Network Working Group CY. Lee
Internet-Draft Alcatel
Expires: January 18, 2006 A. Farrel
Old Dog Consulting
S. De Cnodder
Alcatel
July 17, 2005
Exclude Routes - Extension to RSVP-TE
draft-ietf-ccamp-rsvp-te-exclude-route-04.txt
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
The RSVP-TE specification, "RSVP-TE: Extensions to RSVP for LSP
Tunnels" (RFC 3209) and GMPLS extensions to RSVP-TE, "Generalized
Multi-Protocol Label Switching (GMPLS) Signaling Resource ReserVation
Protocol-Traffic Engineering (RSVP-TE) Extensions" (RFC 3473) allow
abstract nodes and resources to be explicitly included in a path
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setup, but not to be explicitly excluded.
In some networks where precise explicit paths are not computed at the
head end it may be useful to specify and signal abstract nodes and
resources that are to be explicitly excluded from routes. These
exclusions may apply to the whole path, or to parts of a path between
two abstract nodes specified in an explicit path. How Shared Risk
Link Groups (SLRGs) can be excluded is also specified in this
document.
This document specifies ways to communicate route exclusions during
path setup using RSVP-TE.
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Table of Contents
1. Requirements notation . . . . . . . . . . . . . . . . . . . . 4
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1 Scope of Exclude Routes . . . . . . . . . . . . . . . . . 6
2.2 Relationship to MPLS TE MIB . . . . . . . . . . . . . . . 7
3. Shared Risk Link Groups . . . . . . . . . . . . . . . . . . . 8
3.1 SRLG ERO Subobject . . . . . . . . . . . . . . . . . . . . 8
4. Exclude Route List . . . . . . . . . . . . . . . . . . . . . . 10
4.1 Exclude Route Object (XRO) . . . . . . . . . . . . . . . . 10
4.1.1 IPv4 prefix Subobject . . . . . . . . . . . . . . . . 11
4.1.2 IPv6 Prefix Subobject . . . . . . . . . . . . . . . . 12
4.1.3 Unnumbered Interface ID Subobject . . . . . . . . . . 13
4.1.4 Autonomous System Number Subobject . . . . . . . . . . 14
4.1.5 SRLG Subobject . . . . . . . . . . . . . . . . . . . . 15
4.2 Processing Rules for the Exclude Route Object (XRO) . . . 15
5. Explicit Exclusion Route . . . . . . . . . . . . . . . . . . . 18
5.1 Explicit Exclusion Route Subobject (EXRS) . . . . . . . . 18
5.2 Processing Rules for the Explicit Exclusion Route
Subobject (EXRS) . . . . . . . . . . . . . . . . . . . . . 19
6. Processing of XRO together with EXRS . . . . . . . . . . . . . 21
7. Minimum compliance . . . . . . . . . . . . . . . . . . . . . . 22
8. Security Considerations . . . . . . . . . . . . . . . . . . . 23
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
9.1 New RSVP-TE Class Numbers . . . . . . . . . . . . . . . . 24
9.2 New ERO Subobject Type . . . . . . . . . . . . . . . . . . 24
9.3 New ERO and XRO Subobject Type . . . . . . . . . . . . . . 24
9.4 New Error Codes . . . . . . . . . . . . . . . . . . . . . 25
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 26
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
11.1 Normative References . . . . . . . . . . . . . . . . . . . 27
11.2 Informational References . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 28
A. applications . . . . . . . . . . . . . . . . . . . . . . . . . 29
A.1 Inter-area LSP protection . . . . . . . . . . . . . . . . 29
A.2 Inter-AS LSP protection . . . . . . . . . . . . . . . . . 30
A.3 Protection in the GMPLS overlay model . . . . . . . . . . 31
A.4 LSP protection inside a single area . . . . . . . . . . . 33
Intellectual Property and Copyright Statements . . . . . . . . 34
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1. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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2. Introduction
The RSVP-TE specification [RFC3209] and GMPLS extensions [RFC3473]
allow abstract nodes and resources to be explicitly included in a
path setup, using the Explicit Route Object (ERO).
In some systems it may be useful to specify and signal abstract nodes
and resources that are to be explicitly excluded from routes. This
may be because loose hops or abstract nodes need to be prevented from
selecting a route through a specific resource. This is a special
case of distributed path calculation in the network.
Two types of exclusions are required:
1. Exclusion of certain abstract nodes or resources on the whole
path. This set of abstract nodes is referred to as the Exclude
Route list.
2. Exclusion of certain abstract nodes or resources between a
specific pair of abstract nodes present in an ERO. Such specific
exclusions are referred to as Explicit Exclusion Route.
