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
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.
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.
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.
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
remove interface vlan 40
remove vlan 40