
TRIP peers before the routes are deleted from the system.
Unless specified explicitly, the Data field of the NOTIFICATION
message that is sent to indicate an error MUST be empty.
6.1 Message Header Error Detection and Handling
All errors detected while processing the Message Header are
indicated by sending the NOTIFICATION message with Error Code
Message Header Error. The Error Subcode elaborates on the specific
nature of the error. The error checks in this section MUST be
performed by each LS on receipt of every message.
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If the Length field of the message header is less than 3 or greater
than 4096, or if the Length field of an OPEN message is less than
the minimum length of the OPEN message, or if the Length field of an
UPDATE message is less than the minimum length of the UPDATE
message, or if the Length field of a KEEPALIVE message is not equal
to 3, or if the Length field of a NOTIFICATION message is less than
the minimum length of the NOTIFICATION message, then the Error
Subcode MUST be set to Bad Message Length. The Data field contains
the erroneous Length field.
If the Type field of the message header is not recognized, then the
Error Subcode MUST be set to 'Bad Message Type.' The Data field
contains the erroneous Type field.
6.2 OPEN Message Error Detection and Handling
All errors detected while processing the OPEN message are indicated
by sending the NOTIFICATION message with Error Code 'OPEN Message
Error.' The Error Subcode elaborates on the specific nature of the
error. The error checks in this section MUST be performed by each LS
on receipt of every OPEN message.
If the version number contained in the Version field of the received
OPEN message is not supported, then the Error Subcode MUST be set to
'Unsupported Version Number.' The Data field is a 1-octet unsigned
integer, which indicates the largest locally supported version
number less than the version the remote TRIP peer bid (as indicated
in the received OPEN message).
If the ITAD field of the OPEN message is unacceptable, then the
Error Subcode MUST be set to 'Bad Peer ITAD.' The determination of
acceptable ITAD numbers is outside the scope of this protocol.
If the Hold Time field of the OPEN message is unacceptable, then the
Error Subcode MUST be set to 'Unacceptable Hold Time.' An
implementation MUST reject Hold Time values of one or two seconds.
An implementation MAY reject any proposed Hold Time. An
implementation that accepts a Hold Time MUST use the negotiated
value for the Hold Time.
If the TRIP Identifier field of the OPEN message is not valid, then
the Error Subcode MUST be set to 'Bad TRIP Identifier.' A TRIP
identifier is 4-octets and can take any value. An LS considers the
TRIP Identifier invalid if it has an already open connection with
another peer LS that has the same ITAD and TRIP Identifier.
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Any two LSs within the same ITAD MUST NOT have equal TRIP Identifier
values. This restriction does not apply to LSs in differrent ITADs
since the purpose is to uniquely identify an LS using its TRIP
Identifier and its ITAD number.
If one of the Optional Parameters in the OPEN message is not
recognized, then the Error Subcode MUST be set to 'Unsupported
Optional Parameters.'
If the Optional Parameters of the OPEN message include Capability
Information with an unsupported capability (unsupported in either
capability type or value), then the Error Subcode MUST be set to
'Unsupported Capability,' and the entirety of the unsupported
capabilities MUST be listed in the Data field of the NOTIFICATION
message.
If the Optional Parameters of the OPEN message include Capability
Information which do not match the receiving LS's capabilities, then
the Error Subcode MUST be set to 'Capability Mismatch,' and the
entirety of the mismatched capabilities MUST be listed in the Data
field of the NOTIFICATION message.
6.3 UPDATE Message Error Detection and Handling
All errors detected while processing the UPDATE message are
indicated by sending the NOTIFICATION message with Error Code
'UPDATE Message Error.' The Error Subcode elaborates on the specific
nature of the error. The error checks in this section MUST be
performed by each LS on receipt of every UPDATE message. These
error checks MUST occur before flooding procedures are invoked with
internal peers.
If any recognized attribute has Attribute Flags that conflict with
the Attribute Type Code, then the Error Subcode MUST be set to
'Attribute Flags Error.' The Data field contains the erroneous
attribute (type, length and value).
If any recognized attribute has Attribute Length that conflicts with
the expected length (based on the attribute type code), then the
Error Subcode MUST be set to 'Attribute Length Error.' The Data
field contains the erroneous attribute (type, length and value).
If any of the mandatory well-known attributes are not present, then
the Error Subcode MUST be set to 'Missing Well-known Mandatory
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Attribute.' The Data field contains the Attribute Type Code of the
missing well-known mandatory attributes.
If any of the well-known attributes are not recognized, then the
Error Subcode MUST be set to 'Unrecognized Well-known Attribute.'
The Data field contains the unrecognized attribute (type, length and
value).
If any attribute has a syntactically incorrect value, or an
undefined value, then the Error Subcode is set to 'Invalid
Attribute.' The Data field contains the incorrect attribute (type,
length and value). Such a NOTIFICATION message is sent, for example,
when a NextHopServer attribute is received with an invalid address.
The information carried by the AdvertisementPath attribute is
checked for ITAD loops. ITAD loop detection is done by scanning the
full AdvertisementPath, and checking that the ITAD number of the
local ITAD does not appear in the AdvertisementPath. If the local
ITAD number appears in the AdvertisementPath, then the route MAY be
stored in the Adj-TRIB-In, but unless the LS is configured to accept
routes with its own ITAD in the advertisement path, the route MUST
not be passed to the TRIP Decision Process. The operation of an LS
that is configured to accept routes with its own ITAD number in the
advertisement path are outside the scope of this document.
If the UPDATE message was received from an internal peer and either
the WithdrawnRoutes, ReachableRoutes, or ITAD Topology attribute
does not have the Link-State Encapsulation flag set, then the Error
Subcode is set to 'Invalid Attribute' and the data field contains
the attribute. Likewise, the attribute is invalid if received from
an external peer and the Link-State Flag is set.
If any attribute appears more than once in the UPDATE message, then
the Error Subcode is set to 'Malformed Attribute List.'
6.4 NOTIFICATION Message Error Detection and Handling
If a peer sends a NOTIFICATION message, and there is an error in
that message, there is unfortunately no means of reporting this
error via a subsequent NOTIFICATION message. Any such error, such as
an unrecognized Error Code or Error Subcode, should be noticed,
logged locally, and brought to the attention of the administration
of the peer. The means to do this, however, are outside the scope of
this document.
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6.5 Hold Timer Expired Error Handling
If a system does not receive successive messages within the period
specified by the negotiated Hold Time, then a NOTIFICATION message
with 'Hold Timer Expired' Error Code MUST be sent and the TRIP
connection MUST be closed.
6.6 Finite State Machine Error Handling
An error detected by the TRIP Finite State Machine (e.g., receipt of
an unexpected event) MUST result in sending a NOTIFICATION message
with Error Code 'Finite State Machine Error' and the TRIP connection
MUST be closed.
6.7 Cease
In the absence of any fatal errors (that are indicated in this
section), a TRIP peer MAY choose at any given time to close its TRIP
connection by sending the NOTIFICATION message with Error Code
'Cease.' However, the Cease NOTIFICATION message MUST NOT be used
when a fatal error indicated by this section exists.
6.8 Connection Collision Detection
If a pair of LSs try simultaneously to establish a transport
connection to each other, then two parallel connections between this
pair of speakers might well be formed. We refer to this situation as
connection collision. Clearly, one of these connections must be
closed.
