how to bridge two vlans on switch

Unanswered Question
Jun 9th, 2010

Hi, me again.

I am in the unhappy situation to renumber my vlans.

I would like to cross-connect (bridge) the old-vlans

with the new ones (without plugging cables)

so the client-ports may migrate smooth .

Problem are not the access-ports, but

when dot-q trunks go into a firewall or an esx-server.

The spanning-tree problematic has been solved already,

bpdu's must not be forwarded between old and new vlans.

So is there a way to configure it on Cisco Catalys switch

(3560E/2350/4900M) ?

sw1#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
vlan 200
sw1(config-vlan)#tb-vlan1 501
VLAN 200 TLB 1 VLAN value 501 have similar types (Ethernet)
APPLY VLAN changes failed.

This does not work,

and the switchport vlan map xxx to yyy port command for a trunk interface

seems not to be supported on my hardware.

Thank you for any hints,

Jürgen Marenda.

I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
j-marenda Wed, 06/09/2010 - 05:24


Yes, you can do it with a vlan-capable router and bridge-groups,

but i have mutliple GigEthernet vlans to renumber;

a Router of that size must do other work for me than bridgeing.

The other point is that on current catalyst switches,

there are no bridge-groups like like on IOS for Routers.

Since i could mangage it by hardware

(plug some X-Cable,

with access-vlan xxx port on the one side,

access-vlan yyy on the other side,

(and bpdufilter enabled on both sides)

all works fine

(yes, i do this on exactly ONE point,

not multiple times, to prohibit broadcast storms).

Iff i can physically create the desired behaviour,

there must also be a soft, command-line solution, i believe,

since my problem seems to be a

Jürgen Marenda.

Giuseppe Larosa Wed, 06/09/2010 - 05:56

Hello Jurgen,

the feature is called fallback bridging I was able to use it on C3550 with 12.1EA image but it had a limitation: it could not apply to IPv4 traffic.


>> All protocols except IP (Version 4 and Version 6),  Address Resolution Protocol (ARP), reverse ARP (RARP), LOOPBACK, Frame  Relay ARP, and shared STP packets are fallback bridged.

so it may be of limited use.

Hope to help



This Discussion

Related Content