The automatic ABR selection for an inter-area LSP does not change the prior implementation of inter-area LSP behavior for many of the LSP-level and path-level options. However, there are a number of enhancements introduced by the automatic ABR selection feature.
Features such as path bandwidth reservation and admin-groups continue to operate within the scope of all areas since they rely on propagating the parameter information in the PATH message across the area boundary.
The TE graceful shutdown feature continues to support MBB of the LSP path to avoid the link or node that originated the PathErr message as long as the link or node is in the local area of the ingress LER. If the PathErr originated in a remote area, the ingress LER is not able to avoid the link or node when it performs the MBB since it computes the path to the local exit ABR only. However, there is an exception to this. An enhancement has been added to cause the upstream ABRs in the current path of the LSP to record the link or node to avoid and use the record in subsequent ERO expansions. This means that if the ingress LER computes a new MBB path that goes through the same exit ABR as the current path, and all ABRs upstream of the node or link that originated the PathErr message are also selected in the new MBB path when the ERO is expanded, then the new path will also avoid this link or node.
MBB support has been expanded to avoid the ABR when the node is put into TE graceful shutdown.
The use-te-metric option in CSPF cannot be propagated across the area boundary and therefore operates within the scope of the local area of the ingress LER. This is a new behavior.
The srlg option on the bypass LSP continues to operate locally at each PLR within each area. The PLR protecting the ABR checks the SRLG constraint for the path of the bypass within the local area.
The srlg option on the secondary path is allowed to operate within the scope of the local area of the ingress LER with the automatic ABR selection feature.
The least-fill option support with an inter-area LSP is introduced with the automatic ABR selection feature. When this option is enabled, CSPF applies the least-fill criterion to select the path segment to the exit ABR in the local area.
The PLR must indicate to CSPF that a request to a one-to-one detour LSP path must remain within the local area. If the destination for the detour, which is the same as that of the LSP, is outside of the area, CSPF must return no path.
With the automatic ABR selection feature, timer-based resignaling of the inter-area LSP path is supported and the path is resignaled if the cost of the path segment to the local exit ABR changes. The cost shown for the inter-area LSP at the ingress LER is the cost of the path segments to the ABR.