Based on the value of the TRIP Identifier a convention is
established for detecting which TRIP connection is to be preserved
when a collision occurs. The convention is to compare the TRIP
Identifiers of the peers involved in the collision and to retain
only the connection initiated by the LS with the higher-valued TRIP
Identifier.
Upon receipt of an OPEN message, the local LS MUST examine all of
its connections that are in the OpenConfirm state. An LS MAY also
examine connections in an OpenSent state if it knows the TRIP
Identifier of the peer by means outside of the protocol. If among
these connections there is a connection to a remote LS whose TRIP
Identifier equals the one in the OPEN message, then the local LS
MUST perform the following collision resolution procedure:
The TRIP Identifier and ITAD of the local LS is compared to the TRIP
Identifier and ITAD of the remote LS (as specified in the OPEN
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message). TRIP Identifiers are treated as 4-octet unsigned integers
for comparison.
If the value of the local TRIP Identifier is less than the remote
one, or if the two TRIP Identifiers are equal and the value of ITAD
of the local LS is less than value of the ITAD of the remote LS,
then the local LS MUST close the TRIP connection that already exists
(the one that is already in the OpenConfirm state), and accepts the
TRIP connection initiated by the remote LS:
1. Otherwise, the local LS closes newly created TRIP connection
(the one associated with the newly received OPEN message), and
continues to use the existing one (the one that is already in
the OpenConfirm state).
2. If a connection collision occurs with an existing TRIP
connection that is in the Established state, then the LS MUST
unconditionally close of the newly created connection. Note
that a connection collision cannot be detected with connections
that are in Idle, Connect, or Active states.
3. To close the TRIP connection (that results from the collision
resolution procedure), an LS MUST send a NOTIFICATION message
with the Error Code 'Cease' and the TRIP connection MUST be
closed.
7. TRIP Version Negotiation
Peer LSs may negotiate the version of the protocol by making
multiple attempts to open a TRIP connection, starting with the
highest version number each supports. If an open attempt fails with
an Error Code 'OPEN Message Error' and an Error Subcode 'Unsupported
Version Number,' then the LS has available the version number it
tried, the version number its peer tried, the version number passed
by its peer in the NOTIFICATION message, and the version numbers
that it supports. If the two peers support one or more common
versions, then this will allow them to rapidly determine the highest
common version. In order to support TRIP version negotiation, future
versions of TRIP must retain the format of the OPEN and NOTIFICATION
messages.
8. TRIP Capability Negotiation
An LS MAY include the Capabilities Option in its OPEN message to a
peer to indicate the capabilities supported by the LS. An LS
receiving an OPEN message MUST NOT use any capabilities that were
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not included in the OPEN message of the peer when communicating with
that peer.
9. TRIP Finite State Machine
This section specifies TRIP operation in terms of a Finite State
Machine (FSM). Following is a brief summary and overview of TRIP
operations by state as determined by this FSM. A condensed version
of the TRIP FSM is found in Appendix 1. There is a TRIP FSM per
peer and these FSMs operate independently.
Idle state:
Initially TRIP is in the Idle state for each peer. In this state,
TRIP refuses all incoming connections. No resources are allocated to
the peer. In response to the Start event (initiated by either the
system or the operator), the local system initializes all TRIP
resources, starts the ConnectRetry timer, initiates a transport
connection to the peer, starts listening for a connection that may
be initiated by the remote TRIP peer, and changes its state to
Connect. The exact value of the ConnectRetry timer is a local
matter, but should be sufficiently large to allow TCP
initialization.
If an LS detects an error, it closes the transport connection and
changes its state to Idle. Transitioning from the Idle state
requires generation of the Start event. If such an event is
generated automatically, then persistent TRIP errors may result in
persistent flapping of the LS. To avoid such a condition, Start
events MUST NOT be generated immediately for a peer that was
previously transitioned to Idle due to an error. For a peer that was
previously transitioned to Idle due to an error, the time between
consecutive Start events, if such events are generated
automatically, MUST exponentially increase. The value of the initial
timer SHOULD be 60 seconds, and the time SHOULD be at least doubled
for each consecutive retry up to some maximum value.
Any other event received in the Idle state is ignored.
Connect state:
In this state, an LS is waiting for a transport protocol connection
to be completed to the peer, and is listening for inbound transport
connections from the peer.
If the transport protocol connection succeeds, the local LS clears
the ConnectRetry timer, completes initialization, sends an OPEN
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message to its peer, sets its Hold Timer to a large value, and
changes its state to OpenSent. A Hold Timer value of 4 minutes is
suggested.
If the transport protocol connect fails (e.g., retransmission
timeout), the local system restarts the ConnectRetry timer,
continues to listen for a connection that may be initiated by the
remote LS, and changes its state to Active state.
In response to the ConnectRetry timer expired event, the local LS
cancels any outstanding transport connection to the peer, restarts
the ConnectRetry timer, initiates a transport connection to the
remote LS, continues to listen for a connection that may be
initiated by the remote LS, and stays in the Connect state.
If the local LS detects that a remote peer is trying to establish a
connection to it and the IP address of the peer is not an expected
one, then the local LS rejects the attempted connection and
continues to listen for a connection from its expected peers without
changing state.
If an inbound transport protocol connection succeeds, the local LS
clears the ConnectRetry timer, completes initialization, sends an
OPEN message to its peer, sets its Hold Timer to a large value, and
changes its state to OpenSent. A Hold Timer value of 4 minutes is
suggested.
The Start event is ignored in the Connect state.
In response to any other event (initiated by either the system or
the operator), the local system releases all TRIP resources
associated with this connection and changes its state to Idle.
Active state:
In this state, an LS is listening for an inbound connection from the
peer, but is not in the process of initiating a connection to the
peer.
If an inbound transport protocol connection succeeds, the local LS
clears the ConnectRetry timer, completes initialization, sends an
OPEN message to its peer, sets its Hold Timer to a large value, and
changes its state to OpenSent. A Hold Timer value of 4 minutes is
suggested.
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In response to the ConnectRetry timer expired event, the local
system restarts the ConnectRetry timer, initiates a transport
connection to the TRIP peer, continues to listen for a connection
that may be initiated by the remote TRIP peer, and changes its state
to Connect.
If the local LS detects that a remote peer is trying to establish a
connection to it and the IP address of the peer is not an expected
one, then the local LS rejects the attempted connection and
continues to listen for a connection from its expected peers without
changing state.
Start event is ignored in the Active state.
In response to any other event (initiated by either the system or
the operator), the local system releases all TRIP resources
associated with this connection and changes its state to Idle.
OpenSent state:
In this state, an LS has sent an OPEN message to its peer and is
waiting for an OPEN message from its peer. When an OPEN message is
received, all fields are checked for correctness. If the TRIP
message header checking or OPEN message checking detects an error
(see Section 6.2) or a connection collision (see Section
6.8), the local system sends a NOTIFICATION message and changes its
state to Idle.
If there are no errors in the OPEN message, TRIP sends a KEEPALIVE
message and sets a KeepAlive timer. The Hold Timer, which was
originally set to a large value (see above), is replaced with the
negotiated Hold Time value (see Section 4.2). If the negotiated Hold
Time value is zero, then the Hold Time timer and KeepAlive timers
are not started. If the value of the ITAD field is the same as the
local ITAD number, then the connection is an 'internal' connection;
otherwise, it is 'external' (this will affect UPDATE processing).
