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LABEL-SWITCHED PATH (LSP) ECHO REPLY VIA CO-ROUTED PATH IN SEGMENT ROUTED (SR) NETWORK

IP.com Disclosure Number: IPCOM000241126D
Publication Date: 2015-Mar-27

Publishing Venue

The IP.com Prior Art Database

Related People

Nagendra Kumar Nainar: AUTHOR [+3]

Abstract

Techniques are presented herein in which a Label-Switched Path (LSP) Initiator builds a co-routed return path from a Target FEC Stack (forward path). The Initiator marks the co-routed return segment stack with an index based on a local calculation. The Transit node uses the number of segments in the stack to detect the index and extract the return segment stack. These techniques help with a transit node (not just the egress node) reply via a co-routed path. No path computation is required on any transit/replying node.

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LABEL-SWITCHED PATH (LSP) ECHO REPLY VIA CO-ROUTED PATH IN SEGMENT ROUTED (SR) NETWORK

AUTHORS:

Nagendra Kumar Nainar Carlos Pignataro

Nobo Akiya

CISCO SYSTEMS, INC.

ABSTRACT

    Techniques are presented herein in which a Label-Switched Path (LSP) Initiator builds a co-routed return path from a Target FEC Stack (forward path). The Initiator marks the co-routed return segment stack with an index based on a local calculation. The Transit node uses the number of segments in the stack to detect the index and extract the return segment stack. These techniques help with a transit node (not just the egress node) reply via a co-routed path. No path computation is required on any transit/replying node.

DETAILED DESCRIPTION

     There is much interest in the industry to control the return path taken by the Multiprotocol Label Switching (MPLS) Echo Reply. Currently proposals are to carry a stack of label or relevant details that can be used by an egress responder to reply back. These Type Length Values (TLVs) are meaningful (and thus helpful) only for the egress node. They do not help with the transit node understanding the path taken by the packet and therefore cannot be used to reply back via the same path.

    It is desirable for some service providers to have the MPLS Echo Reply to be sent back via a co-routed path even from transit nodes. Presented herein is an indexed return TLV carrying the stack of segments with a respective index. The transit node can use a combination of an incoming segment stack and a Target FEC stack length to detect the index and extract the segment list to use for the co-routed return path.

Copyright 2015 Cisco Systems, Inc.

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    Generally, techniques are presented in which an Initiator, while generating the Echo Request, will build an end-to-end co-routed return path segment stack and associate an index to each segment. Any transit node or egress node can use the number of segments in a stack and use the index to detect the return segment to be used for the co- routed return path.

FIG. 1

    In the topology shown in FIG. 1, R1 (Initiator) will include

to follow R1-R2-R5-R6-R3-R4 path and would like to have the Echo Reply from any transit node take the co-routed return path. For example, R5 while replying back should not use R5-R8-R1. Instead, it should reply back via R5-R2-R1.

    Deriving return path segment stack from Target FEC stack by Initiator: Co-Routed Adjacency --> For each Adj-SID in interface I by Node N, the co- routed Adj-SID is the adjacency SID assigned by nexthop on I for N. In the above topology, the co-routed adjacency for 2012 on R1 is 2021 on R2.

    The Initiator will take the following steps to generate the indexed return segment stack:

a. Include incoming interface details as bottom segments:

1. Use the interface on which the ECHO Request will be sent and identify the co-routed Adj-SID. Include this as bottom segment.

2. Include the Node SID of co-routed Adj-SID on top of it.

Copyright 2015 Cisco Sy...