draft-ietf-ccamp-loose-path-reopt-01.txt   draft-ietf-ccamp-loose-path-reopt-02.txt 
CCAMP Working Group Jean-Philippe Vasseur Networking Working Group JP. Vasseur, Ed.
IETF Internet Draft (Editor) Internet-Draft Cisco Systems, Inc
Proposed status: Informational Cisco Systems Proposed Status: Informational Y. Ikejiri
Yuichi Ikejiri Expires: August 12, 2006 NTT Communications Corporation
NTT Communications R. Zhang
Corporation BT Infonet
Raymond Zhang February 8, 2006
Infonet Service Corporation
Expires: November 2005 May 2005
Reoptimization of Multiprotocol Label Switching (MPLS) Traffic Reoptimization of Multiprotocol Label Switching (MPLS) Traffic
Engineering (TE) loosely routed Label Switch Path (LSP) Engineering (TE) loosely routed Label Switch Path (LSP)
draft-ietf-ccamp-loose-path-reopt-01.txt draft-ietf-ccamp-loose-path-reopt-02.txt
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2005). All Rights Reserved. Copyright (C) The Internet Society (2006).
Abstract Abstract
This document defines a mechanism for the reoptimization of loosely This document defines a mechanism for the reoptimization of loosely
routed MPLS and GMPLS (Generalized Multiprotocol Label Switching) routed MPLS and GMPLS (Generalized Multiprotocol Label Switching)
Traffic Engineering LSPs. A loosely routed LSP is defined as one Traffic Engineering (TE) LSPs signaled with RSVP-TE. This document
that does not contain a full explicit route identifying each LSR proposes a mechanism that allows a TE LSP head-end LSR to trigger a
along the path of the LSP at the time it is signaled by the ingress new path re-evaluation on every hop having a next hop defined as a
LSR. Such an LSP is signaled with no ERO, with an ERO that contains loose or abstract hop and a mid-point LSR to signal to the head-end
at least one loose hop, or with an ERO that contains an abstract LSR that a better path exists (compared to the current path in use)
node that is not a simple abstract node (that is, an abstract node or that the TE LSP must be reoptimized because of some maintenance
that identifies more than one LSR). This document proposes a required on the TE LSP path. The proposed mechanism applies to the
mechanism that allows a TE LSP head-end LSR to trigger a new path re- cases of intra and inter-domain (IGP area or Autonomous System)
evaluation on every hop having a next hop defined as a loose or packet and non-packet TE LSPs following a loosely routed path.
abstract hop and a mid-point LSR to signal to the head-end LSR that a
better path exists (compared to the current path in use) or that the
TE LSP must be reoptimized because of some maintenance required on
the TE LSP path.
The proposed mechanism applies to the cases of intra and inter-domain
(IGP area or Autonomous System) packet and non-packet TE LSPs
following a loosely routed path.
Conventions used in this document Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119. document are to be interpreted as described in RFC 2119 [RFC2119].
Table of contents Table of Contents
1. Notice.........................................................3 1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction...................................................3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Establishment of a loosely routed TE LSP.......................4 3. Establishment of a loosely routed TE LSP . . . . . . . . . . . 4
4. Reoptimization of a loosely routed TE LSP path.................5 4. Reoptimization of a loosely routed TE LSP path . . . . . . . . 6
5. Signalling extensions..........................................6 5. Signalling extensions . . . . . . . . . . . . . . . . . . . . 6
5.1 Path re-evaluation request.................................6 5.1. Path re-evaluation request . . . . . . . . . . . . . . . . 7
5.2 New error value sub-codes..................................6 5.2. New error value sub-codes . . . . . . . . . . . . . . . . 7
6. Mode of operation..............................................7 6. Mode of operation . . . . . . . . . . . . . . . . . . . . . . 7
6.1 Head-end reoptimization control............................7 6.1. Head-end reoptimization control . . . . . . . . . . . . . 7
6.2 Reoptimization triggers....................................7 6.2. Reoptimization triggers . . . . . . . . . . . . . . . . . 8
6.3 Head-end request versus mid-point explicit notification 6.3. Head-end request versus mid-point explicit
modes..........................................................7 notification functions . . . . . . . . . . . . . . . . . . 8
5.3.1 Head-end request mode.......................................7 6.3.1. Head-end request function . . . . . . . . . . . . . . 8
5.3.2 Mid-point explicit notification mode........................9 6.3.2. Mid-point explicit notification . . . . . . . . . . . 9
5.3.3 ERO caching.................................................9 6.3.3. ERO caching . . . . . . . . . . . . . . . . . . . . . 10
7. Interoperability..............................................10 7. Applicability and Interoperability . . . . . . . . . . . . . . 10
8. Security considerations.......................................10 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
9. IANA considerations...........................................10 9. Security Considerations . . . . . . . . . . . . . . . . . . . 11
10. Acknowledgments..............................................10 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
11. Intellectual property considerations.........................11 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
12. References...................................................11 11.1. Normative References . . . . . . . . . . . . . . . . . . . 12
11.1 Normative references........................................11 11.2. Informative References . . . . . . . . . . . . . . . . . . 12
11.2 Informative references......................................11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
13. Authors' Addresses...........................................12 Intellectual Property and Copyright Statements . . . . . . . . . . 14
14. Full Copyright Statement.....................................12
1. Notice 1. Terminology
The procedures described in this document are entirely optional Terminology used in this document
within an MPLS or GMPLS network. Implementations that do not support
the procedures described in this document will interoperate
seamlessly with those that do. Further, an implementation that does
not support the procedures described in this document will not be
impacted or implicated by a neighboring implementation that does
implement the procedures.
