GMPLS Segment Recovery :: RFC4873
Network Working Group L. Berger
Request for Comments: 4873 LabN Consulting
Updates: 3473, 4872 I. Bryskin
Category: Standards Track ADVA Optical
D. Papadimitriou
Alcatel
A. Farrel
Old Dog Consulting
May 2007
GMPLS Segment Recovery
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document describes protocol specific procedures for GMPLS
(Generalized Multi-Protocol Label Switching) RSVP-TE (Resource
ReserVation Protocol - Traffic Engineering) signaling extensions to
support label switched path (LSP) segment protection and restoration.
These extensions are intended to complement and be consistent with
the RSVP-TE Extensions for End-to-End GMPLS Recovery (RFC 4872).
Implications and interactions with fast reroute are also addressed.
This document also updates the handling of NOTIFY_REQUEST objects.
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Table of Contents
1. Introduction ....................................................3
1.1. Conventions Used in This Document ..........................3
2. Segment Recovery ................................................4
2.1. Segment Protection .........................................6
2.2. Segment Re-routing and Restoration .........................6
3. ASSOCIATION Object ..............................................6
3.1. Format .....................................................7
3.2. Procedures .................................................7
3.2.1. Recovery Type Processing ............................7
3.2.2. Resource Sharing Association Type Processing ........7
4. Explicit Control of LSP Segment Recovery ........................8
4.1. Secondary Explicit Route Object Format .....................8
4.1.1. Protection Subobject ................................8
4.2. Explicit Control Procedures ................................9
4.2.1. Branch Failure Handling ............................10
4.2.2. Resv Message Processing ............................11
4.2.3. Admin Status Change ................................12
4.2.4. Recovery LSP Teardown ..............................12
4.3. Teardown From Non-Ingress Nodes ...........................12
4.3.1. Modified NOTIFY_REQUEST Object Processing ..........13
4.3.2. Modified Notify and Error Message Processing .......14
5. Secondary Record Route Objects .................................14
5.1. Format ....................................................14
5.2. Path Processing ...........................................15
5.3. Resv Processing ...........................................15
6. Dynamic Control of LSP Segment Recovery ........................16
6.1. Modified PROTECTION Object Format .........................16
6.2. Dynamic Control Procedures ................................17
7. Updated RSVP Message Formats ...................................18
8. Security Considerations ........................................20
9. IANA Considerations ............................................21
9.1. New Association Type Assignment ...........................21
9.2. Definition of PROTECTION Object Reserved Bits .............21
9.3. Secondary Explicit Route Object ...........................21
9.4. Secondary Record Route Object .............................21
9.5. New Error Code ............................................22
9.6. Use of PROTECTION Object C-type ...........................22
10. References ....................................................23
10.1. Normative References .....................................23
10.2. Informative References ...................................23
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1. Introduction
[RFC4427] covers multiple types of protection, including end-to-end
and segment-based approaches. "RSVP-TE Extensions in Support of
End-to-End Generalized Multi-Protocol Label Switching (GMPLS)
Recovery" [RFC4872] defines a set of extensions to support multiple
types of recovery. The supported types include 1+1 unidirectional/
1+1 bidirectional protection, LSP protection with extra-traffic
(including 1:N protection with extra-traffic), pre-planned LSP re-
routing without extra-traffic (including shared mesh), and full LSP
re-routing. In all cases, the recovery is provided on an end-to-end
basis, i.e., the ingress and egress nodes of both the protected and
the protecting LSP are the same.
[RFC4090] provides a form of segment recovery for packet MPLS-TE
networks. Two methods of fast reroute are defined in [RFC4090]. The
one-to-one backup method creates detour LSPs for each protected LSP
at each potential point of local repair. The facility backup method
creates a bypass tunnel to protect a potential failure point that is
shared by multiple LSPs and uses label stacking. Neither approach
supports the full set of recovery types supported by [RFC4872].
Additionally, the facility backup method is not applicable to most
non-PSC (packet switch capable) switching technologies.
