The automatic ABR selection for an inter-area LSP does not change prior implementation inter-area LSP behavior of many of the LSP and path level options. There is, however, a number of enhancements introduced by the automatic ABR selection feature as described in the following.
Features such as path bandwidth reservation and admin-groups continue to operate within the scope of all areas because they rely on propagating the parameter information in the Path message across the area boundary.
The TE graceful shutdown and soft preemption features 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 because it computes the path to the local ABR exit router only. There is, however, an exception to this for the TE graceful shutdown case only. An enhancement has been added to cause the upstream ABR nodes in the current path of the LSP to record the link or node to avoid and use it in subsequent ERO expansions. This means that if the ingress LER computes a new MBB path which goes via the same exit ABR router as the current path and all ABR upstream nodes of the node or link which originated the PathErr message are also selected in the new MBB path when the ERO is expanded, the new path indeed avoids this link or node. The latter is a new behavior introduced with the automatic ABR selection feature.
The support of MBB to avoid the ABR node when the node is put into TE Graceful Shutdown is a new behavior introduced with the automatic ABR selection feature.
The metric-type te option in CSPF cannot be propagated across the area boundary and operates within the scope of the local area of the ingress LER node. This is a new behavior introduced with the automatic ABR selection feature.
The srlg option on bypass LSP continues to operate locally at each PLR within each area. The PLR node protecting the ABR checks the SRLG constraint for the path of the bypass within the local area.
The srlg option on secondary path is allowed to operate within the scope of the local area of the ingress LER node 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 node in the local area.
The PLR node must indicate to CSPF that a request to 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.
The propagate-admin-group option under the LSP still needs to be enabled on the inter-area LSP if the user wants to have admin-groups propagated across the areas.
With the automatic ABR selection feature, timer based re-signal of the inter-area LSP path is supported and re-signals the path if the cost of the path segment to the local exit ABR changed. The cost shown for the inter-area LSP at ingress LER is the cost of the path segments to the ABR node.