MPLS & RSVP Working Groups Daniel Awduche
Internet Draft UUNET Technologies, Inc.
Expiration Date: February 1999
Der-Hwa Gan
Juniper Networks, Inc.
Tony Li
Juniper Networks, Inc.
George Swallow
Cisco Systems, Inc.
Vijay Srinivasan
Torrent Networks, Inc.
August 1998
Extensions to RSVP for Traffic Engineering
draft-swallow-mpls-rsvp-trafeng-00.txt
Status of this Memo
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Abstract
This document describes the use of RSVP, including all the necessary
extensions, to support traffic engineering with MPLS as specified in
[6].
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We propose several additional objects that extend RSVP, allowing the
establishment of explicitly routed label switched paths (LSPs), using
RSVP as a signaling protocol. The result is the instantiation of
label-switched sessions which can be automatically routed away from
network failures, congestion, and bottlenecks.
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Contents
1 Introduction ........................................... 4
2 Overview of operation .................................. 5
2.1 Service Classes ........................................ 6
2.2 Reservation styles ..................................... 6
2.2.1 Fixed Filter (FF) style ................................ 7
2.2.2 Wildcard Filter (WF) style ............................. 7
2.2.3 Shared Explicit (SE) style ............................. 8
2.3 LSP Tunnels ............................................ 8
2.4 Rerouting LSP Tunnels .................................. 9
3 RSVP Message Formats ................................... 10
3.1 Path message ........................................... 10
3.2 Resv message ........................................... 11
4 Objects ................................................ 11
4.1 Label Object ........................................... 11
4.1.1 Handling Label Objects in Resv messages ................ 12
4.1.2 Non-support of the Label Object ........................ 13
4.2 Label Request Object ................................... 13
4.2.1 Handling of LABEL_REQUEST .............................. 14
4.2.2 Non-support of the Label Request Object ................ 14
4.3 Explicit Route Object .................................. 15
4.3.1 Subobjects ............................................. 15
4.3.2 Applicability .......................................... 16
4.3.3 Semantics of the Explicit Route Object ................. 16
4.3.4 Strict and Loose subobjects ............................ 17
4.3.5 Loops .................................................. 18
4.3.6 Subobject semantics .................................... 18
4.3.7 Processing of the Explicit Route Object ................ 20
4.3.8 Non-support of the Explicit Route Object ............... 21
4.4 Record Route Object .................................... 22
4.4.1 Subobjects ............................................. 22
4.4.2 Applicability .......................................... 24
4.4.3 Handling RRO ........................................... 25
4.4.4 Loop Detection ......................................... 26
4.4.5 Non-support of RRO ..................................... 26
4.5 Error subcodes for ERO and RRO ......................... 27
4.6 Session, Sender Template, and Filter Spec Objects ...... 27
4.6.1 Session Object ......................................... 27
4.6.2 Sender Template Object ................................. 28
4.6.3 Filter Specification Object ............................ 29
4.6.4 Reroute procedure ...................................... 29
4.7 Session Attribute Object ............................... 30
5 RSVP Aggregate Message ................................. 33
5.1 Aggregate Header ....................................... 33
5.2 Message Formats ........................................ 35
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5.3 Sending RSVP Aggregate Messages ........................ 35
5.4 Receiving RSVP Aggregate Messages ...................... 36
5.5 Forwarding RSVP Aggregate Messages ..................... 37
5.6 Aggregate-capable bit .................................. 37
6 Tear Confirm ........................................... 37
7 Security Considerations ................................ 39
8 Acknowledgments ........................................ 39
9 References ............................................. 39
1. Introduction
For hosts and routers that support both RSVP [1] and Multi-Protocol
Label Switching [2], it is possible to associate labels with RSVP
flows [4]. The result is that a router can identify the appropriate
reservation state for a packet based on its label value, thus greatly
simplifying packet classification. This design also improves network
performance because the same label lookup identifies forwarding
information of the packet.
Using RSVP to establish label switched paths (LSPs) clearly enables
the allocation of resources to an LSP. For example, you can allocate
bandwidth to an LSP using standard RSVP reservations and Integrated
Services service classes [7]. While this is useful, reservations are
not required. An LSP can also be established to carry best-effort
traffic without a resource reservation.
It is possible to add explicit routing capability on top of label-
switched RSVP flows [3] [5] by adding a simple EXPLICIT_ROUTE object
to RSVP. By using this object, the paths taken by label-switched
RSVP flows can be predetermined, independent of conventional IP
routing. The hops in the path can be manually configured, or
computed automatically based on the QoS requirements of the flow and
the current network load.
The purpose of this document is to organize all the objects from [3],
[4], and [5] into a single document that fully describes all the
procedures and packet formats so that interoperable implementations
are possible. A few new objects are also suggested for enhancing
management and diagnostics of LSPs. All objects described are
optional, and this document describes what happens when an object is
not supported by a node.
Finally, an RSVP aggregate message is proposed to help alleviate one
of the RSVP scaling issues: how to efficiently handle large number of
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RSVP messages that are periodically transmitted between neighbors.
The document concentrates on unicast LSPs. Explicitly routed
multicast LSPs are left for further study.
2. Overview of operation
When an RSVP flow originates in or crosses an MPLS domain, the flow
may be label switched. To initiate label switching, the first MPLS
node inserts a LABEL_REQUEST object into the Path message. The
LABEL_REQUEST object indicates that a label binding for this path is
requested, and also provides an indication of the network layer
protocol that is to be carried over this path. The reason for this is
that the network layer protocol sent down an LSP cannot be assumed to
be IPv4, and cannot be deduced from the L2 header, which simply
identifies the higher layer protocol as being MPLS.
If the sender node has prior knowledge of an alternative route that
has better likelihood of meeting the flow's QoS requirement or that
makes more efficient use of network resources, the node can decide to
reroute some of its sessions. To do this, the node adds an
EXPLICIT_ROUTE object to the Path message.
If, during a session, the sender node finds a better route, the
session can be rerouted on the fly by simply changing the
EXPLICIT_ROUTE object. If there are problems with an EXPLICIT_ROUTE
object, either because it causes a routing loop or some intermediate
routers do not support it, the sender node is notified.
If the RECORD_ROUTE object is added to Path messages, the sender node
can receive information about the exact routing path and can prompt
for notifications from the network if the routing path changes for
any reason.
Finally, a SESSION_ATTRIBUTE object can be added to Path messages for
aiding in session identification and diagnostics. Additional control
information, such as preemption, priority, and fast-reroute, is also
included in this object.
When the EXPLICIT_ROUTE object (ERO) is present, the Path message is
forwarded towards its destination along a path specified by the ERO.
Each node along the path records the ERO in its path state block.
Nodes may also modify the ERO before forwarding the Path message, in
which case the modified ERO should be stored in the path state block.
The LABEL_REQUEST object requests intermediate routers and receiving
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nodes to provide a label binding for the session. If a node is
incapable of providing a label binding it sends a PathErr message
with an "unknown object class" error. If the LABEL_REQUEST object is
not supported end to end, the sender node will be notified by the
first node which lacks the support.
