Network Working Group Pierre Francois
Internet-Draft IMDEA Networks
Intended status: Standards Track Clarence Filsfils
Expires: October 3, 2014 Cisco Systems, Inc.
Bruno Decraene
Orange
Rob Shakir
BT
April 1, 2014
Use-cases for Resiliency in SPRING
draft-francois-spring-resiliency-use-case-01
Abstract
This document describes the use cases for resiliency in SPRING
networks.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Path protection . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Management-free local protection . . . . . . . . . . . . . . . 4
4. Managed local protection . . . . . . . . . . . . . . . . . . . 4
5. Co-existence . . . . . . . . . . . . . . . . . . . . . . . . . 5
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5
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1. Introduction
SPRING aims at providing a network architecture supporting services
with tight SLA guarantees [1]. This document reviews various use
cases for Fast Reroute (FRR) of services in a SPRING network. Note
that these use cases are in particular applicable to existing LDP
based and pure IP networks.
A FRR technique involves the pre-computation and dataplane pre-
installation of backup paths so as to repair traffic in 50msec upon
failure detection. The term "protection" is often used as a synonym
for FRR. Such techniques suppose the existence of a sub-10msec
failure detection mechanism.
Three key alternatives are described: path protection, local
protection without operator management and local protection with
operator management.
The purpose of this document is to illustrate the different
techniques and explain how an operator could combine them in the same
network. Solutions are not defined in this document.
PE1
/ \
/ \
B------C------D------E
/| | \ / | \ / |\
/ | | \/ | \/ | \
A | | /\ | /\ | Z
\ | | / \ | / \ | /
\| |/ \|/ \|/
F------G------H------I
Figure 1: Reference topology
We use Figure 1 as a reference topology throughout the document. We
describe the various use-cases in the next sections. All link
metrics are equal to 1, with the exception of the links of PE1 which
are configured with a metric of 100.
2. Path protection
A first protection strategy consists in excluding any local repair
but instead use end-to-end path protection.
For example, a Pseudo Wire (PW) from A to Z can be "path protected"
in the direction A to Z in the following manner: the operator
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configures two SPRING paths T1 and T2 from A to Z. The two paths are
installed in the forwarding plane of A and hence are ready to forward
packets. The two paths are made disjoint using the SPRING
architecture.
T1 is established over path {AB, BC, CD, DE, EZ} and T2 over path
{AF, FG, GH, HI, IZ}. When T1 is up, the packets of the PW are sent
on T1. When T1 fails, the packets of the PW are sent on T2. When T1
comes back up, the operator either allows for an automated reversion
of the traffic onto T1 or selects an operator-driven reversion. The
solution to detect the end-to-end liveness of the path is out of the
scope of this document.
From a SPRING viewpoint, we would like to highlight the following
requirement: the two configured paths T1 and T2 MUST NOT benefit from
local protection.
3. Management-free local protection
An alternative protection strategy consists in management-free local
protection.
For example, a PW from C to E, transported over the shortest path to
E provided by the SPRING architecture, benefits from management-free
local protection by having each node along the path (e.g. C and D)
automatically pre-compute and pre-install a backup path for the
destination E. Upon local detection of the failure, the traffic is
repaired over the backup path in sub-50msec.
The backup path computation should support the following
requirements:
o 100% link, node, and SRLG protection in any topology
o Automated computation by the IGP
o Selection of the backup path such as to minimize the chance for
transient congestion and/or delay during the protection period, as
reflected by the IGP metric configuration in the network.
4. Managed local protection
There may be cases where a management free repair does not fit the
policy of the operator. For example, the operator may want the
backup path to end at the next-hop (or next-next-hop for node
failure) hence excluding IPFRR/LFA types of backup path. Also, the
operator might want to tightly control the backup path to the next-
hop: for the destination Z upon the failure of link CD, the backup
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path CGHD might be desired while the backup paths CGD and CHD are
refused.
The protection mechanism must support the explicit configuration of
the backup path either under the form of high-level constraints (end
at the next-hop, end at the next-next-hop, minimize this metric,
avoid this SRLG...) or under the form of an explicit path.
5. Co-existence
The operator may want to support several very-different services on
the same packet-switching infrastructure. As a result, the SPRING
architecture SHOULD allow for the co-existence of the different use
cases listed in this document, in the same network.
Let us illustrate this with the following example.
o Flow F1 is supported over path {C, C-D, E}
o Flow F2 is supported over path {C, C-D, I)
o Flow F3 is supported over path {C, C-D, Z)
o It should be possible for the operator to configure the network to
achieve path protection for F1, management free local protection
for F2, and managed protection over path {C-H, H-D, Z} for F3.
6. References
[1] Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R., Ytti,
S., Henderickx, W., Tantsura, J., and E. Crabbe, "Segment
Routing Architecture", draft-filsfils-rtgwg-segment-routing-01
(work in progress), October 2013.
Authors' Addresses
Pierre Francois
IMDEA Networks
Leganes
ES
Email: pierre.francois@imdea.org
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Clarence Filsfils
Cisco Systems, Inc.
Brussels
BE
Email: cfilsfil@cisco.com
Bruno Decraene
Orange
Issy-les-Moulineaux
FR
Email: bruno.decraene@orange.com
Rob Shakir
BT
London
UK
Email: rob.shakir@bt.com
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