Network Working Group CY. Lee
Internet-Draft Alcatel
Expires: August 22, 2005 A. Farrel
Old Dog Consulting
S. De Cnodder
Alcatel
February 18, 2005
Exclude Routes - Extension to RSVP-TE
draft-ietf-ccamp-rsvp-te-exclude-route-03.txt
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
The current 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
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Protocol-Traffic Engineering (RSVP-TE) Extensions" (RFC 3473) allow
abstract nodes and resources to be explicitly included in a path
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
1.1 Changes compared to version 01 . . . . . . . . . . . . . . 4
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1 Scope of Exclude Routes . . . . . . . . . . . . . . . . . 5
2.2 Relationship to MPLS TE MIB . . . . . . . . . . . . . . . 7
3. Shared Risk Link Groups . . . . . . . . . . . . . . . . . . . 8
3.1 SRLG ERO Subobject . . . . . . . . . . . . . . . . . . . . 8
4. Exclude Route List . . . . . . . . . . . . . . . . . . . . . . 9
4.1 Exclude Route Object (XRO) . . . . . . . . . . . . . . . . 9
4.1.1 Subobject 1: IPv4 prefix . . . . . . . . . . . . . . 10
4.1.2 Subobject 2: IPv6 Prefix . . . . . . . . . . . . . . 11
4.1.3 Subobject 32: Autonomous System Number . . . . . . . 11
4.1.4 Subobject TBD: SRLG . . . . . . . . . . . . . . . . . 12
4.1.5 Subobject 4: Unnumbered Interface ID Subobject . . . . 12
4.2 Semantics and Processing Rules for the Exclude Route
Object (XRO) . . . . . . . . . . . . . . . . . . . . . . . 13
5. Explicit Exclude Route . . . . . . . . . . . . . . . . . . . . 16
5.1 Explicit Exclusion Route Subobject (EXRS) . . . . . . . . 16
5.2 Semantics and Processing Rules for the EXRS . . . . . . . 17
6. Minimum compliance . . . . . . . . . . . . . . . . . . . . . . 18
7. Security Considerations . . . . . . . . . . . . . . . . . . . 19
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
8.1 New Class Numbers . . . . . . . . . . . . . . . . . . . . 20
8.2 New Subobject Types . . . . . . . . . . . . . . . . . . . 20
8.3 New Error Codes . . . . . . . . . . . . . . . . . . . . . 20
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
10.1 Normative References . . . . . . . . . . . . . . . . . . . 22
10.2 Informational References . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 23
A. applications . . . . . . . . . . . . . . . . . . . . . . . . . 24
A.1 Inter-area LSP protection . . . . . . . . . . . . . . . . 24
A.2 Inter-AS LSP protection . . . . . . . . . . . . . . . . . 25
A.3 Protection in the GMPLS overlay model . . . . . . . . . . 26
A.4 LSP protection inside a single area . . . . . . . . . . . 28
Intellectual Property and Copyright Statements . . . . . . . . 29
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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].
1.1 Changes compared to version 01
o References updated.
o Editorial updates.
o Added Unnumbered Interface exclusions
o Acknowledgements updated.
o IPR section.
o Appendix A with applications is added.
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2. Introduction
The current 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. Exclude any of the abstract nodes in a given set anywhere on the
path. This set of abstract nodes is referred to as the Exclude
Route list.
2. Exclude 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 introcuded 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 subobject type the Explicit Exclude
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 of a 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.
This subobject might also be appropriate for use within Explicit
Routes or Record Routes, but that discussion is outside the scope of
this document.
2.1 Scope of Exclude Routes
This document does not preclude a route exclusion from listing many
nodes or network elements to avoid. The intent is, however, to
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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: (C1, C2)
|
ERO: (A3-strict, A4-strict, AB2-strict, Egress-loose)
XRO: (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,
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AB2-strict, Egress-loose) and (B1, B2, BC1, C1, C2) respectively. At
AB2 the ERO and XRO could be (B3-strict, B4-strict, BC2-strict,
Egress-loose) and (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-
OSPF].
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.
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].
Length
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
Zero on transmission. Ignored on receipt
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4. Exclude Route List
The exclude route identifies a list of abstract nodes that MUST 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, 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. The subobjects are identical to
those defined in [RFC3209] and [RFC3473] for use in EROs.
The following subobject types are supported.
Type Subobject
1 IPv4 prefix
2 IPv6 prefix
4 Unnumbered Interface ID
32 Autonomous system number
TBD SRLG
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 [RSPV-TE], is
reused here to indicate that an abstract node MUST be avoided (value
0) or SHOULD be avoided (value 1).
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An Attribute octet is introduced in the subobjects that define IP
addresses to indicate the attribute (e.g. interface, node, SRLG)
associated with the IP addresses that can be excluded from the path.
For instance, the attribute node allows a whole node to be excluded
from the path, in contrast to the attribute interface, which allows
specific interfaces to be excluded from the path. The attribute SRLG
allows all SRLGs associated with an IP address to be excluded from
the path.
4.1.1 Subobject 1: IPv4 prefix
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 associ-
ated with the IP prefix should be excluded or avoided
node
1 indicates that the node or set of nodes associated with
the IP prefix should be excluded or avoided
SRLG
2 indicates that all the SRLGs associated with the IP
prefix should be excluded or avoided
The rest of the fields are as defined in [RFC3209].
