Network Working Group M. Dai, Ed.
Internet-Draft Y. Rekhter
Intended status: Best Current Practice E. Aries
Expires: September 10, 2015 Facebook
Muhammad Nauman Chaudhry
Verizon Communications
March 9, 2015
MPLS RSVP-TE MBB Label Reuse
draft-dai-mpls-rsvp-te-mbb-label-reuse-00
Abstract
The concept of "make-before-break (MBB)" while rerouting MPLS RSVP-TE
tunnels is discussed in [RFC3209]. In the procedure that is
outlined, the behavior of downstream label assignment for the new LSP
(new tunnel instance) is not well defined. As a general practice, a
different label is assigned by each downstream router and advertised
to the upstream router in the RESV message for the new LSP; this
results in a separate end-to-end data-plane path for the new LSP
(with the exception of PHP LSPs or UHP LSP with explicit label on the
last hop). This practice allows independent end to end LSP path
data-plane verification for each tunnel instance. The consequence of
this practice is that the label entry gets added/deleted in the LFIB
at every non-ingress router along the LSP path during MBB. Also, the
ingress router would need to update all the applications using this
LSP when switching to the new tunnel instance, as the new tunnel
instance uses different outgoing label. This in turn may also cause
other elements of the network which are dependent on the LSP to do
the update.
Such network churn can be avoided/minimized if the same label can be
re-used (kept intact) wherever it is affecting neither the routing
functionalities nor the data path verification of each instance. In
addition, whenever label is reused, the setup time for the new tunnel
instance would be faster because there is no need for the transit
routers along the path of the new LSP to wait for the new LFIB entry
to be added. This document proposes a set of procedures to
facilitate label reuse when there is a total or partial path overlap
between the two tunnel instances during MBB.
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Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on September 10, 2015.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Common LSP MBB triggers . . . . . . . . . . . . . . . . . 3
2. Recommended conditions for label reuse . . . . . . . . . . . 3
3. Control of label-reuse behavior . . . . . . . . . . . . . . . 4
3.1. Enable/Disable label-reuse capability . . . . . . . . . . 4
3.2. Prefer overlapping path to facilitate label-reuse . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
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6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
7. Normative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
MPLS RSVP-TE make-before-break (MBB) procedure is defined in
[RFC3209]. The behavior of downstream label assignment for the new
LSP (new tunnel instance) is not well-defined in this procedure. In
most MBB implementations, a different label is assigned by each
downstream router and advertised to upstream router in the RESV
message for the new Label Switched Path (LSP). This means a separate
end-to-end data-plane path for the new tunnel instance (with the
exception of PHP LSPs or UHP LSPs with explicit NULL label at the
last hop). Although this allows for independent end-to-end path
verification for each tunnel instance, it requires an LFIB entry add/
delete at every non-ingress router along the path of the LSP during
MBB even if the paths for the new tunnel instance and the old tunnel
instance might be partially or totally overlapping. Label reuse
under partial or total overlap condition reduces unnecessary LFIB
update, reduces the possibility of errors and improves network
convergence latency. In cases where there is a total overlap of
paths between the two tunnel instances and the label is reused at
each hop along the overlapping path, the necessity of data plane
verification for the new tunnel instance is no longer needed.
1.1. Common LSP MBB triggers
The MBB procedure can be triggered because of a change to any
property of the RSVP-TE tunnel. The most common case is a change to
the bandwidth requirement, especially with the widely implemented
auto-bandwidth feature, which dynamically adjusts the LSP bandwidth
based on traffic-monitoring feedback. With CSPF commonly used to
compute path to meet the new bandwidth requirements, it is possible
that the existing path is still one of the best paths which can
satisfy the new requirements. This provides the opportunity to reuse
labels to maximize the benefits described. If given the choice and
the goal of selecting the best path is not the highest priority, CSPF
can also prefer the existing path to other possible paths to take
full advantage of the label reuse as long as the requirements are
still met by the existing path.
2. Recommended conditions for label reuse
The notion of "Label reuse" can be applied for both point-to-point
(P2P) LSP and point-to-multipoint (P2MP) LSP, but due to the
complexity of P2MP and many possible variations of the solutions,
this document will only focus on the recommendations for P2P LSPs.
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Labels can be reused when the primary paths of the two tunnel
instances have complete overlap starting from a certain point in the
paths and going all the way to the egress router of the LSP. The
best case scenario is complete overlap of the two paths end to end;
in which case there is no need for any label changes and LFIB
updates, both in the transit as well as in the ingress routers. In
this scenario there is also no need to perform data plane
verification for the new tunnel instance. For the case where the two
paths overlaps only from a certain transit router (rather than from
the ingress), label reuse starts at that router and continues all the
way to the egress router. In this case the existing data plane
verification method can still be used to verify new tunnel instance
as before. Data traversing on either instance will take a different
label path from the ingress to this transit router and from then on
the traffic will merge into the shared label switched path towards
the egress router.
The conditions under which label reuse can be applied are as
following:
o Egress router of LSP: Reuse-label functionality can always be
applied.
o Transit routers of the LSP: For any given transit router of P2P
LSP, label can be reused if the following conditions are met:
(a) Downstream label received is the same
(b) NHOP is the same
o Ingress router of the LSP: When the same conditions as listed
under transit router are met, instead of no label change, there is
no need for ingress route update for LSP to applications depending
on it.
The label reuse procedure starts from the egress of the LSP as RESV
traverses upstream towards the ingress of the LSP; it terminates at
the first transit router where paths of the two tunnel instances
diverge towards the ingress of the LSP or at the transit router which
doesn't support label reuse.
3. Control of label-reuse behavior
3.1. Enable/Disable label-reuse capability
This document recommends enabling "label-reuse" capability by
default. Allow it to be disabled if needed by changing
configuration.
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3.2. Prefer overlapping path to facilitate label-reuse
In order to take full advantage of the label-reuse capability, path
computation for the new tunnel instance may seek to maximize path
overlap. This can be achieved through two approaches.
o The first approach is to select from the best paths available the
path which has the most path overlap with the existing path
starting from the egress router.
o The second approach is to prefer the existing path if it still
satisfies the new requirement, even though it might not be the
best path.
The choice between the approaches is a matter of local computation
policy and can be different for different types of MBB trigger.
4. IANA Considerations
This document makes no request for IANA action.
5. Security Considerations
This document does not introduce new security issues.
6. Acknowledgements
The authors wish to thank Vishnu Pavan Beeram for his input,
feedback, and helpful suggestions.
7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
Authors' Addresses
Minjie Dai (editor)
Juniper Networks
Email: mdai@juniper.net
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Yakov Richter
Juniper Networks
Email: yakov@juniper.net
Ebben Aries
Facebook
1 Hacker Way
Menlo Park, CA 94025
US
Email: exa@fb.com
Muhammad Nauman Chaudhry
Verizon Communications
Email: muhammd.n.chaudhry@verizon.com
Raveendra Torvi
Juniper Networks
Email: rtorvi@juniper.net
Markus Work
Juniper Networks
Email: mjork@juniper.net
Yimin Shen
Juniper Networks
Email: yshen@juniper.net
Natrajan Venkatraman
Juniper Networks
Email: natv@juniper.net
Harish Sitaraman
Juniper Networks
Email: hsitaraman@juniper.net
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