RSVP-TE Signaling Procedure for End-to-End GMPLS Restoration and Resource Sharing
draft-ietf-teas-gmpls-resource-sharing-proc-02
The information below is for an old version of the document.
| Document | Type | Active Internet-Draft (teas WG) | |
|---|---|---|---|
| Authors | Xian Zhang , Haomian Zheng , Rakesh Gandhi , Zafar Ali , Gabriele Galimberti , Pawel Brzozowski | ||
| Last updated | 2015-08-04 | ||
| Replaces | draft-ietf-ccamp-gmpls-resource-sharing-proc | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Formats | plain text htmlized pdfized bibtex | ||
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draft-ietf-teas-gmpls-resource-sharing-proc-02
TEAS Working Group Xian Zhang
Internet-Draft Haomian Zheng, Ed.
Intended Status: Informational Huawei
Expires: February 5, 2016 Rakesh Gandhi, Ed.
Zafar Ali
Gabriele Maria Galimberti
Cisco Systems, Inc.
Pawel Brzozowski
ADVA Optical
August 4, 2015
RSVP-TE Signaling Procedure for End-to-End GMPLS Restoration and
Resource Sharing
draft-ietf-teas-gmpls-resource-sharing-proc-02
Abstract
In transport networks, there are requirements where Generalized
Multi-Protocol Label Switching (GMPLS) end-to-end recovery scheme
needs to employ restoration Label Switched Path (LSP) while keeping
resources for the working and/or protecting LSPs reserved in the
network after the failure occurs.
This document reviews how the LSP association is to be provided using
Resource Reservation Protocol - Traffic Engineering (RSVP-TE)
signaling in the context of GMPLS end-to-end recovery scheme when
using restoration LSP where failed LSP is not torn down. In
addition, this document clarifies the RSVP-TE signaling procedure to
support resource sharing-based setup and teardown of LSPs as well as
LSP reversion. No new extensions are defined by this document, and
it is strictly informative in nature.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
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material or to cite them other than as "work in progress."
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Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. 1+R Restoration . . . . . . . . . . . . . . . . . . . . . 4
2.2. 1+1+R Restoration . . . . . . . . . . . . . . . . . . . . 5
2.3. Resource Sharing By Restoration LSP . . . . . . . . . . . 6
3. RSVP-TE Signaling Procedure . . . . . . . . . . . . . . . . . 6
3.1. Restoration LSP Association . . . . . . . . . . . . . . . 6
3.2. Resource Sharing-based Restoration LSP Setup . . . . . . . 7
3.3. LSP Reversion . . . . . . . . . . . . . . . . . . . . . . 8
3.3.1. Make-while-break Reversion . . . . . . . . . . . . . . 8
3.3.2. Make-before-break Reversion . . . . . . . . . . . . . 9
4. Security Considerations . . . . . . . . . . . . . . . . . . . 11
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
6. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.1. Normative References . . . . . . . . . . . . . . . . . . . 12
7.2. Informative References . . . . . . . . . . . . . . . . . . 12
8. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945] defines
a set of protocols, including Open Shortest Path First - Traffic
Engineering (OSPF-TE) [RFC4203] and Resource ReserVation Protocol -
Traffic Engineering (RSVP-TE) [RFC3473]. These protocols can be used
to setup Label Switched Paths (LSPs) in transport networks. The
GMPLS protocol extends MPLS to support interfaces capable of Time
Division Multiplexing (TDM), Lambda Switching and Fiber Switching.
These switching technologies provide several protection schemes
[RFC4426][RFC4427] (e.g., 1+1, 1:N and M:N).
Resource Reservation Protocol - Traffic Engineering (RSVP-TE)
signaling has been extended to support various GMPLS recovery
schemes, such as end-to-end recovery [RFC4872] and segment recovery
[RFC4873]. As described in [RFC6689], ASSOCIATION object can be used
to identify the LSPs for restoration using Association Type set to
"Recovery" [RFC4872]. [RFC6689] Section 2.2 reviews the procedure
for providing LSP associations for GMPLS end-to-end recovery and
covers the schemes where the failed working LSP and/or protecting LSP
are torn down.
