Segment Routing L3VPN and TE

In my previous post Segment Routing I described basic concept of SR and how it works from data-plane and control-plane perspective. In this article I am going to focus how SR interact with L3VPN and MPLS TE. To do so I am going to use below network topology with Cisco IOS-XE 16.10.


The L3VPN configuration with SR is no different than traditional MPLS L3VPN deployment apart there is no LDP requirement. The CSR3 is configured as VPNv4 RR and basic VRF configuration is on each PE router.

This is configuration on the CSR1, no fancy stuff just simple VPNv4 configuration for BGP and redistribution connected into the VRF.

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Segment Routing

Segment routing (SR) is describe in RFC 8402 and offer flexible way to provide traffic engineering based on the source routing. With SR there is no longer needs to maintain a per-application and per-flow state, and traffic can obey the forwarding instruction provided in the packet.

SR relies on some extension to the routing protocols ISIS and OSPF. The SR can support any type of control plane such as distributed, centralized or hybrid.

Each control plane model provide different set of capabilities and how instructions are allocated and signaled. In a distributed scenario, the segments are allocated and signaled by IS-IS or OSPF or BGP and each node individually decides how to proceed with a packet.

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