802.1Q Tag Transport Between Trunks

Unanswered Question
Mar 28th, 2008


I have topology like that

c3750 A----c2960-------c3750 B

link between them are configured as trunk. Lets suppose i configured three vlans 10, 20, 30 on 3750 switches. To transport tagged traffic for any vlan from 3750-A switch to 3750-B, i also have to configure those vlans on middle switch 2950. Conceptual its true but is there any why that switch 2950 recieve 802.1q tagged frames from ingress trunk and forward as it is to egress trunk without removing tag and retag again. Simple said, I don't want to configure all those vlans on 2950 switch and still want to pass traffic back and forth.

Waiting for Responses.

Best Regards

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Joseph W. Doherty Sat, 03/29/2008 - 05:40

I would think, but am not positive, that any switch supporting 802.1q tagged frames had trunk ports connecting to other such switches, and without further configuration, it would flood all received tagged frames to other trunk ports for unknown MACs. (Similar as it would do for untagged frames.) Have you tried this and it didn't work?


If you also have a concern about defining VLANs on various switches, remember that Cisco also offers VTP.

bmarms Sat, 03/29/2008 - 05:44

you could make all 3 switches part of the same VTP domain so vlan info is passed between them. If the 2960 does not need to participate in these advertisements, but you still want vlan info forwarded you would configure that switch to operate in VTP tranparent mode. Make sure you are using VTP version 2.


This Discussion