In GMPLS end-to-end recovery schemes generally considered,
restoration LSP is signaled after the failure has been detected and
notified on the working LSP. For revertive recovery mode, a
restoration LSP is signaled while working LSP and/or protecting LSP
are not torn down in control plane due to a failure. In transport
networks, as working LSPs are typically signaled over a nominal path,
service providers would like to keep resources associated with the
working LSPs reserved. This is to make sure that the service
(working LSP) can be reverted to the nominal path when the failure is
repaired to provide deterministic behavior and guaranteed Service
Level Agreement (SLA).
Following behaviors are not fully documented in the existing
standards for LSP associations, resource sharing based LSP setup,
teardown and LSP reversion in transport networks:
o The procedure for providing LSP associations for the GMPLS
recovery using restoration LSP where working and protecting LSPs are
not torn down after the failure is not clearly documented.
o In [RFC3209], the MBB method assumes the old and new LSPs share
the SESSION object and signal Shared Explicit (SE) flag in
SESSION_ATTRIBUTE object. According to [RFC6689], ASSOCIATION object
with Association Type "Resource sharing" enables the sharing of
resources across LSPs with different SESSION objects. However,
existing documents do not mention the usage of SE flag for resource
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sharing with ASSOCIATION object.
o As described in [RFC3209], Section 2.5, the purpose of make before
break (MBB) is "not to disrupt traffic, or adversely impact network
operations while TE tunnel rerouting is in progress". In transport
networks, the label has a mapping into the data plane resource used
and the nodes along the LSP need to send triggering commands to data
plane for setting up cross-connections accordingly during the RSVP-TE
signaling procedure. Due to the nature of transport networks, node
may not be able to fulfill this purpose when sharing resources in
some scenarios.
o When using end-to-end recovery with revertive mode, methods for
LSP reversion and resource sharing have not been described.
This document reviews how the LSP association is to be provided for
GMPLS end-to-end recovery when using restoration LSP where working
and protecting LSP resources are kept reserved in the network after
the failure. In addition, this document clarifies the signaling
procedure for sharing resources during setup and teardown of LSPs as
well as LSP reversion. This document is strictly informative in
nature and does not define any RSVP-TE signaling extensions.
2. Overview
The GMPLS end-to-end recovery scheme, as defined in [RFC4872] and
being considered in this document, "fully dynamic rerouting switches
normal traffic to an alternate LSP that is not even partially
established only after the working LSP failure occurs. The new
alternate route is selected at the LSP head-end node, it may reuse
resources of the failed LSP at intermediate nodes and may include
additional intermediate nodes and/or links". Two examples, 1+R and
1+1+R are described in the following sections.
2.1. 1+R Restoration
One example of the recovery scheme considered in this document is 1+R
recovery. The 1+R recovery is exemplified in Figure 1. In this
example, working LSP on path A-B-C-Z is pre-established. Typically
after a failure detection and notification on the working LSP, a
second LSP on path A-H-I-J-Z is established as a restoration LSP.
Unlike protection LSP, restoration LSP is signaled per need basis.
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+-----+ +-----+ +-----+ +-----+
| A +----+ B +-----+ C +-----+ Z |
+--+--+ +-----+ +-----+ +--+--+
\ /
\ /
+--+--+ +-----+ +--+--+
| H +-------+ I +--------+ J |
+-----+ +-----+ +-----+
Figure 1: An Example of 1+R Recovery Scheme
During failure switchover with 1+R recovery scheme, in general,
working LSP resources are not released so that working and
restoration LSPs coexist in the network. Nonetheless, working and
restoration LSPs can share network resources. Typically when failure
is recovered on the working LSP, restoration LSP is no longer
required and torn down, while the traffic is reverted to the original
working LSP.
2.2. 1+1+R Restoration
Another example of the recovery scheme considered in this document is
1+1+R. In 1+1+R, a restoration LSP is signaled for the working LSP
and/or the protecting LSP after the failure has been detected, and
this recovery is exemplified in Figure 2.
