TEAS Working Group X. Zhang
Internet-Draft H. Zheng, Ed.
Intended Status: Informational Huawei
Expires: February 15, 2016 R. Gandhi, Ed.
Z. Ali
G. Galimberti
Cisco Systems, Inc.
P. Brzozowski
ADVA Optical
August 14, 2015
RSVP-TE Signaling Procedure for End-to-End GMPLS Restoration and
Resource Sharing
draft-ietf-teas-gmpls-resource-sharing-proc-03
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 discusses resource sharing-based setup and
teardown of LSPs as well as LSP reversion procedures for transport
networks. No new signaling 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.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
Zhang, et al Expires February 15, 2016 [Page 1]
Internet-Draft GMPLS Restoration and Resource Sharing August 14, 2015
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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 . . . . . . . . . . . . . . . . . 7
3.1. Restoration LSP Association . . . . . . . . . . . . . . . 7
3.2. Resource Sharing-based Restoration LSP Setup . . . . . . . 7
3.3. LSP Reversion . . . . . . . . . . . . . . . . . . . . . . 9
3.3.1. Make-while-break Reversion . . . . . . . . . . . . . . 9
3.3.2. Make-before-break Reversion . . . . . . . . . . . . . 10
4. Security Considerations . . . . . . . . . . . . . . . . . . . 11
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.1. Normative References . . . . . . . . . . . . . . . . . . . 12
6.2. Informative References . . . . . . . . . . . . . . . . . . 12
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
Zhang, et al Expires February 15, 2016 [Page 2]
Internet-Draft GMPLS Restoration and Resource Sharing August 14, 2015
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] and also identify the LSPs for resource sharing
using Association Type set to "Resource Sharing" [RFC4873].
[RFC6689] Section 2.2 reviews the procedure for providing LSP
associations for GMPLS end-to-end recovery and Section 2.4 reviews
the procedure for providing LSP associations for sharing resources.
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).
In this document, procedures for transport networks are reviewed for
LSP associations, resource sharing based LSP setup, teardown and LSP
reversion, including following:
o Review the procedure for providing LSP associations for the GMPLS
end-to-end recovery using restoration LSP where working and
protecting LSPs are not torn down and resources are kept reserved in
the network after the failure.
o In [RFC3209], the make-before-break (MBB) method assumes the old
and new LSPs share the SESSION object and signal Shared Explicit (SE)
flag in SESSION_ATTRIBUTE object for sharing resources. According to
Zhang, et al Expires February 15, 2016 [Page 3]
Internet-Draft GMPLS Restoration and Resource Sharing August 14, 2015
[RFC6689], ASSOCIATION object with Association Type "Resource
Sharing" enables the sharing of resources across LSPs with different
SESSION objects. Procedure for resource sharing using the SE flag in
conjunction with ASSOCIATION object is discussed in this document.
o When using end-to-end recovery with revertive mode, methods for
LSP reversion and resource sharing are summarized in this document.
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.
+-----+ +-----+ +-----+ +-----+
| A +----+ B +-----+ C +-----+ Z |
+--+--+ +-----+ +-----+ +--+--+
\ /
\ /
+--+--+ +-----+ +--+--+
| H +-------+ I +--------+ J |
+-----+ +-----+ +-----+
Figure 1: An Example of 1+R Recovery Scheme
Zhang, et al Expires February 15, 2016 [Page 4]
Internet-Draft GMPLS Restoration and Resource Sharing August 14, 2015
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.
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
original (working or protecting) LSP is repaired and the traffic is
reverted to the original LSP.
There are four possible models when using restoration LSP with 1+1+R
Zhang, et al Expires February 15, 2016 [Page 5]
Internet-Draft GMPLS Restoration and Resource Sharing August 14, 2015
recovery scheme:
o A restoration LSP is signaled after either working or protecting
LSP fails. Only one restoration LSP is present at a time.
o A restoration LSP is signaled after either working or protecting
LSP fails. Two different restoration LSPs may be present, one for
the working LSP and one for the protecting LSP.
o A restoration LSP is signaled after both working and protecting
LSPs fail. Only one restoration LSP is present.
o Two different restoration LSPs are signaled after both working and
protecting LSPs fail, one for the working LSP and one for the
protecting LSP.
