[cisco-nas] Dialup Routing Q

[Voralt]

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

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