Interdomain Routing Working Group Yakov Rekhter
Internet Draft cisco Systems
<draft-ietf-idr-idrp-v4v6-02.txt> Paul Traina
cisco Systems
January 1996
IDRP for IP v4 and v6
Status of this memo
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1 Overview
IDRP [5] is defined as the protocol for exchange of Inter-Domain
routing information between routers to support forwarding of ISO 8473
(Connectionless Network Layer Protocol (CLNP))[6] packets.
The network reachability information exchanged via IDRP provides
sufficient information to detect routing loops and enforce routing
decisions based on performance preference and policy constraints as
outlined in RFC 1104 [1]. In particular, IDRP exchanges routing
information containing full domain-level paths and enforces routing
policies based on configuration information.
IDRP may be viewed as an extension of BGP-4 ([9], [10]) that provides
(among other things) much better scaling with respect to support for
routing information aggregation based on CIDR ([2], [11]), as well as
stronger capabilities for policy based routing (e.g. ability to
impose control over transit traffic). Enhanced scaling capabilities
are provided via the concept of Routing Domain Confederations (RDCs),
that allow to express both topology and policy information in terms
of aggregates (confederations) rather than individual entities
(domains). IDRP also provides capability to carry reachability and
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forwarding information associated with multiple network layer
protocols (e.g. IPv6, IPv4).
This document contains the adaptation of the IDRP protocol
definition that enables it to be used as a protocol for the exchange
of inter-domain system routing information among routers to support
the forwarding of IPv6 packets across multiple domains. We refer to
IDRP with this adaptation as "IDRP for IPv6". While this document
doesn't cover use of IDRP to support routing for other network layer
protocols (e.g. IPv4), it is expected that IDRP for IPv6 will be able
to operate in a multiprotocol environment as well.
2 Terminology
This document assumes that the reader is familiar with the following
documents:
IPv6 protocol specification [3], IPv6 Addressing Architecture [4],
and IDRP specification (IS 10747) [5].
A few definitions are in order to aid the reader:
BIS - a Boundary Intermediate System (or border router)
BISPDU - an IDRP message exchanged between a pair of BISs
ES - End System (host)
FIB - Forwarding Information Base (IP forwarding table)
IS - Intermediate System (router)
NET - Network Entity Title (a network layer address for a router)
NLRI - Network Layer Reachability Information (set of reachable
destinations)
NPDU - an IPv6 packet
NSAP - Network Service Access Point (a network layer address)
PDU - a packet
SNPA - subnetwork point of attachment (Data Link address)
It is expected that the above definitions should be adequate for
understanding of IDRP. Familiarity with any of the documents listed
in the normative references of the protocol specifications (section 2
of [5]) is not required.
Unless stated otherwise here, any reference to the above terms in [5]
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should be interpreted based on the above definitions.
3 The Adaptation Layer
The Inter-Domain Routing Protocol (IDRP) or, more formally,
"The Protocol for the Exchange of Inter-Domain Routing information
among Intermediate Systems to support Forwarding of ISO 8473 PDUs
(IDRP)"
is the inter-domain routing protocol defined to support the
forwarding of Connectionless Network Layer Protocol (CLNP) [6]
packets that traverse multiple routing domains.
IDRP document [5] covers both the protocol specifications and the
usage issues (which is in contrast to BGP-4 documentation that has a
separate document that defines the protocol [10], and a separate
document that describes the protocol's usage [9]).
While IDRP was developed within ISO, it makes few, if any, ISO-
specific assumptions. In particular, it does not require
participating domains to support any specific ISO Intra-Domain
protocol, such as IS-IS [7], nor does it require participating
routers to run ES-IS [8].
The only requirements imposed by the protocol on the participating
routers is that the protocol information can be exchanged among them
over a connectionless network layer (which in the case of OSI is
CLNP), and that the network layer connectivity between routers
within a single routing domain should be provided by means outside of
IDRP (e.g., via some intra-domain routing protocol). IDRP does not
place any restrictions on the structure of reachability information,
as long it can be expressed as an arbitrary set of variable length
address prefixes.
Since IPv4 and IPv6 can provide connectionless service between
routers, and since reachable IPv4/IPv6 destinations can be expressed
as IP address prefixes, IDRP can be easily adapted to be an inter-
domain routing protocol which can be used in the IP Internet.