The destination node includes a LABEL object in its response Resv
message. The LABEL object is inserted in the filter spec list
immediately following the filter spec to which it pertains. When the
LABEL object propagates upstream to the sender node, a label-switched
path is already set up for use.
The Resv message is sent back towards the sender. A node that
receives a Resv message containing a label uses that label for
outgoing traffic on this path. It also allocates a new label and
places that label in the corresponding LABEL object of the Resv
message before sending it upstream. This is the label that this node
will use for incoming traffic on this path. This label now serves as
shorthand for the Filter Spec.
2.1. Service Classes
This document does not restrict the type of Integrated Service
requested on a reservations. However, an implementation should
always be ready to accept the Controlled-Load service [7].
An LSP may not need a bandwidth reservation or a QoS guarantee. Such
LSPs can be used to deliver best-effort traffic, even if RSVP is used
for setting up LSPs. When no resources need to be allocated to the
LSP, the Sender_TSpec in the Path message can specify a token bucket
rate of zero and a token bucket size of zero. The corresponding
FLOWSPEC (in the Resv message) should carry a zero rate and size as
well. LSPs with no bandwidth reservation are not subject to
Admission Control and do not require traffic policing.
2.2. Reservation styles
The receiver node can select from among a set of possible reservation
styles for each session, and each RSVP session must have a particular
style. Senders have no influence on the choice of reservation style.
The receiver can choose different reservation styles for different
LSPs. An RSVP session is identified by a unique (destination
address, protocol, destination port) tuple.
An RSVP session can create one or more LSPs, depending on the
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reservation style chosen.
Some reservation styles, such as FF, dedicate a particular
reservation to an individual sender node. Other reservation styles,
such as WF and SE, can share a reservation among several sender
nodes. The following sections discuss the different reservation
styles and their advantages and disadvantages.
2.2.1. Fixed Filter (FF) style
The Fixed Filter (FF) reservation style creates a distinct
reservation for traffic from each sender that is not shared by other
senders. This style is common for applications in which traffic from
each sender is likely to be concurrent and independent. The total
amount of reserved bandwidth on a link for sessions using FF is the
sum of the reservations for the individual senders.
Because each sender has its own reservation, a unique label and a
separate label-switched-path is assigned to each sender. This
results in a point-to-point LSP between every sender/receiver pair.
Because the network state overhead is proportional to the number of
LSPs, having more LSPs means that more network resources are
consumed.
2.2.2. Wildcard Filter (WF) style
With the Wildcard Filter (WF) reservation style, a single shared
reservation is used for all senders. The total reservation on a link
remains the same regardless of the number of senders. This style is
useful in applications in which not all senders send traffic at the
same time. A phone conference, for example, is an application where
not all speakers talk at the same time.
A single label-switched-path is created for all senders, because all
senders to the session are covered by the reservation. On links that
senders share, a single label is allocated. If there is only one
sender, the LSP looks like normal point-to-point connection. When
multiple senders are present, a multipoint-to-point LSP (a reversed
tree) is created. This has the advantage of minimizing the number of
LSPs (and the memory and CPU resources used for each LSP), allowing
the network to scale better.
Because of the merging rules, EXPLICIT_ROUTE objects cannot be used
with WF reservations. Hence, the use of the WF style should be
discouraged in the presence of ERO.
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2.2.3. Shared Explicit (SE) style
Unlike the WF style, where any sender is allowed to share the
reservation, the Shared Explicit (SE) style allows a receiver to
explicitly specify the senders to be included. There is a single
reservation on a link for all the senders listed.
Only listed senders can join the reservation.
Because each sender is explicitly listed in the Resv message, you can
assign separate labels to each sender, therefore creating separate
LSPs for each sender. [4] describes the reason why separate LSPs are
needed.
Having separate LSPs for each sender also eliminates the
incompatibility with the EXPLICIT_ROUTE object. Path messages from
different senders can carry their own ERO, and the paths taken by the
senders can converge and diverge at any point.
Unlike the FF style, all SE LSPs share the single reservation.
Unlike the WF style, a separate LSP is created for each sender.
2.3. LSP Tunnels
When LSPs are used to carry flows, it becomes possible to be more
flexible in the definition of a flow. The first node in an LSP can
use any of a variety of means to determine which packets will be
assigned a particular label. Once that label is assigned, the label
becomes the definition of the flow. We refer to such an LSP as an
LSP Tunnel due to the opaque nature of the flow.
In support of this, a new SESSION object, LSP_TUNNEL_IPv4 is defined.
The semantics of this object are that the flow is defined solely on
the basis of packets arriving from the PHOP with the particular label
value(s) assigned by this node to senders to the session. In fact,
the IPv4 appearing in the object name only denotes that the
destination address is an IPv4 address.
An application of particular interest is traffic engineering. By
establishing ER-LSPs a node at the edge of an MPLS domain can control
the path which traffic from this node will take through that domain.
These capabilities can be used to optimize the utilization of network
resources and enhance traffic oriented performance characteristics.
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2.4. Rerouting LSP Tunnels
One of the requirements for Traffic Engineering is the ability to
have an LSP tunnel re-routed upon a failure of a resource along its
current path. A further requirement is the ability to have the LSP
tunnel return to its original path when the failed resource is
restored.
It is also desirable not to disrupt traffic while rerouting is in
progress. The adaptive rerouting requirement calls for establishing
a new LSP while keeping the old LSP intact.
On links that old and new LSPs share, one wishes to (1) not release
resources from the old LSP that one wants to use for the new LSP, and
(2) not double-count reservations, because this might cause Admission
Control to deny the new LSP.
The combination of the LSP_TUNNEL_IPv4 SESSION object and the SE
reservation style naturally achieves smooth transitions. The
LSP_TUNNEL_IPv4 SESSION object is used to narrow the scope of the
RSVP session to the particular tunnel in question. To uniquely
identify a tunnel we use the combination of the destination IP
address, a Tunnel ID, and the sender's IP address which is placed in
the Extended Tunnel ID field.
During the reroute operation, the source needs to be able to appear
as two different sources to RSVP. This is achieved by the use of a
"LSP ID", which is carried in the SENDER_TEMPLATE and FILTER_SPEC
objects. Since the semantics of these objects is changed, a new C-
Type is assigned.
To effect a reroute, the source node picks a new LSP ID and forms a
new SENDER_TEMPLATE. It creates a new ERO to define the new path.
The node sends a new Path Message using the original SESSION object
and the new SENDER_TEMPLATE and ERO. It continues to use the old LSP
and refresh the old Path message. On links which are not in common,
the new Path message is treated as any new LSP tunnel setup. On
links held in common, the shared SESSION object and SE style allow
the LSP to be established sharing the same resources. Once the
sender receives a Resv message for the new LSP, it is free to begin
using it and to tear down the old LSP.
Also new C-Types are assigned for the SESSION, SENDER_TEMPLATE, and
FILTER_SPEC objects.