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4.1.2 Subobject 2: IPv6 Prefix
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
interface
0 indicates that the interface or set of interfaces associ-
ated with the IP prefix should be excluded or avoided
node
1 indicates that the node or set of nodes associated with
the IP prefix should be excluded or avoided
SRLG
2 indicates that all the SRLG associated with the IP
prefix should be excluded or avoided
The rest of the fields are as defined in [RFC3209].
4.1.3 Subobject 32: Autonomous System Number
The L bit of an Autonomous System Number subobject has meaning in an
Exclude Route (contrary to its usage in an Explict Route defined in
[RFC3209]. The meaning is as for other subobjects described above.
That is:
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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.
4.1.4 Subobject TBD: SRLG
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.
4.1.5 Subobject 4: 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) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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
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
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convenient to use subobjects from RRO, in specifying the
exclusions)
SRLG
2 indicates that all the SRLGs associated with the
interface should be excluded or avoided
Reserved
Zero on transmission. Ignored on receipt.
The rest of the fields are as defined in [RFC3477].
4.2 Semantics and 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".
3. The subobjects in the ERO and XRO SHOULD not contradict each
other. If they do contradict, the subobjects with the L flag not
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set, strict or MUST be excluded, respectively, in the ERO or XRO
MUST take precedence. If there is still a conflict, a PathErr
with error code "Routing Problem" and error value of "Route
blocked by Exclude Route" should be returned.
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 exlicit nodes or abstract nodes with
the L flag set to "avoid" should be minimised.
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
subob- jects.
The XRO Class-Num is of the form 11bbbbbb so that nodes which do not
support the XRO will forward it uninspected and will not apply the
extensions to ERO processing described above. This makes the XRO a
'best effort' process.
This 'best-effort' 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 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 of the processing rules mentioned
above:
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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.
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5. Explicit Exclude Route
The Explicit Exclude Route defines abstract nodes or resources (such
as links, unnumbered interfaces or labels) that must 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 Exclude Route
Subobject (EXRS) has type [TBD]. The EXRS may not be present in an
RRO or XRO.
The format of the EXRS is as follows.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--------------//---------------+
|L| Type | Length | EXRS subobjects |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--------------//---------------+
L
ignored and must be zero [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]
EXRS subobjects
An EXRS subobject indicates the abstract node or resource to be
excluded. The format of this field is exactly the format of an
XRO subobject and may include an SRLG subobject. Both subob-
jects are as described earlier in this document.
Thus, an EXRO subobject for an IP hop might 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 |L| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 address (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | Attribute | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Note: The Most Significant Bit in the Type field could be used to
indicate exclusion of IPv4/IPv6, AS and SRLG subobjects, eliminating
the need to prepend the subobject with an additional TLV header.
This would reduce the number bytes require for each subobject by 2
bytes. However, this approach would reduce the ERO Type field space
by half. This issue need WG discussion and feedback.
5.2 Semantics and Processing Rules for the 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. 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 EXRO Subobject
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 avoided.
The subobjects in the ERO and EXRS SHOULD not contradict each other.
If they do contradict, the subobjects with the L bit not set, strict
or MUST be excluded, respectively, in the ERO or XRO MUST take pre-
cedence. If there is still a conflict, the subobjects in the ERO
MUST take precedence.
If a node is called upon to process an EXRS and does not support
handling of exclusions it will return a PathErr with a "Bad
EXPLICIT_ROUTE object" error.
If the presence of EXRO Subobjects 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. 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 attriubute value of "interface" and
"node". Other prefix values and attribute values MAY be
supported.
2. The EXRS SHOULD 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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7. 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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8. IANA Considerations
It might be considered that a possible 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.
8.1 New Class Numbers
One new class number is required.
EXCLUDE_ROUTE
Class-Num = 011bbbbb
CType: 1
8.2 New Subobject Types
A new subobject type for the Exclude Route Object and Explicit
Exclude Route Subobject is required.
SRLG subobject
A new subobject type for the ERO is required.
Explicit Exclude Route subobject
8.3 New Error Codes
New error values are needed for the error code 'Routing Problem'.
Unsupported Exclude Route Subobject Type [TBD]
Inconsistent Subobject [TBD]
Local Node in Exclude Route [TBD]
Route Blocked by Exclude Route [TBD]
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9. 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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10. References
10.1 Normative References
[GMPLS-OSPF]
Kompella, K. and Y. Rekhter, "OSPF Extensions in Support
of Generalized Multi-Protocol Label Switching",
draft-ietf-ccamp-ospf-gmpls-extensions-12.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.
10.2 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, July
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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 also 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 would be a links 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 adn 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
much similar as 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 subob-
ject, which contains the IP address of the inter-AS link traversed by
the primary LSP (in the assumption 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 destinatin 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 indicition 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 diversaty
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
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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 functional-
ity would be to indicate in the Path message of the backup LSP, the
primary LSP together witn an indication which type of protection is
required. This latter solution would work for link and node protec-
tion, but not for SRLG protection.
Discussion on the length of the XRO: 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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