To convey these constructs within the signaling protocol, a new RSVP
object and a new ERO subobject are introduced respectively.
1. A new RSVP-TE object is introduced to convey the Exclude Route
list. This object is the Exclude Route Object (XRO).
2. The second type of exclusion is achieved through a modification
to the existing ERO. A new ERO subobject type the Explicit
Exclusion Route Subobject (EXRS) is introduced to indicate an
exclusion between a pair of included abstract nodes.
The knowledge of SRLGs, as defined in [INTERAS-REQ], may be used to
compute diverse paths that can be used for protection. In systems
where it is useful to signal exclusions, it may be useful to signal
SRLGs to indicate groups of resources that should be excluded on the
whole path or between two abstract nodes specified in an explicit
path.
This document introduces an ERO subobject to indicate an SRLG to be
signaled in either of the two exclusion methods described above and
this document does not assume or preclude any other usage for this
subobject. This subobject might also be appropriate for use within
Explicit Routes or Record Routes, but this is outside the scope of
this document.
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2.1 Scope of Exclude Routes
This document does not preclude a route exclusion from listing
arbitrary nodes or network elements to avoid. The intent is,
however, to indicate only the minimal number of subobjects to be
avoided. For instance it may be necessary to signal only the SRLGs
(or Shared Risk Groups) to avoid.
It is envisaged that most of the conventional inclusion subobjects
are specified in the signaled ERO only for the area where they are
pertinent. The number of subobjects to be avoided, specified in the
signaled XRO may be constant throughout the whole path setup, or the
subobjects to be avoided may be removed from the XRO as they become
irrelevant in the subsequent hops of the path setup.
For example, consider an LSP that traverses multiple computation
domains. A computation domain may be an area in the administrative
or IGP sense, or may be an arbitrary division of the network for
active management and path computational purposes. Let the primary
path be (Ingress, A1, A2, AB1, B1, B2, BC1, C1, C2, Egress) where:
o Xn denotes a node in domain X, and
o XYn denotes a node on the border of domain X and domain Y.
Note that Ingress is a node in domain A, and Egress is a node in
domain C. This is shown in Figure 1 where the domains correspond with
areas.
area A area B area C
<-------------------> <---------------->
<------------------>
Ingress-----A1----A2----AB1----B1----B2----BC1----C1----C2----Egress
^ \ / | \ / | \ /
| \ / | \ / | \ /
| A3----------A4--AB2--B3--------B4--BC2--C3----------C4
| ^ ^
| | |
| | ERO: (C3-strict, C4-strict,
| | Egress-strict)
| | XRO: Not needed
| |
| ERO: (B3-strict, B4-strict, BC2-strict, Egress-loose)
| XRO: (BC1, C1, C2)
|
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ERO: (A3-strict, A4-strict, AB2-strict, Egress-loose)
XRO: (AB1, B1, B2, BC1, C1, C2, Egress)
Consider the establishment of a node-diverse protection path in the
example above. The protection path must avoid all nodes on the
primary path. The exclusions for area A are handled during
Constrained Shortest Path First (CSPF) computation at Ingress, so the
ERO and XRO signaled at Ingress could be (A3-strict, A4-strict, AB2-
strict, Egress-loose) and (AB1, B1, B2, BC1, C1, C2) respectively.
At AB2 the ERO and XRO could be (B3-strict, B4-strict, BC2-strict,
Egress-loose) and (BC1, C1, C2) respectively. At BC2 the ERO could
be (C3-strict, C4-strict, Egress-strict) and an XRO is not needed
from BC2 onwards.
In general, consideration should be given (as with explicit route) to
the size of signaled data and the impact on the signaling protocol.
2.2 Relationship to MPLS TE MIB
[RFC3812] defines managed objects for managing and modeling MPLS-
based traffic engineering. Included in [RFC3812] is a means to
configure explicit routes for use on specific LSPs. This
configuration allows the exclusion of certain resources.
In systems where the full explicit path is not computed at the
ingress (or at a path computation site for use at the ingress) it may
be necessary to signal those exclusions. This document offers a
means of doing this signaling.
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3. Shared Risk Link Groups
The identifier of a SRLG is defined as a 32 bit quantity in [GMPLS-
RTG]. An SRLG ERO subobject is introduced such that it can be used
in the exclusion methods as described in the following sections.
This document does not assume or preclude any other usage for this
subobject. This subobject might also be appropriate for use within
Explicit Routes or Record Routes, but this is outside the scope of
this document.
3.1 SRLG ERO Subobject
The format of the ERO and its subobjects are defined in [RFC3209].
The new SRLG subobject is defined by this document as follows.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type | Length | SRLG Id (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SRLG Id (continued) | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.
