From: James MacDonald (j4m3sm63@yahoo.ca)
Date: Fri Nov 14 2008 - 19:42:08 ARST
if the interface actually goes down/down the connected route has to be removed from the routing table ... and then the static route will be removed as well as it fails the next hop reachability test. If there is a problem somewhere in a WAN environment where the local interface is still up/up then obviously then the route sticks and it causes a problem since the default will not take over.
At least this is the way i've seen this occur in practice ... i've seen many floating static route configurations that simply don't work because of this. If statics must be used (rather then a link state protocol) then you can put a GRE tunnel over top of the ethernet link ... the keep alives are end-to-end in that case.
------------------------------
Jim MacDonald
j4m3sm63@yahoo.ca
------------------------------
________________________________
From: Hyunseog Ryu <r.hyunseog@ieee.org>
To: Joe <joe.clyde@utah.edu>
Cc: Cisco certification <ccielab@groupstudy.com>
Sent: Friday, November 14, 2008 1:02:27 PM
Subject: Re: Recursive lookups
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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