Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
Community Member

Need help with dot1q topology!!

Ok so my issue is simple but I am having a bit of a hard time finding the answer.

The Topology:

I have two 7200 One is North and the other is South.

The north router is connected to the south via a 100 Meg Full connection (crossover cable) in this lab test this represents an L2TPv3 tunnel that will carry traffic through an IP cloud.

The other side of the North and South routers is connected via 100 meg full interfaces to several layer 2 devices. These devices are VLAN aware and speak 802.1q.

So I am bridging VLAN 100 and using this to carry BPDUs around the network. The Layer 2 devices have the ability to port switch the layer 2 traffic based on VLAN ID and thus it comes in one interface and leaves another with out change. So I also have VLAN 200 configured and this VLAN will carry customer traffic and is bridged out to all of the layer 2 devices which are in turn bridging on VLAN 200 with learning turned on.

So VLAN 100 protects the network from bridge loops and VLAN 200 carries the real traffic. The problem I am having is in the configuration of the 7200s as I have them configured for the VLANS and the sub-interfaces for vlan 100 are members of bridge group 1 and the sub interfaces for vlan 200 are in bridge group 2. I have spanning-disable in the config for vlan 200.

When the network is whole it seems to work fine, but if I fail the connections between the layer 2 devices then spanning tree does its thing and un blocks but traffic does not seem to actually get forwarded. Meaning I can not ping any of the devices hanging off of the layer 2 devices (which I could before the network was broken and spanning tree converged).

So any ideas?? Or at least if this issue is interesting I can certainly find a better way to explain it better.

Let me know if anybody has any ideas or can help out with this one.




Re: Need help with dot1q topology!!

Such kind of problems can be expected with a setup like this. Do you absolutely need to bridge that traffic? I would rather use the link between north & south as a layer3 connection and route the traffic. This will automatically create separate STP-domains on either side of the link and will hence eliminate the STP-problem that you are facing.



CreatePlease to create content