Migration of vlan IDs

[mbrunton77]

I need to change the ID for a vlan and would like to minimize the outage for migrating the hosts. Our environment are Nexus cores using a VPCs to 5ks.  The SVI for the vlan resides on the Nexus cores and only L2 on the Nexus 5ks.  For example I have vlan100 with an SVI of 10.1.1.0/24 on the cores and it is trunked down to the Nexus 5ks using a vPC.  I need to keep the same IP scheme but change the vlan ID to 300.  I am trying to do this with very little down time.

I am thinking I could create the new vlan300 as an L2 only on the cores and trunk it down to the 5ks.  On nexus core 1, connect a cable from a port that is in vlan100 to vlan300 with the ports being configured as access ports.  Essentially I am creating a path for vlan300 to communicate with vlan100.  Would this solution work?  Of course this would be only temporary to migrate the hosts over the new vlan and then I would move the SVI address to the new vlan300.

See diagram

[Jon Marshall]

I haven't used Nexus switches but I am struggling to see what you gain from your solution.

I know with vPCs Nexus handles STP differently but with other switches I have used joining two vlans together in the core of the network is not something I would really consider, or at least not for this.

The IPs are staying the same. So the main issue is when you shut the existing SVI and bring up the new one it could have a different virtual mac address which means all the servers mac to IP mapping for the default gateway would need clearing.

I just checked the N7K configuration guide and if you use the same HSRP group it should generate the same virtual mac. And if you don't you can actually configure your own virtual mac.

So that just leaves migrating the hosts and the Nexus switches support ranges of interfaces.

So I would just have the SVIs ready, then simply move all servers at once into the new vlan, shutdown the old SVI and bring up the new one.

There will obviously be an outage but there would anyway when you switch SVIs.

Like I say I haven't used Nexus so perhaps there is something I am overlooking but I cannot see what benefit you get and creating that link could potentially have a far bigger impact on your environment.

Jon

[mbrunton77]

Thanks for the reply.  I like your idea around the HSRP group and might look into it.  But I think I might take your advice and not create a loop on the core.