The adaptation described in this document consists of: specifying the
parts of the protocol that are not needed, specifying
modifications/clarifications to certain parts of the protocol to
reflect IP specifics and operational experience with BGP-4, adding
new features to reflect operational experience with BGP-4.
4 Features in IDRP which shall not be implemented
The following lists the functions that shall not be implemented by
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IDRP for IPv4 an IPv6 (all references are with respect to [5]):
Support for distinguishing path attributes according to sections 5.7,
7.11.2 and 7.11.3 Expense according to section 7.12.10 Security
according to section 7.12.14 Priority according to section 7.12.16
Procedures for detecting inconsistent routing decisions, according to
section 7.15.1 Forwarding CLNP packets according to section 8 The
interface to CLNP according to section 9 support of the Network
Management information described in the IDRP GDMO according to
section 11
All the material presented in the sections listed above may be
ignored.
5 Features in IDRP which shall be implemented
An implementation of IDRP for IPv4 and IPv6 shall contain all
mandatory features
of IDRP, except those mentioned in section 4 of this document. In
addition, a BIS for IDRP for IPv4 and IPv6 shall implement the
following (all references are with respect to this document):
an interface to the IPv4 and IPv6 protocol, as described in section
5.1 Modifications to the encoding of reachability and forwarding
information, as well as the ability to identify and extract IPv4 and
IPv6 reachability and forwarding information as described in sections
5.2 and 5.3 Modifications to the ROUTE_SEPARATOR and
MULTI_EXIT_DISCRIMINATOR path attributes, as described in section 5.4
Support for the ATOMIC_AGGREGATE path attribute, as described in
section 5.5 Modifications to the tie-breaking procedures, as
described in sections 5.6 Modifications to handling Hold Time, as
described in section 5.7 Constructing forwarding address (next hop),
as described in section 5.8 Modifications to the UPDATE PDU format,
as described in section 5.9 Modifications to the OPEN PDU format, as
described in section 5.10 Modifications to the RIB REFRESH PDU
format, as described in section 5.11 New Error Subcodes, as described
in section 5.12
Naming and addressing conventions discussed in sections 5.10, 5.11
and 7.1 of [5] do not apply to IDRP for IPv4 and IPv6, and thus
should be ignored. Section 6 of this document contains the material
that covers naming and addressing conventions for IDRP for IPv4 and
IPv6.
Deployment guidelines for IDRP for IPv4 and IPv6 are specified in
section 7 of this document. These guidelines supersede the material
presented in section 7.2 of [5].
Domain configuration information for IDRP for IPv4 and IPv6 is
defined in section 8 of this document. The material of that section
supersedes the material presented in section 7.3 of [5].
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5.1 An interface to IP
This sections supersedes the material in section 7.5 of [5].
IDRP information is carried between a pair of BISs in the form of
BISPDUs. For IDRP for IPv6 these BISPDUs are carried in the data
field of IP packets of protocol type 45.
IDRP relies on IP to perform the initial processing of incoming
BISPDUs. The IP protocol machine shall process inbound packets
according to the appropriate IP functions.
If a fixed header of an IP packet contains a protocol type that
identifies IDRP, and the packet's source address identifies any
system listed in managed objects internalBIS or externalBISNeighbor,
then the packet contains a BISPDU. The BISPDU shall be passed to the
IDRP finite state machine defined in section 7.6.1 of [5].
5.2 Encoding IP reachability information
The text in this section supersedes the material presented in section
6.3.2 of [5].
The Network Layer Reachability information is a variable length field
that contains a list of reachable destinations encoded as zero or
more triples of the form <Address Family, Addr_length, Addr_info>,
whose fields are described below:
+---------------------------+
| Address Family (2 octets) |
+---------------------------+
| Addr_length (2 octets) |
+---------------------------+
| Addr_info (variable) |
+---------------------------+
The use and meaning of these fields are as follows:
Address Family:
This field carries the identity of the protocol associated with
the address information that follows. Presently defined values
for this field are specified in RFC1700. A conformant
implementation of IDRP for IPv6 may ignore any address
information indicating other than IPv6. A conformant
implenetation of IDRP for IPv4 may ignore any address
information indicating other than IPv4. Address Family.