For exclusions (as used by XRO and EXRS defined in this
document), the L bit SHOULD be set to zero and ignored.
Type
The type of the subobject [TBD by IANA].
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 8.
SRLG Id
The 32 bit identifier of the SRLG.
Reserved
This field is reserved. It MUST be set to zero on transmission
and MUST be ignored on receipt.
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4. Exclude Route List
The exclude route identifies a list of abstract nodes that should not
be traversed along the path of the LSP being established. It is
RECOMMENDED to limit size of the exlude route list to a value local
to the node originating the exclude route list.
4.1 Exclude Route Object (XRO)
Abstract nodes to be excluded from the path are specified via the
EXCLUDE_ROUTE object (XRO). The Exclude Route Class value is [TBD].
Currently one C_Type is defined, Type 1 Exclude Route. The
EXCLUDE_ROUTE object has the following format:
Class = TBD by IANA, 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// (Subobjects) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Subobjects
The contents of an EXCLUDE_ROUTE object are a series of variable-
length data items called subobjects. This specification adapts ERO
subojbects as defined in [RFC3209], [RFC3473], and [RFC3477] for use
in route exclusions. The SRLG ERO subobject as defined in Section 3
of this document and its processing within ERO have not been defined
before. The SRLG ERO subobject is defined here for use with route
exclusions.
The following subobject types are supported.
Type Subobject
1 IPv4 prefix
2 IPv6 prefix
4 Unnumbered Interface ID
32 Autonomous system number
TBD SRLG
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The defined values for Type above are specified in [RFC3209] and in
this document.
The concept of loose or strict hops has no meaning in route
exclusion. The L bit, defined for ERO subobjects in [RFC3209], is
reused here to indicate that an abstract node MUST be avoided (value
0) or SHOULD be avoided (value 1).
Subobjects 1, 2, and 4 refer to an interface or a set of interfaces.
An Attribute octet is introduced in these subobjects to indicate the
attribute (e.g. interface, node, SRLG) associated with the interfaces
that should be excluded from the path. For instance, the attribute
node allows a whole node to be excluded from the path by specifying
an interface of that node in the XRO subobject, in contrast to the
attribute interface, which allows a specific interface (or multiple
interfaces) to be excluded from the path without excluding the whole
nodes. The attribute SRLG allows all SRLGs associated with an
interface to be excluded from the path.
4.1.1 IPv4 prefix Subobject
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type | Length | IPv4 address (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 address (continued) | Prefix Length | Attribute |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
L
0 indicates that the attribute specified MUST be excluded
1 indicates that the attribute specified SHOULD be avoided
Attribute
interface
0 indicates that the interface or set of interfaces
associated with the IPv4 prefix should be excluded or avoided
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node
1 indicates that the node or set of nodes associated with
the IPv4 prefix should be excluded or avoided
SRLG
2 indicates that all the SRLGs associated with the IPv4
prefix should be excluded or avoided
The rest of the fields are as defined in [RFC3209].
4.1.2 IPv6 Prefix Subobject
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type | Length | IPv6 address (16 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 address (continued) | Prefix Length | Attribute |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
L
0 indicates that the attribute specified MUST be excluded
1 indicates that the attribute specified SHOULD be avoided
Attribute
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interface
0 indicates that the interface or set of interfaces associated
with the IPv6 prefix should be excluded or avoided
node
1 indicates that the node or set of nodes associated with
the IPv6 prefix should be excluded or avoided
SRLG
2 indicates that all the SRLG associated with the IPv6
prefix should be excluded or avoided
The rest of the fields are as defined in [RFC3209].
4.1.3 Unnumbered Interface ID Subobject
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type | Length | Reserved | Attribute |
| | | |(must be zero) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TE Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface ID (32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
L
0 indicates that the attribute specified MUST be excluded
1 indicates that the attribute specified SHOULD be avoided
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Attribute
interface
0 indicates that the Interface ID specified should be
excluded or avoided
node
1 indicates that the node with the Router ID should be
excluded or avoided (this can be achieved using IPv4/v6
subobject as well, but is included here because it may be
convenient to use information from subobjects of an RRO
as defined in [RFC3477], in specifying the exclusions).
SRLG
2 indicates that all the SRLGs associated with the
interface should be excluded or avoided
Reserved
This field is reserved. It MUST be set to zero on transmission
and MUST be ignored on receipt.
The rest of the fields are as defined in [RFC3477].
4.1.4 Autonomous System Number Subobject
The meaning of the L bit is as follows:
0 indicates that the abstract node specified MUST be excluded
1 indicates that the abstract node specified SHOULD be avoided
The rest of the fields are as defined in [RFC3209]. There is no
Attribute octet defined.
