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SEGMENT ROUTING FOR INTERNET PROTOCOL VERSION 6 DATAPLANE BASED PROTECTED PATH TRAFFIC FLOW SIGNALING

IP.com Disclosure Number: IPCOM000250773D
Publication Date: 2017-Aug-31
Document File: 6 page(s) / 384K

Publishing Venue

The IP.com Prior Art Database

Related People

Nagendra Kumar Nainar: AUTHOR [+2]

Abstract

Described are techniques to reduce Total Time on Backup (TTOB) for Segment Routing for Internet Protocol version 6 (SRv6). A transit node may redirect a packet over a backup path (built using any Loop-Free Alternate (LFA) technique). The transit node may encapsulate the packet in an outer Segment Routing Header (SRH) and set the P flag in the outer SRH. A Segment Routing (SR) node may perform a lookup in the SRH and determine that the path to the next segment is the backup path. If the SR node makes this determination, the SR node may set the P flag in the SRH. If a packet is received with the P flag set in outer SRH to signal that the node is decapsulating the header, the node may propagate the P flag from the outer to the inner SRH. When applied by multiple nodes, this may help propagate the flag from any Point of Local Repair (PLR) to egress. The egress may use the flag to signal back to ingress. For example, if a Bidirectional Forwarding Detection (BFD) packet is received with the P flag set, the egress may signal back with a new code. If a data packet is received with the P flag and the inband BFD set, the egress may signal with a new code.

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Copyright 2017 Cisco Systems, Inc. 1

SEGMENT ROUTING FOR INTERNET PROTOCOL VERSION 6 DATAPLANE BASED PROTECTED PATH TRAFFIC FLOW SIGNALING

AUTHORS: Nagendra Kumar Nainar

Carlos M. Pignataro

CISCO SYSTEMS, INC.

ABSTRACT

Described are techniques to reduce Total Time on Backup (TTOB) for Segment

Routing for Internet Protocol version 6 (SRv6). A transit node may redirect a packet over

a backup path (built using any Loop-Free Alternate (LFA) technique). The transit node

may encapsulate the packet in an outer Segment Routing Header (SRH) and set the P flag

in the outer SRH. A Segment Routing (SR) node may perform a lookup in the SRH and

determine that the path to the next segment is the backup path. If the SR node makes this

determination, the SR node may set the P flag in the SRH. If a packet is received with the

P flag set in outer SRH to signal that the node is decapsulating the header, the node may

propagate the P flag from the outer to the inner SRH. When applied by multiple nodes, this

may help propagate the flag from any Point of Local Repair (PLR) to egress. The egress

may use the flag to signal back to ingress. For example, if a Bidirectional Forwarding

Detection (BFD) packet is received with the P flag set, the egress may signal back with a

new code. If a data packet is received with the P flag and the inband BFD set, the egress

may signal with a new code.

DETAILED DESCRIPTION

With advancements in Fast Reroute (FRR) techniques such as Loop-Free Alternate

(LFA) / Remote LFA (rLFA) / Topology-Independent LFA (TI-LFA), any transit node can

build a backup path the protect the traffic in case of link/node failure. Software Defined

Networking (SDN) concepts such as Path Computation Element (PCE) allows an operator

to pre-build paths/tunnels from ingress to egress that satisfies the Service Level Agreement

(SLA) constraints for the customer traffic. Currently, FRR triggered by a transit node due

to a transit link failure cannot be detected via multihop Bidirectional Forwarding Detection

(BFD) from the head end as BFD also survives over the FRR path. The control plane

Copyright 2017 Cisco Systems, Inc. 2

provides instructions for upstream network elements or a controller, introducing delay and

increasing total time on backup (TTOB) for a traffic flow over an undesired path until

convergence.

Figure 1 below illustrates an example network topology that highlights this problem.

Figure 1

In the above topology, Segment Routing for Internet Protocol version 6 (SRv6)-R1

has a primary path and a secondary path computed based on SLA requirements (low

latency). The primary path is {SRv6-R1 -> R2 -> R4 -> SRv6-R6}, and the secondary path

is {SRv6-R1 -> R3 -> R5 -> SRv6-R6}. R2 protects link R2-R4 using a Segment Routing

Header (SRH) tunnel with the Service Level (SL) set to 2001::8. When link R2-R4 fails,

traffic may be protected over a high latency path until Interior Gateway Protocol (IGP)

converges. Described herein are techniques to notify a source that...