An ingress implementation that chooses not to support the procedures ABR: Area Border Router.
described in this document may still achieve re-optimization by
periodically issuing a speculative make-before-break replacement of ERO: Explicit Route Object.
an LSP without trying to discovery whether a more optimal path is
available in a downstream domain. Such a procedure would not be in LSR: Label Switch Router.
conflict with any mechanisms not already documented in [RFC3209] and
[RFC3473]. TE LSP: Traffic Engineering Label Switched Path.
TE LSP head-end: head/source of the TE LSP.
TE LSP tail-end: tail/destination of the TE LSP.
IGP Area: OSPF Area or IS-IS level.
Intra-area TE LSP: TE LSP whose path does not transit across areas.
Inter-area TE LSP: A TE LSP whose path transits across at least two
different IGP areas.
Inter-AS MPLS TE LSP: A TE LSP whose path transits across at least
two different ASs or sub-ASs (BGP confederations).
2. Introduction 2. Introduction
The Traffic Engineering Work Group has specified a set of This document defines a mechanism for the reoptimization of loosely
requirements for inter-area [INTER-AREA-TE-REQ] and inter-AS [INTER- routed MPLS and GMPLS (Generalized Multiprotocol Label Switching)
AS-TE-REQ] MPLS Traffic Engineering. Both requirements documents Traffic Engineering LSPs signaled with RSVP-TE (see [RFC3209] and
specify the need for some mechanism providing an option for the head- [RFC3473]). A loosely routed LSP is defined as one that does not
end to control the reoptimization process, should a more optimal path contain a full explicit route identifying each LSR along the path of
exist in a downstream domain (IGP area or Autonomous System). the LSP at the time it is signaled by the ingress LSR. Such an LSP
is signaled with no ERO, with an ERO that contains at least one loose
hop, or with an ERO that contains an abstract node that is not a
simple abstract node (that is, an abstract node that identifies more
than one LSR).
This document defines a solution to meet this requirement and The Traffic Engineering Working Group (TE WG) has specified a set of
proposes a set of mechanisms that allow: requirements for inter-area and inter-AS MPLS Traffic Engineering
(see [RFC4105] and [RFC4216]). Both requirements documents specify
the need for some mechanism providing an option for the head-end to
control the reoptimization process should a more optimal path exist
in a downstream domain (IGP area or Autonomous System). This
document defines a solution to meet this requirement and proposes two
mechanisms:
- The TE LSP head-end LSR to trigger a new path re-evaluation on (1) The first mechanism allows a head-end LSR to trigger a new path
every hop having a next hop defined as a loose hop or abstract re-evaluation on every hop having a next hop defined as a loose hop
node, or abstract node and get a notification from the mid-point on whether
a better path exists.
- A mid-point LSR to signal to the head-end LSR that either a (2) The second mechanism allows a mid-point LSR to explicitly signal
better path exists to reach a loose/abstract hop (compared to the to the head-end LSR that either a better path exists to reach a
current path in use) or that the TE LSP must be reoptimized because loose/abstract hop (compared to the current path in use) or that the
of some maintenance required on the TE LSP path. A better path is TE LSP must be reoptimized because of some maintenance required along
defined as a lower cost path, where the cost is determined by the the TE LSP path. In this case, the notification is sent by the mid-
metric used to compute the path. point LSR without being polled by the head-end LSR.
A better path is defined as a lower cost path, where the cost is
determined by the metric used to compute the path.
3. Establishment of a loosely routed TE LSP 3. Establishment of a loosely routed TE LSP
The aim of this section is purely to remind the mechanisms involved
in the establishment of a loosely routed TE LSP (in line with
[RFC3209]) and does not introduce any new protocol extensions or
mechanisms.
In the context of this document, a loosely routed LSP is defined as In the context of this document, a loosely routed LSP is defined as
one that does not contain a full explicit route identifying each LSR one that does not contain a full explicit route identifying each LSR
along the path of the LSP at the time it is signaled by the ingress along the path of the LSP at the time it is signaled by the ingress
LSR. Such an LSP is signaled with no ERO, with an ERO that contains LSR. Such an LSP is signaled with no ERO, with an ERO that contains
at least one loose hop, or with an ERO that contains an abstract at least one loose hop, or with an ERO that contains an abstract node
node that is not a simple abstract node (that is, an abstract node that is not a simple abstract node (that is, an abstract node that
that identifies more than one LSR). As defined in [RFC3209], loose identifies more than one LSR). As specified in [RFC3209], loose hops
hops are listed in the Explicit Route Object (ERO) of the RSVP Path are listed in the ERO object of the RSVP Path message with the L flag
message with the L flag of the IPv4 or the IPv6 prefix sub-object of the IPv4 or the IPv6 prefix sub-object set.
set.