+-----+ +-----+ +-----+
| D +-------+ E +--------+ F |
+--+--+ +-----+ +--+--+
/ \
/ \
+--+--+ +-----+ +-----+ +--+--+
| A +----+ B +-----+ C +-----+ Z |
+--+--+ +-----+ +-----+ +--+--+
\ /
\ /
+--+--+ +-----+ +--+--+
| H +-------+ I +--------+ J |
+-----+ +-----+ +-----+
Figure 2: An Example of 1+1+R Recovery Scheme
In this example, working LSP on path A-B-C-Z and protecting LSP on
path A-D-E-F-Z are pre-established. After a failure detection and
notification on a working LSP or protecting LSP, a third LSP on path
A-H-I-J-Z is established as a restoration LSP. The restoration LSP
in this case provides protection against a second order failure.
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During failure switchover with 1+1+R recovery scheme, in general,
failed LSP resources are not released so that working, protecting and
restoration LSPs coexist in the network. Nonetheless, restoration
LSP with working LSP it is restoring as well as restoration LSP with
protecting LSP it is restoring can share network resources.
Typically, restoration LSP is torn down when the failure on the
working or protecting LSP is repaired and while the traffic is
reverted to the original LSP.
2.3. Resource Sharing By Restoration LSP
+-----+ +-----+
| F +------+ G +--------+
+--+--+ +-----+ |
| |
| |
+-----+ +-----+ +--+--+ +-----+ +--+--+
| A +----+ B +-----+ C +--X---+ D +-----+ E |
+-----+ +-----+ +-----+ +-----+ +-----+
Figure 3: Resource Sharing in 1+R Recovery Scheme
Using the network shown in Figure 3 as an example, LSP1 (A-B-C-D-E)
is the working LSP and it allows for resource sharing when the LSP is
dynamically rerouted due to link failure. Upon detecting the failure
of a link along the LSP1, e.g. Link C-D, node A needs to decide which
alternative path it will use to signal restoration LSP and reroute
traffic. In this case, A-B-C-F-G-E is chosen as the restoration LSP
path and the resources on the path segment A-B-C are re-used by this
LSP when working LSP is not torn down as in 1+R recovery scheme.
3. RSVP-TE Signaling Procedure
3.1. Restoration LSP Association
Where GMPLS end-to-end recovery scheme needs to employ restoration
LSP while keeping resources for the working and/or protecting LSPs
reserved in the network after the failure, restoration LSP is
signaled with ASSOCIATION object that has Association Type set to
"Recovery" [RFC4872] with the association ID set to the LSP ID of the
LSP it is restoring. For example, when a restoration LSP is signaled
for a working LSP, the ASSOCIATION object in the restoration LSP
contains the association ID set to the LSP ID of the working LSP.
Similarly, when a restoration LSP is signaled for a protecting LSP,
the ASSOCIATION object in the restoration LSP contains the
association ID set to the LSP ID of the protecting LSP.
The procedure for signaling the PROTECTION object is specified in
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[RFC4872]. Specifically, restoration LSP being used as a working LSP
is signaled with P bit cleared and being used as a protecting LSP is
signaled with P bit set.
3.2. Resource Sharing-based Restoration LSP Setup
GMPLS LSPs can share resources if they have Shared Explicit (SE) flag
set in their SESSION_ATTRIBUTE objects and:
o As defined in [RFC3209], LSPs have identical SESSION objects
and/or
o As defined in [RFC6689], LSPs have matching ASSOCIATION object
with Association Type set to "Resource Sharing". LSPs in this case
can have different SESSION objects i.e. different tunnel ID, source
and destination.
For LSP restoration upon failure, as explained in Section 11 of
[RFC4872], reroute procedure may re-use existing resources. The
behavior of the intermediate nodes during rerouting process to
reconfigure cross-connections does not further impact the traffic
since it has been interrupted due to the already failed LSP.
The node behavior for setting up the restoration LSP can be
categorized into the following three categories:
Table 1: Node Behavior during Restoration LSP Setup
---------+---------------------------------------------------------
Category | Node Behavior during Restoration LSP Setup
---------+---------------------------------------------------------
C1 + Reusing existing resource on both input and output
+ interfaces (node A & B in Figure 3).