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4.1.5 SRLG Subobject
The meaning of the L bit is as follows:
0 indicates that the SRLG specified MUST be excluded
1 indicates that the SRLG specified SHOULD be avoided
The Attribute octet is not present. The rest of the fields are as
defined in the "SRLG ERO Subobject" section of this document.
4.2 Processing Rules for the Exclude Route Object (XRO)
The exclude route list is encoded as a series of subobjects con-
tained in an EXCLUDE_ROUTE object. Each subobject identifies an
abstract node in the exclude route list.
Each abstract node may be a precisely specified IP address belonging
to a node, or an IP address with prefix identifying interfaces of a
group of nodes, or an Autonomous System.
The Explicit Route and routing processing is unchanged from the
description in [RFC3209] with the following additions:
1. When a Path message is received at a node, the node must check
that it is not a member of any of the abstract nodes in the XRO
if it is present in the Path message. If the node is a member of
any of the abstract nodes in the XRO with the L-flag set to
"exclude", it should return a PathErr with the error code
"Routing Problem" and error value of "Local node in Exclude
Route". If there are SRLGs in the XRO, the node should check
that the resources the node uses are not part of any SRLG with
the L-flag set to "exclude" that is specified in the XRO. If it
is, it should return a PathErr with error code "Routing Problem"
and error value of "Local node in Exclude Route".
2. Each subobject must be consistent. If a subobject is not con-
sistent then the node should return a PathErr with error code
"Routing Problem" and error value "Inconsistent Subobject". An
example of an inconsistent subobject is an IPv4 Prefix subobject
containing the IP address of a node and the attribute field is
set to "interface" or "SRLG".
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3. The subobjects in the ERO and XRO MUST NOT contradict each other.
If a Path message is received that contains contradicting ERO and
XRO subobjects, then:
* subobjects in the XRO with the L flag not set (zero) MUST take
precedence over the subobjects in the ERO - that is, a
mandatory exclusion expressed in the XRO MUST be honored and
an implementation MUST reject such a Path message. This means
that a PathErr with error code "Routing Problem" and error
value of "Route blocked by Exclude Route" is returned.
* subobjects in the XRO with the L flag set do not take
precedence over ERO subobjects - that is, an implementation
MAY choose to reject a Path message because of such a
contradiction, but MAY continue and set up the LSP (ignoring
the XRO subobjects contradicting the ERO subobjects).
4. When choosing a next hop or expanding an explicit route to
include additional subobjects, a node:
1. must not introduce an explicit node or an abstract node that
equals or is a member of any abstract node that is specified
in the Exclude Route Object with the L-flag set to "exclude".
The number of introduced explicit nodes or abstract nodes
with the L flag set to "avoid", which indicate that it is not
mandatory to be excluded but that it is less preferred,
should be minimised in the computed path.
2. must not introduce links, nodes or resources identified by
the SRLG Id specified in the SRLG subobjects(s). The number
of introduced SLRGs with the L flag set to "avoid" should be
minimised.
If these rules preclude further forwarding of the Path message,
the node should return a PathErr with the error code "Routing
Problem" and error value of "Route blocked by Exclude Route".
Note that the subobjects in the XRO is an unordered list of
subobjects.
The XRO Class-Num is of the form 11bbbbbb so that nodes which do not
support the XRO, forward it uninspected and do not apply the
extensions to ERO processing described above. This approach is
chosen to allow route exclusion to traverse parts of the network that
are not capable of parsing or handling the new function. Note that
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Record Route may be used to allow computing nodes to observe
violations of route exclusion and attempt to re-route the LSP
accordingly.
If a node supports the XRO, but not a particular subobject or part of
that subobject, then that particular subobject is ignored. Examples
of a part of a subobject that can be supported are: (1) only prefix
32 of the IPv4 prefix subobject could be supported, or (2) a
particular subobject is supported but not the particular attribute
field.
When a node forwards a Path message, it can do the following three
operations related to XRO besides the processing rules mentioned
above:
1. If no XRO was present, an XRO may be included.
2. If an XRO was present, it may remove the XRO if it is sure that
the next nodes do not need this information anymore. An example
is where a node can expand the ERO to a full strict path towards
the destination. See Figure 1 where BC2 is removing the XRO from
the Path message.
3. If an XRO was present, the content of the XRO can be modified.
Subobjects can be added or removed. See Figure 1 for an example
where AB2 is stripping off some subobjects.
In any case, a node MUST NOT introduce any explicit or abstract node
in the XRO (irrespective of the value of the L flag) that it also has
introduced in the ERO.