The extensions defined in this document allow for support of the full
set of recovery types supported by [RFC4872], but on a segment, or
portion of the LSP, basis. The extensions allow (a) the signaling of
desired LSP segment protection type, (b) upstream nodes to optionally
identify where segment protection starts and stops, (c) the optional
identification of hops used on protection segments, and (d) the
reporting of paths used to protect an LSP. The extensions also widen
the topological scope over which protection can be supported. They
allow recovery segments that protect against an arbitrary number of
nodes and links. They enable overlapping protection and nested
protection. These extensions are intended to be compatible with fast
reroute, and in some cases used with fast reroute.
1.1. Conventions Used in This Document
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].
In addition, the reader is assumed to be familiar with the
terminology used in [RFC3209], [RFC3471], and [RFC3473], as well as
[RFC4427], [RFC4426], [RFC4872], and [RFC4090].
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2. Segment Recovery
Segment recovery is used to provide protection and restoration over a
portion of an end-to-end LSP. Such segment protection and
restoration is useful to protect against a span failure, a node
failure, or failure over a particular portion of a network used by an
LSP.
Consider the following topology:
A---B---C---D---E---F
\ /
G---I
In this topology, end-to-end protection and recovery is not possible
for an LSP going between node A and node F, but it is possible to
protect/recover a portion of the LSP. Specifically, if the LSP uses
a working path of [A,B,C,D,E,F], then a protection or restoration LSP
can be established along the path [C,G,I,E]. This LSP protects
against failures on spans {C,D} and {D,E}, as well as a failure of
node D. This form of protection/restoration is referred to as
Segment Protection and Segment Restoration, or as Segment Recovery,
collectively. The LSP providing the protection or restoration is
referred to as a segment protection LSP or a segment restoration LSP.
The term "segment recovery LSP" is used to cover either a segment
protection LSP or a segment restoration LSP. The term "branch node"
is used to refer to a node that initiates a recovery LSP, e.g., node
C in the figure shown above. This is equivalent to the point of
local repair (PLR) used in [RFC4090]. As with [RFC4090], the term
"merge node" is used to refer to a node that terminates a recovery
LSP, e.g., node E in the figure shown above.
Segment protection or restoration is signaled using a working LSP and
one or more segment recovery LSPs. Each segment recovery LSP is
signaled as an independent LSP. Specifically, the Sender_Template
object uses the IP address of the node originating the recovery path,
e.g., node C in the topology shown above, and the Session object
contains the IP address of the node terminating the recovery path,
e.g., node E shown above. There is no specific requirement on LSP ID
value, Tunnel ID, and Extended Tunnel ID. Values for these fields
are selected normally, including consideration for the make-before-
break concept (as described in [RFC3209]). Intermediate nodes follow
standard signaling procedures when processing segment recovery LSPs.
A segment recovery LSP may be protected itself using segment or end-
to-end protection/restoration. Note, in PSC environments, it may be
desirable to construct the Sender_Template and Session objects per
[RFC4090].
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When [RFC4090] isn't being used, the association between segment
recovery LSPs with other LSPs is indicated using the ASSOCIATION
object defined in [RFC4872]. The ASSOCIATION object is used to
associate recovery LSPs with the LSP they are protecting. Working
and protecting LSPs, as well as primary and secondary LSPs, are
identified using LSP Status as described in [RFC4872]. The O-bit in
the segment flags portion of the PROTECTION object is used to
identify when a recovery LSP is carrying the normal (active) traffic.
An upstream node can permit downstream nodes to dynamically identify
branch and merge points by setting the desired LSP segment protection
bits in the PROTECTION object. These bits are defined below.
Optionally, an upstream node, usually the ingress node, can identify
the endpoints of a segment recovery LSP. This is accomplished using
a new object. This object uses the same format as an Explicit Route
Object (ERO) and is referred to as a Secondary Explicit Route object
(SERO); see Section 4.1. SEROs also support a new subobject to
indicate the type of protection or restoration to be provided. At a
minimum, an SERO will indicate a recovery LSP's initiator,
protection/restoration type and terminator. Standard ERO semantics
(see [RFC3209]) can optionally be used within and SERO to explicitly
control the recovery LSP. A Secondary Record Route object (SRRO) is
defined for recording the path of a segment recovery LSP; see Section
5.
SEROs are carried between the node creating the SERO, typically the
ingress, and the node initiating a recovery LSP. The node initiating
a recovery LSP uses the SERO to create the ERO for the recovery LSP.