+
+ This type of nodes only needs to book the existing
+ resources and no cross-connection setup
+ command is needed.
---------+---------------------------------------------------------
C2 + Reusing existing resource only on one of the interfaces,
+ either input or output interfaces and need to use new
+ resource on the other interface. (node C & E in Figure 3).
+
+ This type of nodes needs to book the resources and send
+ the re-configuration cross-connection command to its
+ corresponding data plane node on the interfaces where new
+ resources are needed and re-use the
+ existing resources on the other interfaces.
---------+---------------------------------------------------------
C3 + Using new resources on both interfaces.
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+ (node F & G in Figure 3).
+
+ This type of nodes needs to book the new resources
+ and send the cross-connection setup
+ command on both interfaces.
---------+---------------------------------------------------------
Depending on whether the resource is re-used or not, the node
behaviors differ. This deviates from normal LSP setup since some
nodes do not need to re-configure the cross-connection, and it should
not be viewed as an error. Also, the judgment whether the control
plane node needs to send a cross-connection setup/modification
command to its corresponding data plane node(s) relies on the check
whether the LSPs are sharing resources.
3.3. LSP Reversion
If the end-to-end LSP recovery is revertive, as described in Section
2, traffic can be reverted from the restoration LSP to the working or
protecting LSP after its failure is recovered. The LSP reversion can
be achieved using two methods:
1. Make-while-break reversion, where resources associated with
working or protecting LSP are reconfigured while removing
reservations for the restoration LSP.
2. Make-before-break reversion, where resources associated with
working or protecting LSP are reconfigured before removing the
restoration LSP.
In transport networks, both of the above reversion methods will
result in some traffic disruption when the restoration LSP and the
LSP being restored are sharing resources and the cross-connections
need to be reconfigured on intermediate nodes.
3.3.1. Make-while-break Reversion
In this reversion method, restoration LSP is simply requested to be
deleted by the head-end. Removing reservations for restoration LSP
triggers reconfiguration of resources associated with working or
protecting LSP on every node where resources are shared. Whenever
reservation for restoration LSP is removed from a node, data plane
configuration changes to reflect reservations of working or
protection LSP as signaling progresses. Eventually, after the whole
restoration LSP is deleted, data plane configuration will fully match
working or protecting LSP reservations on the whole path. Thus
reversion is complete.
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Make-while-break, while being relatively simple in its logic, has few
limitations as follows which may not be acceptable in some networks:
o No rollback
Deletion of restoration LSPs is not a revertive process. If for some
reason reconfiguration of data plane on one of the nodes to match
working or protection LSP reservations fails, falling back to
restoration LSP is no longer an option, as its state might have
already been removed from other nodes.
o No completion guarantee
Deletion of an LSP provides no guarantees of completion. In
particular, if RSVP packets are lost due to nodal or DCN failures it
is possible for an LSP to be only partially deleted. To mitigate
this, RSVP could maintain soft state reservations and hence
eventually remove remaining reservations due to refresh timeouts.
This approach is not feasible in transport networks however, where
control and data channels are often separated and hence soft state
reservations are not useful.
Finally, one could argue that graceful LSP deletion [RFC3473] would
provide guarantee of completion. While this is true for most cases,
many implementations will time out graceful deletion if LSP is not
removed within certain amount of time, e.g. due to a transit node
fault. After that, deletion procedures which provide no completion
guarantees will be attempted. Hence, in corner cases completion
guarantee cannot be provided.
o No explicit notification of completion to head-end node
In some cases, it may be useful for a head-end node to know when the
data plane has been reconfigured to match working or protection LSP
reservations. This knowledge could be used for initiating operations
like enabling alarm monitoring, power equalization and others.
Unfortunately, for the reasons mentioned above, make-while-break
reversion lacks such explicit notification.
3.3.2. Make-before-break Reversion
This reversion method can be used to overcome limitations of
make-while-break reversion. It is similar in spirit to MBB concept
used for re-optimization. Instead of relying on deletion of
restoration LSP, head-end chooses to establish a new LSP to
reconfigure resources on the working or protection LSP path, and uses
identical ASSOCIATION and PROTECTION objects from the LSP it is
replacing. Only if setup of this LSP is successful will other
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(restoration and working/protecting) LSPs be deleted by the head-end.