Each LSR along the path whose next hop is specified as a loose hop or Each LSR along the path whose next hop is specified as a loose hop or
a non-specific abstract node triggers a path computation (also a non-specific abstract node triggers a path computation (also
referred to as an ERO expansion), before forwarding the RSVP Path referred to as an ERO expansion), before forwarding the RSVP Path
message downstream. The computed path may either be partial (up to message downstream. The computed path may either be partial (up to
the next loose hop) or complete (set of strict hops up to the TE LSP the next loose hop) or complete (set of strict hops up to the TE LSP
destination). destination).
Note that the examples in the rest of this document are provided in Note that the examples in the rest of this document are provided in
the context of MPLS inter-area TE but the proposed mechanism equally the context of MPLS inter-area TE but the proposed mechanism equally
applies to loosely routed paths within a single routing domain and applies to loosely routed paths within a single routing domain and
across multiple Autonomous Systems. across multiple Autonomous Systems. The examples below are provided
with OSPF as the IGP but the described set of mechanisms similarly
The examples below are provided with OSPF as the IGP but the apply to IS-IS.
described set of mechanisms similarly apply to IS-IS.
An example of an explicit loosely routed TE LSP signaling. An example of an explicit loosely routed TE LSP signaling.
<---area 1--><-area 0--><-area 2-> <---area 1--><-area 0--><-area 2->
R1---R2----R3---R6 R8---R10 R1---R2----R3---R6 R8---R10
| | | / | \ | | | | / | \ |
| | | / | \ | | | | / | \ |
| | | / | \| | | | / | \|
R4---------R5---R7----R9---R11 R4---------R5---R7----R9---R11
skipping to change at page 4, line 44 skipping to change at page 5, line 16
<---area 1--><-area 0--><-area 2-> <---area 1--><-area 0--><-area 2->
R1---R2----R3---R6 R8---R10 R1---R2----R3---R6 R8---R10
| | | / | \ | | | | / | \ |
| | | / | \ | | | | / | \ |
| | | / | \| | | | / | \|
R4---------R5---R7----R9---R11 R4---------R5---R7----R9---R11
Assumptions Assumptions
- R3, R5, R8 and R9 are ABRs - R3, R5, R8 and R9 are ABRs
- The path of an inter-area TE LSP T1 from R1 (head-end LSR) to R11 - The path of an inter-area TE LSP T1 from R1 (head-end LSR) to R11
(tail-end LSR) is defined on R1 as the following loosely routed path: (tail-end LSR) is defined on R1 as the following loosely routed path:
R1-R3(loose)-R8(loose)-R11(loose). R3, R8 and R11 are defined as R1-R3(loose)-R8(loose)-R11(loose). R3, R8 and R11 are defined as
loose hops. loose hops.
Step 1: R1 determines that the next hop (R3) is a loose hop (not Step 1: R1 determines that the next hop (R3) is a loose hop (not
directly connected to R1) and then performs an ERO expansion directly connected to R1) and then performs an ERO expansion
operation to reach the next loose hops R3. The new ERO becomes: operation to reach the next loose hops R3. The new ERO becomes:
R2(S)-R3(S)-R8(L)-R11(L) where: R2(S)-R3(S)-R8(L)-R11(L) where: S: Strict hop (L=0) L: Loose hop
S: Strict hop (L=0) (L=1)
L: Loose hop (L=1)
The R1-R2-R3 path obeys T1's set of constraints. The R1-R2-R3 path satisfies T1's set of constraints.
Step 2: the RSVP Path message is then forwarded by R1 following the Step 2: the RSVP Path message is then forwarded by R1 following the
ERO path and reaches R3 with the following content: R8(L)-R11(L) path specified in the ERO object and reaches R3 with the following
content: R8(L)-R11(L).
Step 3: R3 determines that the next hop (R8) is a loose hop (not Step 3: R3 determines that the next hop (R8) is a loose hop (not
directly connected to R3) and then performs an ERO expansion directly connected to R3) and then performs an ERO expansion
operation to reach the next loose hops R8. The new ERO becomes: operation to reach the next loose hops R8. The new ERO becomes:
R6(S)-R7(S)-R8(S)-R11(L). R6(S)-R7(S)-R8(S)-R11(L).
Note: in this example, the assumption is made that the path is Note: in this example, the assumption is made that the path is
computed on a per loose hop basis, also referred to a partial route computed on a per loose hop basis, also referred to a partial route
computation. Note that some path computation techniques may result in computation. Note that other path computation techniques may result
complete paths (set of strict hops up to the final destination). in complete paths (set of strict hops up to the final destination).
Step 4: the same procedure applies at R8 to reach T1's destination Step 4: the same procedure is repeated by R8 to reach T1's
(R11). destination (R11).