Finally, the state is changed to OpenConfirm.
If the local LS detects that a remote peer is trying to establish a
connection to it and the IP address of the peer is not an expected
one, then the local LS rejects the attempted connection and
continues to listen for a connection from its expected peers without
changing state.
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If a disconnect notification is received from the underlying
transport protocol, the local LS closes the transport connection,
restarts the ConnectRetry timer, continues to listen for a
connection that may be initiated by the remote TRIP peer, and goes
into the Active state.
If the Hold Timer expires, the local LS sends NOTIFICATION message
with Error Code 'Hold Timer Expired' and changes its state to Idle.
In response to the Stop event (initiated by either system or
operator) the local LS sends NOTIFICATION message with Error Code
'Cease' and changes its state to Idle.
The Start event is ignored in the OpenSent state.
In response to any other event the local LS sends NOTIFICATION
message with Error Code 'Finite State Machine Error' and changes its
state to Idle.
Whenever TRIP changes its state from OpenSent to Idle, it closes the
transport connection and releases all resources associated with that
connection.
OpenConfirm state:
In this state, an LS has sent an OPEN to its peer, received an OPEN
from its peer, and sent a KEEPALIVE in response to the OPEN. The LS
is now waiting for a KEEPALIVE or NOTIFICATION message in response
to its OPEN.
If the local LS receives a KEEPALIVE message, it changes its state
to Established.
If the Hold Timer expires before a KEEPALIVE message is received,
the local LS sends NOTIFICATION message with Error Code 'Hold Timer
Expired' and changes its state to Idle.
If the local LS receives a NOTIFICATION message, it changes its
state to Idle.
If the KeepAlive timer expires, the local LS sends a KEEPALIVE
message and restarts its KeepAlive timer.
If a disconnect notification is received from the underlying
transport protocol, the local LS closes the transport connection,
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restarts the ConnectRetry timer, continues to listen for a
connection that may be initiated by the remote TRIP peer, and goes
into the Active state.
In response to the Stop event (initiated by either the system or the
operator) the local LS sends NOTIFICATION message with Error Code
'Cease' and changes its state to Idle.
Start event is ignored in the OpenConfirm state.
In response to any other event the local LS sends NOTIFICATION
message with Error Code 'Finite State Machine Error' and changes its
state to Idle.
Whenever TRIP changes its state from OpenConfirm to Idle, it closes
the transport connection and releases all resources associated with
that connection.
Established state:
In the Established state, an LS can exchange UPDATE, NOTIFICATION,
and KEEPALIVE messages with its peer.
If the negotiated Hold Timer is zero, then no procedures are
necessary for keeping a peering session alive. If the negotiated
Hold Time value is non-zero, the procedures of this paragraph apply.
If the Hold Timer expires, the local LS sends a NOTIFICATION message
with Error Code 'Hold Timer Expired' and changes its state to Idle.
If the KeepAlive Timer expires, then the local LS sends a KeepAlive
message and restarts the KeepAlive Timer. If the local LS receives
an UPDATE or KEEPALIVE message, then it restarts its Hold Timer.
Each time the LS sends an UPDATE or KEEPALIVE message, it restarts
its KeepAlive Timer.
If the local LS receives a NOTIFICATION message, it changes its
state to Idle.
If the local LS receives an UPDATE message and the UPDATE message
error handling procedure (see Section6.3) detects an error, the
local LS sends a NOTIFICATION message and changes its state to Idle.
If a disconnect notification is received from the underlying
transport protocol, the local LS changes its state to Idle.
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In response to the Stop event (initiated by either the system or the
operator), the local LS sends a NOTIFICATION message with Error Code
'Cease' and changes its state to Idle.
The Start event is ignored in the Established state.
In response to any other event, the local LS sends NOTIFICATION
message with Error Code 'Finite State Machine Error' and changes its
state to Idle.
Whenever TRIP changes its state from Established to Idle, it closes
the transport) connection, releases all resources associated with
that connection. Additionally, if the peer is an external peer, the
LS deletes all routes derived from that connection.
10. UPDATE Message Handling
An UPDATE message may be received only in the Established state.
When an UPDATE message is received, each field is checked for
validity as specified in Section 6.3. The rest of this section
presumes that the UPDATE message has passed the error-checking
procedures of Section 6.3.
If the UPDATE message was received from an internal peer, the
flooding procedures of Section 10.1 MUST be applied. The flooding
process synchronizes the Loc-TRIBs of all LSs within the domain.
Certain routes within the UPDATE may be marked as old or duplicates
by the flooding process and are ignored during the rest of the
UPDATE processing.
If the UPDATE message contains withdrawn routes, then the
corresponding previously advertised routes shall be removed from the
Adj-TRIB-In. This LS MUST run its Decision Process since the
previously advertised route is no longer available for use.
If the UPDATE message contains a route, then the route MUST be
placed in the appropriate Adj-TRIB-In, and the following additional
actions MUST be taken:
1. If its destinations are identical to those of a route currently
stored in the Adj-TRIB-In, then the new route MUST replace the
older route in the Adj-TRIB-In, thus implicitly withdrawing the
older route from service. The LS MUST run its Decision Process
since the older route is no longer available for use.
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2. If the new route is more specific than an earlier route
contained in the Adj-TRIB-In and has identical attributes, then
no further actions are necessary.
3. If the new route is more specific than an earlier route
contained in the Adj-TRIB-In but does not have identical
attributes, then the LS MUST run its Decision Process since the
more specific route has implicitly made a portion of the less
specific route unavailable for use.
4. If the new route has destinations that are not present in any
of the routes currently stored in the Adj-TRIB-In, then the LS
MUST run its Decision Process.
5. If the new route is less specific than an earlier route
contained in the Adj-TRIB-In, the LS MUST run its Decision
Process on the set of destinations that are described only by
the less specific route.
10.1 Flooding Process
When an LS receives an UPDATE message from an internal peer, the LS
floods the new information from that message to all of its other
internal peers. Flooding is used to efficiently synchronize all of
the LSs within a domain without putting any constraints on the
domain's internal topology. The flooding mechanism is based on the
techniques used in OSPF [3] and SCSP [5]. One may argue that TRIP's
flooding process is in reality a controlled broadcast mechanism.
10.1.1 Database Information
The LS MUST maintain the sequence number and originating TRIP
identifier for each link-state encapsulated attribute in an internal
Adj-TRIB-In. These values are included with the route in the
ReachableRoutes, WithdrawnRoutes, and ITAD Topology attributes. The
originating TRIP identifier gives the internal LS that originated
this route into the ITAD, the sequence number gives the version of
this route at the originating LS.
10.1.2 Determining Newness
For each route in the ReachableRoutes or WithdrawnRoutes field, the
LS decides if the route is new or old. This is determined by
comparing the Sequence Number of the route in the UPDATE with the
Sequence Number of the route saved in the Adj-TRIB-In. The route is
new if either the route does not exist in the Adj-TRIB-In for the
originating LS, or if the route does exist in the Adj-TRIB-In but
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the Sequence Number in the UPDATE is greater than the Sequence
Number saved in the Adj-TRIBs-In. Note that the newness test is
independently applied to each link-state encapsulated attribute in
the UPDATE (WithdrawnRoutes or ReachableRoutes).
