I decided to read the posts regarding this draft (hybrid-bcast-p2mp), since it is related to OSPF-MANET, and have a few comments.
It was mentioned that RFC 5820 (OSPF-MANET with smart peering) solves the problem of this draft, assuming that smart peering and unsynchronized adjacencies are used. (E.g., Sheth's post on 2/10/2011.) I also want to point out that RFC 5614 (OSPF-MANET-MDR or OSPF-MDR), which uses CDS flooding via MDRs (MANET Designated Routers), not only solves the problem of this draft, but provides almost the same solution as this draft when OSPF-MDR (with full-topology LSAs and biconnected adjacencies) is applied to single-hop broadcast networks. The hybrid-bcast-p2mp draft is nice because it requires only minimal modifications to OSPF, keeping the DR and BDR and the same adjacencies. The reason that OSPF-MDR applied to single-hop broadcast networks provides almost the same solution as this draft is because it generalizes the concept of DRs and BDRs to MANETs, and requires only 2 adjacencies for a non-DR/BDR (or non-MDR/BMDR) in a single-hop broadcast network. More on this (near) equivalence below. In contrast, the solution of draft-retana-ospf-manet, which applies RFC 5820 with smart peering to single-hop broadcast networks, is quite different, resulting in a more random selection of adjacencies, which are not common to any single node such as a DR. Thus, unlike the other two solutions, draft-retana-ospf-manet is conceptually quite different from OSPF broadcast, since it does not use the concept of the DR and BDR. One of the goals in the design of OSPF-MDR was to minimize changes to OSPF. Thus, instead of throwing out the DR and BDR, they were generalized to multi-hop networks, and were kept essentially the same in the special case of a single-hop network, for the purpose of flooding and forming adjacencies. More information on OSPF-MDR can be found at www.manet-routing.org. Now more on the (near) equivalence between hybrid-bcast-p2mp and OSPF-MDR when applied to a single-hop broadcast network. In this case, the MDR selection algorithm is very similar to the DR election algorithm of OSPF, and both select a single DR/MDR. (There are a few minor differences that are not important to this discussion.) Also, if AdjConnectivity = 2, each node forms an adjacency with the MDR and BMDR. The origination of router LSAs is also nearly equivalent. The rules in Section 3.6 of hybrid-bcast-p2mp, which specifies which Type 1 links a non-DR includes in its router LSA, are similar to the corresponding rules in RFC 5614 when LSAFullness = 4 (full-topology LSAs). In that case, a router includes all bidirectional (2-Way or higher) neighbors that are "routable", where a neighbor is routable if SPF has calculated a route to the neighbor. Note that SPF will calculate such a route to the neighbor as long as both the router itself and the neighbor are fully adjacent to the MDR. This is slightly different from Section 3.6 of hybrid-bcast-p2mp, which only requires that the router itself be fully adjacent to the DR (thus relying on the requirement of SPF that the neighbor must include a link back to the router in its LSA). But both solutions achieve the same goal, in a similar way, using a single DR/MDR that becomes adjacent with all neighbors. Richard _______________________________________________ OSPF mailing list [email protected] https://www.ietf.org/mailman/listinfo/ospf