At this (branch) node, all local objects are removed, and the new
protection subobject is used to create the PROTECTION object for the
recovery LSP. It is also possible to control the handling of a
failure to establish a recovery LSP.
SRROs are carried in Path messages between the node terminating a
recovery LSP, the merge node, and the egress. SRROs are used in Resv
messages between a branch node and the ingress. The merge node of a
recovery LSP creates an SRRO by copying the RRO from the Path message
of the associated recovery LSP into a new SRRO object. Any SRROs
present in the recovery LSP's Path message are also copied. The
branch node of a recovery LSP creates an SRRO by copying the RRO from
the Resv message of associated recovery LSP into a new SRRO object.
Any SRROs present in the recovery LSP's Resv message are also copied.
Notify request processing is also impacted by LSP segment recovery.
Per [RFC3473], only one NOTIFY_REQUEST object is meaningful and
should be propagated. Additional NOTIFY_REQUEST objects are used to
identify recovery LSP branch nodes.
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2.1. Segment Protection
Three approaches for end-to-end protection are defined in [RFC4872]:
1+1 Unidirectional Protection (Section 5), 1+1 Bidirectional
Protection (Section 6), and 1:1 Protection With Extra-Traffic
(Section 7). The segment protection forms of these protection
approaches all operate much like their end-to-end counterparts. Each
behaves just like its end-to-end counterpart, with the exception that
the protection LSP protects only a portion of the working LSP. The
type of protection to be used on a segment protection LSP is
indicated, to the protection LSP's ingress, using the protection SERO
subobject defined in Section 4.1.
The switch-over processing for segment 1+1 Bidirectional protection
and 1:1 Protection With Extra-Traffic follows the same procedures as
end-to-end protection forms; see Sections 6.2 and 7.2 of [RFC4872]
for details.
2.2. Segment Re-routing and Restoration
Three re-routing and restoration approaches are defined in [RFC4872]:
Re-routing without Extra-Traffic (Section 8), Shared-Mesh Restoration
(Section 9), (Full) LSP Re-routing (Section 11). As with protection,
these approaches are supported on a segment basis. The segment forms
of re-routing and restoration operate exactly like their end-to-end
counterparts, with the exception that the restoration LSP recovers
only a portion of the working LSP. The type of re-routing or
restoration to be used on a segment restoration LSP is indicated, to
the restoration LSP's ingress, using the new protection SERO
subobject.
3. ASSOCIATION Object
The ASSOCIATION object is used for the association of segment
protection LSPs when [RFC4090] isn't being used. The ASSOCIATION
object is defined in [RFC4872]. In this document, we define a new
Association Type field value to support make-before-break; the
formats and procedures defined in [RFC4872] are not otherwise
modified.
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3.1. Format
Association Type: 16 bits
Value Type
----- ----
2 Resource Sharing (R)
See [RFC4872] for the definition of other fields and values.
3.2. Procedures
The ASSOCIATION object is used to associate different LSPs with each
other. In the protection and restoration context, the object is used
to associate a recovery LSP with the LSP it is protecting. The
ASSOCIATION object is also used to support resource sharing during
make-before-break. This object MUST NOT be used when association is
made according to the methods defined in [RFC4090].
3.2.1. Recovery Type Processing
Recovery type processing procedures are the same as those defined in
[RFC4872], but processing and identification occur with respect to
segment recovery LSPs. Note that this means that multiple
ASSOCIATION objects of type recovery may be present on an LSP.
3.2.2. Resource Sharing Association Type Processing
The ASSOCIATION object with an Association Type with the value
Resource Sharing is used to enable resource sharing during make-
before-break. Resource sharing during make-before-break is defined
in [RFC3209]. The defined support only works with LSPs that share
the same LSP egress. With the introduction of segment recovery LSPs,
it is now possible for an LSP endpoint to change during make-before-
break.
A node includes an ASSOCIATION object with a Resource Sharing
Association Type in an outgoing Path message when it wishes to
indicate resource sharing across an associated set of LSPs. The
Association Source is set to the originating node's router address.
The Association ID MUST be set to a value that uniquely identifies
the association of LSPs. This MAY be set to the working LSP's LSP
ID. Once included, an ASSOCIATION object with a Resource Sharing
Association Type SHOULD NOT be removed from the Path messages
associated with an LSP.
