[c-nsp] Different behaviour for static route on different IOS?

[Gert Doering]

Hi,

On Tue, Feb 15, 2005 at 08:25:29AM -0800, Tim Bulger wrote:
> Thanks, but we are discussing static routes, not BGP learned routes.
> Obviously recursive next hop lookup is necessary for BGP as that is how the
> protocol is designed.  

The forwarding part of the machine doesn't care where the route came from.

Besides that, it doesn't need to be so complicated - *every* route that
points to a gateway IP address (as opposed to "to an interface") is 
recursive:

 interface eth0
   ip address 10.1.1.1 255.255.255.0

 ip route 0.0.0.0 0.0.0.0 10.1.1.2

- that's already recursive routing.  With static.

> Wei's example clearly illustrates different behavior between IOS versions
> regarding static routes.  In the 12.0 example, there is no recursive next
> hop lookup taking place for the static.  In the 12.3 example, there is.  

It's funny indeed, and classful stuff seems to play a role here.

I've done some experimenting with 12.0(27) right now, and the specific
behaviour depends on the target IP - if route and gateway in the same 
"class A" (10.44.44.0/24 -> 10.0.0.1), the route will not be used, but
if it's a different network (10.44.44.0/24 -> 192.168.0.1), it *will*
be used:

Cisco#sh ip route 10.44.44.0
Routing entry for 10.44.44.0/24
  Known via "static", distance 1, metric 0
  Routing Descriptor Blocks:
  * 192.168.0.1
      Route metric is 0, traffic share count is 1

Cisco#sh ip route 192.168.0.1
Routing entry for 192.168.0.0/16, supernet
  Known via "eigrp 99", distance 170, metric 1807872, type external
  Redistributing via eigrp 99
  Last update from 195.30.X.X on Serial3/0, 5w2d ago

funny stuff.  

It's *great* that this has been cleaned up, to work in a deterministic and
not classful-addressing-related way.

gert
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Gert Doering - Munich, Germany                             gert at greenie.muc.de
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