Why configure domain IDs for OSPF on S series switches

OSPF domain IDs apply to VPNs.
When the domain ID of the remote PE is the same as that of the local PE, Type 1, Type 2, and Type 3 LSAs generate Type 3 LSAs, and Type 5 and Type 7 LSAs generate Type 5 and Type 7 LSAs (related to the area type).
When the domain ID of the remote PE is different from that of the local PE, Type 1, Type 2, and Type 3 LSAs generate Type 5 or Type 7 LSAs, and Type 5 and Type 7 LSAs generate Type 5 and Type 7 LSAs (related to the area type).

Before advertising the remote routes to CEs, PEs need to determine the type of OSPF routes (Type 3 or Type 5) to be advertised to CEs according to domain IDs. If local domain IDs are the same as or compatible with remote domain IDs in BGP routes, PEs advertise Type 3 routes. If not, PEs advertise Type 5 routes.

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