[Xorp-hackers] Adding static routes with unresolved next-hop router

Mark Handley M.Handley@cs.ucl.ac.uk
Fri, 13 Aug 2004 09:00:53 +0100


>It is the job of the routing protocols to install or remove routes. All
>routing protocols are responsible for monitoring the status of the the
>next hops. If a next hop transitions between resolvable states the
>routing protocol should take the appropriate action (add/delete).

Well, this is certainly true for all the normal dynamic routing
protocols:

 - In BGP a route is not eligable for Decision unless the nexthop is
   resolvable.  BGP has to explicitly monitor the RIB state to do this.

 - In RIP, if an interface goes down, the routes from neighbours on
   that interface will timeout without RIP needing to do anything
   special about nexthop reachability.

 - In OSPF/IS-IS, if an interface goes down, the link will be remove
   from the link state table, and the SPF calculation will remove any
   routes whose nexthop was over that interface.  Again, no special
   monitoring of nexthop reachability needed beyond what OSPF does
   itself.

The question is really one of whether static_routes behaves like a
"normal" routing protocol (in which case it will need to monitor RIB
or interface state in a similar way to BGP, because unlike RIP, OSPF
or IS-IS, it doesn't have its own link state monitoring mechanism),
or whether it's something different.

Cheers,
	Mark