IS-IS SR-TE TI-LFA Backup Path From SR Mapping Server Advertisements

This feature enhances topology-independent loop- free alternates (TI-LFAs) to support the backup path for prefix SIDs derived from Segment Routing Mapping Server (SRMS) advertisements in an IS-IS network. In a network configured with segment routing, IS-IS uses the SRMS advertisements to derive prefix SIDs from LDP FEC label bindings, which is required in LDP-to-segment routing interworking scenarios. However, this feature provides the enhancement for IPv4 only, and SRMS advertisements for IPv6 are not supported. 

The backup path for prefix SIDs from SRMS advertisements are not created in the following scenarios: 

• If some hops are present in a non-segment routing domain. 
• If the segment routing node is advertising a prefix and a prefix SID index directly, then the prefix SID index is used and the SRMS advertisement for that prefix is disregarded.
• If a backup path requires an adjacency SID from the LDP domain, then the backup path cannot be installed. 
• If the PLR is unable to determine the label mapping using LDP.