CHAPTER 13
L2VPN Services over Segment Routing for Traffic
Engineering Policy
Segment Routing (SR) is a flexible and scalable way of performing source routing. The source device selects
a path and encodes it in the packet header as an ordered list of segments. Segments are identifiers for any type
of instruction.
Segment routing for traffic engineering (SR-TE) takes place through a tunnel between a source and destination
pair. SR-TE uses the concept of source routing, where the source calculates the path and encodes it in the
packet header as a segment. In SR-TE preferred path, each segment is an end-to-end path from the source to
the destination, and instructs the routers in the provider core network to follow the specified path instead of
the shortest path calculated by the IGP. The destination is unaware of the presence of the tunnel.
The user can achieve better resilience and convergence for the network traffic, by transporting MPLS L2VPN
services using segment routing, instead of MPLS LDP. Segment routing can be directly applied to the MPLS
architecture without changing the forwarding plane. In a segment-routing network that uses the MPLS data
plane, LDP or other signaling protocol is not required; instead label distribution is performed by IGP. Removing
protocols from the network simplifies its operation and makes it more robust and stable by eliminating the
need for protocol interaction. Segment routing utilizes the network bandwidth more effectively than traditional
MPLS networks and offers lower latency.
Preferred tunnel path functionality allows you map pseudowires to specific traffic-engineering tunnel paths.
Attachment circuits are cross-connected to specific SR traffic engineering tunnel interfaces instead of remote
PE router IP addresses reachable using IGP or LDP. Using preferred tunnel path, the traffic engineering tunnel
transports L2 or L3 traffic between the source and destination PE routers. A path is selected for an SR Policy
when the path is valid and its preference is the best (highest value) among all the candidate paths of the SR
Policy.
The following L2VPN services are supported over SR-TE policy:
• EVPN VPWS Preferred Path over SR-TE Policy
• L2VPN VPLS or VPWS Preferred Path over SR-TE Policy
• EVPN VPWS On Demand Next Hop with SR-TE
• EVPN VPWS Preferred Path over SR-TE Policy, on page 620
• L2VPN VPLS or VPWS Preferred Path over SR-TE Policy, on page 634
• EVPN VPWS On-Demand Next Hop with SR-TE, on page 650
• Overview of Segment Routing , on page 665
• How Segment Routing Works , on page 666
L2VPN and Ethernet Services Configuration Guide for Cisco ASR 9000 Series Routers, IOS XR Release 6.3.x
619
To Next Page
Loading...
Need help?
General
