The default router preferences RFC seems to be internally inconsistent
on the scope of the "non-reachable router" implications.
Section 3.2 contains:
using route preference values as a tie-breaker if
multiple matching routes have the same prefix length. If the best
route points to a non-reachable router, this router is remembered for
the algorithm described in Section 3.5 below, and the next best route
is consulted.
thus it talks about multiple matching routes *with the same prefix
length*. Nothing in section 3.5 contradicts this.
Yet the example in section 3.6 talks about falling back to the default
route (or any route with a shorter match) when all the longest match
routes lead to unreachable routers.
It is quite odd that the example is the only source of this novel behavior.
I'm concerned that going to shorter matching routes isn't only complex
to implement, makes the protocol operationally unpredictable (who knows
how quickly a host might decide a router is unreachable when there is
non-zero packet loss), but also charters completely new territory in
terms on longest-match routing.
Have this example behavior in section 3.6 been implemented?
Do we have any operational experience with it?
Erik
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