10.1.3 Flooding
Each route in the ReachableRoutes or WithdrawnRoutes field that is
determined to be old is ignored in further processing. If the route
is determined to be new then the following actions occur.
If the route is being withdrawn, then the LS MUST flood the
withdrawn route to all other internal peers, and MUST mark the route
as withdrawn. An LS MUST maintain routes marked as withdrawn in its
databases for MaxPurgeTime seconds.
If the route is being updated, then the LS MUST update the route in
the Adj-TRIB-In and MUST flood it to all other internal peers.
If these procedures result in changes to the Adj-TRIB-In, then the
route is also made available for local route processing as described
early in Section 10.
To implement flooding, the following is recommended. All routes
received in a single UPDATE message that are determined to be new
should be forwarded to all other internal peers in a single UPDATE
message. Other variations on flooding are possible, but the local
LS MUST ensure that each new route (and any associated attributes)
received from an internal peer get forwarded to every other internal
peer.
10.1.4 Sequence Number Considerations
The Sequence Number is used to determine when one version of a route
is newer than another version of a route. A larger Sequence Number
indicates a newer version. The Sequence Number is assigned by the
LS originating the route into the local ITAD. The Sequence Number
is an unsigned 4-octet integer in the range of 1 thru 2^31-1
(MinSequenceNum thru MaxSequenceNum). The value 0 is reserved.
When an LS first originates a route into its ITAD, it MUST originate
it with a Sequence Number of MinSequenceNum. Each time the route is
updated within the ITAD by the originator, the Sequence Number MUST
be increased.
If it is ever the case that the sequence number is MaxSequenceNum-1
and it needs to be increased, then the TRIP module of the LS MUST be
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disabled for a period of TripDisableTime so that all routes
originated by this LS with high sequence numbers can be removed.
10.1.5 Purging a Route Within the ITAD
To withdraw a route that it originated within the ITAD, an LS
includes the route in the WithdrawnRoutes field of an UPDATE
message. The Sequence Number MUST be greater than the last valid
version of the route. The LS MAY choose to use a sequence number of
MaxSequenceNum when withdrawing routes within its ITAD, but this is
not required.
After withdrawing a route, an LS MUST mark the route as 'withdrawn'
in its database, and maintain the withdrawn route in its database
for MaxPurgeTime seconds. If the LS needs to re-originate a route
that had been purged but is still in its database, it can either re-
originate the route immediately using a Sequence Number that is
greater than that used in the withdraw, or the LS may wait until
MaxPurgeTime seconds have expired since the route was withdrawn.
10.1.6 Receiving Self-Originated Routes
It is common for an LS to receive UPDATES for routes that it
originated within the ITAD via the flooding procedure. If the LS
receives an UPDATE for a route that it originated that is newer (has
a higher sequence number) than the LSs current version, then special
actions must be taken. This should be a relatively rare occurrence
and indicates that a route still exists within the ITAD since the
LSs last restart/reboot.
If an LS receives a self-originated route update that is newer than
the current version of the route at the LS, then the following
actions MUST be taken. If the LS still wishes to advertise the
information in the route, then the LS MUST the increase the Sequence
Number of the route to a value greater than that received in the
UPDATE and re-originate the route. If the LS does not wish to
continue to advertise the route, then it MUST purge the route as
described in Section 10.1.5.
10.1.7 Removing Withdrawn Routes
An LS SHOULD ensure that routes marked as withdrawn are removed from
the database in a timely fashion after the MaxPurgeTime has expired.
This could be done, for example, by periodically sweeping the
database, and deleting those entries that were withdrawn more than
MaxPurgeTime seconds ago.
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10.2 Decision Process
The Decision Process selects routes for subsequent advertisement by
applying the policies in the local Policy Information Base (PIB) to
the routes stored in its Adj-TRIBs-In. The output of the Decision
Process is the set of routes that will be advertised to all peers;
the selected routes will be stored in the local LS's Adj-TRIBs-Out.
The selection process is formalized by defining a function that
takes the attributes of a given route as an argument and returns a
non-negative integer denoting the degree of preference for the
route. The function that calculates the degree of preference for a
given route shall not use as its inputs any of the following: the
existence of other routes, the non-existence of other routes, or the
attributes of other routes. Route selection then consists of
individual application of the degree of preference function to each
feasible route, followed by the choice of the one with the highest
degree of preference.
All internal LSs in an ITAD MUST run the Decision Process and apply
the same decision criteria, other it will not be possible to
synchronize their Loc-TRIBs.
The Decision Process operates on routes contained in each Adj-TRIBs-
In, and is responsible for:
- selection of routes to be advertised to internal peers
- selection of routes to be advertised to external peers
- route aggregation and route information reduction
The Decision Process takes place in three distinct phases, each
triggered by a different event:
a) Phase 1 is responsible for calculating the degree of preference
for each route received from an external peer, and for
advertising to all the internal peers the routes from external
peers that have the highest degree of preference for each
distinct destination.
b) Phase 2 is invoked on completion of phase 1. It is responsible
for choosing the best route out of all those available for each
distinct destination, and for installing each chosen route into
the Loc-TRIB.
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c) Phase 3 is invoked after the Loc-TRIB has been modified. It is
responsible for disseminating routes in the Loc-TRIB to each
external peer, according to the policies contained in the PIB.
Route aggregation and information reduction can optionally be
performed within this phase.
10.2.1 Phase 1: Calculation of Degree of Preference
The Phase 1 decision function shall be invoked whenever the local LS
receives from a peer an UPDATE message that advertises a new route,
a replacement route, or a withdrawn route.
The Phase 1 decision function is a separate process that completes
when it has no further work to do.
The Phase 1 decision function shall lock an Adj-TRIB-In prior to
operating on any route contained within it, and shall unlock it
after operating on all new or replacement routes contained within
it.
The local LS MUST determine a degree of preference for each newly
received or replacement route. If the route is learned from an
internal peer, the value of the LocalPreference attribute MUST be
taken as the degree of preference. If the route is learned from an
external peer, then the degree of preference MUST be computed based
on pre-configured policy information and used as the LocalPreference
value in any intra-domain TRIP advertisement. The exact nature of
this policy information and the computation involved is a local
matter.
The output of the degree of preference determination process is the
local preference of a route. The local LS computes the local
preference of routes learned from external peers or originated
internally at that LS. The local preference of a route learned from
an internal peer is included in the LocalPreference attribute
associated with that route.
10.2.2 Phase 2: Route Selection
The Phase 2 decision function shall be invoked on completion of
Phase 1. The Phase 2 function is a separate process that completes
when it has no further work to do. Phase 2 consists of two sub-
phases: 2a and 2b. The same route selection function is applied in
both sub-phases, but the inputs to each phase are different. The
Phase 2a process MUST consider as inputs all external routes, that
are present in the Adj-TRIBs-In of external peers, and all local
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routes. The output of Phase 2a is inserted into the Ext-TRIB. The
Phase 2b process shall be invoked upon completion of Phase 2a and it
MUST consider as inputs all routes in the Ext-TRIB and all routes
that are present in the Adj-TRIBs-In of internal LSs. The output of
Phase 2b is stored in the Loc-TRIB.
The Phase 2 decision function MUST be blocked from running while the
Phase 3 decision function is in process. The Phase 2 function MUST
lock all Adj-TRIBs-In and the Ext-TRIB prior to commencing its
function, and MUST unlock them on completion.
