Flat network layer 2 issues

[howithink]

I need help. We are in the process of changing a large  L2 network. Everything terminates into a single small FW. The IP range is 172.16.10.0/22 so the end of the port configured on the FW is 172.16.10.1/22. This is where everything terminates. 

Now we want to remove this function from the FW and introduce a L3 device with a vlan which i created called VLan4 and the ip address i assigned to it is 172.16.10.1/22. Also made necessary route changes to send traffic to FW and out. 

I was hoping that when we unplug the cable from the FW and into the L3 that everything will work, but it is not. I am getting Arp incomplete. It looks like behind the L3 there are other devices (hubs/switches) and when i do show cdp neigh, my port on L3 shows as connected to 2 different devices. 

What am i doing wrong?

[balaji.bandi]

If all the Switches are L2, then you need to create an SVI with Vlan 1 and allocate FW IP address to that SVI ( and keep that in shutdown mode)

follow below steps on Switch :

config t

!

interface vlan 1

ip address 172.16.10.1/22

shutdown

!

When the maintenance window agreed, remove the FW Cable, from Swtich

in the switch

config t

! 

interface vlan 1

no shutdown

!

ping from device and advise.

once this is success, you need to create FW different IP address and accordingly for internet and NATiing part.

Hope this steps helps.