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Software Defined networking (SDN) – Segment routing

In the IP NGN part of the networking world, service providers, large enterprise, public customers running MPLS networks today are striving towards cost reduction while increasing service velocity.

Two domains come to the surface in order to achieve these goals :

  • network simplification
  • creation of flexible service infrastructure

There are various components which come into play in each domain, and some have hooks in both.  We will cover multiple components in the upcoming SP technical blogs.

The one innovative piece we’ll cover in this blog is called segment routing.  Segment routing (SR) is coming to a conclusion in the IETF and is clearly playing in the ‘network simplification’ domain, however, segment routing also opens up opportunities to benefit from Cisco’s SDN orchestration technology which is also known as ‘Open Network Environment’ (ONE).

To quote the IETF draft :

segment routing

segment routing

It is simple to deploy and operate as it removes the need for any signalling state in the network (i.e. RSVP-TE)  for explicit paths (i.e. for traffic engineering).  The state is no longer in the network, but in the packet.

The forwarding state (aka segment) is established by the IGP, which can be ISIS or OSPF and is agnostic to forwarding dataplane ; which can be IPv6 or MPLS.

The benefits of SR include :

  • automated and guaranteed Fast ReRoute (FRR)
  • An SR core router scales much better than with RSVP-TE
    – The state is not in the router but in the packet
    – N+A vs N^2 (N= #nodes ; A= #adjacencies)
  • CoS based TE
  • full control and OAM
  • The network is simple, highly programmable and responsive to rapid changes
    – perfect support for centralized optimization efficiency, if required

In the following video, Clarence provides some more info on SR :

And the following SP360 blog also covers segment routing :


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