From: Hyunseog Ryu (r.hyunseog@ieee.org)
Date: Fri Nov 14 2008 - 17:37:51 ARST
As long as it can find any network containing next-hop IP address from
routing table.
So if you have default route (0.0.0.0/0), it will be hit as very last
resort.
Therefore it will pick up the next-hop ip address from default route to
replace "down"ed interface ip address next-hop ip address.
Joe wrote:
> Ya, this is what I have seen. Again, at what point is the route NOT specific
> enough for the static to disappear and is that something you can configure?
>
>
>
> On 11/14/08 11:02 AM, "Hyunseog Ryu" <r.hyunseog@ieee.org> wrote:
>
>
>> 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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