Addr_Length:
This field specifies the total length in octets of the address
information that follows.
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Addr_Info:
This is a variable length field that contains a list of IP
address prefixes for the routes that are being advertised.
Each IP address prefix is encoded as a 2-tuple of the form
<Length, Prefix>, whose fields are described below:
+---------------------------+
| Length (1 octet) |
+---------------------------+
| Prefix (variable) |
+---------------------------+
The use and the meaning of these fields are as follows:
a) Length:
The Length field indicates the length in bits of the IP
address prefix. A length of zero indicates a prefix that
matches all IPv4 or IPv6 (as specified by the address
family) addresses (with prefix, itself, of zero octets).
b) Prefix:
The Prefix field contains IP address prefixes followed by
enough trailing bits to make the end of the field fall on an
octet boundary. Note that the value of trailing bits is
irrelevant.
5.3 Encoding IP forwarding information
IPv6 forwarding information is carried in the NEXT_HOP path
attribute. As specified in [5], the attribute has a Proto_type,
Proto_Length and Protocol fields which indicate the protocol family
for the address of the NEXT_HOP (see section 6.3.1.4 of [5]). This
document replaces these three fields (Proto_type, Proto_Length, and
Protocol) with a single field -- Address Family. This 2-octets field
carries the identity of the protocol associated with the address
information that follows. Presently defined values for this field are
specified in RFC1700. A conformant implementation of IDRP for IPv6
may ignore any address information indicating other than IPv6 Address
Family. A conformant implementation of IDRP for IPv4 may ignore any
address information other than the IPv4 Address Family.
An implementation of IDRP for IPv4 or IPv6 shall have the following
values in the NEXT_HOP field:
IPv6:
Length of NET: 16
NET of Next Hop: an IPv6 unicast address
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SNPA information: as appropriate for the subnetwork type in use
IPv4:
Length of NET: 4
NET of Next Hop: an IPv4 unicast address
SNPA information: as appropriate for the subnetwork type in use
All other fields of the NEXT_HOP attribute remains as specified in
[5].
5.4 Modification to the existing path attributes
To facilitate operations, IDRP for IPv6 modifies the following path
attributes:
LOCAL_PREF field in the ROUTE_SEPARATOR attribute (see section
6.3.1.1) is changed from 1 octet to 4 octets. The ROUTE-ID field in
the ROUTE_SEPARATOR attribute is eliminated. As a result the length
of the ROUTE_SEPARATOR attribute is changed from 5 to 4 octets. The
length of the MULTI_EXIT_DISCRIMINATOR attribute is changed from 1
octet to 4 octets.
Semantics, as well as handling of the modified attributes is left
intact.
5.5 New path attributes
IDRP for IPv6 defines the following new attribute:
AGGREGATOR (Type Code 17):
AGGREGATOR is an optional transitive attribute of length 32.
The attribute contains the last RDI that formed the
aggregate route (encoded as 16 octets), followed by the IP
address of the BIS that formed the aggregate route (encoded
as 16 octets, IPv4 addresses are prefixed with 12 octets of
zeros). The BIS that formed the aggregate route may decline
to encode its address and instead insert a value of all
zeros into that field.
The attribute may be included in routes which are formed by
route aggregation. A BIS that performs the aggregation may
add the AGGREGATOR attribute which shall contain BIS's own
RDI and IPv6 address.
ATOMIC_AGGREGATE (Type Code 18):
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ATOMIC_AGGREGATE is a well-known discretionary attribute of
length 0. It is used by a BIS to inform other BISs that the
local system selected for advertisement a less specific
route without selecting a more specific route which is
included in it.
If a BIS, when presented with a set of overlapping routes
from one of its peers, selects the less specific route
without selecting the more specific one, then the local
system shall attach the ATOMIC_AGGREGATE attribute to the
route when propagating it to other BISs (if that attribute
is not already present in the received less specific route).
A BIS that receives a route with the ATOMIC_AGGREGATE
attribute shall not remove the attribute from the route when
propagating it to other BISs. A BIS that receives a route
with the ATOMIC_AGGREGATE attribute shall not make any NLRI
of that route more specific when advertising this route to
other BISs. A BIS that receives a route with the
ATOMIC_AGGREGATE attribute needs to be cognizant of the fact
that the actual path to destinations, as specified in the
NLRI of the route, while having the loop-free property, may
traverse domains/confederations that are not listed in the
RD_PATH attribute.