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5. Explicit Exclusion Route
The Explicit Exclusion Route defines abstract nodes or resources
(such as links, unnumbered interfaces or labels) that must not or
should not be used on the path between two inclusive abstract nodes
or resources in the explicit route.
5.1 Explicit Exclusion Route Subobject (EXRS)
A new ERO subobject type is defined. The Explicit Exclusion Route
Subobject (EXRS) has type [TBD by IANA]. Although the EXRS is an ERO
subobject and the XRO is reusing the ERO subobject, an EXRS MUST NOT
be present in an XRO. An EXRS is an ERO subobject, which contains
one or more subobjects in its own, called EXRS subobjects.
The format of the EXRS is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// one or more EXRS subobjects //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
L
It MUST be set to zero on transmission and MUST be ignored on
receipt. [Note: The L bit in an EXRS subobject is as defined
for the XRO subobjects]
Type
The type of the subobject, i.e. EXRS [TBD by IANA]
Reserved
This field is reserved. It MUST be set to zero on transmission
and MUST be ignored on receipt.
EXRS subobjects
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An EXRS subobject indicates the abstract node or resource to be
excluded. The format of an EXRS subobject is exactly the same
as the format of a subobject in the XRO. An EXRS may include
all subobjects defined in this document for the XRO.
Thus, an EXRS for an IP hop may look as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type | Length | IPv4 address (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 address (continued) | Prefix Length | Attribute |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5.2 Processing Rules for the Explicit Exclusion Route Subobject (EXRS)
Each EXRS may carry multiple exclusions. The exclusion is encoded
exactly as for XRO subobjects and prefixed by an additional Type and
Length.
The scope of the exclusion is the step between the previous ERO
subobject that identifies an abstract node, and the subsequent ERO
subobject that identifies an abstract node. The processing rules of
the EXRS are the same as the processing rule of the XRO within this
scope. Multiple exclusions may be present between any pair of
abstract nodes.
Exclusions may indicate explicit nodes, abstract nodes or Autonomous
Systems that must not be traversed on the path to the next abstract
node indicated in the ERO.
Exclusions may also indicate resources (such as unnumbered
interfaces, link ids, labels) that must not be used on the path to
the next abstract node indicated in the ERO.
SRLGs may also be indicated for exclusion from the path to the next
abstract node in the ERO by the inclusion of an EXRS containing an
SRLG subobject. If the L-bit value in the SRLG subobject is zero,
the resources (nodes, links, etc.) identified by the SRLG MUST not be
used on the path to the next abstract node indicated in the ERO. If
the L-bit is set, the resources identified by the SRLG SHOULD be
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avoided.
If a node is called upon to process an EXRS and does not support
handling of exclusions it will behave as described in [RFC3209] when
an unrecognized ERO subobject is encountered. This means that this
node will return a PathErr with error code "Routing Error" and error
value "Bad Explicit Route Object" with the EXPLICIT_ROUTE object
inlcuded, truncated (on the left) to the offending EXRS.
If the presence of EXRS precludes further forwarding of the Path
message, the node should return a PathErr with the error code
"Routing Problem" and error value of "Route blocked by Exclude
Route".
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6. Processing of XRO together with EXRS
When an LSR performs ERO expansion and finds both the XRO in the Path
message and EXRS in the ERO, it MUST exclude all the SRLGs, nodes,
links and resources listed in both places. Where some elements
appears in both lists it MUST be handled according to the stricter
exclusion request - that is, if one list says that an SRLG, node,
link or resource must be excluded and the other says only that it
should be avoided then the element MUST be excluded.
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7. Minimum compliance
An implementation must be at least compliant with the following:
1. The XRO MUST be supported with the following restrictions:
* The IPv4 Prefix subobject MUST be supported with a prefix
length of 32, and an attribute value of "interface" and
"node". Other prefix values and attribute values MAY be
supported.
* The IPv6 Prefix subobject MUST be supported with a prefix
length of 128, and an attribute value of "interface" and
"node". Other prefix values and attribute values MAY be
supported.
2. The EXRS MAY be supported. If supported, the same restrictions
as for the XRO apply.
3. If XRO or EXRS are supported, the implementation MUST be
compliant with the processing rules of the supported, not
supported, or partially supported subobjects as specified within
this document.
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8. Security Considerations
The new exclude route object poses no security exposures over and
above [RFC3209] and [RFC3473]. Note that any security concerns that
exist with Explicit Routes should be considered with regard to route
exclusions.