Detailed descriptions of the new objects are given in later sections.
All new objects are optional with respect to RSVP. An implementation
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3. RSVP Message Formats
Five new objects are defined in this document:
Object name Applicable RSVP messages
--------------- ------------------------
LABEL_REQUEST Path
LABEL Resv
EXPLICIT_ROUTE Path
RECORD_ROUTE Path, Resv
SESSION_ATTRIBUTE Path
can choose to support some but not other objects. However, the
LABEL_REQUEST and LABEL objects are mandatory with respect to this
document.
The LABEL and RECORD_ROUTE objects, are sender specific. They must
immediately follow either the SENDER_TEMPLATE in Path messages, or
the FILTER_SPEC in Resv messages.
The placement of EXPLICIT_ROUTE, LABEL_REQUEST, and SESSION_ATTRIBUTE
objects is simply a suggestion. While it is recommended that an
implementation follow this format, the ordering of these objects is
not important, so an implementation must be prepared to accept
objects in any order.
3.1. Path message
The format of the Path message is as follows:
<Path Message> ::= <Common Header> [ <INTEGRITY> ]
<SESSION> <RSVP_HOP>
<TIME_VALUES>
[ <EXPLICIT_ROUTE> ]
<LABEL_REQUEST>
[ <SESSION_ATTRIBUTE> ]
[ <POLICY_DATA> ... ]
[ <sender descriptor> ]
<sender descriptor> ::= <SENDER_TEMPLATE> [ <SENDER_TSPEC> ]
[ <ADSPEC> ]
[ <RECORD_ROUTE> ]
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3.2. Resv message
The format of the Resv message is as follows:
<Resv Message> ::= <Common Header> [ <INTEGRITY> ]
<SESSION> <RSVP_HOP>
<TIME_VALUES>
[ <RESV_CONFIRM> ] [ <SCOPE> ]
[ <POLICY_DATA> ... ]
<STYLE> <flow descriptor list>
<WF flow descriptor> ::= <FLOWSPEC> <LABEL>
[ <RECORD_ROUTE> ]
<FF flow descriptor list> ::= <FLOWSPEC> <FILTER_SPEC> <LABEL>
[ <RECORD_ROUTE> ]
| <FF flow descriptor list> <FF flow descriptor>
<FF flow descriptor> ::= [ <FLOWSPEC> ] <FILTER_SPEC> <LABEL>
[ <RECORD_ROUTE> ]
<SE flow descriptor> ::= <FLOWSPEC> <SE filter spec list>
<SE filter spec list> ::= <SE filter spec>
| <SE filter spec list> <SE filter spec>
<SE filter spec> ::= <FILTER_SPEC> <LABEL> [ <RECORD_ROUTE> ]
Note: LABEL and RECORD_ROUTE (if present), are bound to the
preceding FILTER_SPEC. No more than one LABEL and/or
RECORD_ROUTE may follow each FILTER_SPEC.
4. Objects
4.1. Label Object
Labels may be carried in Resv messages. When a label is to be
associated with a single sender, it must immediately follow the
FILTER_SPEC for that sender in the Resv message.
The LABEL object was first documented in [4]. The LABEL object has
the following format:
The contents of a LABEL object are a stack of labels, where each
label is encoded right aligned in 4 octets. The top of the stack is
in the right 4 octets of the object contents. A LABEL object that
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LABEL class = 16, C_Type = 1
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length (bytes) | Class-Num | C-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// (Object contents) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (top label) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
contains no labels is illegal.
Each label is an unsigned integer in the range 0 through 1048575.
The decision of whether to create a label stack with more than one
label, when to push a new label, and when to pop the label stack are
to be specified in a separate document. For implementations that do
not support a label stack, only the top label is examined. The rest
of the label stack should be passed through unchanged. Such
implementations are required to generate a label stack of depth 1
when initiating the first LABEL.
4.1.1. Handling Label Objects in Resv messages
For unicast sessions, only Resv messages contain the LABEL object.
If a router does not wish to support MPLS for the session, the router
can ignore the received LABEL objects and continue processing the
rest of Resv message.
The router uses the top label carried in the LABEL object as the
outgoing label associated with the session (if WF) or sender (if FF
or SE). The router allocates a new label and binds it to the
incoming interface of this session/sender. This is the same
interface that the router uses to forward Resv messages to the
previous hops.
To construct a new LABEL object, the router replaces the top label
(from the received Resv message) with the locally allocated new
label. The router then sends the new LABEL object as part of the
Resv message to the previous hop. The LABEL object should be kept in
the Reservation State Block. It is then used in the next Resv
refresh event for formatting the Resv message.
A router can decide to send a Resv message before its refresh timers
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expire if the contents of the LABEL object have changed. A received
Resv message without a LABEL object indicates that the next-hop
router does not wish to support MPLS for this session/sender. A
label can be withdrawn without removing the reservation by sending a
Resv with no LABEL object. The receiving router should stop sending
label switched packets toward the next-hop router. The RSVP session
itself is not affected.
If, however, the session is of type LSP_TUNNEL_IPv4, then the label
withdrawal procedure must not be used and a ResvTear sent instead.
4.1.2. Non-support of the Label Object
An RSVP router that does not recognize the LABEL object sends a
ResvErr with the error code "Unknown object class" toward the
receiver. This causes the reservation to fail. The receiver should
notify management that a LSP cannot be established, and possibly take
action to continue the reservation without the LABEL object.
RSVP is designed to cope gracefully with non-RSVP routers anywhere
between senders and receivers. However, non-RSVP routers cannot
receive label-switched packets conveyed in PATH or RESV messages.
This means that if a router has a neighbor who is not RSVP capable,
the router must not advertise the LABEL object when sending messages
that pass through the non-RSVP router. [1] describes how routers can
determine the presence of non-RSVP routers.
4.2. Label Request Object
The LABEL_REQUEST object was first documented in [3]. A
LABEL_REQUEST object has the following format:
class = 19, C_Type = 1 (need to get an official class num from
the IANA)
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length (bytes) | Class-Num | C-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | L3PID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The L3PID is an identifier of the layer 3 protocol using this path.
Standard Ethertype values are used.
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4.2.1. Handling of LABEL_REQUEST
The sender creates a Path message with a LABEL_REQUEST object. The
LABEL_REQUEST object indicates that a label binding for this path is
requested and provides an indication of the network layer protocol
that is to be carried over this path. This permits non-IP network
layer protocols to be sent down an LSP. The information can also be
useful in assigning the actual label on a link, because some reserved
labels are protocol specific. See [8].
The LABEL_REQUEST should be stored in the Path State Block, so that
refreshes of the Path messages will also contain the LABEL_REQUEST
object. When the Path message reaches its receiver, the presence of
the LABEL_REQUEST object triggers the receiver to allocate a label
and to place the label in the LABEL object for the corresponding Resv
message. A receiver that accepts a LABEL_REQUEST object, must
include a LABEL object in Resv messages.
