The mapping server feature supports the configuration and advertisement, in IS-IS, of the node SID index for prefixes of routers in the LDP domain. This is performed in the router acting as a mapping server and using a prefix-SID sub-TLV within the SID/label binding TLV in IS-IS.
Use the following command syntax to configure the SR mapping database in IS-IS:
configure
— router
— [no] isis
— segment-routing
— no segment-routing
— mapping-server
— sid-map node-sid {index 0..4294967295 [range 0..65535]} prefix {{ip-address/mask} | {ip-address}{netmask}} [set-flags {s}] [level {1 | 2 | 1/2}]
— no sid-map node-sid index 0..4294967295
The user enters the node SID index, for one prefix or a range of prefixes, by specifying the first index value and, optionally, a range value. The default value for the range option is 1. Only the first prefix in a consecutive range of prefixes must be entered. If the user enters the first prefix with a mask lower than 32, the SID/label binding TLV is advertised, but a router that receives it does not resolve the prefix SID and instead generates a trap.
The no form of the sid-map command deletes the range of node SIDs beginning with the specified index value. The no form of the mapping-server command deletes all node SID entries in the IS-IS instance.
The S-flag indicates to the IS-IS routers in the network that the flooding scope of the SID/label binding TLV is the entire domain. In that case, a router receiving the TLV advertisement leaks it between IS-IS levels. If leaked from Level 2 to Level 1, the D-flag must be set; this prevents the TLV from being leaked back into level 2. Otherwise, the S-flag is clear by default and routers receiving the mapping server advertisement do not leak the TLV.
SR OS does not leak this TLV between IS-IS instances and does not support the multi-topology SID/label binding TLV format. In addition, the user can specify the flooding scope of the mapping server for the generated SID/label binding TLV using the level option. This option allows further narrowing of the flooding scope configured under the router IS-IS level-capability for one or more SID/label binding TLVs if required. The default flooding scope of the mapping server is L1 or L2, which can be narrowed by what is configured under the router IS-IS level-capability.
The A-flag indicates that a prefix for which the mapping server prefix SID is advertised is directly attached. The M-flag advertises a SID for a mirroring context to provide protection against the failure of a service node. None of these flags are supported on the mapping server; the mapping client ignores them.
Each time a prefix or a range of prefixes is configured in the SR mapping database in any routing instance, the router issues for this prefix, or range of prefixes, a prefix-SID sub-TLV within an IS-IS SID/label binding TLV in that instance. The flooding scope of the TLV from the mapping server is determined as previously described. No further check of the reachability of that prefix in the mapping server route table is performed. No check of the SID index is performed to determine whether the SID index is a duplicate of an existing prefix in the local IGP instance database or if the SID index is out of range with the local SRGB.