4. Reoptimization of a loosely routed TE LSP path 4. Reoptimization of a loosely routed TE LSP path
Once a loosely routed explicit TE LSP is set up, it is maintained Once a loosely routed explicit TE LSP is set up, it is maintained
through normal RSVP procedures. During TE LSP life time, a more through normal RSVP procedures. During TE LSP life time, a more
optimal path might appear between an LSR and its next loose hop (for optimal path might appear between an LSR and its next loose hop (for
the sake of illustration, suppose in the example above that a link the sake of illustration, suppose in the example above that a link
between R6 and R8 is added or restored that provides a preferable between R6 and R8 is added or restored that provides a preferable
path between R3 and R8 (R3-R6-R8) than the existing R3-R6-R7-R8 path between R3 and R8 (R3-R6-R8) than the existing R3-R6-R7-R8
path). Since a preferable (e.g. shorter) path might not be visible path). Since a preferable (e.g. shorter) path might not be visible
from the head-end LSR by means of the IGP if it does not belong to from the head-end LSR by means of the IGP if the head-end LSR does
the head-end IGP area, the head-end cannot make use of this shorter not belong to the head-end IGP area, the head-end cannot make use of
path (and reroute the LSP using a make before break) when this shorter path (and reroute the LSP using a make-before-break
appropriate. Hence, some mechanism is required to detect the technique as described in [RFC3209]) when appropriate. Hence, a new
existence of such a preferable path and to notify the head-end mechanisms specified in this document is required to detect the
existence of such a preferable path and to notify the head-end LSR
accordingly. accordingly.
This document defines a mechanism that allows: This document defines a mechanism that allows:
- A head-end LSR to trigger on every LSR whose next hop is a - A head-end LSR to trigger on every LSR whose next hop is a loose
loose hop or an abstract node the re-evaluation of the current hop or an abstract node the re-evaluation of the current path in
path in order to detect a potential more optimal path, order to detect a potentially more optimal path,
- A mid-point LSR whose next hop is a loose-hop or an abstract - A mid-point LSR whose next hop is a loose-hop or an abstract node
node to signal (using a new Error value sub-code carried in a to signal (using a new Error value sub-code carried in a RSVP PERR
RSVP PathErr message) to the head-end that a more preferable message) to the head-end LSR that a more preferable path exists (a
path exists (a path with a lower cost, where the cost definition path with a lower cost, where the cost definition is determined by
is determined by some metric). some metric).
Then once the existence of such a preferable path is notified to the Once the existence of such a preferable path has been notified to the
head-end LSR, the head-end LSR can decide (depending on the TE LSP head-end LSR, the head-end LSR can decide (depending on the TE LSP
characteristics) whether to perform a TE LSP graceful reoptimization characteristics) whether to perform a TE LSP graceful reoptimization
such as the "Make Before Break" procedure defined in [RFC3209]. such as the "make-before-break" procedure.
There is another scenario whereby notifying the head-end of the There is another scenario whereby notifying the head-end LSR of the
existence of a better path is desirable: if the current path is about existence of a better path is desirable: if the current path is about
the fail due to some (link or node) required maintenance. the fail due to some (link or node) required maintenance.
This allows the head-end to reoptimize a TE LSP making use of the non This mechanism allows the head-end LSR to reoptimize a TE LSP making
disruptive make before break procedure if and only if a preferable use of the non disruptive make-before-break procedure if and only if
path exists and if such a reoptimization is desired. a preferable path exists and if such a reoptimization is desired.
5. Signalling extensions 5. Signalling extensions
A new flag in the SESSION ATTRIBUTE object and new Error value sub- A new flag in the SESSION ATTRIBUTE object and new Error value sub-
codes in the ERROR SPEC object are proposed in this document (to be codes in the ERROR SPEC object are proposed in this document (to be
assigned by IANA). assigned by IANA).
5.1 Path re-evaluation request 5.1. Path re-evaluation request
The following new flag of the SESSION_ATTRIBUTE object (C-Type 1 and The following new flag of the SESSION_ATTRIBUTE object (C-Type 1 and
7) is defined (suggested value to be confirmed by IANA): 7) is defined (suggested value to be confirmed by IANA):
Path re-evaluation request: 0x20 Path re-evaluation request: 0x20
This flag indicates that a path re-evaluation (of the current path in This flag indicates that a path re-evaluation (of the current path in
use) is requested. Note that this does not trigger any LSP Reroute use) is requested. Note that this does not trigger any LSP Reroute
but instead just signals the request to evaluate whether a preferable but instead just signals the request to evaluate whether a preferable
path exists. path exists.
Note: in case of link bundling for instance, although the resulting Note: in case of link bundling for instance, although the resulting
ERO might be identical, this might give the opportunity for a mid- ERO might be identical, this might give the opportunity for a mid-
point LSR to locally select another link within a bundle, although point LSR to locally select another link within a bundle, although
strictly speaking, the ERO has not changed. strictly speaking, the ERO has not changed.
5.2 New error value sub-codes 5.2. New error value sub-codes
As defined in [RFC3209], the ERROR-CODE 25 in ERROR SPEC object As defined in [RFC3209], the ERROR-CODE 25 in ERROR-SPEC object
corresponds to a Notify Error. corresponds to a Notify Error.
This document adds three new error value sub-codes (suggested values This document adds three new error value sub-codes (suggested values
to be confirmed by IANA): to be confirmed by IANA):
6 Preferable path exists 6 Preferable path exists
7 Local link maintenance required 7 Local link maintenance required
8 Local node maintenance required 8 Local node maintenance required
The details about the local maintenance required modes are detailed The details about the local maintenance required modes are detailed
in section 5.3.2 in section 6.3.2.