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Any node processing a Path message for which the node does not have a
matching state, and which contains an ASSOCIATION object with a
Resource Sharing type, examines existing LSPs for matching
Association Type, Association Source, and Association ID values. If
any match is found, then [RFC3209] style resource sharing SHOULD be
provided between the new and old LSPs. See [RFC3209] for additional
details.
4. Explicit Control of LSP Segment Recovery
Secondary Explicit Route objects, or SEROs, are defined in this
document. They may be used to indicate the branch and merge nodes of
recovery LSPs. They may also provide additional information that is
to be carried in a recovery LSP's ERO. When upstream control of
branch and merge nodes is not desired, SEROs are not used.
4.1. Secondary Explicit Route Object Format
The format of a SECONDARY_EXPLICIT_ROUTE object is the same as an
EXPLICIT_ROUTE object. This includes the definition of subobjects
defined for EXPLICIT_ROUTE object. The class of the
SECONDARY_EXPLICIT_ROUTE object is 200 (of the form 11bbbbbb).
4.1.1. Protection Subobject
A new subobject, called the protection subobject, is defined for use
in the SECONDARY_EXPLICIT_ROUTE object. As mentioned above, the new
protection subobject is used to create the PROTECTION object for the
recovery LSP. Specific procedures related to the protection
subobject are provided in Section 4.2. The protection subobject is
not valid for use with the Explicit and Record Route objects and MUST
NOT be included in those objects.
The format of the protection subobject is defined 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 | C-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PROTECTION Object Contents |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
L-bit
This is defined in [RFC3209] and MUST be set to zero for
protection subobjects.
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Type
37 Protection
Length
As defined in [RFC3209], Section 4.3.3.
Reserved
This field is reserved. It MUST be set to zero on transmission
and MUST be ignored on receipt.
C-Type
The C-Type of the included PROTECTION object.
PROTECTION Object Contents
The contents of the PROTECTION object, with the format matching
the indicated C-Type, excluding the object header.
4.2. Explicit Control Procedures
SEROs are carried in Path messages and indicate at which node a
recovery LSP is to be initiated relative to the LSP carrying the
SERO. More than one SERO MAY be present in a Path message.
To indicate the branch and merge nodes of a recovery LSP, an SERO is
created and added to the Path message of the LSP being recovered.
The decision to create and insert an SERO is a local matter and
outside the scope of this document.
An SERO SHOULD contain at least three subobjects. The first
subobject MUST indicate the node that is to originate the recovery
LSP, i.e. the segment branch node. The address used SHOULD also be
listed in the ERO or another SERO. This ensures that the branch node
is along the LSP path. The second subobject SHOULD be a protection
subobject and should indicate the protection or restoration to be
provided by the recovery LSP. When the protection subobject is
present, the LSP Segment Recovery Flags in the protection subobject
MUST be ignored. The final subobject in the SERO MUST be the merge
node of the recovery LSP, and MAY have the L-bit set. Standard ERO
subobjects MAY be inserted between the protection subobject and the
final subobject. These subobjects MAY be loose or strict.
A node receiving a Path message containing one or more SEROs SHOULD
examine each SERO to see if it indicates a local branch point. This
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determination is made by examining the first object of each SERO and
seeing if the address indicated in the subobject can be associated
with the local node. If any of indicated addresses are associated
with the local node, then the local node is a branch node. If the
local node is not a branch node, all received SEROs MUST be
transmitted, without modification, in the corresponding outgoing Path
message.
At a branch node, the SERO, together with the Path message of LSP
being recovered, provides the information to create the recovery LSP.
The Path message for the recovery LSP is created at the branch node
by cloning the objects carried in the incoming Path message of the
LSP being protected. Certain objects are replaced or modified in the
recovery LSP's outgoing Path message. The Sender_template object
MUST be updated to use an address (in its Tunnel Sender Address
field) on the local node, and the LSP ID MUST be updated to ensure
uniqueness. The Session object MUST be updated to use the address
indicated in the final subobject of the SERO as the tunnel endpoint
address, the tunnel ID MAY be updated, and the extended tunnel ID
MUST be set to the local node address. The PROTECTION object is
replaced with the contents of the matching SERO protection subobject,
when present. In all cases, the R-bit of a new PROTECTION object is
reset (0). Any RROs and EROs present in the incoming Path message
MUST NOT be included in the recovery LSP. A new ERO MUST be
included, with the contents of the SERO that indicated a local
branch. As with all EROs, no local information (local address and
any protection subobjects) is carried in the ERO carried in the
recovery LSP's outgoing Path message. The SERO that indicated a
local branch MUST be omitted from the recovery LSP's outgoing Path
message. Note, by default, all other received SEROs are passed in
the recovery LSP's outgoing Path message. SEROs MAY be omitted, from
the recovery LSP's outgoing Path message as well as the outgoing Path
message for the LSP being protected, when the SERO does not relate to
the outgoing path message.
