From: Hyunseog Ryu (r.hyunseog@ieee.org)
Date: Fri Nov 14 2008 - 16:02:27 ARST
We had this issue in the past.
If int X fails, 11.11.11.0/24 will still exist in routing table because
of recursive lookup.
That's why you have to use interface name instead of next-hop IP address
if possible.
Joe wrote:
> I have a question on recursive lookups, hopefully I can phrase it in a way
> that makes sense. Thanks
>
> If I have a static route like:
> Ip route 11.11.11.0 255.255.255.0 10.10.10.1
>
> And I have a route table that looks something like this:
> C 10.10.10.0/24 via int X
> O 10.10.0.0/16 via x.x.x.x
> E 10.0.0.0/8 via x.x.x.x
> B 0.0.0.0
>
> Hopefully you get the idea of the route table...doesn't matter how the
> routes are learned... just the idea of multiple routes (each less specific).
>
> What happens when I lose my directly connected interface? How "un-specific"
> of a route will the router use for a recursive lookup? *I know in this
> example if I lost the /24 then the next most specific /16 in this case is
> next in line but at what point will the router say it won't use a valid
> route (as far as the route table) for a recursive lookup?
>
> I don't believe it will ever use a default route but it seems like I've seen
> it try to recurse off a /14 route. In my opinion that is an undesirable
> behavior (let's say you have a summary address to null 0, you wouldn't want
> you statics still showing up as accessible because the next hop is reachable
> via a /16 net lets say). I know, I can avoid that issue by adding a specific
> interface to the static route, but would still like to know at what point do
> I not do a recursive lookup. Thanks for the help
>
>
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