6. Mode of operation 6. Mode of operation
6.1 Head-end reoptimization control 6.1. Head-end reoptimization control
The notification process of a preferable path (shorter path or new The notification process of a preferable path (shorter path or new
path due to some maintenance required on the current path) is by path due to some maintenance required on the current path) is by
nature de-correlated from the reoptimization operation. In other nature de-correlated from the reoptimization operation. In other
words, the location where a potentially preferable path is discovered words, the location where a potentially preferable path is discovered
does not have to be where the TE LSP is actually reoptimized. This does not have to be where the TE LSP is actually reoptimized. This
document applies to the context of a head-end reoptimization. document applies to the context of a head-end reoptimization.
6.2 Reoptimization triggers 6.2. Reoptimization triggers
There are three possible reoptimization triggers: There are several possible reoptimization triggers. For example,
such reoptimization triggers are:
- Timer-based: a reoptimization is triggered (process evaluating - Timer-based: a reoptimization is triggered (process evaluating
whether a more optimal path can be found) when a configurable timer whether a more optimal path can be found) when a configurable timer
expires, expires,
- Event-driven: a reoptimization is triggered when a particular - Event-driven: a reoptimization is triggered when a particular
network event occurs (such as a "Link-UP" event), network event occurs (such as a "Link-UP" event),
- Operator-driven: a reoptimization is manually triggered by the - Operator-driven: a reoptimization is manually triggered by the
Operator. Operator.
It is RECOMMENDED for an implementation supporting the extensions It is RECOMMENDED for an implementation supporting the extensions
proposed in this document to support the aforementioned modes as path proposed in this document to support the aforementioned modes as path
re-evaluation triggers. re-evaluation triggers.
6.3 Head-end request versus mid-point explicit notification modes 6.3. Head-end request versus mid-point explicit notification functions
This document defines two modes: This document defines two functions:
1) "Head-end requesting mode": the request for a new path 1) "Head-end requesting function": the request for a new path
evaluation of a loosely routed TE LSP is requested by the head- evaluation of a loosely routed TE LSP is requested by the head-end
end LSR. LSR.
2) "Mid-point explicit notification": a mid-point LSR having 2) "Mid-point explicit notification function": a mid-point LSR having
determined that a preferable path (than the current path is use) determined that a preferable path (than the current path is use)
exists or having the need to perform a link/node local exists or having the need to perform a link/node local maintenance
maintenance explicitly notifies the head-end LSR which will in explicitly notifies the head-end LSR that will in turn decide whether
turn decide whether to perform a reoptimization. to perform a reoptimization.
6.3.1 Head-end request mode 6.3.1. Head-end request function
In this mode, when a timer-based reoptimization is triggered on the When a timer-based reoptimization is triggered on the head-end LSR or
head-end LSR or the operator manually requests a reoptimization, the the operator manually requests a reoptimization, the head-end LSR
head-end LSR immediately sends an RSVP Path message with the "Path immediately sends an RSVP Path message with the "Path re-evaluation
re-evaluation request" bit of the SESSION-ATTRIBUTE object set. This request" bit of the SESSION-ATTRIBUTE object set. This bit is then
bit is then cleared in subsequent RSVP path messages sent downstream. cleared in subsequent RSVP path messages sent downstream. In order
In order to handle the case of a lost Path message, the solution to handle the case of a lost Path message, the solution consists of
consists of relying on the reliable messaging mechanism described in relying on the reliable messaging mechanism described in [RFC2961].
[REFRESH-REDUCTION].
Upon receiving a Path message with the "Path re-evaluation request" Upon receiving a Path message with the "Path re-evaluation request"
bit set, every LSR for which the next abstract node contained in the bit set, every LSR for which the next abstract node contained in the
ERO is defined as a loose hop/abstract node, performs the following ERO is defined as a loose hop/abstract node performs the following
set of actions: set of actions:
A path re-evaluation is triggered and the newly computed path is A path re-evaluation is triggered and the newly computed path is
compared to the existing path: compared to the existing path:
- If a preferable path can be found, the LSR performing the path - If a preferable path can be found, the LSR performing the path re-
re-evaluation MUST immediately send an RSVP PathErr to the head- evaluation MUST immediately send an RSVP PErr to the head-end LSR
end LSR (Error code 25 (Notify), Error sub-code=6 (better path (Error code 25 (Notify), Error sub-code=6 (better path exists)). At
exists)). At this point, the LSR MAY decide to not propagate this point, the LSR MAY decide to not propagate such bit in
such bit in subsequent RSVP Path messages sent downstream for subsequent RSVP Path messages sent downstream for the re-evaluated TE
the re-evaluated TE LSP: this mode is the RECOMMENDED mode for LSP: this mode is the RECOMMENDED mode for the reasons described
the reasons described below. below.
