bring up empty vlan

Unanswered Question
Nov 4th, 2008

Dear Sir,

Do you know how can we bring up a empty vlan, which has not device connected?

Thanks

I have this problem too.
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francisco_1 Tue, 11/04/2008 - 01:14

Joseph,

as far as i know i dont think the vlan interface line protocol will come up unless a layer 2 port exist in the vlan and that port status is connected.

Francisco.

Jon Marshall Tue, 11/04/2008 - 01:22

Joseph

Francisco is correct. You either

i) have a port in that vlan up and active

OR

ii) have an active trunk link with that vlan on it

Jon

mark.cronin Tue, 11/04/2008 - 07:44

On some older switches you could use this command

!

vlan database

vlan 100 state active

exit

!

John Blakley Tue, 11/04/2008 - 07:51

If it's a L3 switch, you can assign an SVI to it, and it'll bring it up also.

This is from memory (so don't quote me.) :-)

Router(config)# vlan 5

Router(config-vlan)#exit

Router(config)# int vlan 5

Router(config-if)#ip address 192.168.5.1 255.255.255.0

Router(config-if)# exit

It should show the vlan come up even though you don't have anything attached.

L2 switches require something to be attached and a member of that vlan for them to come up.

--John

Jon Marshall Tue, 11/04/2008 - 08:16

John

From memory as well :-) but pretty sure this won't work. On a L3 switch if you configure a L3 SVI and there is no active trunk port with that vlan on it nor an active port assigned into that vlan then it will briefly come up/up but then go down.

Jon

John Blakley Tue, 11/04/2008 - 08:20

Jon,

You may be right. I have one port that trunks all vlans, so by default when I add a new vlan and SVI, it automatically belongs to that trunked port.

Good catch. :-)

John

francisco_1 Tue, 11/04/2008 - 08:34

for a test i created vlan 100 on my L3 switch and created the SVI for the vlan 100 with ip address 155.1.0.1/24. the vlan 100 SVI line protocol will not come up unless i add a l2 port in vlan 100 and the l2 interface line protocol is ip. when i remove the L2 port from the vlan 100 and put it in to vlan 2, the vlan 100 SVI goes down again.

so that shows that the vlan SVI line protocol will not come up unless a layer 2 port exist in the vlan and that port status is connected

Francisco.

josephschung Tue, 11/04/2008 - 17:53

vlan is created on two 3560 switches(HSRP) and is trunked to two 2960 switches. On the two 2960, I added servers to the vlan. But the vlan on the two 3560 are still down. And the HSRP for the vlan is not working. It shows "unknown" on both 3560 switches.

I suppose once the servers are connected to 2960, the vlan on 3560 will up at once.

Any idea? Thanks.

francisco_1 Wed, 11/05/2008 - 02:21

what bhargav suggested about the vlan available between the 3650's for the HSRP to work. if the vlan is not allowed, then the switches will not exchange mutlicast traffic. perhaps you should "debug standby errors/events" to see why HSRP is not working.

Francisco.

Jon Marshall Tue, 11/04/2008 - 07:55

Hello Mark, heard you had moved on. Hope your new job is better than the one you left - how couldn't it be :-)

Jon

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