Normally on VLAN’s and interfaces, I’m use to setting static IP’s on these. I had a situation where I had to have a WAN interface obtain an IP address from DHCP and it could not be static.
Here’s how to do it.
! interface Vlan1 Description ***WAN INTERFACE*** ip address dhcp !
Simple as that, yea I was unaware that I also had to change the default route.
ip route 0.0.0.0 0.0.0.0 Vlan1
ip route 0.0.0.0 0.0.0.0 Vlan1 dhcp
If you have an access list on the VLAN ensure you allow dhcp through on this. The same is for an interface if it is a Layer 3 interface.