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9. IANA Considerations
It might be considered that an alternative approach would be to
assign one of the bits of the ERO sub-object type field (perhaps the
top bit) to identify that a sub-object is intended for inclusion
rather than exclusion. However, [RFC3209] states that the type field
(seven bits) should be assigned as 0 - 63 through IETF consensus
action, 64 - 95 as first come first served, and 96 - 127 are reserved
for private use. It would not be acceptable to disrupt existing
implementations so the only option would be to split the IETF
consensus range leaving only 32 sub-object types. It is felt that
that would be an unacceptably small number for future expansion of
the protocol.
9.1 New RSVP-TE Class Numbers
One new class number is required for Exclude Route object (XRO)
defined in section "Exclude Route Object (XRO)".
EXCLUDE_ROUTE
Class-Num of type 11bbbbbb
Suggested value 232
Defined CType: 1 (Exclude Route)
Subobjects 1, 2, 4 and 32 as for Explicit Route Object.
Additional SRLG subobject as requested in "New ERO and XRO
Subobject Type"
9.2 New ERO Subobject Type
The Explicit Exclusion Route subobject (EXRS) is defined in section
"Explicit Exclusion Route Subobject (EXRS)". This subobject may be
present in the Explicit Route Object, but not in the Route Record
Object, nor in the new Exclude Route Object.
Suggested value 33
9.3 New ERO and XRO Subobject Type
The SRLG subobject is defined in section "SRLG ERO Subobject". This
subobject may be present in the Exclude Route Object or in the
Explicit Route Object, but not in the Route Record Object.
Suggested value 34
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9.4 New Error Codes
New error values are needed for the error code 'Routing Problem'
(24).
Unsupported Exclude Route Subobject Type Suggested value 64
Inconsistent Subobject Suggested value 65
Local Node in Exclude Route Suggested value 66
Route Blocked by Exclude Route Suggested value 67
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10. Acknowledgments
This document reuses text from [RFC3209] for the description of
EXCLUDE_ROUTE.
The authors would like to express their thanks to Lou Berger, Steffen
Brockmann, Igor Bryskin, Dimitri Papadimitriou, Cristel Pelsser, and
Richard Rabbat for their considered opinions on this draft. Also
thanks to Yakov Rekhter for reminding us about SRLGs!
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11. References
11.1 Normative References
[GMPLS-RTG]
Kompella, K. and Y. Rekhter, "Routing Extensions in
Support of Generalized Multi-Protocol Label Switching",
draft-ietf-ccamp-gmpls-routing-9.txt, work in progress,
October 2003.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[RFC3473] Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Resource ReserVation Protocol-Traffic
Engineering (RSVP-TE) Extensions", RFC 3473, January 2003.
[RFC3477] Kompella, K. and Y. Rekhter, "Signalling Unnumbered Links
in Resource ReSerVation Protocol - Traffic Engineering
(RSVP-TE)", RFC 3477, January 2003.
11.2 Informational References
[CRANKBACK]
Farrel, A., Satyanarayana, A., Iwata, A., Ash, G., and S.
Marshall-Unitt, "Crankback Signaling Extensions for MPLS
Signaling", draft-ietf-ccamp-crankback-02.txt, work in
progress, July 2004.
[INTERAS] De Cnodder, S. and C. Pelsser, "Protection for inter-AS
MPLS tunnels",
draft-decnodder-ccamp-interas-protection-00.txt, work in
progress, July 2004.
[INTERAS-REQ]
Zhang, R. and JP. Vasseur, "MPLS Inter-AS Traffic
Engineering requirements",
draft-ietf-tewg-interas-mpls-te-req-09.txt, work in
progress, September 2004.
[MPLS-BUNDLE]
Kompella, K., Rekhter, Y., and L. Berger, "Link Bundling
in MPLS Traffic Engineering",
draft-ietf-mpls-bundle-04.txt, work in progress,
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July 2002.
[OVERLAY] Swallow, G., Drake, J., Ishimatsu, H., and Y. Rekhter,
"GMPLS UNI: RSVP Support for the Overlay Model",
draft-ietf-ccamp-gmpls-overlay-04.txt, work in progress,
April 2004.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
September 2003.
[RFC3784] Smit, H. and T. Li, "Intermediate System to Intermediate
System (IS-IS) Extensions for Traffic Engineering (TE)",
RFC 3784, June 2004.
[RFC3812] Srinivasan, C., Viswanathan, A., and T. Nadeau,
"Multiprotocol Label Switching (MPLS) Traffic Engineering
(TE) Management Information Base (MIB)", RFC 3812,
June 2004.