MBB reversion consists of two parts:
A) Make part:
Creating a new reversion LSP following working or protection LSP's
path. Reversion LSP is sharing resources both with working and
restoration LSPs. As reversion LSP is created, resources are
reconfigured to match its reservations. Hence, after reversion LSP
is created, data plane configuration essentially reflects working or
protecting LSP reservations.
B) Break part:
After "make" part is finished, working and restoration LSPs are torn
down. Removing reservations for working and restoration LSPs does
not cause any resource reconfiguration on reversion LSP's path -
nodes follow same procedures as for "break" part of any MBB
operation. Hence, after working and restoration LSPs are removed,
data plane configuration is exactly the same as before starting
restoration. Thus reversion is complete.
MBB reversion uses make-before-break characteristics to overcome
challenges related to make-while-break reversion as follow:
o Rollback
If "make" part fails, (existing) restoration LSP will still be used
to carry existing traffic. Same logic applies here as for any MBB
operation failure.
o Completion guarantee
LSP setup is resilient against RSVP message loss, as Path and Resv
messages are refreshed periodically. Hence, given that network
recovers its DCN eventually, reversion LSP setup is guaranteed to
finish with either success or failure.
o Explicit notification of completion to head-end node
Head-end knows that data plane has been reconfigured to match working
or protection LSP reservations on intermediate nodes when it receives
Resv for the reversion LSP.
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4. Security Considerations
This document reviews procedures defined in [RFC3209] [RFC4872]
[RFC4873] and [RFC6689] and does not define any new procedure. This
document does not introduce any new security issues other than those
already covered in [RFC3209] [RFC4872] [RFC4873] and [RFC6689].
5. IANA Considerations
This informational document does not make any request for IANA
action.
6. Acknowledgement
The authors would like to thank George Swallow for the discussions on
the GMPLS restoration.
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7. References
7.1. Normative References
[RFC3209] D. Awduche et al, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[RFC4872] J.P. Lang et al, "RSVP-TE Extensions in Support of
End-to-End Generalized Multi-Protocol Label Switching
(GMPLS) Recovery", RFC 4872, May 2007.
[RFC4873] L. Berger et al, "GMPLS Segment Recovery", RFC 4873, May
2007.
[RFC6689] L. Berger, "Usage of the RSVP ASSOCIATION Object", RFC
6689, July 2012.
7.2. Informative References
[PCEP-RSO] X. Zhang, et al, "Extensions to Path Computation Element
Protocol (PCEP) to Support Resource Sharing-based Path
Computation", work in progress, February 2014.
[RFC3473] L. Berger, Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation
Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC
3473, January 2003.
[RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching
(GMPLS) Architecture", RFC 3945, October 2004.
[RFC4203] Kompella, K., and Rekhter, Y., "OSPF Extensions in
Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4203, October 2005.
[RFC4426] Lang, J., Rajagopalan, B., and Papadimitriou, D.,
"Generalized Multiprotocol Label Switching (GMPLS)
Recovery Functional Specification", RFC 4426, March 2006.
[RFC4427] Mannie, E., and Papadimitriou, D., "Recovery (Protection
and Restoration) Terminology for Generalized Multi-
Protocol Label Switching", RFC 4427, March 2006.
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8. Authors' Addresses
Xian Zhang
Huawei Technologies
F3-1-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129 P.R.China
EMail: zhang.xian@huawei.com
Haomian Zheng (editor)
Huawei Technologies
F3-1-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129 P.R.China
EMail: zhenghaomian@huawei.com
Rakesh Gandhi (editor)
Cisco Systems, Inc.
EMail: rgandhi@cisco.com
Zafar Ali
Cisco Systems, Inc.
EMail: zali@cisco.com
Gabriele Maria Galimberti
Cisco Systems, Inc.
EMail: ggalimbe@cisco.com
Pawel Brzozowski
ADVA Optical
EMail: PBrzozowski@advaoptical.com
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