The resulting Path message is used to create the recovery LSP. From
this point on, Standard Path message processing is used in processing
the resulting Path message.
4.2.1. Branch Failure Handling
During setup, it is possible that a processing node will be unable to
support a requested branch. Additionally, during setup and normal
operation, PathErr messages may be received at a branch node. The
processing of these events depend on a number of factors.
When a failure or received PathErr message is associated with the LSP
being protected, the event is first processed per standard processing
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rules. This includes generation of a standard PathErr message. When
LSP state is removed due to a local failure or a PathErr message with
the Path_State_Removed flag set (1), the node MUST send a PathTear
message downstream on all other branches.
When a failure or received PathErr message is associated with a
recovery LSP, processing is based on the R-bit in addition to the
Path_State_Removed flag. In all cases, a received PathErr message is
first processed per standard processing rules and the failure or
received PathErr message SHOULD trigger the generation of a PathErr
message upstream for the LSP being protected. The outgoing PathErr
message SHOULD indicate an error of "Routing Problem/LSP Segment
Protection Failed". The outgoing PathErr message MUST include any
SEROs carried in a received PathErr message. If no SERO is present
in a received PathErr message or when the failure is local, then an
SERO that matches the errored LSP or failed branch MUST be added to
the outgoing PathErr message.
When a PathErr message with the Path_State_Removed flag cleared (0)
is received, the outgoing (upstream) PathErr message SHOULD be sent
with the Path_State_Removed flag cleared (0).
When a PathErr message for a recovery LSP with the Path_State_Removed
flag set (1) is received, the processing node MUST examine the R-bit
(as defined below) of the LSP being protected. The R-bit is carried
in the PROTECTION object that triggered the initiation of the
recovery LSP. When the R-bit is not set (0), the outgoing (upstream)
PathErr message SHOULD be sent with the Path_State_Removed flag
cleared (0). When the R-bit is set (1), the outgoing (upstream)
PathErr message MUST be sent with the Path_State_Removed flag set
(1).
In all cases where an outgoing (upstream) PathErr message is sent
with the Path_State_Removed flag set (1), all path state for the LSP
being protected MUST be removed, and the node MUST send a PathTear
message downstream on all active branches.
4.2.2. Resv Message Processing
Branch nodes will process Resv messages for both recovery LSPs and
LSPs being protected. Resv messages are propagated upstream of
branch nodes only after a Resv message is received for the protected
LSP. Resv messages on recovery LSPs will typically not trigger
transmission of upstream Resv messages (for the LSP being protected).
Exceptions to this include when RROs/SRROs are being collected and
during certain ADMIN_STATUS object processing. See below for more
information on related processing.
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4.2.3. Admin Status Change
In general, objects in a recovery LSP are created based on the
corresponding objects in the LSP being protected. The ADMIN_STATUS
object is created the same way, but it also requires some special
coordination at branch nodes. Specifically, in addition to normal
processing, a branch node that receives an ADMIN_STATUS object in a
Path message also MUST relay the ADMIN_STATUS object in a Path on
every recovery LSP. All Path messages MAY be concurrently sent
downstream.
Downstream nodes process the change in the ADMIN_STATUS object per
[RFC3473], including generation of Resv messages. When the most
recently received upstream ADMIN_STATUS object has the R bit set,
branch nodes wait for a Resv message with a matching ADMIN_STATUS
object to be received on all branches before relaying a corresponding
Resv message upstream.
4.2.4. Recovery LSP Teardown
Recovery LSP removal follows standard procedures defined in [RFC3209]
and [RFC3473]. This includes with and without setting the
administrative status.