If the LS determines that the NextHopServer listed in a route is
unreachable, then the route MAY be excluded from the Phase 2
decision function. The means by which such a determination is made
is not mandated here.
For each set of destinations for which one or more routes exist, the
local LS's route selection function MUST identify the route that
has:
a) the highest degree of preference, or
b) is selected as a result of the tie breaking rules specified
in 10.2.2.1.
Withdrawn routes MUST be removed from the Loc-TRIB, Ext-TRIB, and
the Adj-TRIBs-In.
10.2.2.1 Breaking Ties (Phase 2)
Several routes to the same destination that have the same degree of
preference may be input to the Phase 2 route selection function. The
local LS can select only one of these routes for inclusion in the
associated Ext-TRIB (Phase 2a) or Loc-TRIB (Phase 2b). The local LS
considers all routes with the same degrees of preference. The
following algorithm shall be used to break ties.
a) If the local LS is configured to use the MultiExitDisc
attribute to break ties, and candidate routes received from
the same neighboring ITAD differ in the value of the
MultiExitDisc attribute, then select the route that has the
larger value of MultiExitDisc.
b) If at least one of the routes was originated by an internal
LS, select the route route that was advertised by the
internal LS that has the lowest TRIP ID.
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c) Otherwise, select the route that was advertised by the
neighbor domain that has the lowest ITAD number.
10.2.3 Phase 3: Route Dissemination
The Phase 3 decision function MUST be invoked upon completion of
Phase 2 if Phase 2 results in changes to the Loc-TRIB or when a new
LS-to-LS peer session is established.
The Phase 3 function is a separate process that completes when it
has no further work to do. The Phase 3 routing decision function
MUST be blocked from running while the Phase 2 decision function is
in process.
All routes in the Loc-TRIB shall be processed into a corresponding
entry in the associated Adj-TRIBs-Out. Route aggregation and
information reduction techniques (see 10.3.4) MAY optionally be
applied.
When the updating of the Adj-TRIBs-Out is complete, the local LS
MUST run the external update process of 10.3.2.
10.2.4 Overlapping Routes
When overlapping routes are present in the same Adj-TRIB-In, the
more specific route shall take precedence, in order from more
specific to least specific.
The set of destinations described by the overlap represents a
portion of the less specific route that is feasible, but is not
currently in use. If a more specific route is later withdrawn, the
set of destinations described by the more specific route will still
be reachable using the less specific route.
If an LS receives overlapping routes, the Decision Process MUST take
into account the semantics of the overlapping routes. In particular,
if an LS accepts the less specific route while rejecting the more
specific route from the same peer, then the destinations represented
by the overlap may not forward along the domains listed in the
AdvertisementPath attribute of that route. Therefore, an LS has the
following choices:
a) Install both the less and the more specific routes
b) Install the more specific route only
c) Install the non-overlapping part of the less specific route
only (that implies disaggregation of the less-specific route)
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d) Aggregate the two routes and install the aggregated route
e) Install the less specific route only
f) Install neither route
If an LS chooses e), then it SHOULD add AtomicAggregate attribute to
the route. A route that carries AtomicAggregate attribute MUST NOT
be de-aggregated. That is, the route cannot be made more specific.
Forwarding along such a route does not guarantee that route
traverses only domains listed in the RoutedPath of the route. If an
LS chooses a), then it MUST NOT advertise the more general route
without the more specific route.
10.3 Update-Send Process
The Update-Send process is responsible for advertising UPDATE
messages to all peers. For example, it distributes the routes chosen
by the Decision Process to other LSs that may be located in either
the same ITAD or a neighboring ITAD. Rules for information exchange
between peer LSs located in different ITADs are given in 10.3.2;
rules for information exchange between peer LSs located in the same
ITAD are given in 10.3.1.
Before forwarding routes to peers, an LS MUST determine which
attributes should be forwarded along with that route. If an
optional non-transitive attribute is unrecognized, it is quietly
ignored. If an optional dependent-transitive attribute is
unrecognized, and the NextHopServer attribute has been changed by
the LS, the unrecognized attribute is quietly ignored. If an
optional dependent-transitive attribute is unrecognized, and the
NextHopServer attribute has not been modified by the LS, the Partial
bit in the attribute flags octet is set to 1, and the attribute is
retained for propagation to other TRIP speakers. Similarly, if an
optional independent-transitive attribute is unrecognized, the
Partial bit in the attribute flags octet is set to 1, and the
attribute is retained for propagation to other TRIP speakers.
If an optional attribute is recognized, and has a valid value, then,
depending on the type of the optional attribute, it is updated, if
necessary, for possible propagation to other TRIP speakers.
10.3.1 Internal Updates
The Internal update process is concerned with the distribution of
routing information to internal peers.
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When an LS receives an UPDATE message from another TRIP LS located
in its own ITAD, it is flooded as described in Section 10.1.
When an LS receives a new route from an LS in a neighboring ITAD, or
if a local route is inserted injected into TRIP, the LS determines
the preference of that route. If the new route has the highest
degree of preference for all external routes and local routes to a
given destination (or if the route was selected via a tie-breaking
procedure as specified in 10.3.1.1), the LS MUST insert that new
route into the Ext-TRIB database and the LS MUST advertise that
route to all other LSs in its ITAD by means of an UPDATE message.
The LS MUST advertise itself as the Originator of that route within
the ITAD.
When an LS receives an UPDATE message with a non-empty
WithdrawnRoutes attribute from an external peer, or if a local route
is withdrawn from TRIP, the LS MUST remove from its Adj-TRIB-In all
routes whose destinations were carried in this field. If the
withdrawn route was previously selected into the Ext-TRIB, the LS
MUST take the following additional steps:
i) If a new route is selected for advertisement for those
destinations, then the LS MUST insert the replacement route
into Ext-TRIB to replace the withdrawn route and advertise it
to all internal LSs.
ii) If a replacement route is not available for advertisement,
then the LS MUST include the destinations of the route in the
WithdrawnRoutes attribute of an UPDATE message, and MUST send
this message to each internal peer. The LS MUST also remove
the withdrawn route from the Ext-TRIB.
10.3.1.1 Breaking Ties (Internal Updates)
If an LS has connections to several external peers, there will be
multiple Adj-TRIBs-In associated with these peers. These databases
might contain several equally preferable routes to the same
destination, all of which were advertised by external peers. The
local LS shall select one of these routes according to the following
rules:
a) If the LS is configured to use the MultiExitDisc attribute to
break ties, and the candidate routes differ in the value of
the MultiExitDisc attribute, then select the route that has
the lowest value of MultiExitDisc, else
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b) Select the route that was advertised by the external LS that
has the lowest TRIP Identifier.
10.3.2 External Updates
The external update process is concerned with the distribution of
routing information to external peers. As part of Phase 3 route
selection process, the LS has updated its Adj-TRIBs-Out. All newly
installed routes and all newly unfeasible routes for which there is
no replacement route MUST be advertised to external peers by means
of UPDATE messages.
Any routes in the Loc-TRIB marked as withdrawn MUST be removed.
Changes to the reachable destinations within its own ITAD SHALL also
be advertised in an UPDATE message.
10.3.3 Controlling Routing Traffic Overhead
The TRIP protocol constrains the amount of routing traffic (that is,
UPDATE messages) in order to limit both the link bandwidth needed to
advertise UPDATE messages and the processing power needed by the
Decision Process to digest the information contained in the UPDATE
messages.