5.6 Modifications to tie-breaking procedures for phase 2
This section supersedes the material in section 7.16.2.1 and 7.16.1.1
of [5].
In its Adj-RIBs-In a BIS may have several routes to the same
destination that have the same degree of preference. The local BIS
can select only one of these routes for inclusion in the associated
Loc-RIB. The local BIS considers all equally preferable routes, both
those received from BISs located in adjacent RDs, and those received
from other BISs located in the local BIS's own RD.
Ties shall be broken according to the following algorithm:
a) If the local BIS is configured to take into account
MULTI_EXIT_DISC, and the candidate routes differ in their
MULTI_EXIT_DISC attribute, select the route that has the lowest
value of the MULTI_EXIT_DISC attribute. If the local BIS is
configured to take into account MULTI_EXIT_DISC, but that
attribute is not present, a locally defined "default"
MULTI_EXIT_DISC may be assumed as a basis for performing tie-
breaking.
b) Otherwise, if the local BIS can ascertain the cost of a path to
the entity depicted by the NEXT_HOP attribute of the candidate
route, select the route with the lowest cost (interior distance)
to the entity depicted by the NEXT_HOP attribute of the route. If
there are several routes with the same cost, then the tie-breaking
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shall be broken as follows:
- if at least one of the candidate routes was advertised by the
BIS in an adjacent RD, select the route that was advertised by
the BIS in an adjacent RD whose address has the lowest value
among all other BIS in adjacent RDs;
- otherwise, select the route that was advertised by the BIS
whose address has the lowest value.
5.7 Modifications to handling Hold Time
Upon receipt of an OPEN BISPDU, a BIS 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 BISPDU.
IDRP for IPv6 requires the value of the Hold Time field carried in
the OPEN BISPDU to be either zero or at least 3 seconds. An
implementation must reject Hold Time values of one or two seconds.
An implementation may reject any proposed Hold Time. An
implementation which accepts a Hold Time must use the negotiated
value for the Hold Time. If the negotiated Hold Time interval is
zero, then periodic KEEPALIVE messages shall not be sent.
In addition to the OPEN PDU error handling procedures specified in
section 7.20.2 of [5] this document specifies that if the Hold Time
field of the OPEN message is unacceptable, then the Error Subcode
shall be set to Unacceptable Hold Time.
5.8 Determining the forwarding address (Next Hop)
Next hop forwarding information information associated with a
particular route shall be derived from the NEXT_HOP attribute in the
UPDATE BISPDU that carries the route. If that attribute is not
present, the next hop (forwarding address) shall be derived from the
source IPv6 address of the IPv6 packet that carries the UPDATE BISPDU
containing the route.
In addition to the procedures for handling the NEXT_HOP attribute
specified in section 7.12.4 of [5], IDRP for IPv4 and IPv6 specifies
the following:
A BIS must never advertise an address of a peer to that peer as a
NEXT_HOP, for a route that the speaker is originating. A BIS must
never install a route with itself as the next hop. When a BIS
advertises the route to a BIS located in its own domain, the
advertising BIS should not modify the NEXT_HOP attribute associated
with the route. When a BIS receives the route from an internal
neighbor BIS, it may use the NEXT_HOP address as the forwarding
address, provided that the address is on a common subnet with the
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local BIS.
5.9 Modifications to the UPDATE PDU
This document specifies that NLRI of a route, rather than the Route-
ID of the route, shall be used to withdraw a previously advertised
route from service.
The Withdrawn Routes field in the UPDATE PDU is specified as a
variable length field that contains a list of NLRIs (rather than the
list of Route-IDs) for the routes that are being withdrawn from
service. Each NLRI is encoded as specified in Section 5.2 of this
document. An UPDATE PDU can list multiple routes to be withdrawn
from service. Each such route is identified by its NLRI, which
unambiguously identifies the route in the context of the BIS-BIS
connection in which it had been previously been advertised.
Eliminating Route-ID is also reflected in the encoding of the
ROUTE_SEPARATOR attribute (see Section 5.4 of this document).