The sending of an RSVP PathErr Notify message "Preferable path The sending of an RSVP PERR Notify message "Preferable path exists"
exists" to the head-end LSR will notify the head-end LSR of the to the head-end LSR will notify the head-end LSR of the existence of
existence of a preferable path (e.g in a downstream area/AS or a preferable path (e.g in a downstream area/AS or in another location
in another location within a single domain). Hence, triggering within a single domain). Hence, triggering additional path re-
additional path re-evaluations on downstream nodes is evaluations on downstream nodes is unnecessary. The only motivation
unnecessary. The only motivation to forward subsequent RSVP Path to forward subsequent RSVP Path messages with the "Path re-evaluation
messages with the "Path re-evaluation request" bit of the request" bit of the SESSION-ATTRIBUTE object set would be to trigger
SESSION-ATTRIBUTE object set would be to trigger path re- path re-evaluation on downstream nodes that could in turn cache some
evaluation on downstream nodes that could in turn cache some potentially better paths downstream with the objective to reduce the
potentially better paths downstream with the objective to reduce signaling setup delay, should a reoptimization be performed by the
the signaling setup delay, should a reoptimization be performed head-end LSR.
by the head-end LSR.
- If no preferable path can be found, the recommended mode is - If no preferable path can be found, the recommended mode is for an
for an LSR to relay the request (by setting the "Path re- LSR to relay the request (by setting the "Path re-evaluation" bit of
evaluation" bit of the SESSION-ATTRIBUTE object in RSVP path the SESSION-ATTRIBUTE object in RSVP path message sent downstream).
message sent downstream).
Note that, by preferable path, we mean a path having a lower cost. Note that, by preferable path, we mean a path having a lower cost.
If the RSVP Path message with the "Path re-evaluation request" bit If the RSVP Path message with the "Path re-evaluation request" bit
set is lost, then the next request will be sent when the next set is lost, then the next request will be sent when the next
reoptimization trigger will occur on the head-end LSR. The solution reoptimization trigger will occur on the head-end LSR. The solution
to handle RSVP reliable messaging has been defined in [REFRESH- to handle RSVP reliable messaging has been defined in [RFC2961].
REDUCTION].
The network administrator may decide to establish some local policy The network administrator may decide to establish some local policy
specifying to ignore such request or to consider those requests not specifying to ignore such request or to consider those requests not
more frequently than a certain rate. more frequently than a certain rate.
The proposed mechanism does not make any assumption of the path The proposed mechanism does not make any assumption of the path
computation method performed by the ERO expansion process. computation method performed by the ERO expansion process.
6.3.2 Mid-point explicit notification mode 6.3.2. Mid-point explicit notification
In this mode, a mid-point LSR whose next hop is a loose hop or an By contrast with the head-end request function, in this case, a mid-
abstract node can locally trigger a path re-evaluation when a point LSR whose next hop is a loose hop or an abstract node can
configurable timer expires, some specific events occur (e.g. link-up locally trigger a path re-evaluation when a configurable timer
event for example) or the user explicitly requests it. If a expires, some specific events occur (e.g. link-up event for example)
preferable path is found compared to the existing one, the LSR sends or the user explicitly requests it. If a preferable path is found
an RSVP PathErr to the head-end LSR (Error code 25 (Notify), Error compared to the path in use, the LSR sends an RSVP PERR to the head-
sub-code=6 ("preferable path exists"). end LSR (Error code 25 (Notify), Error sub-code=6 ("preferable path
exists").
There are other circumstances whereby any mid-point LSR MAY send an There are other circumstances whereby any mid-point LSR MAY send an
RSVP PathErr message with the objective for the TE LSP to be rerouted RSVP PERR message with the objective for the TE LSP to be rerouted by
by its head-end LSR: when a link or a node will go down for local its head-end LSR: when a link or a node will go down for local
maintenance reasons. In this case, the LSR where a local maintenance maintenance reasons. In this case, the LSR where a local maintenance
must be performed is responsible for sending an RSVP PathErr message must be performed is responsible for sending an RSVP PERR message
with Error code 25 and Error sub-code=7 or 8 depending on the with Error code 25 and Error sub-code=7 or 8 depending on the
affected network element (link or node). Then the first upstream node affected network element (link or node). Then the first upstream
having performed the ERO expansion MUST perform the following set of node having performed the ERO expansion MUST perform the following
actions: set of actions:
- The link (sub-code=7) or the node (sub-code=8) MUST be - The link (sub-code=7) or the node (sub-code=8) MUST be locally
locally registered for further reference (the TE database must registered for further reference (the TE database must be updated)
be updated)
- The RSVP PathErr message MUST be immediately forwarded - The RSVP PERR message MUST be immediately forwarded upstream to the
upstream to the head-end LSR. Note that in the case of TE LSP head-end LSR. Note that in the case of TE LSP spanning multiple
spanning multiple administrative domains, it may be desirable administrative domains, it may be desirable for the boundary LSR to
for the boundary LSR to modify the RSVP PathErr message and modify the RSVP PERR message and insert its own address for
insert its own address for confidentiality reason. confidentiality reason.
Upon receiving an RSVP PathErr message with Error code 25 and Error Upon receiving an RSVP PERR message with Error code 25 and Error sub-
sub-code 7 or 8, the Head-end LSR MUST perform a TE LSP code 7 or 8, the Head-end LSR SHOULD perform a TE LSP reoptimization.
reoptimization.
Note that those modes are not exclusive: both the timer and event- Note that the two functions (head-end and mid-point driven) are not
driven reoptimization triggers can be implemented on the head-end exclusive from each other: both the timer and event-driven
and/or any mid-point LSR with potentially different timer values for reoptimization triggers can be implemented on the head-end and/or any
the timer driven reoptimization case. mid-point LSR with potentially different timer values for the timer
driven reoptimization case.