10.3.3.1 Frequency of Route Advertisement
The parameter MinRouteAdvertisementInterval determines the minimum
amount of time that must elapse between advertisements of routes to
a particular destination from a single LS. This rate limiting
procedure applies on a per-destination basis, although the value of
MinRouteAdvertisementInterval is set on a per LS peer basis.
Two UPDATE messages sent from a single LS that advertise feasible
routes to some common set of destinations received from external
peers MUST be separated by at least MinRouteAdvertisementInterval.
Clearly, this can only be achieved precisely by keeping a separate
timer for each common set of destinations. This would be unwarranted
overhead. Any technique which ensures that the interval between two
UPDATE messages sent from a single LS that advertise feasible routes
to some common set of destinations received from external peers will
be at least MinRouteAdvertisementInterval, and will also ensure a
constant upper bound on the interval is acceptable.
Two UPDATE messages, sent from a single LS to an external peer, that
advertise feasible routes to some common set of destinations
received from internal peers MUST be separated by at least
MinRouteAdvertisementInterval.
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Since fast convergence is needed within an ITAD, this rate limiting
procedure does not apply to routes received from internal peers and
being broadcast to other internal peers. To avoid long-lived black
holes, the procedure does not apply to the explicit withdrawal of
routes (that is, routes whose destinations explicitly withdrawn by
UPDATE messages.
This procedure does not limit the rate of route selection, but only
the rate of route advertisement. If new routes are selected multiple
times while awaiting the expiration of
MinRouteAdvertisementInterval, the last route selected shall be
advertised at the end of MinRouteAdvertisementInterval.
10.3.3.2 Frequency of Route Origination
The parameter MinITADOriginationInterval determines the minimum
amount of time that must elapse between successive advertisements of
UPDATE messages that report changes within the advertising LS's own
ITAD.
10.3.3.3 Jitter
To minimize the likelihood that the distribution of TRIP messages by
a given LS will contain peaks, jitter should be applied to the
timers associated with MinITADOriginationInterval, KeepAlive, and
MinRouteAdvertisementInterval. A given LS shall apply the same
jitter to each of these quantities regardless of the destinations to
which the updates are being sent; that is, jitter will not be
applied on a 'per peer' basis.
The amount of jitter to be introduced shall be determined by
multiplying the base value of the appropriate timer by a random
factor that is uniformly distributed in the range from 0.75 to 1.0.
10.3.4 Efficient Organization of Routing Information
Having selected the routing information that it will advertise, a
TRIP speaker may use methods to organize this information in an
efficient manner. These methods are discussed in the following
sections.
10.3.4.1 Information Reduction
Information reduction may imply a reduction in granularity of policy
control - after information is collapsed, the same policies will
apply to all destinations and paths in the equivalence class.
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The Decision Process may optionally reduce the amount of information
that it will place in the Adj-TRIBs-Out by any of the following
methods:
a) ReachableRoutes:
A set of destinations can be usually represented in compact form.
For example, a set of E.164 phone numbers can be represented in more
compact form using E.164 prefixes.
b) AdvertisementPath:
AdvertisementPath information can be represented as ordered
AP_SEQUENCEs or unordered AP_SETs. AP_SETs are used in the route
aggregation algorithm described in Section 5.4.4. They reduce the
size of the AP_PATH information by listing each ITAD number only
once, regardless of how many times it may have appeared in multiple
advertisement paths that were aggregated.
An AP_SET implies that the destinations advertised in the UPDATE
message can be reached through paths that traverse at least some of
the constituent ITADs. AP_SETs provide sufficient information to
avoid route looping; however their use may prune potentially
feasible paths, since such paths are no longer listed individually
as in the form of AP_SEQUENCEs. In practice this is not likely to be
a problem, since once an call arrives at the edge of a group of
ITADs, the LS at that point is likely to have more detailed path
information and can distinguish individual paths to destinations.
10.3.4.2 Aggregating Routing Information
Aggregation is the process of combining the characteristics of
several different routes in such a way that a single route can be
advertised. Aggregation can occur as part of the decision process
to reduce the amount of routing information that is placed in the
Adj-TRIBs-Out.
Aggregation reduces the amount of information an LS must store and
exchange with other LSs. Routes can be aggregated by applying the
following procedure separately to attributes of like type.
Routes that have the following attributes shall not be aggregated
unless the corresponding attributes of each route are identical:
MultiExitDisc, NextHopServer.
Attributes that have different type codes cannot be aggregated.
Attributes of the same type code may be aggregated. The rules for
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aggregating each attribute MUST be provided together with attribute
definition. For example, aggregation rules for TRIP's basic
attributes, e.g., ReachableRoutes and AdvertisementPath, are given
in Section 5.
10.4 Route Selection Criteria
Generally speaking, additional rules for comparing routes among
several alternatives are outside the scope of this document. There
are two exceptions:
- If the local ITAD appears in the AdvertisementPath of the new
route being considered, then that new route cannot be viewed as
better than any other route. If such a route were ever used, a
routing loop could result (see Section 6.3).
- In order to achieve successful distributed operation, only routes
with a likelihood of stability can be chosen. Thus, an ITAD must
avoid using unstable routes, and it must not make rapid
spontaneous changes to its choice of route. Quantifying the terms
'unstable' and 'rapid' in the previous sentence will require
experience, but the principle is clear.
10.5 Originating TRIP routes
An LS may originate local routes by injecting routing information
acquired by some other means (e.g. via an intra-domain routing
protocol or through manual configuration or some dynamic
registration mechanism/protocol) into TRIP. An LS that originates
TRIP routes shall assign the degree of preference to these routes by
passing them through the Decision Process (see Section 10.2). To
TRIP local routes are identical to external routes and are subjected
to the same two phase route selection mechanism. A local route which
is selected into the Ext-TRIB MUST be advertised to all internal
LSs. The decision whether to distribute non-TRIP acquired routes
within an ITAD via TRIP or not depends on the environment within the
ITAD (e.g. type of intra-domain routing protocol) and should be
controlled via configuration.
11. TRIP Transport
This specification defines the use of TCP as the transport layer for
TRIP. TRIP uses TCP port 6069. Running TRIP over other transport
protocols is for further study.
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12. ITAD Topology
There are no restrictions on the intra-domain topology of TRIP LSs.
For example, LSs in an ITAD can be configured in a full mesh, star,
or any other connected topology. Similarly, there are no
restrictions on the topology of TRIP ITADs. For example, the ITADs
can be organized in a flat topology (mesh or ring) or in multi-level
hierarchy or any other topology.
The border between two TRIP ITADs may be located either on the link
between two TRIP LSs or it may coincide on a TRIP LS. In the latter
case, the same TRIP LS will be member in more than one ITAD, and it
appears to be an internal peer to LSs in each ITAD it is member of.
13. IANA Considerations
13.1 TRIP Capabilities
Requests to add TRIP capabilities other than those defined in
Section 4.2.1.1 must be submitted to iana@iana.org. The request
should include:
- A description, or a reference to a description, of the capability,
the possible values it may take, and what constitutes a capability
mismatch.
- Contact information (postal and email address).