5.10 Modifications to the OPEN PDU
Since IDRP for IPv6 doesn't support any Distinguishing Attrbutes, the
RIB-AttsSet field is eliminated from the OPEN PDU. (PST--bring back
DA's?)
The last two fields of the OPEN PDU message, Authentication Code and
Authentication Data, are replaced with the following two fields:
Optional Parameters Length:
This 2-octet unsigned integer indicates the total length of the
Optional Parameters following this field in octets. If the
value of this field i s 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 Flags, Parameter
Type, Parameter Length, Parameter Value> vector.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
| Parm Flags | Parm. Type | Parm. Length | Parameter Value (variable)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
(PST: grab BGP/4 flags text and talk to yakov about making
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length extensible
just like attribute length in BGP)
Parameter Flags is a one octet field that (PST: grab text from
BGP-4)
Parameter Type is a one octet field that unambiguously
identifies individual parameters. Parameter Length is a one
octet field that contains the length of the Parameter Value
field in octets. Parameter Value is a variable length field
that is interpreted according to the value of the Parameter
Type field.
This document defines the following Optional Parameters:
a) Authentication Information (Parameter Type 1):
This optional parameter may be used to authenticate a BIS
peer. The Parameter Value field contains a 1-octet
Authentication Code followed by a variable length
Authentication Data.
0 1 2 3 4 5 6 7 8
+-+-+-+-+-+-+-+-+
| Auth. Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Authentication Data (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The syntax and semantics of these two field is left
unchanged (as specified in section 6.2 of [5]).
Absence of any Authentication Information in an OPEN PDU shall be
treated as if the PDU carries Authentication Information with
Authentication Type 1 (see section 7.1.1 of [5]).
In addition to the OPEN PDU error handling procedures specified in
section 7.20.2 of [5] this document specifies that if one of the
Optional Parameters in the OPEN message is not recognized, then the
Error Subcode is set to Unsupported Optional Parameters.
5.11 Modifications to the RIB REFRESH PDU
This sections supersedes the material in section 6.7 of [5].
The RIB REFRESH PDU is used to allow a BIS to send a refresh of the
routeing information in an Adj-RIB-Out to a neighbor BIS, or to
solicit a neighbor BIS to send a refresh of its Adj-RIB-Out to the
local BIS. The RIB REFRESH PDU contains a fixed header and also the
additional fields shown below:
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+---------------------------------------+
| Fixed Header |
+---------------------------------------+
| OpCode (1 octet) |
+---------------------------------------+
| Optional Parameter Length (1 octet) |
+---------------------------------------+
| Optional Parameters (variable) |
+---------------------------------------+
The use and meaning of these fields is as follows:
There are three OpCode values defined:
+------------+---------------------+
| Code | Operation |
+------------+---------------------+
| 1 | RIB Refresh Request |
+------------+---------------------+
| 2 | RIB Refresh Start |
+------------+---------------------+
| 3 | RIB Refresh End |
+------------+---------------------+
Optional Parameters Length:
This 1-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
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
| Parm. Type | Parm. Length | Parameter Value (variable)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
Parameter Type is a one octet field that unambiguously
identifies individual parameters. Parameter Length is a one
octet field that contains the length of the Parameter Value
field in octets. Parameter Value is a variable length field
that is interpreted according to the value of the Parameter
Type field.
When a BIS receives a RIB REFRESH PDU that contains one or more
Optional Parameters, and the BIS doesn't support or does't recognize
at least one of the parameters, the BIS processes the PDU as if it
wouldn't have any Optional Parameters. This document doesn't specify
any Optional Parameters.
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Usage of RIB REFRESH PDU is defined in 7.10.3 of [5].
5.12 Additional Error Subcodes
In addition to the Error subcodes defined in section 5.4 of [5], this
document defines the following OPEN PDU Error subcodes:
8 - Unacceptable Hold Time (see Section 5.7 of this document)
9 - Unsupported Optional Parameter (see Section 5.12 of this
document)
6 Naming and addressing conventions
This section supersedes the material of sections 5.10, 5.11 and 7.1
of [5].
IDRP for IPv4 and IPv6 does not assume or require any particular
structure for IP addresses. That is, as long as the domain
administrator assigns addresses that are consistent with the
deployment constraints of section 7 of this document, the protocol
will operate correctly.
