Re-number VLAN

[Matt Roberts]

Is it possible to rrenumber an existing VLAN?

I have a VLAN 40 using 172.20.252.x and want renumber it to VLAN 252

[JohnTylerPearce]

I don't think you can Matt. You would have to remove VLAN 40 and then create a VLAN 252. I know you can rename the actually name of the VLAN but not the number of the VLAN. I could be wrong, but I don't think you can do that.

[Matt Roberts]

Would there be any issues creating another vlan on the same subnet and move the devices from the vlan 40 to vlan 252?

[JohnTylerPearce]

Yes and No Matt. You can create another vlan, but if you give it a VLAN interface IP within that subnet range to use as the default gateway for the new vlan 252, I'm not sure if it could cause ICMP redirects or not. If you did this during down time, which you would obviosuly want to do anything, you could do it that way. Just create a vlan interface ip of what you want to use for the default gateway, and move the ports that you want to move from VLAN 40 to VLAN 252.

[Richard Burts]

Matt

As far as the layer 2 VLAN there should be no problem in creating a new VLAN 252 and moving all the ports from the old VLAN 40 to the new VLAN. There is probably a small issue with the layer 3 SVI for the VLAN. You can certainly create interface vlan 252. But you would not be able to have the same subnet on both interfaces (assuming that both interfaces were on the same box). So you would need to remove the address from the old interface vlan 40 and then apply it to the new interface vlan 252.

None of this is hard. But it will have some impact on users. Depending on how quickly you move ports from the old VLAN to the new VLAN there might be some impact on devices that think they are locally connected but are in fact in different VLANs (and therefore in different broadcast domains). And devices moved to the new VLAN will have limited connectivity until you get the subnet moved from the old vlan interface to the new vlan interface. So bear that in mind as you plan the time to make the changes.

HTH

Rick

[Geert Reijnders]

You can't create a vlan with an ip in an excisting subnet. It will give an error message. The way I would do this is like this:

create vlan 252 on every switch

move all the devices from vlan 40 to vlan 252

shut down interface vlan 40

create the correct ip on interface vlan 252

test everything

remove interface vlan 40

remove vlan 40

[Matt Roberts]

Currently VLAN 40 has an IP 172.20.252.1 what if I gave VLAN 252 the IP 172.20.252.2, would that work?

[JohnTylerPearce]

Well both addresses will still be in the same subnet unless you choose a different IP and change the mask.

[Matt Roberts]

True, would that cause issues? It would temporary just until I get all server ports changed to the new VLAN, then I'd shut down the old one.

[Geert Reijnders]

it is simply not possible to create two SVI's in the same subnet on the same switch.

[glen.grant]

You could change both to vlan 252 and put a primary gateway of .2 and a secondary of .1   if that would work for you. You would have to shutdown vlan 40 to do it though .

[ylandrum]

So I know this is an old question, but here's how I did it. If it is feasible to reload the switch, you can just edit the startup config and change all instances of the vlan number, both at the vlan interface itself and for all ports using that vlan:

OLD:
!
interface GigabitEthernet1/0/23
switchport access vlan 40
spanning-tree portfast
spanning-tree guard root
!

...

!
interface TenGigabitEthernet1/0/2
switchport access vlan 40
spanning-tree portfast
spanning-tree guard root
!

...

!
interface Vlan40
ip address 172.20.252.1 255.255.255.0
no ip unreachables
no ip proxy-arp
!

NEW:
!
interface GigabitEthernet1/0/23
switchport access vlan 252
spanning-tree portfast
spanning-tree guard root
!
...

!
interface TenGigabitEthernet1/0/2
switchport access vlan 252
spanning-tree portfast
spanning-tree guard root
!

...

!
interface Vlan252
ip address 172.20.252.1 255.255.255.0
no ip unreachables
no ip proxy-arp
!

Then reload the switch. When it comes back up, your vlan and all ports that use it will be renumbered using the existing subnet.

[Joseph W. Doherty]

Some considerations using such an approach . . .

Editing the startup config, without touching the running config, might be unknown for less experienced engineers.

Additionally, if VTP is being used, the startup doesn't have VLAN information, which is also defined separately from the SVI (although defining a SVI with an unknown VLAN might auto define the VLAN [?], unless switch running as VTP client [?].  If VTP is active, although the new VLAN might be auto defined, the old VLAN [not the SVI], would still be defined.)

Using this approach is probably more disruptive than what the other posters suggested.

[ylandrum]

Well, I'd say that less experienced engineers would do well to go the more tedious yet traditional route until they gain the experience needed.

As for your other points, you may be right for certain environments; the OP didn't specify a particular switch, ios, or any interconnectivity with other switches in his question. And of course if you have multiple switches with a core providing layer 3 it'll have to be changed for all of them that use that vlan.

The only other comment I can make is that I have used this method successfully every year for the last 12 or so at our full offsite disaster recovery test. This is on a 3570X colo core stack with no other switches hanging off of it, but with a 10g trunk to the recovery environment stack. Works like a boss.

Your mileage may vary.