A node that accepts a LABEL_REQUEST object must be ready to accept
and correctly process a LABEL object in the corresponding Resv
messages.
A node that recognizes a LABEL_REQUEST object, but that is unable to
support it (possibly because of a failure to allocate labels), should
send a PathErr with the error code "Routing problem" and the subcode
"MPLS label allocation failure." If a node cannot support the
protocol L3PID, it should send a PathErr with the error code "Routing
problem" and the subcode "Unsupported L3PID." This causes the RSVP
session to fail.
4.2.2. Non-support of the Label Request Object
An RSVP router that does not recognize the LABEL_REQUEST object sends
a PathErr with the error code "Unknown object class" toward the
sender. This causes the path setup to fail. The sender should
notify management that a LSP cannot be established and possibly take
action to continue the reservation without the LABEL_REQUEST.
RSVP is designed to cope gracefully with non-RSVP routers anywhere
between the sender and the receiver. However, non-RSVP routers cannot
receive label-switched packets. This means that if a router has a
neighbor that is not RSVP capable, the router must not advertise
LABEL_REQUEST objects when sending messages that pass through the
non-RSVP routers. The router should send a PathErr back to the
sender, with the error code "Routing problem" and the subcode "MPLS
being negotiated, but a non-RSVP capable router stands in the path."
[1] describes how routers can determine the presence of non-RSVP
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routers.
4.3. Explicit Route Object
As stated earlier, explicit routes are to be specified through a new
EXPLICIT_ROUTE object in RSVP. RSVP Path messages carry this object.
The EXPLICIT_ROUTE object has the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length (bytes) | Class-Num | C-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// (Object contents) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Class-Num
The Class-Num for an EXPLICIT_ROUTE object is 193 (need to get
an official one from the IANA with the high order two bits set
to 11)
C-Type
The C-Type for an EXPLICIT_ROUTE object is 1 (need to get an
official one from the IANA)
If a Path message contains multiple EXPLICIT_ROUTE objects, only the
first object is meaningful. Subsequent EXPLICIT_ROUTE objects may be
ignored and should not be propagated.
4.3.1. Subobjects
The contents of an EXPLICIT_ROUTE object are a series of variable-
length data items called subobjects. Each subobject has the form:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-------------//----------------+
|L| Type | Length | (Subobject contents) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-------------//----------------+
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L
The L bit is an attribute of the subobject. The L bit is set
if the subobject represents a loose hop in the explicit route.
If the bit is not set, the subobject represents a strict hop in
the explicit route.
Type
The Type indicates the type of contents of the subobject.
Currently defined values are:
0 Reserved
1 IPv4 prefix
2 IPv6 prefix
32 Autonomous system number
64 MPLS label switched path termination
Length
The Length contains the total length of the subobject in bytes,
including the L, Type and Length fields. The Length must
always be a multiple of 4, and at least 4.
4.3.2. Applicability
The EXPLICIT_ROUTE object is intended to be used only for unicast
situations. Applications of explicit routing to multicast are a
topic for further research.
The EXPLICIT_ROUTE object is to be used only when all routers along
the explicit route support RSVP and the EXPLICIT_ROUTE object. The
mechanisms for determining, a priori, that such support is present
are beyond the scope of this document.
4.3.3. Semantics of the Explicit Route Object
An explicit route is a particular path in the network topology.
Typically, the explicit route is computed by a node, with the intent
of directing traffic down that path.
An explicit route is described as a list of groups of nodes along the
explicit route. Certain operations to be performed along the path
can also be encoded in the EXPLICIT_ROUTE object.
In addition to the ability to identify specific nodes along the path,
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an explicit route can identify a group of nodes that must be
traversed along the path. This capability allows the routing system
a significant amount of local flexibility in fulfilling a request for
an explicit route. In turn, this allows the generator of the
explicit route to have imperfect information about the details of the
path.
The explicit route is encoded as a series of subobjects contained in
an EXPLICIT_ROUTE object. Each subobject may identify a group of
nodes in the explicit route or may be an operation to be performed
along the path. An explicit route is then a path including all of
the identified groups of nodes, with the specified operations
occurring along the path.
To simplify the discussion, we call each group of nodes an abstract
node. Thus, we can also say that an explicit route is a path
including all of the abstract nodes, with the specified operations
occurring along that path.
As an example, consider an explicit route that consists solely of
autonomous system number subobjects. Each subobject corresponds to
an autonomous system in the network topology. Each autonomous system
is an abstract node. In this case, the explicit route is a path
including each of the specified autonomous systems. There may be
multiple hops within each autonomous system.
4.3.4. Strict and Loose subobjects
The L bit in the subobject is a one-bit attribute. If the L bit is
set, then the value of the attribute is `loose.' Otherwise, the
value of the attribute is `strict.' For brevity, we say that if the
value of the subobject attribute is `loose' then it is a `loose
subobject.' Otherwise, it's a `strict subobject.' Further, we say
that the abstract node of a strict or loose subobject is a strict or
a loose node, respectively. Loose and strict nodes are always
interpreted relative to their prior abstract nodes.
The path between a strict node and its prior node MUST include only
network nodes from the strict node and its prior abstract node.
The path between a loose node and its prior node MAY include other
network nodes that are not part of the strict node or its prior
abstract node.
The L bit has no meaning in operation subobjects.
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4.3.5. Loops
While the EXPLICIT_ROUTE object is of finite length, the existence of
loose nodes implies that it is possible to construct forwarding loops
during transients in the underlying routing protocol. This can be
detected by the originator of the explicit route through the use of
another opaque route object called the RECORD_ROUTE object. The
RECORD_ROUTE object is used to collect detailed path information and
is useful for loop detection as well as diagnostic purposes.
4.3.6. Subobject semantics
4.3.6.1. Subobject 1: The IPv4 prefix
The contents of an IPv4 prefix subobject are a 4-octet IPv4 address,
a 1-octet prefix length, and a 1-octet pad. The abstract node
represented by this subobject is the set of nodes that have an IP
address which lies within this prefix. Note that a prefix length of
32 indicates a single IPv4 node.
The length of the IPv4 prefix subobject is 8 octets. The contents of
the 1 octet of padding must be zero on transmission and must not be
checked on receipt.
4.3.6.2. Subobject 2: The IPv6 address
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | IPV6 address (16 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPV6 address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPV6 address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPV6 address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPV6 address (continued) | Mask | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
0x82 IPv6 address
Length
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The Length contains the total length of the subobject in
bytes, including the Type and Length fields. The Length
is always 20.
IPv6 address
A 128-bit unicast host address.
Mask
128
Padding
Zero on transmission. Ignored on receipt.
4.3.6.3. Subobject 32: The autonomous system number
The contents of an autonomous system (AS) number subobject are a 2-
octet autonomous system number. The abstract node represented by
this subobject is the set of nodes belonging to the autonomous
system.
The length of the AS number subobject is 4 octets.