IP address prefixes provide a compact way for identifying groups of
systems that reside in a given domain or confederation. A prefix may
have a length that is either smaller than, or the same size as the IP
address (an IPv4 or IPv6 address is a special case of an address
prefix). The length of an encoded prefix is specified in bits.
Each routing domain and routing domain confederation whose BIS(s)
implement IDRP for IPv4 and IPv6 shall have an unambiguous routing
domain identifier (RDI), which is an IPv4 or IPv6 address prefix. In
the case of IPv4 address prefixes, the prefix value shall be
prepended with 12 octets of zeros.
An RDI is assigned statically and does not change based on the
operational status of a routing domain. An RDI identifies routing
domain or confederation uniquely, but does not necessarily convey any
information about policies or identities of its members.
7 Deployment guidelines
This section supersedes the material in section 7.2 of [5].
Hosts and routers may use any IP unicast addresses, provided that
these addresses are globally unambiguous. However correct and
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efficient operation of this protocol can only be guaranteed if the
address assignment reflects the actual topology -- addresses are
topologically significant. One possible architecture for IPv6 address
assignment that satisfies this requirement is described in [12].
8 Domain Configuration Information
Correct Operation of IDRP described in [5] assumes that a minimum
amount of information is available to both the inter-domain and
intra-domain routing protocols. This information is static in
nature, and is not expected to change frequently. This document
assumes that this information is supplied via IDRP MIB. While the
following in phrased in terms of MIB, this document allows
alternative mechanisms (e.g. configuration files) as well.
The information required by a BIS that implements the IDRP for IPv4
and IPv6 protocol is:
Location and identity of adjacent Intra-Domain routers:
The MIB table IntraIS lists the IP addresses of the routers to which
the local BIS may deliver an inbound NPDU whose destination lies
within the BIS's routing domain. These routers listed in the IntraIS
table support the intra-domain routing protocol of this domain, and
share at least one common subnet with the BIS.
In particular, if the local BIS participates in both the inter-
domain routing protocol (IDRP) and the intra-domain routing
protocol, then the IP address of the local BIS will be listed in the
IntraIS table.
Location and identity of BISs in the BIS's domain:
This information permits a BIS to identify all other BISs located
within its routing domain. This information is contained in the MIB
table InternalBIS, which contains a set of IPv6 addresses which
identify the BISs in the domain.
Location and identity of BISs in adjacent domains:
Each BIS needs information to identify the IP address of each BIS
located in an adjacent RD and reachable via a single subnetwork hop.
This information is contained in the IDRP MIB table
externalBISNeighbor, which is a table of IPv6 addresses.
IP network address information for all systems in the routing domain:
This information is used by the BIS to construct its network layer
reachability information. This information is contained in the MIB
table internalSystems, which lists NLRI (expressed as address
prefixes) of the systems within the routing domain.
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Local RDI:
This information is contained in managed object localRDI; it is the
RDI of the routing domain in which the BIS is located.
RDC-Config:
This information identifies all the routing domain confederations
(RDCs) to which the RD of the local BIS belongs, and it describes the
nesting relationships that are in force between them. It is contained
in the MIB table rdcConfig.
Note that since a domain is not required to belong to a confederation
this information is optional and needs to be present only at BISs of
the domains that are part of one or more of RDCs.
9 Multiple IDRP sessions between the same pair of routers
An IP router may have multiple IP addresses, one for each interface.
In contrast, an OSI Intermediate System has only one Network Entity
Title (network address). An OSI BIS thus may not have multiple IDRP
sessions with another BIS, since the NET is unique and there is no
mechanism for multiplexing sessions. However, an IP router may
potentially have multiple IDRP sessions with another router, since
each BIS may have multiple IP addresses, and one BIS may not be able
to ascertain that those addresses correspond to the same BIS.
Multiple IDRP sessions between BISs may not be efficient, but they
are not illegal, nor do they impact the robustness of the IDRP for IP
protocol; they will simply appear as multiple paths to the same
neighboring domain. One possible way of avoiding multiple parallel
IDRP sessions between a pair of BISs within a single domain is to
bind all source addresses of outgoing BISPDUs to the IPv6 address of
a particular interface (either physical or logical) of the BIS.
