[cisco-nas] Dialup Routing Q

[Dennis Peng]

Voralt [peder at voralt.net] wrote:
> I have a dialup routing question.
> 
> Say I have several users dialing in via ISDN.  They each have a class C from
> the 172.16.x.x block and on the main site router I have the following
> routes:
> 
> ip route 172.16.1.0 255.255.255.0 172.16.1.1
> ip route 172.16.2.0 255.255.255.0 172.16.2.1
> ip route 172.16.3.0 255.255.255.0 172.16.3.1
> ip route 0.0.0.0 0.0.0.0 1.1.1.1
> 
> 
> Each remote router is either 1.1, 2.1 or 3.1.  The users dialin ok and
> everything works fine, but if they are not connected, I am wondering what
> happens to data destined for their network.  So if the ISDN user at 1.1 is
> not dialed in, the static route is still there,

The 172.16.1.0 route should not be in the routing table unless
172.16.1.1 is connected. Can you verify that?

> but it appears that the data is sent out the default route, which
> then sends it back in and the TTL eventually expires.

Yes, I'd expect that it would use the default route.

> I also have a summary static set to NULL0, which I
> would think would drop the traffic, but that doesn't appear to be the case.
> 
> ip route 172.16.0.0 255.255.0.0 NULL0 240

I would think this should work. It would be nice to have "sh ip ro" to
get the full context of what your routing table looks like.

Dennis

> Can anybody explain exactly what's happening?  To summarize one more time, a
> central router has all of the routes listed above.  Traffic is sent to
> 172.16.1.1, but that router is not dialed in at the moment, so what happens
> to traffic destined for that network?
> 
> Thanks in advance.
> 
> Peder
> 
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