4.3.6.4. Subobject 64: MPLS label switched path termination
The contents of an MPLS label switched path termination subobject are
2 octets of padding. The subobject is an operation subobject. This
object is only meaningful if there is a LABEL_REQUEST object in the
Path message.
If a LABEL_REQUEST object is present in the Path message, this Path
message is being used to establish a Label Switched Path. In this
case, this subobject indicates that the prior abstract node should
remove one level of label from all packets following this Label
Switched Path.
The length of the MPLS label termination subobject is 4 octets.
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4.3.7. Processing of the Explicit Route Object
4.3.7.1. Selection of the next hop
A Path message containing an EXPLICIT_ROUTE object must determine the
next hop for this path. Selection of this next hop may involve a
selection from a set of possible alternatives. The mechanism for
making a selection from this set is implementation dependent and is
outside of the scope of this specification. Selection of particular
paths is also outside of the scope of this specification, but it is
assumed that each node will make a best effort attempt to determine a
loop-free path. Note that such best efforts may be overridden by
local policy.
To determine the next hop for the path, a node performs the following
steps:
1) The node receiving the RSVP message must first evaluate the first
subobject. If the node is not part of the abstract node described by
the first subobject, it has received the message in error and should
return a "Bad initial subobject" error. If the first subobject is an
operation subobject, the message is in error and the system should
return a "Bad EXPLICIT_ROUTE object" error. If there is no first
subobject, the message is also in error and the system should return
a "Bad EXPLICIT_ROUTE object" error.
2) If there is no second subobject, this indicates the end of the
explicit route. The EXPLICIT_ROUTE object should be removed from the
Path message. This node may or may not be the end of the path.
Processing continues with section 4.3.2, where a new EXPLICIT_ROUTE
object may be added to the Path message.
3) Next, the node evaluates the second subobject. If the subobject
is an operation subobject, the node records the subobject, deletes it
from the EXPLICIT_ROUTE object and continues processing with step 2,
above. Note that this changes the third subobject into the second
subobject in subsequent processing. The precise operations to be
performed by this node must be defined by the operation subobject.
4) If the node is also a part of the abstract node described by the
second subobject, then the node deletes the first subobject and
continues processing with step 2, above. Note that this makes the
second subobject into the first subobject of the next iteration.
5) The node determines whether it is topologically adjacent to the
abstract node described by the second subobject. If so, the node
selects a particular next hop which is a member of the abstract node.
The node then deletes the first subobject and continues processing
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with section 4.3.2.
6) Otherwise, the node selects a next hop within the abstract node of
the first subobject that is along the path to the abstract node of
the second subobject. If no such path exists then there are two
cases:
6a) If the second subobject is a strict subobject, there is an error
and the node should return a "Bad strict node" error.
6b) Otherwise, if the second subobject is a loose subobject, the node
selects any next hop that is along the path to the next abstract
node. If no path exists, there is an error, and the node should
return a "Bad loose node" error.
7) Finally, the node replaces the first subobject with any subobject
that denotes an abstract node containing the next hop. This is
necessary so that when the explicit route is received by the next
hop, it will be accepted.
4.3.7.2. Adding subobjects to the Explicit Route Object
After selecting a next hop, the node may alter the explicit route in
the following ways.
If, as part of executing the algorithm in section 4.3.1, the
EXPLICIT_ROUTE object is removed, the node may add a new
EXPLICIT_ROUTE object.
Otherwise, if the node is a member of the abstract node for the first
subobject, a series of subobjects may be inserted before the first
subobject or may replace the first subobject. Each subobject in this
series must denote an abstract node that is a subset of the current
abstract node.
Alternately, if the first subobject is a loose subobject, an
arbitrary series of subobjects may be inserted prior to the first
subobject.
4.3.8. Non-support of the Explicit Route Object
An RSVP router that does not recognize the EXPLICIT_ROUTE object
sends a PathErr with the error code "Unknown object class" toward the
sender. This causes the path setup to fail. The sender should
notify management that a LSP cannot be established and possibly take
action to continue the reservation without the EXPLICIT_ROUTE or via
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a different explicit route.
4.4. Record Route Object
The format of the RECORD_ROUTE object (RRO) is described below.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length (bytes) | Class-Num | C-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// (Subobjects) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Class-Num
The Class-Num for a RECORD_ROUTE object is 194 (need to get an
official one from the IANA with the high order two bits set to
11)
C-Type
The C-Type for a RECORD_ROUTE object is 1 (need to get an
official one from the IANA)
The RRO can show up in both RSVP Path and Resv messages. The
presence of the RRO in Path messages is semantically unrelated
to the presence of RRO in Resv message. The presence of RRO in
one message type does not necessarily require RRO in other
message types.
If a message contains multiple RROs, only the first RRO is
meaningful. Subsequent RROs can be ignored and should not be
propagated.
4.4.1. Subobjects
The contents of a RECORD_ROUTE object are a series of variable-length
data items called subobjects. Each subobject has its own Length
field, the Length contains the total length of the subobject in
bytes, including the Type and Length fields. The length must always
be a multiple of 4, and at least 4.
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Subobjects are organized as a last-in-first-out stack. The first
subobject relative to the beginning of RRO is considered the top.
The last subobject is considered bottom. When a new subobject is
added, it is always added to the top.
An empty RRO with no subobjects is considered illegal.
Two kinds of subobjects are currently defined.
4.4.1.1. Subobject 1: The IPv4 address
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | IPV4 address (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPV4 address (continued) | Mask | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
0x81 IPv4 address
IPv4 address
A 32-bit unicast, host address. Any network-reachable
interface address is allowed here. Illegal addresses,
such as loopback addresses, should not be used.
Length
The Length contains the total length of the subobject in
bytes, including the Type and Length fields. The Length
is always 8.
Mask
32
Padding
Zero on transmission. Ignored on receipt.
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4.4.1.2. Subobject 2: The IPv6 address
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | IPV6 address (16 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPV6 address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPV6 address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPV6 address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPV6 address (continued) | Mask | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
0x82 IPv6 address
Length
The Length contains the total length of the subobject in
bytes, including the Type and Length fields. The Length
is always 20.
IPv6 address
A 128-bit unicast host address.
Mask
128
Padding
Zero on transmission. Ignored on receipt.
4.4.2. Applicability
In Path messages, the RRO can be used for both unicast and multicast
RSVP sessions. In Resv messages, only the procedure for use in
unicast sessions is defined here.
There are three possible uses of RRO in RSVP. First, it can function
as a loop detection mechanism to discover L3 routing loops. The exact
procedure for doing so is described in later sections of this
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document.
Second, RRO collects up-to-date detailed path information hop-by-hop
about RSVP sessions, providing valuable information to the sender or
receiver. Any path change (due to network topology changes) is
quickly reported.
Third, RRO syntax is designed so that, with minor changes, the whole
object can be used as input to the EXPLICIT_ROUTE object. This is
useful if the sender receives RRO from the receiver in a Resv
message, applies it to EXPLICIT_ROUTE object in the next Path message
in order to "pin down session path".