Likewise, for a pair of BISs located in adjacent domains, binding the
source addresses to a single address of an interface attached to a
common subnetwork allows for the elimination of multiple parallel
sessions.
10 Required set of supported routing policies
Policies are provided to IDRP in the form of configuration
information. This information is not directly encoded in the
protocol. Therefore, IDRP can provide support for very complex
routing policies (an example of such policy is presented in Annex K
of [5]). However, it is not required that all IDRP implementations
support such policies.
We are not attempting to standardize the routing policies that must
be supported in every IDRP implementation; we strongly encourage all
implementors to support the following set of routing policies:
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IDRP implementations should allow a domain to control announcements
of IDRP-learned routes to adjacent domains. Implementations should
also support such control with at least the granularity of a single
address prefix. Implementations should also support such control
with the granularity of a domain, where the domain may be either the
domain that originated the route, or the domain that advertised the
route to the local system (adjacent domain). Care must be taken when
a BIS selects a new route that can't be announced to a particular
external peer, while the previously selected route was announced to
that peer. Specifically, the local system must explicitly indicate
to the peer that the previous route is now infeasible. IDRP
implementations should allow a domain to prefer a particular path to
a destination (when more than one path is available). At the minimum
an implementation shall support this functionality by allowing to
administratively assign a degree of preference to a route based
solely on the IP address of the neighbor the route is received from.
The allowed range of the assigned degree of preference shall be
between 0 and 2^(31) - 1. IDRP implementations should allow a domain
to ignore routes with certain domains in the RD_PATH path attribute.
Such function can be implemented by assigning "infinity" as "weights"
for such domains. The route selection process must ignore routes that
have "weight" equal to "infinity".
11 Operations over Switched Virtual Circuits
When using IDRP for IPv4 and IPv6 over Switched Virtual Circuit (SVC)
subnetworks it may be desirable to minimize traffic generated by
IDRP. Specifically, it may be desirable to eliminate traffic
associated with periodic KEEPALIVE messages. IDRP for IPv4 and IPv6
includes a mechanism for operation over switched virtual circuit
(SVC) services which avoids keeping SVCs permanently open and allows
it to eliminates periodic sending of KEEPALIVE messages.
This section describes how to operate without periodic KEEPALIVE
messages to minimize SVC usage when using an intelligent SVC circuit
manager. The proposed scheme may also be used on "permanent"
circuits, which support a feature like link quality monitoring or
echo request to determine the status of link connectivity.
The mechanism described in this section is suitable only between the
BISs that are directly connected over a common virtual circuit.
11.1 Establishing an IDRP Connection
The feature is selected by specifying zero Hold Time in the OPEN
BISPDU.
11.2 Circuit Manager Properties
The circuit manager must have sufficient functionality to be able to
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compensate for the lack of periodic KEEPALIVE BISPDU:
It must be able to determine link layer unreachability in a
predictable finite period of a failure occurring. On determining
unreachability it should: start a configurable dead timer (comparable
to a typical Hold timer value). attempt to re-establish the Link
Layer connection.
If the dead timer expires it should: send a deactivate indication to
IDRP FSM. If the connection is re-established it should: cancel the
dead timer. transmit any queued BISPDUs.
11.3 Combined Properties
Some implementations may not be able to guarantee that the IDRP
process and the circuit manager will operate as a single entity; i.e.
they can have a separate existence when the other has been stopped or
has crashed.
If this is the case, a periodic two-way poll between the IDRP process
and the circuit manager should be implemented. If the IDRP process
discovers the circuit manager has gone away it should close all
relevant BIS-BIS connections. If the circuit manager discovers the
IDRP process has gone away it should close all its BIS-BIS
connections associated with the IDRP process and reject any further
incoming BIS-BIS connections.
12 Modifications to the conformance clause
To reflect the list of functions that shall not be implemented (see
section 4 of this document) the following items in the IDRP
conformance clause (section 12.1 of [5]) shall not be implemented:
clause (d): Transit Delay, Residual Error, Expense, clause (m)
clause (r) clause (s) clause (t)
13 Modifications to PICS
The PICS (Protocol Implementation Conformance Statement) provides a
convenient and concise mechanism to define which function need and
need not be implemented for IDRP for IPv4 and IPv6. All references
in this section are with respect to [5].