Authors' Addresses
Cheng-Yin Lee
Alcatel
600 March Road.
Ottawa, Ontario
Canada K2K 2E6
Email: Cheng-Yin.Lee@alcatel.com
Adrian Farrel
Old Dog Consulting
Phone: +44 (0) 1978 860944
Email: adrian@olddog.co.uk
Stefaan De Cnodder
Alcatel
Francis Wellesplein 1
B-2018 Antwerp
Belgium
Phone: +32 3 240 85 15
Email: stefaan.de_cnodder@alcatel.be
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Appendix A. applications
This section describes some applications that can make use of the
XRO. The intention is to show that the XRO is not an application
specific object, but that it can be used for multiple purposes. In a
few examples, other solutions might be possible for that particular
case but the intention is to show that a single object can be used
for all the examples, hence making the XRO a rather generic object
without having to define a solution and new objects for each new
application.
A.1 Inter-area LSP protection
One method to establish an inter-area LSP is where the ingress router
selects an ABR, and then the ingress router computes a path towards
this selected ABR such that the configured constraints of the LSP are
fulfilled. In the example of figure A.1, an LSP has to be
established from node A in area 1 to node C in area 2. If no loose
hops are con- figured, then the computed ERO at A could looks as
follows: (A1- strict, A2-strict, ABR1-strict, C-loose). When the
Path message arrives at ABR1, then the ERO is (ABR1-strict, C-loose)
and it can be expanded by ABR1 to (B1-strict, ABR3-strict, C-loose).
Similar, at ABR3 the received ERO is (ABR3-strict, C-loose) and it
can be expanded to (C1-strict, C2-strict, C-strict). If also a
backup LSP has to be established, then A takes another ABR (ABR2 in
this case) and computes a path towards this ABR that fulfills the
constraints of the LSP and such that is disjoint from the path of the
primary LSP. The ERO generated by A looks as follows for this
example: (A3-strict, A4-strict, ABR2-strict, C-loose).
In order to let ABR2 expand the ERO, it also needs to know the path
of the primary LSP to expand the ERO such that it is disjoint from
the path of the primary LSP. Therefore, A also includes an XRO that
at least contains (ABR1, B1, ABR3, C1, C2). Based on these con-
straints, ABR2 can expand the ERO such that it is disjoint from the
primary LSP. In this example, the ERO computed by ABR2 would be (B2-
strict, ABR4-strict, C-loose), and the XRO generated by B contains at
least (ABR3, C1, C2). The latter information is needed to let ABR4
to expand the ERO such that the path is disjoint from the primary LSP
in area 2.
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Area 1 Area 0 Area 2
<---------------><--------------><--------------->
+---A1---A2----ABR1-----B1-----ABR3----C1---C2---+
| | | | |
| | | | |
A | | | C
| | | | |
| | | | |
+---A3---A4----ABR2-----B2-----ABR4----C3---C4---+
Figure A.1: Inter-area LSPs
In this example, a node performing the path computation, first
selects an ABR and then it computes a strict path towards this ABR.
For the backup LSP, all nodes of the primary LSP in the next areas
has to be put in the XRO (with the exception of the destination node
if node protection and no link protection is required). When an ABR
computes the next path segment, i.e. the path over the next area, it
may remove the nodes from the XRO that are located in that area with
the exception of the ABR where the primary LSP is exiting the area.
The latter information is still required because when the selected
ABR (ABR4 in this example) further expands the ERO, it has to exclude
the ABR on which the primary is entering that area (ABR3 in this
example). This means that when ABR2 generates an XRO, it may remove
the nodes in area 0 from the XRO but not ABR3. Note that not doing
this would not harm in this example because there is no path from
ABR4 to C via ABR3 in area2. If there is a link between ABR4- ABR3
and ABR3-C, then it is required to have ABR3 in the XRO gen- erated
by ABR2.
Discussion on the length of the XRO: when link or node protection is
requested, the length of the XRO is bounded by the length of the RRO
of the primary LSP. It can be made shorter by removing nodes by the
ingress node and the ABRs. In the example above, the RRO of the pri-
mary LSP contains 8 subobjects, while the maximum XRO length can be
bounded by 6 subobjects (nodes A1 and A2 do not have to be in the
XRO. For SRLG protection, the XRO has to list all SRLGs that are
crossed by the primary LSP.
A.2 Inter-AS LSP protection
When an inter-AS LSP is established, which has to be protected by a
backup LSP to provide link or node protection, the same method as for
the inter-area LSP case can be used. The difference is when the
backup LSP is not following the same AS-path as the primary LSP
because then the XRO should always contain the full path of the pri-
mary LSP. In case the backup LSP is following the same AS-path (but
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with different ASBRs - at least in case of node protection), it is
similar to the inter-area case: ASBRs expanding the ERO over the next
AS may remove the XRO subobjects located in that AS. Note that this
can only be done by ingress ASBRs (the ASBR where the LSP is entering
the AS).
Discussion on the length of the XRO: the XRO is bounded by the length
of the RRO of the primary LSP.
