ISDN routing problem on 3620

[phil_carter]

Hello,

I have a 3620 running the below IOS and a 2m line. When the 2m line fails the ISDN comes up, but routing doesn't fully work. Even though there is a 0.0.0.0/0 route, until I manually configure a 10.0.0.0 255.0.0.0 floating static, routing fails to work correctly.

IOS: c3620-js-mz.122-6c.bin

interface Dialer1
ip address 10.12.0.22 255.255.255.252

HAYDEP_D_CR362_01#sh ip ro
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
       * - candidate default, U - per-user static route, o - ODR
       P - periodic downloaded static route

Gateway of last resort is 10.12.0.21 to network 0.0.0.0

     10.0.0.0/8 is variably subnetted, 6 subnets, 5 masks
C       10.12.3.0/24 is directly connected, FastEthernet0/0
S       10.0.0.0/8 [180/0] via 10.12.0.21
C       10.24.2.0/24 is directly connected, FastEthernet0/0
C       10.12.0.20/30 is directly connected, Dialer1
C       10.12.0.21/32 is directly connected, Dialer1
C       10.38.0.0/20 is directly connected, Loopback0
S*   0.0.0.0/0 [180/0] via 10.12.0.21
HAYDEP_D_CR362_01#sh run | in ip route
ip route 0.0.0.0 0.0.0.0 10.12.0.21 180
ip route 10.0.0.0 255.0.0.0 10.12.0.21 180      <<<<<<<<< routing doesn't work until this is added

Is this a known IOS problem and a quick upgrade will fix?

Thanks

Phil

[cadet alain]

Hi,

when you remove your floating static route to 10.0.0.0 is your static default in your routing table and if so

can you do a debug ip packet while pinging an external address.

Regards.

Alain.

[Peter Paluch · Accepted solution]

Phil,

Do you perhaps see the command no ip classless in your configuration? Some of the symptoms you describe remind me of a classful routing behavior. If so, entering the ip classless command in your configuration should activate the "normal" classless routing behavior that we all know and use today.

You may be interested in reading more about the classful routing behavior here:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094823.shtml#forwarding

Best regards,

Peter