I have been fiddling with a Cisco ASR901 for a while now, but I can't wrap my head around configuring it as a layer 2 VLAN switch. Is it not possible to configure one of its Gigabit Ethernet ports as a trunk? I can't use switchport trunk configuration or create a VLAN. I noticed that I can configure an interface vlan, but I, later on, found out that isn't the same thing. I can't even figure out how to designate a port for a particular VLAN.

  • Technically, yes, but you won't like it. (see also: bridging, "BVI") If you need a switch, buy a switch.
    – Ricky
    Apr 6, 2021 at 18:57
  • @Ricky My friend happens to give me this router to use and I thought I can configure it as a VLAN switch since I was able to configure for it on my Cisco E3000 router after flashing it with Tomato, of course. I never work with networking configuration on Cisco commercial routers before, so I assume it should be possible, but I have to learn it the hard way.
    – Ice Drake
    Apr 6, 2021 at 19:22

1 Answer 1


No, those are routers, not switches. You can use subinterfactes on a router interface to have layer-3 interfaces into separate networks (VLANs) as a trunk to an external switch:

interface GigabitEthernet0/0/0
 no shutdown
interface GigabitEthernet0/0/0.10
 encapsulation dot1Q 10              ! Tag traffic for VLAN 10
 ip address  ! Gateway for VLAN 10
 no shutdown
interface GigabitEthernet0/0/0.20
 encapsulation dot1Q 20              ! Tag traffic for VLAN 20
 ip address  ! Gateway for VLAN 20
 no shutdown
! etc.
  • 2
    Perhaps not obivous to everyone: if you configure multiple ports with the same VLAN ID, there's no switching between them on those routed ports.
    – Zac67
    Apr 6, 2021 at 10:53
  • Let me get my understanding straight. What Ron Maupin said about setting up subinterfaces is similar to setting up a layer 3 VLAN interface except it is designated to a particular port rather than to all the ports. Even if I can setup a VLAN subinterface on two different ports with the same VLAN tag, there is no switching involved between the two ports as mentioned by @Zac67. Thus, the answer to my original question remains as a solid "No", correct? It is not possible to configure Cisco ASR901 to handle VLAN switching.
    – Ice Drake
    Apr 6, 2021 at 19:06
  • Yes, that's correct.
    – Zac67
    Apr 6, 2021 at 19:09
  • Right, that is not a switch, it is a router, and routers route between networks, not switch on the same network. Some routers can set up a virtual bridge. See this question and answer.
    – Ron Maupin
    Apr 6, 2021 at 19:14
  • It is getting more complicated than it has to be. Getting a VLAN switch or a Tomato- or OpenWRT-compatible router is more preferred choice. Thanks all.
    – Ice Drake
    Apr 6, 2021 at 19:32

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.