Hello RFC 2328 does not specify how next hop should be computed on PtP ifaces - it is supposed that a next hop IP is not needed [1], which is true for physical PtP links, but not for PtP over LAN, as described in RFC 5309. Although RFC 5309 acknowledges a need for next hop IP on such PtP links, surprisingly it also does not specify how next hop should be computed in OSPFv2 (if i did not miss someting).
To my knowledge, there are at least two currently used schemes: 1) Use value from Link Data field, in a same way of how RFC 2328 specifies next hop computation for Point-to-Multipoint links. This scheme has several problems (e.g. does not work for unnumbered links and there is no reliable way to match links from neighbor's router LSA to my links if there are parallel links). 2) Use neighbor IP address from neighbor data structure of the neighbor on given iface. This is probably more robust, but a bit strange, as neighbor data structure is otherwise not used in routing table calculation. Any comments on how next hop computation should be done in this case? Slightly related question: Is it true that link-back check is broken in OSPFv2 when there are parallel (unnumbered) links between two routers? Footnote [23] says it is OK, but if router A has two links to router B, while router B has just one link (in its router LSA), then router A during routing table computation could select link that independently would fail link-back check. [1] RFC 238: "If the destination is a directly connected network, or a router which connects to the calculating router via a point-to-point interface, no next hop IP address is required." -- Elen sila lumenn' omentielvo Ondrej 'Santiago' Zajicek (email: [email protected]) OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net) "To err is human -- to blame it on a computer is even more so." _______________________________________________ OSPF mailing list [email protected] https://www.ietf.org/mailman/listinfo/ospf
