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Switching Issue


I am having trouble passing traffic and access devices through a switch trunk connected to a 7206 rtr.

I have also attached a simple topology drawing outlining the network.

I have the management VLAN as vlan 1. I can pass traffic through the switch, but I can not access any devices past the switch (weird).

7206 rtr int f0/0 has 4 IP addresses. From anywhere on our network, I can not access (ping) the ip's assigned to this interface, but I CAN access other IP's that belong to each of the 4 subnets, just not the ones assigned to the interface itself.

On 7206 int f6/0, I have one IP address (interface connects to a wireless backhaul to another 7206 at a seperate location). I can not access this IP address from our core 7507 rtr, but traffic does pass over this int, and out the primary rtr interface f3/0 back through our fiber circuit. We run OSPF across all these attached rtr's, and all the routing tables show the correct paths to each network, they are just not reachable from a management stand point.

I added the 2950 switch connected to the 7206 because we added another backhaul for redundancy to our fiber circuit. This created the problem because before I had the primary connection to the 7206 directly connected and had no issues. I am sure this is a switch / vlan config issue, but I am stumped.

Any ideas or suggestions would be much appreciated.


Hall of Fame Super Silver

Re: Switching Issue

Hello Jesse,

I suppose you are using a trunk with 802.1Q (dot1q) encapsulation.

A native vlan mismatch on the trunk can cause problems like the ones you see on a pair of vlans.

On the c2950 check if vlan1 is the native vlan (default) with show interface f0/x switchport.

On the router side verify that:

each subif has encapsulation dot1q, that vlan numbers match the set of vlans permitted on the trunk on the switch side.

Note: C2950 should support only dot1q so may be you just configured the port as a trunk.

Verify if any subif as the option native

example: enc dot1q 3 native makes 3 the native vlan

Be aware that the router will let you to mix subifs with different encapsulations without any warning. But the ones with the wrong encapsulation will be isolated.

You can use show vlan to see per vlan packet statistics

You can use debug vlan packets to see if there are unexpected vlan-id tags on the router.

Hope to help