13.2 TRIP Attributes
When registering a new TRIP attribute with IANA, the following
information must be provided:
- A reference to the description of the proposed attribute, for
example (in order of preference) an RFC, a published paper, a
patent filing, a technical report, documented source code or a
computer manual. The reference must provide all information
required in Section 5.12 of this document.
- Indication of who has change control over the attribute.
- Contact information (postal and email address).
Registration requests must be sent to iana@iana.org. IANA then
assigns Attribute Type Code to the new attribute.
13.3 Destination Address Families
Requests to add TRIP address families other than those defined in
Section 5.1.1.1 must be submitted to iana@iana.org. The request
should include a brief description of the address family, its
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alphabet, and special processing rules and guidelines, such as
guidelines for aggregation, if any.
13.4 TRIP Application Protocols
Requests to add TRIP application protocols other than those defined
in Section 5.1.1.1 must be submitted to iana@iana.org. The request
should include a brief background on the application protocol, and a
description of how TRIP can be used to advertise routes for that
protocol.
13.5 ITAD Numbers
Requests for ITAD numbers must be submitted to iana@iana.org. The
requests should include the following:
- Information about the organization that administers the ITAD.
- Contact information (postal and email address).
14. Security Considerations
This section covers security between peer TRIP LSs when TRIP runs
over TCP in an IP environment.
A security mechanism is clearly needed to prevent unauthorized
entities from using the protocol defined in this document for
setting up unauthorized peer sessions with other TRIP LSs or
interfering with authorized peer sessions. The security mechanism
for the protocol when transported over TCP in an IP networks is
IPsec [10]. IPsec uses two protocols to provide traffic security:
Authentication Header (AH) [11] and Encapsulating Security Payload
(ESP) [12].
The AH header affords data origin authentication, connectionless
integrity and optional anti-replay protection of messages passed
between the peer LSs. The ESP header provides origin authentication,
connectionless integrity, anti-replay protection, and, in addition,
confidentiality of messages.
Implementations of the protocol defined in this document employing
the ESP header SHALL comply with section 5 of [12], which defines a
minimum set of algorithms for integrity checking and encryption.
Similarly, implementations employing the AH header SHALL comply with
section 5 of [11], which defines a minimum set of algorithms for
integrity checking using manual keys.
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Implementations SHOULD use IKE [13] to permit more robust keying
options. Implementations employing IKE SHOULD support authentication
with RSA signatures and RSA public key encryption.
A Security Association (SA) [10] is a simplex 'connection' that
affords security services to the traffic carried by it. Security
services are afforded to an SA by the use of AH, or ESP, but not
both. Two types of SAs are defined: transport mode and tunnel mode
[10]. A transport mode SA is a security association between two
hosts, and is appropriate for protecting the TRIP session between
two peer LSs.
15. Changes Since the Last Revision
- Section 4.2.1.1.2: added 'Capability Mismatch' error code. Change
also affected Section 4.5 and 6.2.
- Section 4.2: An LS MUST use the same TRIP ID with all its peers.
- Section 5.10: on the usage of ITAD Topology attribute. Two
methods for this function are possible. One method advertises the
topology, requires LSs to update their topology only when their
internal peer set changes, and requires LSs to calculate to which
LSs are active within their domain via a connectivity algorithm on
the topology. The second option would require an LS to
periodically issue a 'keep-alive' type advertisement that gets
flooded within the domain. LSs would determine which LSs are
active by the set of received keepalives. Decided to use the
first alternative and updated the text accordingly.
- Changed the size of the ITAD Number from two octets to four
octets. This change impacted Sections 4.2, 5.3.1, and 5.9.1.
- Redefined the base address families in TRIP. The new families are
Decimal Routing Numbers and HexaDecimal Routing Numbers (Sections
5.1.1.1 through 5.1.1.3).
- Added text to explicitly permit mapping from one application
protocol to another (Section 5.2.5). Added a new attrbiute
ConvertedRoute, which indicates when application protocol mapping
occurs (Sections 4.3.4.11 and 5.11).
- Section 5.3.1. Permit specifying the next hop server address as an
IPv6 address in textual format.
- Added Section 12, ITAD Topology. It permits the border between
ITADs to either be on the link between two LSs or to coincide on
an LS.
- Removed the Authentication attribute from the draft. It will be
published as a separate draft.
- Timer values and Rate limiting: revised Sections 10.3.3.1 and
10.3.3.2 to make sure they are agreement with rate limiting
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procedures in both ISIS and BGP-4. Also verified the default
timers values proposed in Appendix A.2.4 in comparison to both
ISIS and BGP-4.
Appendix 1. TRIP FSM State Transitions and Actions
This Appendix discusses the transitions between states in the TRIP
FSM in response to TRIP events. The following is the list of these
states and events when the negotiated Hold Time value is non-zero.
TRIP States:
1 - Idle
2 - Connect
3 - Active
4 - OpenSent
5 - OpenConfirm
6 - Established
TRIP Events:
1 - TRIP Start
2 - TRIP Stop
3 - TRIP Transport connection open
4 - TRIP Transport connection closed
5 - TRIP Transport connection open failed
6 - TRIP Transport fatal error
7 - ConnectRetry timer expired
8 - Hold Timer expired
9 - KeepAlive timer expired
10 - Receive OPEN message
11 - Receive KEEPALIVE message
12 - Receive UPDATE messages
13 - Receive NOTIFICATION message
The following table describes the state transitions of the TRIP FSM
and the actions triggered by these transitions.
Event Actions Message Sent Next State
--------------------------------------------------------------------
Idle (1)
1 Initialize resources none 2
Start ConnectRetry timer
Initiate a transport connection
others none none 1
Connect(2)
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1 none none 2
3 Complete initialization OPEN 4
Clear ConnectRetry timer
5 Restart ConnectRetry timer none 3
7 Restart ConnectRetry timer none 2
Initiate a transport connection
others Release resources none 1
Active (3)
1 none none 3
3 Complete initialization OPEN 4
Clear ConnectRetry timer
5 Close connection 3
Restart ConnectRetry timer
7 Restart ConnectRetry timer none 2
Initiate a transport connection
others Release resources none 1
OpenSent(4)
1 none none 4
4 Close transport connection none 3
Restart ConnectRetry timer
6 Release resources none 1
10 Process OPEN is OK KEEPALIVE 5
Process OPEN failed NOTIFICATION 1
others Close transport connection NOTIFICATION 1
Release resources
OpenConfirm (5)
1 none none 5
4 Release resources none 1
6 Release resources none 1
9 Restart KeepAlive timer KEEPALIVE 5
11 Complete initialization none 6
Restart Hold Timer
13 Close transport connection 1
Release resources
others Close transport connection NOTIFICATION 1
Release resources
Established (6)
1 none none 6
4 Release resources none 1
6 Release resources none 1
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9 Restart KeepAlive timer KEEPALIVE 6
11 Restart Hold Timer KEEPALIVE 6
12 Process UPDATE is OK UPDATE 6
Process UPDATE failed NOTIFICATION 1
13 Close transport connection 1
Release resources
others Close transport connection NOTIFICATION 1
Release resources
-----------------------------------------------------------------
The following is a condensed version of the above state transition
table.
