For When You Can't Have The Real Thing
[ start | index | login ]
start > Cisco > 3750 > 12.2 > Default route not working

Default route not working

Created by dave. Last edited by dave, 5 years and 63 days ago. Viewed 1,249 times. #1
[edit] [rdf]


Cisco 3750 running IOS 12.2(something) can't route across a router. Configuration includes the line

ip route
...which is locally correct.


On the router (which in this case is a FGT-100D cluster (this is not relevant to this particular problem)) we run a packet sniff and catch a ping attempt from another system to the switch in question:

# di sniffer packet Admin-500 'host' 1 50
1.016864 -> icmp: echo request
1.018247 arp who-has tell


The directive ip route... is only effective when the directive ip routing is active in the configuration. Add ip routing in conf t mode and the switch will respect the route as given.

Alternatively: remove the ip route... directive and replace it with ip default-gateway


In this case the Fortigate 100D was replacing the role of a Cisco 6506 core router. Ciscos appear to be smart enough to A) arp locally for systems they have no routes to when not in routing mode and B) be smart enough to answer an arp for a non-local IP if they have a route to said non-local IP. So when the 6506 was in place, it would answer the arp request for and the 3750 would just treat it as apparently local. Take the 6506 away, and that glue is missing.

no comments | post comment
This is a collection of techical information, much of it learned the hard way. Consider it a lab book or a /info directory. I doubt much of it will be of use to anyone else.

Useful: | Copyright 2000-2002 Matthias L. Jugel and Stephan J. Schmidt