4.4.3. Handling RRO
Typically, a node initiates an RSVP session by adding the RRO to the
Path message. The initial RRO contains only one subobject - the
sender's IP addresses.
When a Path message containing a RRO is received by an intermediate
router, the router stores a copy of it in the Path State Block. The
RRO is then used in the next Path refresh event for formating Path
messages. When a new Path message is to be sent, the router adds a
new subobject to the RRO and appends the resulting RRO to the Path
message before transmission.
The newly added subobject must be this router's IP address. The
address to be added should be the interface address of the outgoing
Path messages. If there are multiple addresses to choose from, the
decision is local matter. However, it is recommended that the same
address be chosen consistently. If the newly added subobject causes
the RRO to be too big to fit in a Path message, the Path message
shall be dropped and a PathErr message should be sent back to the
sender.
An RSVP router can decide to send Path messages before its refresh
time if the RRO in the next Path message is different from the
previous one. This can happen if the contents of the RRO received
from the previous hop router changes or if this RRO is newly added to
(or deleted from) the Path message.
A received Path message without an RRO indicates that the sender node
no longer needs route recording. Subsequent Path messages shall not
contain an RRO.
Likewise, RSVP session receiver nodes initiate the RRO process by
adding an RRO to Resv messages. The processing mirrors that of the
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Path messages. The only difference is that the RRO in a Resv message
records the path information in the reverse direction.
4.4.4. Loop Detection
As part of processing an incoming RRO, the intermediate router looks
into all subobjects contained within the RRO. If the router
determines that it is already in the list, a forwarding loop exists.
An RSVP session is loop-free if receiver nodes receive Path messages
with no routing loops detected in the contained RRO or sender nodes
receive Resv messages with no looping detected.
There are two broad classifications of forwarding loops. The first
class is the transient loop, that occurs as a normal part of
operations as L3 routing tries to converge on a consistent forwarding
path for all destinations. The second class of forwarding loop is
the permanent loop, that normally results from network mis-
configuration.
The action performed on receipt depends on the message type in which
the RRO is received.
For Path messages containing a forwarding loop, the router builds and
send a "Routing problem" PathErr message, with the subcode "loop
detected," and drops the Path message. Until the loop is eliminated,
this session is not suitable for forwarding user data packets.
Eliminating the loop is beyond the scope of this document.
For Resv messages containing a forwarding loop, the router simply
drops the message. Resv messages should not loop if Path messages do
not loop.
4.4.5. Non-support of RRO
An RSVP router that does not recognize RRO forwards it unchanged.
This has no impact on the reservation. The presence of non-RSVP
routers anywhere between senders and receivers has no impact on the
object either. The worst result is that RRO does not reflect the
full path information.
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4.5. Error subcodes for ERO and RRO
In the processing described above, certain errors must be reported as
part of a "Routing Problem" PathErr message. The value of the
"Routing Problem" error code is 24 (TBD).
The following defines the subcodes for the routing problem PathErr
message:
Value Error:
1 Bad EXPLICIT_ROUTE object
2 Bad strict node
3 Bad loose node
4 Bad initial subobject
5 No route available toward destination
6 RRO syntax error detected
7 RRO indicated routing loops
8 MPLS being negotiated, but a non-RSVP-capable router
stands in the path
9 MPLS label allocation failure
10 Unsupported L3PID
4.6. Session, Sender Template, and Filter Spec Objects
New C-Types are defined for the SESSION, SENDER_TEMPLATE and
FILTER_SPEC objects. The LSP_TUNNEL_IPv4 objects have the following
format:
4.6.1. Session Object
IPv4 tunnel end point address
IPv4 address of the destination node for the tunnel.
Tunnel ID
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Class = SESSION, C-Type = LSP_TUNNEL_IPv4 (7)
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length (bytes) | Class-Num | C-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 tunnel end point address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must be zero | Tunnel ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Tunnel ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A 16-bit identifier used in the SESSION that remains constant
over the life of the tunnel.
Extended Tunnel ID
A 32-bit identifier used in the SESSION that remains constant
over the life of the tunnel. Normally set to all zeros.
Source nodes which wish to narrow the scope of a SESSION to the
source destination pair may place their IPv4 address here as a
globally unique identifier.
4.6.2. Sender Template Object
Class = SENDER_TEMPLATE, C-Type = LSP_TUNNEL_IPv4 (7)
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length (bytes) | Class-Num | C-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 tunnel sender address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must be zero | LSP ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IPv4 tunnel sender address
IPv4 address for a sender node
LSP ID
a 16-bit identifier used in the SENDER_TEMPLATE and the
FILTER_SPEC that can be changed to allow a sender to share
resources with itself.
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4.6.3. Filter Specification Object
Class = FILTER SPECIFICATION, C-Type = LSP_TUNNEL_IPv4 (7)
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length (bytes) | Class-Num | C-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 tunnel sender address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must be zero | LSP ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IPv4 tunnel sender address
IPv4 address for a sender node
LSP ID
a 16-bit identifier used in the SENDER_TEMPLATE and the
FILTER_SPEC that can be changed to allow a sender to share
resources with itself.
4.6.4. Reroute procedure
A tunnel which is capable of maintaining resource (without double
counting) while it is being rerouted or attempting to increase its
bandwidth is setup as follows. In the initial Path message, the
source node forms a SESSION object, picking a Tunnel_ID and placing
its IPv4 address in the Extended_Tunnel_ID. It forms a
SENDER_TEMPLATE picking a Tunnel_Path_ID. Tunnel setup continues
with normal processing.
The destination node sends a Resv message with the STYLE to Shared
Explicit.
[Note I think we should add a flag to the SESSION_ATTRIBUTE for the
source to indicate that it wishes the SE style.]
When a source node with an established path that wants to change the
path it forms a new Path message as follows. The existing SESSION
object is used, in particular the Tunnel_ID and Extended_Tunnel_ID
are unchanged. It picks a new Tunnel_Path_ID to form a new
SENDER_TEMPLATE. It creates an EXPLICIT_ROUTE object with the new
route. The new Path message is sent. The source node refreshes both
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the old and new path messages
The destination node responds with a Resv message with an SE flow
descriptor formated as:
<FLOW_SPEC><old_FILTER_SPEC><old_LABEL_OBJECT><new_FILTER_SPEC>
<new_LABEL_OBJECT>
(Note that if the PHOPs are different, then two messages are sent
each with the appropriate FILTER_SPEC and LABEL_OBJECT.)
When the Source node receives the Resv Message(s) it may begin using
the new route. It should send a PathTear message for the old route.
4.7. Session Attribute Object
The format of the SESSION_ATTRIBUTE object is described below.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length (bytes) | Class-Num | C-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Setup Prio | Reserv. Prio | Flags | Name Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Session Name (NULL padded display string) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Class-Num
The Class-Num indicates that the object is 207. (TBD)
C-Type
The C-Type is 7.
Flags
0x01 = Fast-reroute
This flag permits transit routers to precompute and
pre-establish detour paths for this session. Upon
fault detection on a immediate downstream link or node,
transit routers reroute traffic onto the
detour path for fast fail-over.
