VLAN shuts down

Unanswered Question
Sep 29th, 2009

I have a 1841 router and a 2950 switch. I am doing the router on a stick configuration. On the 1841 I have configured sub interfaces Fa0/0.120 & Fa0/0.130. On the switch I created VLAN 120 & 130. When I issued the command "no shutdown" on the 120 VLAN the 130 VLAN shuts down and vice versa. I am not sure what is going on.

I have this problem too.
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Overall Rating: 5 (3 ratings)
Jon Marshall Tue, 09/29/2009 - 11:08


Not sure what you mean.

If you mean "no shutdown" on the 2950 switch then you can only have one L3 vlan interface up at any one time as the 2950 is a L2 switch only.

You should be able to have both fa0/0.120 and 1.30 up at the same time on the 1841 router.


HMidkiff Tue, 09/29/2009 - 11:28

Jon - Thanks for replying. I might be wrong put I should be able to have multiple VLAN configure on my 2950 switch at the same time. The port going up to my 1841 is a trunk port. The 1841 has sub interfaces and is doing the routing between the VLAN's. (router on a stick) I have deloyed this config with 2960 switches and didn't have a problem. Could this be a limitation with the 2950?

Jon Marshall Tue, 09/29/2009 - 11:31


You can indeed have multiple vlans on the 2960 but that is L2 vlans ie. if you do "sh vlan" you can have multiple vlans in the output.

However you can only have one L3 vlan interface on the 2950 switch up/up at any one time.


HMidkiff Tue, 09/29/2009 - 11:34

So even though I get a status message saying it is down it should still function?

Jon Marshall Tue, 09/29/2009 - 11:39

Are you referring to the interface on the 2950 switch ?

As i say both interfaces should be up/up on the 1841 router.

On the 2960 you can only use one L3 vlan interface at a time and as Glen has said that is for managing the 2950 switch. If the interface is showing as down you can't use it.


glen.grant Tue, 09/29/2009 - 12:14

I think you are getting the L2 vlan and the L3 vlans mixed up . The 2950 can have up to like 250 L2 vlans on i believe so that shouldn't be an issue. You can only have 1 active L3 SVI on the 2950 to manage the switch with.

glen.grant Tue, 09/29/2009 - 11:21

You only need a single ip address on the 2950 and that's to manage the switch only , so pick an address in one vlan or the other and use that . Your routing is done on the 1841 so why would you need more than 1 address on the 2950 ?

Leo Laohoo Tue, 09/29/2009 - 14:48

Jon & Glen are right (+5 each). The 2950 will allow multiple VLANs instances and interfaces configured, however, the 2950 will only support one active interface VLAN active at any given time. Remember that a Layer 2 switch only has an IP address for management purposes only thus the 2950 (like it's older predecessor, the 2900XL/3500XL) will only allow one active VLAN interface. This limitation will not affect your router-on-a-stick configuration. You'll just have to keep in mind to consistently use the sole-management IP address.

The 3550 is totally a different beast altogether. I'm not sure about the EA-series IOS but if you use the 12.2 version, you can enable multiple interface VLANs active. This holds true for any switches after the 3550: 2970, 2960, 3560, 3750 etc.

Hope this helps.


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