This feature is supported only on the 7210 SAS-Mxp, 7210 SAS-R6, 7210 SAS-R12, and 7210 SAS-Sx/S 1/10GE.
Segment routing (SR) adds to IS-IS and OSPF routing protocols the ability to perform shortest path routing and source routing using the concept of abstract segment. A segment can represent a local prefix of a node, a specific adjacency of the node (interface or next-hop), a service context, or a specific path over the network. For each segment, the IGP advertises an identifier referred to as a segment ID (SID).
When SR is used in combination with the MPLS data plane, the SID acts as a standard MPLS label. A router forwarding a packet using SR therefore pushes one or more MPLS labels. This section describes the SR MPLS feature.
Both shortest path routing and traffic engineering applications can leverage SR MPLS, which encodes a segment as an MPLS label. This section describes the shortest path forwarding applications.
When a received IPv4 prefix SID is resolved, the SR module programs the ILM with a swap operation and the LTN with a push operation, both pointing to the primary/LFA NHLFE. An IPv4 SR tunnel to the prefix destination is also added to the TTM and is available for use by L2 and L3 services.
The SR tunnel in the TTM is available in the following contexts:
IPv4 BGP route label
VLL and LDP VPLS
BGP-AD VPLS when the use-provisioned-sdp option is enabled in the binding to the PW template
intra-AS BGP VPRN for VPN-IPv4 and VPN-IPv6 prefixes, both auto-bind and explicit SDP
The remote LFA feature included in SR expands the coverage of the LFA by computing and automatically programming the SR tunnels that are used as backup next-hops. The SR shortcut tunnels terminate on a remote alternate node, which provides loop-free forwarding for packets of the resolved prefixes. When the loopfree-alternate option is enabled in an IS-IS or OSPF instance, SR tunnels are protected with an LFA backup next-hop. If the prefix of a specific SR tunnel is not protected by the base LFA, the remote LFA automatically computes a backup next-hop using an SR tunnel if the remote-lfa option is also enabled in the IGP instance.
The 7210 SAS-Mxp, 7210 SAS-R6, 7210 SAS-R12, and 7210 SAS-Sx/S 1/10GE do not support remote LFA when services use BGP 3107 labeled route tunnels. The push stack depth in this case exceeds the allowed limit.
The EXP-to-profile mapping for SR is defined in the mpls-lsp-exp-profile-map policy.
On the 7210 SAS-Mxp, 7210 SAS-R6, 7210 SAS-R12, and 7210 SAS-Sx/S 1/10GE, Nokia recommends the use of BGP3107 services using SR to advertise the loopback for BGP 3107 labeled routes to the IGP. This prevents a three-label pop on egress LER.
On the 7210 SAS-Mxp, 7210 SAS-R6, 7210 SAS-R12, and 7210 SAS-Sx/S 1/10GE, when using RLFA with services (and without the use of BGP 3107), if the PQ node is the segment termination, the SR OS always uses the PQ node SID and does not use additional SIDs. Therefore, when the 7210 SAS is configured as an eLER, it always requires two labels to pop and terminate the service packet.
On the 7210 SAS-Mxp, 7210 SAS-R6, 7210 SAS-R12, and 7210 SAS-Sx/S 1/10GE, the maximum label push depth is three MPLS labels, and the maximum label pop depth is two MPLS labels (both push and pop exclude the PW hash label).