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Router interface set up as vlan?

I've noticed in several configs and on some diagrams in the cisco books that router interfaces are set up as vlans. Where can I find information on setting these up and how do I do it.


Re: Router interface set up as vlan?

If you have multiple VLANs in your switched network, and you can create a VLAN trunk that uses IEEE 802.1Q encapsulation from one switch port, you can connect your router to that VLAN trunk port and configure it to route between/among your VLANs using subinterfaces. Here's a helpful link:

Configuring Routing Between VLANs with IEEE 802.1Q Encapsulation

Note: Generally speaking, you need the "Plus" version of whatever IOS you have in order to take advantage of subinterfaces on the LAN side. This may require more RAM on your router than what it shipped with in order to run; likewise, it may take more flash memory to store the "Plus" image than what your router shipped with.

For what it's worth, you can also configure ISL trunks instead of 802.1Q trunks, if the switches and routers are all Cisco products. Again, the key here is using subinterfaces on the LAN connections:

Configuring ISL Trunks on Cisco Routers


Configuring Routing Between VLANs with ISL Encapsulation

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