Our 3560 has a routed interface on the native (untagged) VLAN 1 connected to one port. How would I also pass that VLAN through to another port, but tag it to appear as VLAN 20 on that other port?
EXPLANATION ADDED IN RESPONSE TO COMMENTS:
I have a multi-site Metro Ethernet on the untagged VLAN. Recently added a fiber link from one site to a new site that's not on the Metro. I can just use the native VLAN on the fiber, but I'd like to know if can choose to tag it.
On our Brocade/Foundry FCXs it's easy, and I hoped Cisco had an equivalent:
vlan 20
untagged e 1/1/1
tagged e 1/1/2
You might think of it as a simple form of VLAN translation.
FOLLOW-UP, ADMITTEDLY A STRETCH:
When a physical port sees VLAN 1 (untagged) and VLAN 5 (tagged), can another physical port carry the VLAN 1 traffic but tag it as VLAN 20? In another approach toward a similar end, if port A is an access port in VLAN 1 and port B an access port (untagged) in VLAN 20, can you cross-connect them w/o blowing up the switch, perhaps if you first disable cdp?
Best Answer
Short answer: You have a switch. You can't.
Longer answer: Possible solutions: VLAN 10 on port 1, VLAN 10 (access port = untagged) on port 2, VLAN 20 (access port = untagged) on port 3, VLAN 20 (tagged) on port 4.
Connect port 2 to port 3, disable CDP, DTP and spanning tree (or the switch will know what you're doing and disable the port). Tada! You have now connected VLAN 10 to VLAN 20. Adapt this method to suit your situation. Waste 2 ports per "bridge".
You may also want to look at bridged interfaces (bridge-group, int bri) if your switch supports that. Doesn't do much, but may be what you want in some situations.
If you want to mix and match (output VLAN 10 tagged with dot1q tag 20 on this port) you can't do it with a switch. Well, the least you'll need in a switch would be a 7600 with the expensive linecards, their name escapes me. It's called vlan remapping IIRC.
Remember, even a layer 3 switch is just a switch.