A head-end LSR MAY decide upon receiving an explicit mid-point A head-end LSR MAY decide upon receiving an explicit mid-point
notification to delay its next path re-evaluation request. notification to delay its next path re-evaluation request.
6.3.3 ERO caching 6.3.3. ERO caching
Once a mid-point LSR has determined that a preferable path exists Once a mid-point LSR has determined that a preferable path exists
(after a reoptimization request has been received by the head-end LSR (after a reoptimization request has been received by the head-end LSR
or the reoptimization timer on the mid-point has fired), the more or the reoptimization timer on the mid-point has expired), the more
optimal path MAY be cached on the mid-point LSR for a limited amount optimal path MAY be cached on the mid-point LSR for a limited amount
of time to avoid having to recompute a path once the head-LSR of time to avoid having to recompute a path once the head-LSR
performs a make before break. This mode is optional. A default value performs a make-before-break. This mode is optional. A default
of 5 seconds is suggested. value for the caching timer of 5 seconds is suggested.
7. Interoperability 7. Applicability and Interoperability
The procedures described in this document are entirely optional
within an MPLS or GMPLS network. Implementations that do not support
the procedures described in this document will interoperate
seamlessly with those that do. Further, an implementation that does
not support the procedures described in this document will not be
impacted or implicated by a neighboring implementation that does
implement the procedures.
An ingress implementation that chooses not to support the procedures
described in this document may still achieve re-optimization by
periodically issuing a speculative make-before-break replacement of
an LSP without trying to discovery whether a more optimal path is
available in a downstream domain. Such a procedure would not be in
conflict with any mechanisms not already documented in [RFC3209] and
[RFC3473].
An LSR not supporting the "Path re-evaluation request" bit of the An LSR not supporting the "Path re-evaluation request" bit of the
SESSION-ATTRIBUTE object SHALL forward it unmodified. SESSION-ATTRIBUTE object SHALL forward it unmodified.
A head-end LSR not supporting an RSVP PathErr with Error code 25 A head-end LSR not supporting an RSVP PERR with Error code 25 message
message and Error sub-code = 6, 7 or 8 MUST just silently ignore such and Error sub-code = 6, 7 or 8 MUST just silently ignore such RSVP
RSVP PathErr message. PERR message.
8. Security considerations
This document defines a mechanism for a mid-point LSR to notify the
head-end LSR of this existence of a preferable path or the need to
reroute the TE LSP for maintenance purposes. Hence, in case of a TE
LSP spanning multiple administrative domains, it may be desirable for
a boundary LSR to modify the RSVP PathErr message (Code 25, Error
sub-code=6,7 or 8) so as to preserve confidentiality across domains.
Furthermore, a head-end LSR may decide to ignore explicit
notification coming from a mid-point residing in another domain.
Similarly, an LSR may decide to ignore (or accept but up to a pre-
defined rate) path re-evaluation requests originated by a head-end
LSR of another domain.
9. IANA considerations 8. IANA Considerations
IANA will assign a new flag named "Path re-evaluation request" in the IANA will assign a new flag named "Path re-evaluation request" in the
SESSION-ATTRIBUTE object (C-Type 1 and 7) specified in [RFC3209]. SESSION-ATTRIBUTE object (C-Type 1 and 7) specified in [RFC3209].
Suggested value is (to be confirmed by IANA) 0x20. Suggested value is (to be confirmed by IANA) 0x20.
IANA will also assign three new error sub-code values for the RSVP IANA will also assign three new error sub-code values for the RSVP
PERR Notify message (Error code=25). Suggested values are (to be PERR Notify message (Error code=25). Suggested values are (to be
confirmed by IANA): confirmed by IANA):
6 Preferable path exists 6 Preferable path exists
skipping to change at page 10, line 43 skipping to change at page 11, line 38
IANA will assign a new flag named "Path re-evaluation request" in the IANA will assign a new flag named "Path re-evaluation request" in the
SESSION-ATTRIBUTE object (C-Type 1 and 7) specified in [RFC3209]. SESSION-ATTRIBUTE object (C-Type 1 and 7) specified in [RFC3209].
Suggested value is (to be confirmed by IANA) 0x20. Suggested value is (to be confirmed by IANA) 0x20.
IANA will also assign three new error sub-code values for the RSVP IANA will also assign three new error sub-code values for the RSVP
PERR Notify message (Error code=25). Suggested values are (to be PERR Notify message (Error code=25). Suggested values are (to be
confirmed by IANA): confirmed by IANA):
6 Preferable path exists 6 Preferable path exists
7 Local link maintenance required 7 Local link maintenance required
8 Local node maintenance required 8 Local node maintenance required
10. Acknowledgments 9. Security Considerations
This document defines a mechanism for a mid-point LSR to notify the
head-end LSR of this existence of a preferable path or the need to
reroute the TE LSP for maintenance purposes. Hence, in case of a TE
LSP spanning multiple administrative domains, it may be desirable for
a boundary LSR to modify the RSVP PERR message (Code 25, Error sub-
code=6,7 or 8) so as to preserve confidentiality across domains.