All items with PICS Status as Optional need not be implemented in
IDRP for IPv4 and IPv6. In addition, IDRP for IPv4 and IPv6 should
not support the following items (even if some of the items are listed
as Mandatory):
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Table A.4.3:
MGT
Table A.4.5:
INCONS
Table A.4.8:
PSRCRT, DATTS, MATCH
Table A.4.11:
TDLY, RERR, EXP, LQOSG, SECG, PRTY
Table A.4.12:
TDLYP, RERRP, EXPP, LQOSP, SECP, PRTYP
Table A.4.13:
TDLYR, RERRR, EXPR, LQOSR, SECR, PRTYR
Implementation of all other items with Optional Status not listed in
the previous paragraph is optional.
14 Navigating through IDRP
Here is the list of sections in [5] that are relevant to the IDRP
for IPv6 implementation: chapters 1, 3, 4, 5 (except 5.10 and 5.11),
6, 7 (except for 7.1, 7.2, 7.3, 7.4, 7.12.8, 7.12.9, 7.12.10, 7.12.11
and 7.12.16), 10. The rest of the material in [5] could be safely
ignored.
15 Security Considerations
Security issues are not discussed in this document.
16 Acknowledgements
Large parts of this document are borrowed from the BGP Protocol
specifications and BGP Usage documents ([9], [10]).
We would like to thank Susan Hares (MERIT) and John Scudder (MERIT)
for their work on IDRP for IPv4. Portions of this document are
borrowed from their work.
We would like to thank Tony Li (cisco Systems) for his review of this
document.
Finally we would like to thank the whole Inter-Domain Routing (IDR)
Working Group for their contribution to this document.
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17 References
[1] Braun, H-W., "Models of Policy Based Routing", RFC 1104,
Merit/NSFNET, June 1989.
[2] Fuller, V., Li, T., Yu, J., Varadhan, K., "Classless Inter-Domain
Routing (CIDR): an Address Assignment and Aggregation Strategy", RFC
1519, September 1993
[3] Deering, S., Hinden, B., "Internet Protocol, Version 6 (IPv6)
Specification", RFC1883, January 1996
[4] Hinden, B., Deering, S., "IP Version 6 Addressing Architecture",
RFC1884, January 1996
[5] ISO/IEC IS 10747 - Information Processing Systems -
Telecommunications and Information Exchange between Systems -
Protocol for Exchange of Inter-domain Routing Information among
Intermediate Systems to Support Forwarding of ISO 8473 PDUs, 1993
ftp://networking.raleigh.ibm.com/pub/standards/idrp/is10747.ps
ftp://networking.raleigh.ibm.com/pub/standards/idrp/is10747.txt
[6] ISO 8473 - Information Processing Systems - Data Communications
- Protocol for Providing the Connectionless-mode Network Service,
1988.
[7] ISO/IEC 10589 - Information Processing Systems -
Telecommunications and Information Exchange between systems -
Intermediate System to Intermediate System Intra-Domain routing
information exchange protocol for use in conjunction with the
Protocol for providing the Connectionless-mode Network Service (ISO
8473), 1992.
[8] ISO 9542 - Information Processing Systems - Telecommunications
and information exchange between systems - End system to Intermediate
system routing exchange protocol for use in conjunction with the
Protocol for providing the connectionless-mode network service (ISO
8473)
[9] Rekhter, Y., Gross, P., ``Application of the Border Gateway
Protocol in the Internet'', RFC1655, July 1994
[10] Rekhter, Y., Li, T., ``A Border Gateway Protocol 4 (BGP-4)'',
RFC1654, July 1994
[11] Rekhter, Y., Li, T., "An Architecture for IP Address Allocation
with CIDR", RFC1518, September 1993
[12] Rekhter, Y., Li, T., "An Architecture for IPv6 Unicast Address
Allocation", RFC1887, January 1996
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Authors' Addresses
Yakov Rekhter
cisco Systems, Inc.
170 W. Tasman Dr.
San Jose, CA 95134
email: yakov@cisco.com
Paul Traina
cisco Systems, Inc.
170 W. Tasman Dr.
San Jose, CA 95134
email: pst@cisco.com
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