I have several production VLAN's that I am going to be removing from the FWSM. I wanted to see if anyone out there had real life experience of the effects and connectivity issues (if any) during the removal of the VLAN's from the FWSM. How much connectivity loss and downtime should I expect during the removal of the VLAN's from the FWSM back to the switch?
I'm talking about connectivity within each of the VLAN's I'm removing and connectivity to/from the other parts of the network and VLAN's I'm removing.
You can remove vlans that are allocated to the FWSM with no interruption to other vlans allocated to the FWSM. Make sure you remove from both chassis's if you have redundancy otherwise failover gets in a bit of a state.
As for the vlans you are removing. Well they will no longer have a L3 interface so communication will be broken. What you can do is create the L3 SVI on the MSFC for these vlans but if you have enabled "firewall multiple-vlan-interfaces" then the FWSM won't let you.
Either accept that connectivity to these vlans will be broken while you remove from FWSM and then create the L3 SVI on the MSFC or you could try using the "firewall multiple-vlan-interfaces" command and create the L3 SVI's before removing them from the FWSM. I have never done this though.