Mailing List Archive: Dialup Routing Q

Dialup Routing Q

Jul 6, 2003, 8:22 PM

Post #1 of 5 (1347 views)

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

Re: Dialup Routing Q [ In reply to ]

mitaylor at cisco

Jul 6, 2003, 9:01 PM

Post #2 of 5 (1330 views)

Permalink

hi,

You might want to investigate classless routing (command: 'ip classless')

A description is here:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios113ed/113ed_cr/np1_c/1cipadr.htm#xtocid212805

From what you are describing, you probably have 'ip classless' configured...

OR, you could add extra static routes with an admin distance for each
specific subnet.

e.g.
ip route 172.16.1.0 255.255.255.0 Null0 240
ip route 172.16.2.0 255.255.255.0 Null0 240
ip route 172.16.3.0 255.255.255.0 Null0 240

Hope this helps,
Cheers,
Mike Taylor

At 10:22 PM Sunday 6/07/2003 -0500, Voralt 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, 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
>
>_______________________________________________
>cisco-nas mailing list
>cisco-nas@puck.nether.net
>http://puck.nether.net/mailman/listinfo/cisco-nas

Cisco Systems,
Customer Support Engineer,
Asia Pacific Technical Assistance Centre,
Sydney, Australia
Ph: (+61 2) 8446 6044

Re: Dialup Routing Q [ In reply to ]

peder at voralt

Jul 7, 2003, 5:01 AM

Post #3 of 5 (1335 views)

Permalink

That only works if there is a separate dialer interface designated for each
dial peer, which there isn't in our case.

----- Original Message -----
From: <atticus@the.satanic.org>
To: "Voralt" <peder@voralt.net>
Sent: Sunday, July 06, 2003 11:05 PM
Subject: Re: [cisco-nas] Dialup Routing Q

>
> Point your statics to the dialer interface(s) -- that way the routes will
> actually be removed when the dialer is down, and likewise your summary
> to null0 will be hit..
>
>
> On Sun, 6 Jul 2003, Voralt 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, 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
> >
> > _______________________________________________
> > cisco-nas mailing list
> > cisco-nas@puck.nether.net
> > http://puck.nether.net/mailman/listinfo/cisco-nas
> >
>
>
>

Re: Dialup Routing Q [ In reply to ]

peder at voralt

Jul 7, 2003, 5:15 AM

Post #4 of 5 (1334 views)

Permalink

> You might want to investigate classless routing (command: 'ip classless')
>
> A description is here:
>
http://www.cisco.com/univercd/cc/td/doc/product/software/ios113ed/113ed_cr/n
p1_c/1cipadr.htm#xtocid212805
>
> From what you are describing, you probably have 'ip classless'
configured...

I don't think that's the answer as it appears to be backwards from what I am
seeing. It says that if you have "ip classless" and you have a supernet
configured, it will follow the supernet, which it is not.

> OR, you could add extra static routes with an admin distance for each
> specific subnet.

I tried that, it doesn't work. Backup routes don't appear to have any
affect since the router always thinks the primary is still the best, that is
until it's time to actually forward traffic to the peer.

Re: Dialup Routing Q [ In reply to ]

dpeng at cisco

Jul 9, 2003, 11:36 AM

Post #5 of 5 (1331 views)

Permalink

Voralt [peder@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
>
> _______________________________________________
> cisco-nas mailing list
> cisco-nas@puck.nether.net
> http://puck.nether.net/mailman/listinfo/cisco-nas