Suppose that SRLG protection is required, and the ASs crossed by the
main LSP use a consistent way of allocating SRLG-ids to the links
(i.e. the ASs use a single SRLG space). In this case, the SRLG-ids
of each link used by the main LSP can be recorded by means of the
RRO, which are then used by the XRO. If the SRLG-ids are only
meaningfull local to the AS, putting SRLG-ids in the XRO crossing
many ASs makes no sense. More details on the method of providing
SRLG protection for inter-AS LSPs can be found in [INTERAS].
Basically, the link IP address of the inter-AS link used by the
primary LSP is put into the XRO of the Path message of the detour LSP
or bypass tunnel. The ASBR where the detour LSP or bypass tunnel is
entering the AS can translate this into the list of SRLG-ids known to
the local AS.
Discussion on the length of the XRO: the XRO only contains 1
subobject, which contains the IP address of the inter-AS link
traversed by the primary LSP (assuming that the primary LSP and
detour LSP or bypass tunnel are leaving the AS in the same area, and
they are also entering the next AS in the same area).
A.3 Protection in the GMPLS overlay model
When an edge-node wants to establish an LSP towards another edge-node
over an optical core network as described in [OVERLAY] (see figure
A.2), the XRO can be used for multiple purposes.
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Overlay Overlay
Network +--------------------------------+ Network
+----------+ | | +----------+
| +----+ | | +-----+ +-----+ +-----+ | | +----+ |
| | | | | | | | | | | | | | | |
| --+ EN1+-+-----+--+ CN1 +---+ CN2 +---+ CN3 +---+-----+-+ EN3+-- |
| | | | +--+--+ | | | | +---+--+ | | | |
| +----+ | | | +--+--+ +--+--+ +--+--+ | | | +----+ |
| | | | | | | | | | |
+----------+ | | | | | | | +----------+
| | | | | | |
+----------+ | | | | | | | +----------+
| | | | +--+--+ | +--+--+ | | | |
| +----+ | | | | | +------+ | | | | +----+ |
| | +-+--+ | | CN4 +-------------+ CN5 | | +--+-+ | |
| --+ EN2+-+-----+--+ | | +---+-----+-+ EN4+-- |
| | | | | +-----+ +-----+ | | | | |
| +----+ | | | | +----+ |
| | +--------------------------------+ | |
+----------+ Core Network +----------+
Overlay Overlay
Network Network
Legend:
EN- Edge Node
CN- Core Node
Figure A.2
A first application is where an edge-node wants to establish multiple
LSPs towards the same destination edge-node, and these LSPs need to
have as few or no SRLGs in common. In this case EN1 could establish
an LSP towards EN3 and then it can establish a second LSP listing all
links used by the first LSP with the indication to avoid the SRLGs of
these links. This information can be used by CN1 to compute a path
for the second LSP. If the core network consists of multiple areas,
then the SRLG-ids have to be listed in the XRO. The same example
applies to nodes and links.
Another application is where the edge-node wants to set up a backup
LSP that is also protecting the links between the edge-nodes and
core-nodes. For instance, when EN2 establishes an LSP to EN4, it
sends a Path message to CN4, which computes a path towards EN4 over
for instance CN5. When EN2 gets back the RRO of that LSP, it can
sig- nal a new LSP to CN1 with EN4 as destination and the XRO
computed based on the RRO of the first LSP. Based on this
information, CN1 can compute a path that has the requested diversity
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properties (e.g, a path going over CN2, CN3 and then to EN4).
It is clear that in these examples, the core-node may not edit the
RRO in a Resv message such that it includes only the subobjects from
the egress core-node through the egress edge-node.
A.4 LSP protection inside a single area
The XRO can also be used inside a single area. Take for instance a
network where the TE extensions of the IGPs as described in [RFC3630]
and [RFC3784] are not used, and hence each node has to select a next-
hop and possibly crankback [CRANKBACK] has to be used when there is
no viable next-hop. In this case, when signaling a backup LSP, the
XRO can be put in the Path message to exclude the links, nodes or
SRLGs of the primary LSP. An alternative to provide this
functionality would be to indicate in the Path message of the backup
LSP, the primary LSP together with an indication which type of
protection is required. This latter solution would work for link and
node protec- tion, but not for SRLG protection.
When link or node protection is requested, the XRO is of the same
length as the RRO of the primary LSP. For SRLG protection, the XRO
has to list all SRLGs that are crossed by the primary LSP. Note that
for SRLG protection, the link IP address to reference the SRLGs of
that link cannot be used since the TE extensions of the IGPs are not
used in this example. Hence, a node cannot translate any link IP
address located in that area to its SRLGs.
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