[c-nsp] Combining multiple vlans into a single vlan.

Peter Rathlev peter at rathlev.dk
Sun Dec 14 15:33:17 EST 2008

On Mon, 2008-12-08 at 20:40 -0500, Jeff Cartier wrote:
> Could this be accomplished using a ME3750, using BVI's? and if yes,
> any configuration examples?
> A co-worker said he tried this and couldn't make it work...

BVIs probably only work on "real routers". With the L3 switches you
would need a physical loop cable. (The BVI is the L3 interface by the
way, so just short circuiting the VLANs is just a "bridge-group".)

I'm not adequately familiar with the ME3750, but I guess it can't do
brige-groups. On a device that could, you would do something like this:

! *** On some router ***
bridge irb
interface GigabitEthernet0/0/1.630
 encapsulation dot1q 630
 bridge-group 5
interface GigabitEthernet0/0/1.631
 encapsulation dot1q 631
 bridge-group 5
interface BVI5
 description Optional, only when L3 termination is needed
 ip address
bridge 5 protocol ieee

Still, combining different VLANs this way could lead to lots of
problems, a.o. short circuiting spanning trees.


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