In all models discussed, if the restoration LSP also fails, it is
torn down and a new restoration LSP is signaled.
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
traffic is dynamically restored after the 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 the working LSP is not
torn down (e.g. in 1+R recovery scheme).
Zhang, et al Expires February 15, 2016 [Page 6]
Internet-Draft GMPLS Restoration and Resource Sharing August 14, 2015
3. RSVP-TE Signaling Procedure
3.1. Restoration LSP Association
Where GMPLS end-to-end recovery scheme needs to employ a restoration
LSP while keeping resources for the working and/or protecting LSPs
reserved in the network after the failure, the restoration LSP is
signaled with an ASSOCIATION object that has Association Type set to
"Recovery" [RFC4872], the Association ID and the Association Source
set to the corresponding Association ID and the Association Source
signaled in the LSP it is restoring. For example, when a restoration
LSP is signaled for a failed working LSP, the ASSOCIATION object in
the restoration LSP contains the Association ID and Association
Source set to the Association ID and Association Source signaled in
the working LSP for the "Recovery" Association Type. Similarly, when
a restoration LSP is signaled for a failed protecting LSP, the
ASSOCIATION object in the restoration LSP contains the Association ID
and Association Source set to the Association ID and Association
Source signaled in the protecting LSP for the "Recovery" Association
Type.
The procedure for signaling the PROTECTION object is specified in
[RFC4872]. Specifically, the restoration LSP used for a working LSP
is signaled with P bit cleared in the PROTECTION object and the
restoration LSP used for a protecting LSP is signaled with P bit set
in the PROTECTION object.
3.2. Resource Sharing-based Restoration LSP Setup
GMPLS LSPs can share resources during LSP setup 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/or Destination.
As described in [RFC3209], Section 2.5, the purpose of make-before-
break 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 the transport networks,
node may not be able to fulfill this purpose when sharing resources
Zhang, et al Expires February 15, 2016 [Page 7]
Internet-Draft GMPLS Restoration and Resource Sharing August 14, 2015
in some scenarios.
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.
+ (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.
Zhang, et al Expires February 15, 2016 [Page 8]
Internet-Draft GMPLS Restoration and Resource Sharing August 14, 2015
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
reservations for 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.
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
Zhang, et al Expires February 15, 2016 [Page 9]
Internet-Draft GMPLS Restoration and Resource Sharing August 14, 2015
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
(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:
Zhang, et al Expires February 15, 2016 [Page 10]
Internet-Draft GMPLS Restoration and Resource Sharing August 14, 2015
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.
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.
Zhang, et al Expires February 15, 2016 [Page 11]
Internet-Draft GMPLS Restoration and Resource Sharing August 14, 2015
6. References
6.1. Normative References
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation
Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC
3473, January 2003.
[RFC4872] Lang, J., Ed., Rekhter, Y., Ed., and D. Papadimitriou,
Ed., "RSVP-TE Extensions in Support of End-to-End
Generalized Multi-Protocol Label Switching (GMPLS)
Recovery", RFC 4872, May 2007.
[RFC4873] Berger, L., Bryskin, I., Papadimitriou, D., and A.
Farrel, "GMPLS Segment Recovery", RFC 4873, May 2007.
[RFC6689] L. Berger, "Usage of the RSVP ASSOCIATION Object", RFC
6689, July 2012.
6.2. 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.
[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.
Zhang, et al Expires February 15, 2016 [Page 12]
Internet-Draft GMPLS Restoration and Resource Sharing August 14, 2015
Acknowledgements
The authors would like to thank George Swallow for the discussions
on the GMPLS restoration. The authors would also like to thank
Lou Berger for the review comments and the guidance on this work.
Zhang, et al Expires February 15, 2016 [Page 13]
Internet-Draft GMPLS Restoration and Resource Sharing August 14, 2015
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
Zhang, et al Expires February 15, 2016 [Page 14]