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0x02 = Merging permitted
This flag permits transit routers to merge this session
with other RSVP sessions for the purpose of reducing
resource overhead on downstream transit routers, thereby
providing better network scalability.
Setup Priority
the range of 0 to 7. 0 is the highest priority. The Setup Priority
is used in deciding whether this session should displace another
session.
Reservation Priority
in the range of 0 to 7. 0 is the highest priority. Reservation
Priority is used in deciding whether this session should be displaced
by another session.
Name Length
The length of the display string before padding, in bytes.
Session Name
A null padded string of characters.
The support of setup and reservation priorities is optional. A node
can recognize this information but be unable to perform the requested
operation. The node should pass the information downstream unchanged.
Preemption is implemented by two priorities. The Setup Priority is
the priority for taking resources. The Reservation Priority is the
priority for holding a resource. The Setup Priority should never be
higher than the Reservation Priority. The Reservation Priority is the
priority at which resources assigned to this request will be reserved.
When a new reservation is considered for admission, the bandwidth
requested is compared with the bandwidth available at the priority
specified in the Setup Priority. The bandwidth available at a
particular priority is the unused bandwidth plus the bandwidth
reserved at all priorities lower than the Setup Priority.
If the bandwidth is not available a PathErr message is
returned with a Error Code of 01, Admission Control failure, and an
Error Value of 0x0002. The first 0 means globally defined subcode and
not informational. The 002 means "requested bandwidth unavailable".
If the requested bandwidth is less than the unused bandwidth,
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processing is complete. If the requested bandwidth is available, but
is in use by lower priority sessions, then lower priority sessions
(beginning with the lowest priority) are pre-empted to free the
necessary bandwidth.
When pre-emption is supported, each pre-empted reservation triggers a
TC_Preempt() upcall to local clients, passing a subcode indicating the
reason. A ResvErr and/or PathErr with the code "Policy Control failure"
should be sent toward the downstream receivers and upstream senders.
[Editor: we need to define a subcode; if we stay with
SESSION_ATTRIBUTE (not POLICY) we should also define an error code]
The support of fast-reroute is optional. A node can recognize
this information but be unable to perform the requested operation. The
node should pass the information downstream unchanged.
The support of merging is optional. A node can recognize this
information but be unable to perform the requested operation. The
node should pass the information downstream unchanged.
If a Path message contains multiple SESSION_ATTRIBUTE objects, only
the first SESSION_ATTRIBUTE object is meaningful. Subsequent
SESSION_ATTRIBUTE objects can be ignored and not forwarded.
The contents of the Session Name field are a string, typically
displayable characters. The Length must always be a multiple of 4 and
must be at least 8. For an object length that is not multiple of 4,
the object is padded with trailing NULL characters. The Name Length
field contains the actual string length.
All RSVP routers, whether they support this object or not, shall forward
the object unmodified. The presence of non-RSVP routers anywhere
between senders and receivers has no impact on the object.
Note that the granting of one reservation may result in the preemption
of other reservations. We will also need an error code to indicate
that a reservation has been preempted. I suggest we do that with both
a PathTear and a ResvTear with a Error Code of 02, Policy Control
failure, and a Error Value of 0x8002, where the subcode 002 means
"Reservation Preempted".
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5. RSVP Aggregate Message
The resource requirement (processing and memory) for running RSVP on
a router increases proportionally with the number of sessions.
Supporting a large number of sessions on may present scaling
problems.
This section describes an approach to help alleviate one of the
scaling issues. Path and Resv messages must be periodically
refreshed. The approach here simply reduces the volume of messages
which must be periodically sent and received.
Another way of addressing the refresh volume problem is to increase
the refresh timer R. Increasing the value of R provides linear
improvement on transmission overhead, but at the cost of increasing
refresh timeout. With the proposed aggregate message (see below),
network administrators can reduce R for faster detection of
connectivity problems while enjoying an order of magnitude less
overhead.
If topology failures occur, every node adjacent to the failure might
wish to notify all affected sender and receiver nodes. These
notification messages are either tear or error messages. Depending
on how many sessions are affected and how fast every node is willing
to react, these messages represent a flood that ripples out from the
original failure point. Aggregate messages provide the mechanism to
reduce message flooding and network overload. They also enhance the
efficiency and reliability in delivering of RSVP tear or error
messages.
An RSVP aggregate message consists of an aggregate header followed by
a body consisting of a variable number of standard RSVP messages.
The following subsections define the formats of the aggregate header
and the rules for including standard RSVP messages as part of
message.
5.1. Aggregate Header
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vers | Flags | Msg type | RSVP checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Send_TTL | (Reserved) | RSVP length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format of the aggregate header is identical to the format of the
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RSVP common header [1]. The fields in the header are as follows:
Vers: 4 bits
Protocol version number. This is version 1.
Flags: 4 bits
0x01: Aggregate capable
If set, indicates to RSVP neighbors that this node is willing
and capable of receiving aggregate messages. This bit is
meaningful only between adjacent RSVP neighbors.
0x02-0x08: Reserved
Msg type: 8 bits
12 = Aggregate
RSVP checksum: 16 bits
The one's complement of the one's complement sum of the entire
message, with the checksum field replaced by zero for the
purpose of computing the checksum. An all-zero value means
that no checksum was transmitted. Because individual
submessages carry their own checksum as well as INTEGRITY
object for authentication, this field is recommended to be left
as zero.
Send_TTL: 8 bits
The IP TTL value with which the message was sent. This is used
by RSVP to detect a non-RSVP hop by comparing the IP TTL that
an Aggregate message sent to the TTL in the received message.
RSVP length: 16 bits
The total length of this RSVP aggregate message in bytes,
including the aggregate header and the submessages that follow.
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5.2. Message Formats
An RSVP aggregate message must contain at least one submessage. A
submessage is one of the RSVP Path, PathTear, PathErr, Resv,
ResvTear, ResvErr, or ResvConf messages.
Empty RSVP aggregate message should not be sent. It is illegal to
include another RSVP aggregate message a as submessage.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vers | Flags | 12 | RSVP checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Send_TTL | (Reserved) | RSVP length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// First submessage //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// More submessage... //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5.3. Sending RSVP Aggregate Messages
RSVP Aggregate messages are sent hop by hop between RSVP-capable
neighbors as "raw" IP datagrams with protocol number 46. Raw IP
datagrams are also intended to be used between an end system and the
first/last hop router, although it is also possible to encapsulate
RSVP messages as UDP datagrams for end-system communication that
cannot perform raw network I/O.
RSVP Aggregate messages should not be used if the next-hop RSVP
neighbor does not support RSVP Aggregate messages. Methods for
discovering such information include 1) Manual configuration. 2)
Observing the Aggregate-capable bit (see below) in the received RSVP
messages.
