VLAN problem -- Connecting two switches over a metro-ethernet circuit

[JUSTIN LOUCKS]

I have just turned up a new 'Native LAN' circuit which converts a point-to-point DS-3 circuit to Ethernet on each end. I have the conversion device plugged into an ethernet port on a Catalyst switch at each end. I am having problems getting communications across the link though. The switch ports at the different locations are in different VLANs on their respective switch. I'm wondering if I need to turn one of them into a trunk port or something so that the ports can communicate even though they have different VLAN tags. Can someone please assist or make any recommendations?

Thanks in advance.

[glen.grant]

I think you are either going to have to make both ends in the same vlan or set up both ports to trunk whatever ports you want on the link . Are you seeing anything via cdp neighbor ?

[milan.kulik]

If both ports are configured as access ones, it should work even with differnt VLANs on opposite sides.

It would be better to use the same VLANs on both sides, of course.

If you don't, you might be receiving error messages in your syslog. (Use CDP ver 1 or disable CDP on the line to stop them.)

But the communication should work.

Regards,

Milan

[JUSTIN LOUCKS]

I know that on a Catalyst 2900/3500 the command is 'switchport mode access' on the interface. What is the equivalent command for doing this on a Catalyst 4000/6500 running CatOS?

[milan.kulik]

set trunk mod/port off

disables trunking on the port, see http://www.cisco.com/univercd/cc/td/doc/product/lan/cat4000/rel7_6/command/set_s_z.htm#wp1025473

and

set vlan VLANx mod/port

moves the port to the proper VLAN, see http://www.cisco.com/univercd/cc/td/doc/product/lan/cat4000/rel7_6/command/set_s_z.htm#wp1052100

Regards,

Milan

[Kevin Dorrell]

This looks a bit like a remote bridge. Is the objective to carry a single VLAN across the DS-3 link, or the whole set of VLANs?

If you want to carry a single VLAN, then it should be OK to configure both ends as access ports, and set them in the VLAN you want to bridge. There will be no issue about tagging. CDP may warn you of the VLAN mismatch, but there should be no ill effect from this.

If you want to carry all the VLANs across the link, then you will have to set up both ends as a trunk. But beware that trunking adds a few bytes to the frame size, (4 in the case of 802.1Q, more in the case of ISL) so make sure that the converter box is happy with the slightly increased MTU.

In all cases, I think CDP will be your best tool for debugging the link.

Kevin Dorrell,

Luxembourg