4.2.4.1. Teardown Without Admin Status Change
The node initiating the teardown originates a PathTear message. Each
node that receives a PathTear message processes the PathTear message
per standard processing (see [RFC3209] and [RFC2205]), and MUST also
relay a PathTear on every recovery LSP. All PathTear messages
(received from upstream and locally originated) may be concurrently
sent downstream.
4.2.4.2. Teardown With Admin Status Change
Per [RFC3473], the ingress node originates a Path message with the D
and R bits set in the ADMIN_STATUS object. The admin status change
procedure defined in Section 4.2.3 MUST then be followed. Once the
ingress receives all expected Resv messages, it MUST follow the
teardown procedure described in Section 4.2.4.1.
4.3. Teardown From Non-Ingress Nodes
As with any LSP, any node along a recovery LSP may initiate removal
of the recovery LSP. To do this, the node initiating the teardown
sends a PathErr message with the appropriate Error Code and the
Path_State_Removed flag cleared (0) toward the LSP ingress. As
described above, the recovery LSP ingress will propagate the error to
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the LSP ingress, which can then signal the removal of the recovery
LSP.
It is also possible for the node initiating the teardown to remove a
Recovery LSP in a non-graceful manner. In this case, the initiator
sends a PathTear message downstream and a PathErr message with a
"Confirmation" indication (error code and value set to zero), and the
Path_State_Removed flag set (1) toward the LSP ingress node. This
manner of non-ingress node teardown is NOT RECOMMENDED because in
some cases it can result in the removal of the LSP being protected.
4.3.1. Modified NOTIFY_REQUEST Object Processing
A parallel set of rules are applied at branch and merge nodes to
enable the branch or merge node to add a NOTIFY_REQUEST object to the
Path and Resv messages of protected and recovery LSPs. Branch nodes
add NOTIFY_REQUEST objects to Path messages, and merge nodes add
NOTIFY_REQUEST objects to Resv messages.
When a node is branching or merging a recovery LSP, the node SHOULD
include a single NOTIFY_REQUEST object in the Path message of the
recovery LSP, in the case of a branch node, or the Resv message of
the recovery LSP, in the case of a merge node. The notify node
address MUST be set to the router address of the processing node.
Branch and merge nodes SHOULD also add a NOTIFY_REQUEST object to the
LSP being protected. For branch nodes, the notify node address is
set to the address used in the sender template object of the
associated recovery LSP. For merge nodes, the notify node address is
set to the address used in the session object of the associated
recovery LSP. A locally added NOTIFY_REQUEST object MUST be listed
first in an outgoing message; any received NOTIFY_REQUEST objects
MUST then be listed in the message in the order that they were
received. Note that this can result in a stack (or ordered list) of
objects.
Normal notification procedures are then followed for the LSP being
protected. That is, the notifying node MUST issue a Notify message
to the recipient indicated by the notify address of the first listed
NOTIFY_REQUEST object. Under local policy control, a node issuing a
Notify message MAY also send a Notify message to the Notify Node
Address indicated in the last, or any other, NOTIFY_REQUEST object
carried in the Path or Resv message.
Recovery LSP merge and branch nodes remove the object added by the
recovery branch or merge node from outgoing Path and Resv messages
for the LSP being protected. This is done by removing the
NOTIFY_REQUEST object that, in the case of a merge node, matches the
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source address of the recovery LSP and, in the case of a branch node,
matches the tunnel endpoint address of the recovery LSP. The
matching NOTIFY_REQUEST object will normally be the first of the
listed NOTIFY_REQUEST objects. Note, to cover certain backwards
compatibility scenarios, the NOTIFY_REQUEST object SHOULD NOT be
removed if it is the sole NOTIFY_REQUEST object.
Note this requires the following change to [RFC3473], Section 4.2.1:
o old text:
If a message contains multiple NOTIFY_REQUEST objects, only the
first object is meaningful. Subsequent NOTIFY_REQUEST objects MAY
be ignored and SHOULD NOT be propagated.
o new text:
If a message contains multiple NOTIFY_REQUEST objects, only the
first object used is in notification. Subsequent NOTIFY_REQUEST
objects MUST be propagated in the order received.
4.3.2. Modified Notify and Error Message Processing
Branch and merge nodes MUST support the following modification to
Notify message processing. When a branch or merge node receives
notification of an LSP failure and it is unable to recover from that
failure, it MUST notify the node indicated in the first
NOTIFY_REQUEST object received in the Path message (for branch nodes)
or Resv message (for merge nodes) associated with the LSP.