Events| Idle | Connect | Active | OpenSent | OpenConfirm | Estab
| (1) | (2) | (3) | (4) | (5) | (6)
|-------------------------------------------------------------
1 | 2 | 2 | 3 | 4 | 5 | 6
| | | | | |
2 | 1 | 1 | 1 | 1 | 1 | 1
| | | | | |
3 | 1 | 4 | 4 | 1 | 1 | 1
| | | | | |
4 | 1 | 1 | 1 | 3 | 1 | 1
| | | | | |
5 | 1 | 3 | 3 | 1 | 1 | 1
| | | | | |
6 | 1 | 1 | 1 | 1 | 1 | 1
| | | | | |
7 | 1 | 2 | 2 | 1 | 1 | 1
| | | | | |
8 | 1 | 1 | 1 | 1 | 1 | 1
| | | | | |
9 | 1 | 1 | 1 | 1 | 5 | 6
| | | | | |
10 | 1 | 1 | 1 | 1 or 5 | 1 | 1
| | | | | |
11 | 1 | 1 | 1 | 1 | 6 | 6
| | | | | |
12 | 1 | 1 | 1 | 1 | 1 | 1 or 6
| | | | | |
13 | 1 | 1 | 1 | 1 | 1 | 1
| | | | | |
--------------------------------------------------------------
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Appendix 2. Implementation Recommendations
This section presents some implementation recommendations.
A.2.1. Multiple Networks Per Message
The TRIP protocol allows for multiple address prefixes with the same
advertisement path and next-hop server to be specified in one
message. Making use of this capability is highly recommended. With
one address prefix per message there is a substantial increase in
overhead in the receiver. Not only does the system overhead increase
due to the reception of multiple messages, but the overhead of
scanning the routing table for updates to TRIP peers is incurred
multiple times as well. One method of building messages containing
many address prefixes per advertisement path and next hop from a
routing table that is not organized per advertisement path is to
build many messages as the routing table is scanned. As each address
prefix is processed, a message for the associated advertisement path
and next hop is allocated, if it does not exist, and the new address
prefix is added to it. If such a message exists, the new address
prefix is just appended to it. If the message lacks the space to
hold the new address prefix, it is transmitted, a new message is
allocated, and the new address prefix is inserted into the new
message. When the entire routing table has been scanned, all
allocated messages are sent and their resources released. Maximum
compression is achieved when all the destinations covered by the
address prefixes share a next hop server and common attributes,
making it possible to send many address prefixes in one 4096-byte
message.
When peering with a TRIP implementation that does not compress
multiple address prefixes into one message, it may be necessary to
take steps to reduce the overhead from the flood of data received
when a peer is acquired or a significant network topology change
occurs. One method of doing this is to limit the rate of updates.
This will eliminate the redundant scanning of the routing table to
provide flash updates for TRIP peers. A disadvantage of this
approach is that it increases the propagation latency of routing
information. By choosing a minimum flash update interval that is not
much greater than the time it takes to process the multiple messages
this latency should be minimized. A better method would be to read
all received messages before sending updates.
A.2.2. Processing Messages on a Stream Protocol
TRIP uses TCP as a transport mechanism. Due to the stream nature of
TCP, all the data for received messages does not necessarily arrive
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Internet Draft Telephony Routing over IP November 2000
at the same time. This can make it difficult to process the data as
messages, especially on systems where it is not possible to
determine how much data has been received but not yet processed.
One method that can be used in this situation is to first try to
read just the message header. For the KEEPALIVE message type, this
is a complete message; for other message types, the header should
first be verified, in particular the total length. If all checks are
successful, the specified length, minus the size of the message
header is the amount of data left to read. An implementation that
would 'hang' the routing information process while trying to read
from a peer could set up a message buffer (4096 bytes) per peer and
fill it with data as available until a complete message has been
received.
A.2.3. Reducing Route Flapping
To avoid excessive route flapping an LS which needs to withdraw a
destination and send an update about a more specific or less
specific route SHOULD combine them into the same UPDATE message.
A.2.4. TRIP Timers
TRIP employs five timers: ConnectRetry, Hold Time, KeepAlive,
MaxPurgeTime, TripDisableTime, MinITADOriginationInterval, and
MinRouteAdvertisementInterval The suggested value for the
ConnectRetry timer is 120 seconds. The suggested value for the Hold
Time is 90 seconds. The suggested value for the KeepAlive timer is
30 seconds. The suggested value for the MaxPurgeTime timer is 10
seconds. The suggested value for the TripDisableTime timer is 180
seconds. The suggested value for the MinITADOriginationInterval is
30 seconds. The suggested value for the
MinRouteAdvertisementInterval is 30 seconds.
An implementation of TRIP MUST allow these timers to be
configurable.
A.2.5. AP_SET Sorting
Another useful optimization that can be done to simplify this
situation is to sort the ITAD numbers found in an AP_SET. This
optimization is entirely optional.
Acknowledgments
We wish to thank Dave Oran for his insightful comments and
suggestions.
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References
[1] J. Rosenberg and H. Schulzrinne, 'A Framework for a Gateway
Location Protocol,' IETF RFC 2871, June 2000.
[2] Y. Rekhter and T. Li, 'Border Gateway Protocol 4 (BGP-4),' IETF
RFC 1771, March 1995.
[3] J. Moy, 'Open Shortest Path First Version 2,' IETF RFC 2328,
April, 1998.
[4] 'Intermediate System to Intermediate System Intra-Domain
Routing Exchange Protocol for use in Conjunction with the
Protocol for Providing the Connectionless-mode Network Service
(ISO 8473),' ISO DP 10589, February 1990.
[5] J. Luciani, et al, 'Server Cache Synchronization Protocol
(SCSP),' IETF RFC 2334, April, 1998.
[6] International Telecommunication Union, 'Visual Telephone
Systems and Equipment for Local Area Networks which Provide a
Non-Guaranteed Quality of Service,' Recommendation H.323,
Telecommunication Standardization Sector of ITU, Geneva,
Switzerland, May 1996.
[7] M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg,
'SIP: Session Initiation Protocol,' IETF RFC 2543, March 1999.
[8] R. Braden, 'Requirements for Internet Hosts -- Application and
Support,' IETF RFC 1123, October 1989.
[9] R. Hinden and S. Deering, 'IP Version 6 Addressing
Architecture,' IETF RFC 2373, July 1998.
[10] S. Kent and R. Atkinson, 'Security Architecture for the
Internet Protocol,' IETF RFC 2401, November 1998.
[11] S. Kent and R. Atkinson, 'IP Authentication Header,' IETF RFC
2402, November 1998.
[12] S. Kent and R. Atkinson, 'IP Encapsulating Security Payload
(ESP),' IETF RFC 2406, November 1998.
[13] D. Harkins and D. Carrel, 'The Internet Key Exchange (IKE),'
IETF RFC 2409, November 1998.
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Internet Draft Telephony Routing over IP November 2000
Authors' Addresses
Jonathan Rosenberg
dynamicsoft
72 Eagle Rock Avenue
First Floor
East Hanover, NJ 07936
732-741-7244
email: jdrosen@dynamicsoft.com
Hussein F. Salama
Cisco Systems
Mail Stop SJ-6/3
170 W. Tasman Drive
San Jose, CA 95134
408-527-7147
email: hsalama@cisco.com
Matt Squire
WindWire
4825 Creekstone Drive
Durham, NC 27703
919-247-0820
email: msquire@windwire.com
Rosenberg, Salama, Squire 80
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draft-ietf-iptel-trip-04
Internet-Draft
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This is an older version of an Internet-Draft that was ultimately published as RFC 3219.
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