Advertising Parallel Links
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.