2811SRST/K9 fails to communicate with network

[asiegel]

I have a Cisco2811 SRST/K9 router with a four port FXO that is part of our phone system.  It won't ping to anything on the network except for one particular switch.  I can ping that switch (but nothing else) and that switch can ping the router and telnet into the router; however, when I plug the router into any other switch on my network, it will still only successfully ping that one switch.  It won't ping the switch that it's physically attached to.  I can see the router from the switch when I do a Show CDP Neighbor.  And I can see the switch when I do a Show CDP Neighbor from the router.  But it won't ping.  When I do a Show Adjacency from the router, it returns only that one switch.  I've tried a Clear ARP on both the switch and the router.  I've also compared the config from the router to the config of a working router on the network and everthing looks the same. I can ping anything on my network from these switches - except that router.  I even tried changing the default gateway of the router to be the ip address of the switch with which it can successfully communicate.

I just don't understand how I can connect to one switch but not any other. 

I'd be happy to share configurations with anyone who can help.  In the meantime, I have four phone lines at the library that not working.

Andy Siegel

Dover, DE

asiegel@dover.de.us

[Ivan Krimmel · Accepted solution]

Hi Andy,

since you have 4 phone lines not working in the library, let's try to fix that :)

In order to be able to ping a switch off this new router, they should be on the same IP subnet. The currently working router could and should have a bit different configuration, so be causious while copying its config onto the new box.

In case you have any IGP in your network, this new router might be needed to join this IGP domain, for this it should have connectivity with the existing routers. This can be accomplished by a proper L2 configuration, including proper VLANs being configured on the switches, as well as trunks for example.

If there's no IGP, but there's a default-gateway, this new router should be able to reach the default-gateway. Again, in a switched infrastructure it is a L2-connectivity question first of all. I doubt that currently one your switches is serving as a default gateway.

So in general, first make sure that basic L2 connectivity is configured well, then think out the L3 connectivity.

Good work,

Ivan.

[asiegel]

Well, it works. I assumed that if I configured the swichport for mode trunk, it would pass all VLAN's, but I had to specifically put it in switchport access VLAN 101.  I was just being stupid, I guess.