5. Secondary Record Route Objects
Secondary Record Route objects, or SRROs, are used to record the path
used by recovery LSPs.
5.1. Format
The format of a SECONDARY_RECORD_ROUTE object is the same as a
RECORD_ROUTE object, Class number 21. This includes the definition
of subobjects defined for RECORD_ROUTE object. The class of the
SECONDARY_RECORD_ROUTE object is 201 (of the form 11bbbbbb).
The protection subobject defined above can also be used in
SECONDARY_RECORD_ROUTE objects.
Berger, et al. Standards Track [Page 14]
RFC 4873 GMPLS Segment Recovery May 2007
5.2. Path Processing
SRROs may be carried in Path messages and indicate the presence of
upstream recovery LSPs. More than one SRRO MAY be added and present
in a Path message.
Any received SRRO MUST be transmitted by transit nodes, without
modification, in the corresponding outgoing Path message.
SRROs are inserted in Path messages by recovery LSP merge nodes. The
SRRO is created by copying the contents of an RRO received by the
recovery LSP into a new SRRO object. This SRRO is added to the
outgoing Path message of the recovered LSP. Note that multiple SRROs
may be present. The collection of SRROs is controlled via the
segment-recording-desired flag in the SESSION_ATTRIBUTE object. This
flag MAY be set even when SEROs are not used.
5.3. Resv Processing
SRROs may be carried in Resv messages and indicate the presence of
downstream recovery LSPs. More than one SRRO MAY be added and
present in a Resv message.
Any received SRRO MUST be transmitted by transit nodes, without
modification, in the corresponding outgoing Resv message. When Resv
messages are merged, the resulting merged Resv SHOULD contain all
SRROs received in downstream Resv messages.
SRROs are inserted in Resv messages by branch nodes of recovery LSPs.
The SRRO SHOULD be created with the first two objects being the local
node address, followed by a protection subobject with the contents of
the recovery LSP's PROTECTION object. The remainder of the SRRO
SHOULD be created by copying the contents of the RRO received by the
recovery LSP. This SRRO SHOULD be added to the outgoing Resv message
of the recovered LSP. Again, multiple SRROs may be present.
If the newly added SRRO causes the message to be too big to fit in a
Resv message, SRRO subobjects SHOULD be removed from any present
SRROs. When removing subobjects, the first two subobjects and the
last subobject in an SRRO MUST NOT be removed. Note that the
subobject that followed a removed subobject MUST be updated with the
L-bit set (1). If after removing all but the first and last
subobjects in all SRROs the resulting message is still too large to
fit, then whole SRROs SHOULD be removed until the message does fit.
Berger, et al. Standards Track [Page 15]
RFC 4873 GMPLS Segment Recovery May 2007
6. Dynamic Control of LSP Segment Recovery
Dynamic identification of branch and merge nodes is supported via the
LSP Segment Recovery Flags carried in the PROTECTION object. The LSP
Segment Recovery Flags are carried within one of the Reserved fields
defined in the PROTECTION object defined in [RFC4872]. LSP Segment
Recovery Flags are used to indicate when LSP segment recovery is
desired. When these bits are set, branch and merge nodes are
dynamically identified.
Note, the procedures defined in this section parallel the explicit
control procedures defined above in Section 4.2. The primary
difference is in the creation of a recovery LSP's ERO.
6.1. Modified PROTECTION Object Format
LSP Segment Recovery Flags are carried in the PROTECTION object of
the same C-Type defined in [RFC4872]. The format of the flags are:
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 | Class-Num(37) | C-Type (2) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S|P|N|O| Reserved | LSP Flags | Reserved | Link Flags|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|I|R| Reserved | Seg.Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
In-Place (I): 1 bit
When set (1) indicates that the desired segment recovery type
indicated in the LSP Segment Recovery Flag is already in place
for the associated LSP.
Required (R): 1 bit
When set (1) indicates that failure to establish the indicated
protection should result in a failure of the LSP being
protected.
Segment Recovery Flags (Seg.Flags): 6 bits
This field is used to indicate when an upstream node desires
LSP Segment recovery to be dynamically initiated where
possible. The values used in this field are identical to the
values defined for LSP Flags; see [RFC4872].
