vlan help

matt_heff · ‎02-10-2007

Please try to follow me here:

I have a host connected to a 2950 access layer swicth in building A. The enitre access switch is vlan 100 (first floor). The switch uplinks to a 3550 in the basement on a port dedicated to vlan 100. The 3550 routes between vlans (the different floors) in the building okay and also has a trunk over to a similar 3550 in building B (the trunk includes all vlans.) Here's my problem, vlan 100 in building A can talk to any other vlan in building A, but it can only talk to vlan 100 in building B. It is like this for all vlans in either building-- They can talk to any vlan in the same building, but only the same vlan in the other building. I think this has something to do with the packet structure and the way the headers are aligned, but can't quite seem to figure it out.

I have traced the packet from building A vlan100 and found that it does reach any host (on any vlan) I choose in building B. However, when the packet is coming back from building B's 3550 switch it gets to building A's 3550 and then is dropped. What am I missing here? Please help!

Jon Marshall · ‎02-10-2007

Hi Matt

Are the vlans in building A and building B the same vlans ?

Does the 3550 in building B also route between vlans ?

Sounds like it could be a routing issue in that if you talk to vlan 100 from building A to vlan 100 in building B it is just switched down the trunk link whereas any other vlan would need to be routed.

Jon

matt_heff · ‎02-10-2007

Jon,

Yes the buildings have the same vlans, as so:

Building A 1st Floor vlan 100

Building A 2nd Floor vlan 200

Building A 3rd Floor vlan 300

Building B 1st Floor vlan 100

Building B 2nd Floor vlan 200

Building B 3rd Floor vlan 300

Both 3550s have ip rotuing enabled and route locally just fine. The weird thing is, routing on both sides works okay for a trunked packet to an extent (according to my analyzer the echo requests get all the way to the destination after being routed on the other side to a different destination vlan, but the echo replies are dropped after coming back to the local 3550 where they need to re-routed to the original vlan). Strange. As far as I see it, as long as both 3550s are routing and know the same vlans all should work fine. Right???

Jon Marshall · ‎02-10-2007

Matt

Are you running HSRP between your two 3550's.

Do the vlans use the same IP addressing in both buildings ?

If it isn't the same addressing it still sounds like routing.

If it is then when you send a packet from vlan 100 in building A to vlan 200 in building B the packet will be routed on the 3550 switch in building A and then switched across the trunk link to vlan 200 in building B. The return traffic will be routed on the 3550 in building B and then switched to building A. This doesn't sound from your explanation what is happening.

Could you post configs of both 3550's.

Pick this one up tomorrow morning.

Jon

jain.nitin · ‎02-11-2007

Hi, Can you paste ur config of one of Edge switch i means floor switch in bulding A & Edge switch in building B also both 3550 config so that i can check the config. See it cud be prob of routing, VTP domain & trunking also. So it wud be better if u can send the config. I suggest you to put building B switch as vtp client & let it take vlan from 3550 in building A this is first suggestion. Second you can create one vtp domain & put both the 3550 in vtp server mode & create HSRP between them it wud provide u redundancy as well as easy intervlan routing..anyways first let me try to solve this problem.

Thanks

Ninja