Support for RSVP Aggregate message is optional. While it might help
in scaling RSVP and in reducing processing overhead and bandwidth
consumption, a node is not required to transmit every standard RSVP
message in an Aggregate message. A node must always be ready to
receive standard RSVP messages.
The IP source address is local system that originated the Aggregate
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message. The IP destination address is the next-hop node for which
the submessages are intended. These addresses need not be identical
if submessages are sent as standard RSVP messages.
For example, the IP source address of Path and PathTear messages is
the address of the sender it describes, while the IP destination
address is the DestAddress for the session. These end-to-end
addresses are overridden by hop-by-hop addresses while encapsulated
in an Aggregate message. These addresses can easily be restored from
the SENDER_TEMPLATE and SESSION objects within Path and PathTear
messages. For Path and PathTear messages, the next-hop node can be
learned by looking up DestAddress in forwarding table.
RSVP Aggregate messages do not require the Router Alert IP option
[RFC 2113] in their IP headers. This is because Aggregate messages
are addressed directly to RSVP neighbors.
Each RSVP Aggregate message must occupy exactly one IP datagram. If
it exceeds the MTU, the datagram is fragmented by IP and reassembled
at the recipient node. A single RSVP Aggregate message cannot exceed
the maximum IP datagram size, approximately 64K bytes.
5.4. Receiving RSVP Aggregate Messages
If the local system does not recognize or does not wish to accept an
Aggregate message, the received messages shall be discarded without
further analysis.
The receiver next compares the IP TTL with which an Aggregate message
is sent to the TTL with which it is received. If a non-RSVP hop is
detected, the number of non-RSVP hops is recorded. It is used later
in processing of sub-messages.
Next, the receiver verifies the version number and checksum of the
RSVP aggregate message. Discard message if any mismatch is found.
Start decapsulating individual sub-messages. Each sub-message has
its own complete message length and authentication information.
Process each sub-message according to procedures in RFC 2209.
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5.5. Forwarding RSVP Aggregate Messages
RSVP Aggregate messages could be forwarded by routers in non-RSVP
cloud. Aggregate messages shall not be forwarded RSVP routers.
When individual submessages are being forwarded, they can be
encapsulated in another aggregate message before sending to the
next-hop neighbor. The Send_TTL field in the submessages should be
decremented properly before transmission.
5.6. Aggregate-capable bit
An additional bit is added to RSVP common header, which is defined in
RFC2205 [1].
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vers | Flags | Msg Type | RSVP Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Send_TTL | (Reserved) | RSVP Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Flags: 4 bits
0x01: Aggregate capable
If set, indicates to RSVP neighbors that this node is willing
and capable of receiving aggregate messages. This bit is
meaningful only between adjacent RSVP neighbors.
6. Tear Confirm
The failure of an LSP Tunnel may result in loss of data. Locally
decapsulating the packet and routing is not recommended as this has
the potential of inducing routing loops and may also violate policy.
It is thus desirable to make the teardown function reliable.
Due to the overhead involved in refreshes, administrators may desire
to set the refreseh timers longer. The Tear Confirm mechanism
provides a means of ensuring timely teardown without the necessity of
setting short refresh timers.
This has the effect of both rapidly notifying the source that the
tunnel is inoperative and of freeing the LSP's resources so they may
be reallocated.
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The reliable teardown is accomplished via a combination of (a)
including the CONFIRM object in the Resv Tear message, and (b) new
ResvTear Confirm message. The confirmations occur hop by hop.
When the CONFIRM object is included in the ResvTear message, the code
should:
(a) set a boolean in the upstream RDB indicating that it is
present only for retransmission purposes, and set a relatively
short retransmission interval. The RDB remains subject to normal
timeout mechanisms. If the node is a host, then the RDB should be
timed out in a period based on its previous retransmission timer,
i.e. (K + 0.5)*1.5*R, where R is the retransmission timer and K is
a small integer with the default value of 3.
(b) whenever the retransmission timer fires, if the boolean is
FALSE, do as now: send a refreshing Resv message upstream and set
a longish timer. If it is TRUE, however, set a relatively short
timer and send an Resv Tear message with the CONFIRM object
(c) when such an ResvTear message is received, similarly set the
CONFIRM object and the boolean in the RDB if it exists, and send
an Resv Tear message. If the RDB does not exist, reply ResvTear
Confirm.
(d) in the sender system, when the ResvTear with CONFIRM object is
received, tear down the RDB and reply ResvTear Confirm to the
NHOP. Do so whether the RDB exists on receipt or not.
(e) in the non-sender systems, when the Resv Tear Confirm is
received, tear down the RDB and forward Resv Tear Confirm to the
next NHOP.
Resv Tear Confirm is identical in content to the Resv Confirm, except
that it results in the RDB being torn down, not established.
The value of the MessageType for the Resv Tear Confirm message is 10
(need to get an official one from the IANA).
(We may also want to define a new CONFIRM object with a C-Type >= 192
so that nodes which do not recognize the confirm object in the
ResvTear message will not drop the message and will pass the object
on.)
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7. Security Considerations
We assume that the security procedures defined for RSVP will handle
any security issues that arise from coupling label switching with
RSVP. For example, mechanisms that are used to authenticate RSVP
resource reservation requests may also be used to authenticate
requests to establish explicitly routed label switched paths.
It may be desirable to enable the setup of ER-LSPs without enabling
general purpose resource reservations. This would be done using the
policy mechanisms defined for RSVP. It is likely that explicitly
routed paths would often be setup only within a single administrative
domain, and thus RSVP requests from outside the domain would be
ignored.
8. Acknowledgments
This document contains ideas as well as text which which have
appeared in previous Internet Drafts. The editors/authors of the
current draft wish to thank the authors of those drafts. They are
Steven Blake, Bruce Davie, Roch Guerin, Sanjay Kamat, Yakov Rekhter,
Eric Rosen, and Arun Viswanathan.
9. References
[1] Braden, R. et al. Resource ReSerVation Protocol (RSVP) --
Version 1, Functional Specification, RFC 2205, September 1997.
[2] Rosen, E. et al. A Proposed Architecture for MPLS, Internet
Draft, draft-ietf-mpls-arch-00.txt, August 1997.
[3] Davie, B. et al. Explicit Route Support in MPLS, Internet
Draft, draft-davie-mpls-explicit-routes-00.txt, November 1997
[4] Davie, B. et al. Use of Label Switching With RSVP, Internet
Draft, draft-ietf-mpls-rsvp-00.txt, March 1998.
[5] Guerin, R. et al. Setting up Reservations on Explicit Paths using
RSVP, Internet Draft, draft-guerin-expl-path-rsvp-01.txt,
November 1997.
[6] Awduche, D. et al. Requirements for Traffic Engineering over MPLS,
Internet Draft, draft-awduche-mpls-traffic-eng-00.txt, April 1998.
[7] Wroclawski, J. Specification of the Controlled-Load Network
Element Service, RFC 2211, September 1997.
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[8] Rosen, E. MPLS Label Stack Encoding. Internet Draft,
draft-ietf-mpls-label-encaps-01.txt, February 1998.
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