From: dward@xxxxxxxxxxxxx
Date: Wed Jan 10 2001 - 21:29:07 GMT-3
This is a generated summary route for the class which as a summary is
routed via null0.
Remember a route only gets entered into the table or advertised if it
exists so all summaries get routed to null0 which is the bit bucket
interface and that way the 'route' is active.
If this is a problem turn off classful routing and/or remove auto-summary.
This behaviour also occurs in EIGRP and you have to turn off auto-aummary
or you'll advertise a summary route to other networks not part of the
summary range.
You can also see the same behaviour by manually configuring summarization
such as 'ip summary-address eigrp 1 1.1.1.0 255.255.252.0'
then look at the summary route as it it appears in the routing table.
Darren
On Wed, 10 Jan 2001, Chuck Larrieu wrote:
> i su 172.16.0.0/16 [115/30] via 0.0.0.0, Null0
>
>
> Nigel, the other interesting thing about this route as I see it, is the last
> part of the line.
>
> The source is IS-IS, the su maybe we are guessing it is short for summary,
> but we don't know, and then we get to that route via 0.0.0.0 comma null0
> Without looking at some router output, this looks a bit unusual as well.
> Want to call it one of those Cisco things?
>
> I did not see a route to 0.0.0.0 in either of your show ip route outputs.
> IS-IS level one routers, if my recollection is correct, are analogous to
> OSPF stub area. In fact, it seems to me that on one of tests, I actually saw
> a 0.0.0.0 route generated by a level 1 router. did you spot anything like
> this on any of your level 1's?
>
> I will certainly keep an eye out when I set up next time.
>
>
> Chuck
>
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