Nokia 7705 - 3.12 Segment Routing with Traffic Engineering (SR-TE)

MPLS Guide MPLS and RSVP-TE
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3.12 Segment Routing with Traffic Engineering
(SR-TE)
Segment routing adds the ability to perform shortest path routing and source routing
using the concept of abstract segments to IS-IS and OSPF routing protocols. A
segment can represent a local prefix of a node, a specific adjacency of the node
(interface/next hop), a service context, or a specific explicit path over the network.
For each segment, the IGP advertises an identifier referred to as a Segment ID (SID).
When segment routing is used together with the MPLS data plane, the SID is a
standard MPLS label. A router forwarding a packet using segment routing will
therefore push one or more MPLS labels.
Segment routing using MPLS labels can be used in both shortest path routing
applications (refer to the 7705 SAR Routing Protocols Guide for information) and in
traffic engineering (TE) applications, as described in this section.
The following are the objectives and applications of segment routing:
• ability for a node to specify a unicast shortest-route or source-routed forwarding
path with the same mechanism; IGP can be reused to minimize the number of
control plane protocols
• ability to use IGP-based MPLS tunnels without the addition of any other
signaling protocol
• ability to tunnel services from ingress PE to egress PE with or without an explicit
path and without requiring forwarding plane or control plane state in intermediate
nodes
• ability to use Layer 3 spoke SDP interfaces to support multicast for segment
routing. Refer to the 7705 SAR Routing Protocols Guide, “Multicast for Segment
Routing”.
• FRR: ability to expand coverage of basic LFA to any topology with the use of a
source-routed backup path; precomputation and setup of backup path without
additional signaling
• support for LFA policies with shared-risk constraints, admin-groups, and link/
node protection
• support for SR-TE entropy labels
• support for TE that includes loose/strict options, distributed and centralized TE,
path disjointness, ECMP awareness, and limited or no per-service state on
midpoint and tail-end routers
• support for fine-grained flow steering and service chaining via a centralized
stateful Path Computation Element (PCE) such as the one provided by the
Nokia Network Services Platform (NSP)