Migrate Default VLAN to another vlan

[Mokhalil82]

Hi

We are replacing our core stack of 3750 with a new core setup as a VSS. As part of this migration I want to connect the new core to the old core via trunk links as I migrate the configs over and connections. 

My management vlan is currently vlan 1 but want to move this to vlan 5 as part of the change. I want to keep the same management subnet tho. How can I co-exist management IPs on both switches as part of the same subnet but different vlan. Is this possible or is there an easier way.

I know I can configure the new switch without connecting to the exisiting but the plan is that during the migration, I want to migrate the L2 links first and test and then migrate the L3 links which is why I want to connect the new core to the existing core

Thanks

[Reza Sharifi]

Hi,

Since you need to trunk the new vss to the old 3750 stack, you need to have the same vlan tags on both side of the link.  So, on the old core the mgmt vlan is 1 (tagged) and if you change it to vlan 5  (tagged) on the link between vss and 3750 stack than even though both vlans are in the same subnet they will not be able to communicate with each other because the tags are different. Also, if you have specified vlan 1 as native on your current trunks and when you connect the new core to the old core and if your native vlan is 5, you will see mismatch native vlan.  So, what you can do it use vlan 1 on the trunk connecting vss to the old core with unused IPs (if you have any available) than once you migrate to the new core you can have a maintenance window and change vlan 1 to 5.

HTH

[Mokhalil82]

Hi 

Thanks for the response. So when changing vlan 1 to vlan 5, will the same management IP exist on the same switch but in different vlans. So I am thinking I would do a int vlan 5 and give it the management ip, then clear the management ip from vlan 1, but will both co-exist for that moment while i perform the change. 

Also im guessing I will lose connection as I clear the management ip off vlan 1 and then would have to reconnect to the new vlan

[Reza Sharifi]

Hi,

So, you can't have 2 SVIs being in the same subnet. For example, if the mgmt subnet is 10.10.10.0/24 (vlan1) and your SVI ip is .1 you can't assign .2 to vlan 5.  You can create vlan 5 and SVI ahead of time and during a short maintenance window delete the ip address from vlan 1 and add the same ip to vlan 5.

HTH

[Mokhalil82]

Thanks

That makes sense, but Ive got to do this on all the access switches aswel, will the connection drop if I am ssh'd into the device and then I remove the IP address

[Reza Sharifi · Accepted solution]

Yes, the connection will drop for a very short time.  The transition from vlan 1 to vlan 5 should not take more than a minute if you get everything ready ahead of time. Try connecting to the switch using a user vlan (if possible)  This way you don't lose your connection.  And yes you need to make the same change on all layer-2 access switches. Don't forget to add the new vlan to the trunks.

HTH

[Mokhalil82]

Thanks Reza

[Jon Marshall]

Just to be clear you don't remove the IP address you just type in a new one and it will overwrite the existing one. As Reza says you will be logged out but you should be able to log back in.

Jon