Berger, et al. Standards Track [Page 16]
RFC 4873 GMPLS Segment Recovery May 2007
See [RFC4872] for the definition of other fields.
6.2. Dynamic Control Procedures
LSP Segment Recovery Flags are set to indicate that LSP segment
recovery is desired for the LSP being signaled. The type of recovery
desired is indicated by the flags. The decision to set the LSP
Segment Recovery Flags is a local matter and outside the scope of
this document. A value of zero (0) means that no dynamic
identification of segment recovery branch nodes are needed for the
associated LSP. When the In-Place bit is set, it means that the
desired type of recovery is already in place for that particular LSP.
A transit node receiving a Path message containing a PROTECTION
object with a non-zero LSP Segment Recovery Flags value and the In-
Place bit clear (0) SHOULD consider if it can support the indicated
recovery type and if it can identify an appropriate merge node for a
recovery LSP. Dynamic identification MUST NOT be done when the
processing node is identified as a branch node in an SERO. If a node
is unable to provide the indicated recovery type or identify a merge
node, the Path message MUST be processed normally, and the LSP
Segment Recovery Flags MUST NOT be modified.
When a node dynamically identifies itself as a branch node and
identifies the merge node for the type of recovery indicated in the
LSP Segment Recovery Flags, it attempts to setup a recovery LSP. The
dynamically identified information, together with the Path message of
LSP being recovered, is used to create the recovery LSP.
The Path message for the recovery LSP is created at the branch node
by cloning the objects carried in the incoming Path message of the
LSP being protected. Certain objects are replaced or modified in the
recovery LSP's outgoing Path message. The Sender_template object
MUST be updated to use an address (in its Tunnel Sender Address
field) on the local node, and the LSP ID MUST be updated to ensure
uniqueness. The Session object MUST be updated to use the address of
the dynamically identified merge node as the tunnel endpoint address,
the tunnel ID MAY be updated, and the extended tunnel ID MUST be set
to the local node address. The PROTECTION object is updated with the
In-Place bit set (1). Any RROs and EROs present in the incoming Path
message MUST NOT be included in the recovery LSP. A new ERO MAY be
created based on any path information dynamically computed by the
local node.
Berger, et al. Standards Track [Page 17]
RFC 4873 GMPLS Segment Recovery May 2007
The resulting Path message is used to create the recovery LSP. While
the recovery LSP exists, the PROTECTION object in the original Path
message (unless overridden by local policy) MUST also be updated
with the In-Place bit set (1). From this point on, Standard Path
message processing is used in processing the resulting and original
Path messages.
The merge node of a dynamically controlled recovery LSP SHOULD reset
(0) the In-Place bit in the PROTECTION object of the outgoing Path
message associated with the terminated recovery LSP.
Unlike with explicit control, if the creation of a dynamically
identified recovery LSP fails for any reason, the recovery LSP is
removed, and no error message or indication is sent upstream. With
this exception, all the other procedures for explicitly controlled
recovery LSPs apply to dynamically controlled recovery LSPs. These
other procedures are defined above in Sections 4.2.1 through 4.2.4.
7. Updated RSVP Message Formats
This section presents the RSVP message related formats as modified by
this document. Where they differ, formats for unidirectional LSPs
are presented separately from bidirectional LSPs.
The format of a Path message is as follows:
::= [ ]
[ [ | ] ... ]
[ ]
[ ]
[ ]
[ ... ]
[ ]
[ ... ]
[ ]
[ ... ]
[ ... ]
[ ... ]
Berger, et al. Standards Track [Page 18]
RFC 4873 GMPLS Segment Recovery May 2007
The format of the sender description for unidirectional LSPs is:
::=
[ ]
[ ]
[ ]
[ ]
[ ... ]
The format of the sender description for bidirectional LSPs is:
::=
[ ]
[ ]
[ ]
[ ]
[ ... ]
The format of a PathErr message is as follows:
::= [ ]
[ [ | ] ... ]
[ ]
[ ... ]
[ ... ]
[ ... ]
The format of a Resv message is as follows:
::= [ ]
[ [ | ] ... ]
[ ]
[ ] [ ]
[ ... ]
[ ]
[ ... ]
