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SEGMENT ROUTING AUTOMATIC INTER-IGP-DOMAIN INTER-OPERABILITY WITH THE ABILITY OF ZERO-PACKET-LOSS DOMAIN MERGE

IP.com Disclosure Number: IPCOM000245394D
Publication Date: 2016-Mar-07
Document File: 8 page(s) / 98K

Publishing Venue

The IP.com Prior Art Database

Related People

Ahmed Bashandy: AUTHOR [+2]

Abstract

In summary, presented herein are techniques segment routing inter-operability that allow for merging two segment routing domains running two different Internal Gateway Protocols (IGPs) or two different instances of the same IGP and automatically advertising fragmented Segment Routing Global Block (SRGB) in the correct order. In addition, these techniques enable exchanging traffic between the two domains with minimal operator intervention by requiring non overlapping SRGBs between the two IGP instances running on the Autonomous System Boundary Routers (ASBRs) only. Further still, these techniques enable transitioning from one IGP to another with zero-packet-drop in an incremental approach with no time limit by using automatic or manual resolution of prefix-Segment Identifier (SID) collision coupled with ordered Forwarding Information Base (FIB) download of prefix with labels as well as label cross-connects. For simplicity, it is assumed that one IGP domain runs ISIS and the other runs OSPF. However the algorithms proposed below are applicable to any routing domains whether they are running the same or different routing protocols.

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SEGMENT ROUTING AUTOMATIC INTER-IGP-DOMAIN INTER-OPERABILITY WITH THE ABILITY OF ZERO-PACKET-LOSS DOMAIN MERGE

AUTHORS:

Ahmed Bashandy Robert Hanzl

CISCO SYSTEMS, INC.

ABSTRACT

    In summary, presented herein are techniques segment routing inter-operability that allow for merging two segment routing domains running two different Internal Gateway Protocols (IGPs) or two different instances of the same IGP and automatically advertising fragmented Segment Routing Global Block (SRGB) in the correct order. In addition, these techniques enable exchanging traffic between the two domains with minimal operator intervention by requiring non overlapping SRGBs between the two IGP instances running on the Autonomous System Boundary Routers (ASBRs) only. Further still, these techniques enable transitioning from one IGP to another with zero-packet-drop in an incremental approach with no time limit by using automatic or manual resolution of prefix-Segment Identifier (SID) collision coupled with ordered Forwarding Information Base (FIB) download of prefix with labels as well as label cross-connects. For simplicity, it is assumed that one IGP domain runs ISIS and the other runs OSPF. However the algorithms proposed below are applicable to any routing domains whether they are running the same or different routing protocols.

DETAILED DESCRIPTION

Presented herein are techniques to provide several services.

    1. End-to-end services (L2VPN, L3VPN) in networks consisting of multiple Segment Routing (SR) IGP domains (SR enabled redistribution).

    2. Zero packet loss migration when merging multiple segment routing IGP domains into a single one.

    3. Inter Autonomous System (InterAS) segment routing connection using SR- enabled Border Gateway Protocol (BGP) (InterAS option C for Segment Routing).

Copyright 2016 Cisco Systems, Inc.
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    For the sake of clarity, an example is used of two routing domains: one running the Intermediate System-to-Intermediate System (ISIS) protocol and another running the Open Shortest Path First (OSPF) protocol. The problem can be generalized to any number of domains running any number of ISIS and/or OSPF instances. This proposal solves three related problems:

Problem 1

    Consider the case where we are interconnecting an OSPF and ISIS domains. We want routers in the OSPF domain to be able to send and receive segment routing traffic from routers in the ISIS domain and vice versa. We do NOT want to re-assign prefix- SIDs in either domains even if there is collision. We do not want to force a routing protocol re-advertise prefixes or prefix-SIDs of the native protocol. So the redistributing protocol only advertises new prefixes that it learns from the redistributed protocol. This results in minimum churn in both networks.

Problem 2

    We want to transition all routers in the OSPF domain to ISIS with zero packet loss in both IGP as well as BGP/L2VPN traffic flowing within any of the two domains or between the two domains. For example,...