Furthermore, a head-end LSR may decide to ignore explicit
notification coming from a mid-point residing in another domain.
Similarly, an LSR may decide to ignore (or accept but up to a pre-
defined rate) path re-evaluation requests originated by a head-end
LSR of another domain.
10. Acknowledgements
The authors would like to thank Carol Iturralde, Miya Kohno, Francois The authors would like to thank Carol Iturralde, Miya Kohno, Francois
Le Faucheur, Philip Matthews, Jim Gibson, Jean-Louis Le Roux, Kenji Le Faucheur, Philip Matthews, Jim Gibson, Jean-Louis Le Roux, Kenji
Kumaki, Anca Zafir, Dimitri Papadimitriou for their useful comments. Kumaki, Anca Zafir, Dimitri Papadimitriou for their useful comments.
A special thank to Adrian Farrel for his very valuable inputs. A special thank to Adrian Farrel for his very valuable inputs.
11. Intellectual property considerations 11. References
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
12. References 11.1. Normative References
12.1 Normative references [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC] Bradner, S., "Key words for use in RFCs to Indicate Requirement [RFC2961] Berger, L., Gan, D., Swallow, G., Pan, P., Tommasi, F.,
Levels," RFC 2119. and S. Molendini, "RSVP Refresh Overhead Reduction
Extensions", RFC 2961, April 2001.
[RFC3209] Awduche et al, "RSVP-TE: Extensions to RSVP for LSP [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC3209, December 2001. Tunnels", RFC3209, December 2001.
[RFC3473] Berger L. et al.,"Generalized Multi-Protocol Label [RFC3473] Berger, L., "Generalized Multi-Protocol Label Switching
Switching (GMPLS) Signaling Resource ReserVation Protocol-Traffic (GMPLS) Signaling Resource ReserVation Protocol-Traffic
Engineering (RSVP-TE) Extensions", RFC 3473, January 2003. Engineering (RSVP-TE) Extensions", RFC 3473, January 2003.
[REFRESH-REDUCTION] Berger et al, "RSVP Refresh Overhead Reduction 11.2. Informative References
Extensions", RFC2961, April 2001.
12.2 Informative references
[TE-REQ] Awduche et al, "Requirements for Traffic Engineering over
MPLS", RFC2702, September 1999.
[INTER-AREA-TE-REQ], Le Roux, Vasseur, Boyle et al. "Requirements
for Inter-area MPLS Traffic Engineering", draft-ietf-tewg-interarea-
mpls-te-req-03, November 2004.
[INTER-AS-TE-REQ] Zhang et al, "MPLS Inter-AS Traffic Engineering
requirements", draft-ietf-tewg-interas-mpls-te-req-09.txt, September
2004, Work in progress.
[INTER-DOMAIN-FW] Farrel A., Vasseur JP. and Ayyangar A., "A
Framework for Inter-Domain MPLS Traffic Engineering", draft-ietf-
ccamp-inter-domain-framework-02.txt, May 2005. Work in progress.
[INTER-DOMAIN-SIG] Ayyangar A. and Vasseur JP., "Inter domain GMPLS [RFC4105] Le Roux, J., Vasseur, J., and J. Boyle, "Requirements for
Traffic Engineering - RSVP-TE extensions", draft-ietf-ccamp-inter- Inter-Area MPLS Traffic Engineering", RFC 4105, June 2005.
domain-rsvp-te-00.txt", February 2005. Work in progress.
[INTER-DOMAIN-PATH-COMP] Vasseur JP., Ayyangar A., "A Per-domain [RFC4216] Zhang, R. and J. Vasseur, "MPLS Inter-Autonomous System
path computation method for computing Inter-domain Traffic (AS) Traffic Engineering (TE) Requirements", RFC 4216,
Engineering (TE) Label Switched Path (LSP)", draft-ietf-ccamp-inter- November 2005.
domain-pd-path-comp-00.txt, February 2005. Work in progress.
13. Authors' Addresses Authors' Addresses
Jean-Philippe Vasseur (Editor) JP Vasseur (editor)
CISCO Systems, Inc. Cisco Systems, Inc
300 Beaver Brook 1414 Massachusetts Avenue
Boxborough, MA 01719 Boxborough, MA 01719
USA USA
Email: jpv@cisco.com Email: jpv@cisco.com
Yuichi Ikejiri Yuichi Ikejiri
NTT Communications Corporation NTT Communications Corporation
1-1-6, Uchisaiwai-cho, Chiyoda-ku 1-1-6, Uchisaiwai-cho, Chiyoda-ku
Tokyo 100-8019 Tokyo, 100-8019
JAPAN Japan
Email: y.ikejiri@ntt.com
Email: : y.ikejiri@ntt.com
Raymond Zhang Raymond Zhang
Infonet Services Corporation BT Infonet
2160 E. Grand Ave. 2160 E. Grand Ave.
El Segundo, CA 90025 El Segundo, CA 90025
USA USA
Email: raymond_zhang@infonet.com
14. Full Copyright Statement Email: raymond_zhang@bt.infonet.com
Copyright (C) The Internet Society (2005). This document is subject Intellectual Property Statement
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights. The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
IMPLIED,INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
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