By default, when IS-IS operates over multiple parallel links between two routers, only a single IS-IS neighbor gets advertised regardless of the number of links that may exist to the same router. This reduces the size of the Label Switched Path (LSP) and provides sufficient information for other routers to compute basic IP routing.

Some applications, such as MPLS traffic engineering and segment routing (SR) require all the individual links to be represented by separate IS-IS neighbor advertisements. The advertisement is performed automatically on MPLS or SR enabled devices when either one or both of those features are configured using IS-IS. The BGP-LS feature enabled using distribute link-state advertises all parallel links as well.

However, applications such as, telemetry also require to have full visibility of the link state topology. But, there are no specific configuration item that can be tied to provide the full visibility.

To enable full visibility of the link state topology to other than MPLS or SR applications, advertise link attributes command is introduced. The advertise link attributes command forces IS-IS to advertise IS neighbor information for all links connecting two routers, rather than just one with the lowest cost regardless of whether this is required by other configuration such as SR, MPLS-TE, or BGP-LS. It also adds link endpoint information in the IS neighbor advertisements.

When multiple parallel links to the same neighbor are advertised it is necessary to uniquely identify these links. IS-IS uses local and remote interface identifiers and IP endpoint addresses of the link to uniquely identify multiple parallel links. For numbered link in IPv4 topology, IPv4 endpoint addresses of the link are use, whereas for unnumbered link (as there are no end IPv4 or IPv6 addresses), the link local and remote interface identifiers are used to identify the unnumbered link uniquely.

For links in the IPv6 topology, support for local and remote global address subTLVs are added. This requires adding support for the IPv6 global interface address TLV in hello packets and local or remote interface identifiers subTLV regardless of the address-family and numbered or unnumbered status of the link. Including the interface identifiers allows monitoring applications to associate a unique identifier with the link independent of VRF association and identifies the physical link used by IS neighbor advertisements in different topologies.