Monthly Archives: January 2018

OSPF RFC1583 vs RFC2328 compatibility

Best path selection:
RFC1583 – best path based solely on cost.
RFC2328 – Intra-area paths that use non-backbone areas are always the most preferred.

Can lead to the loops:
https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/117824-config-ospf-00.html

Summary metric:
RFC1583 – lowest metric of the componet routes
RFC2328 – highest metric of the components.

OSPF RFC1587 vs RFC3101 NSSA compatibility.

Path selection
1587:
a. Any type 5 LSA.
b. A type-7 LSA with the P-bit set and the forwarding
address non-zero.
c. Any other type-7 LSA
RFC3101:
1. A Type-7 LSA with the P-bit set.
2. A Type-5 LSA.
3. The LSA with the higher router ID.
The P-bit default is now defined as cleared.
A new area configuration parameter, NSSATranslatorRole, is defined in Appendix D. It specifies whether or not an NSSA router will unconditionally translate Type-7 LSAs to Type-5 LSAs when acting as an NSSA border router.