vlan interfaces on routers

Unanswered Question
Feb 6th, 2007

Hi all, if I have 4 fast ethernet interfaces on my router, and also a vlan interface, can you have an ip address on each fastethernet interface ? and can you have multiple vlans on the router ?

I have this problem too.
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spremkumar Tue, 02/06/2007 - 01:57

Hi Carl

If you are going to connect the trunk port of your switch to the routers ethernet then you need to create subinterfaces with respective vlan id being used as identification on the subinterfaces.

If you are going to connect simple switch ports then you can configure ip address on the ethernet port.

I dont think you can create vlans as you do in normal L2 or L3 switch instead you can create subinterfaces with respective vlan ids for the identification purpose..


carl_townshend Tue, 02/06/2007 - 03:05

This is the config I have seen

interface FastEthernet0


interface FastEthernet1


interface FastEthernet2


interface FastEthernet3


interface Vlan1

description local-LAN

ip address x.x.x.x

ip accounting output-packets

ip route-cache flow

ip tcp adjust-mss 1452

how does this work, i guess so you can use any 4 ethernet ports, Would you have to put your switch as a trunk port so it does intervlan routing ?

spremkumar Tue, 02/06/2007 - 03:10

Hi Carl

I feel you have a ESW module installed in your router which actually works as a Logical Switch installed in your router..

All the fastethernet interfaces will be part of the vlan 1 which is again being assigned with an ip address..


spremkumar Tue, 02/06/2007 - 04:58

Hi Carl

You can have more than 1 Vlan provided your IOS Code supports it..


simonstoll Tue, 02/06/2007 - 05:16

Hi Carl

Depends on your router model, recently I was working with a 870 Series, this models are limited to 4 Vlans, plus one routeable WAN Port which can be DSL or Ethernet. The 4 Fastethernet Ports are just Switchports, the routing has to be done on the VLAN Interfaces. On bigger plattforms this should not be a problem.


boblutton Tue, 02/06/2007 - 08:47

2950 will hold only 1 vlan interface(layer3), in my experience

3550 and above will hold multiple , but depending on OS


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