What is a secondary address used for?

[Andy White]

Hello,

I have just noticed a secondary IP on one of our WAN routers WAN interfaces, I've never seen a secondary addresses before, what could it's purpose be for?

Thanks

[Edison Ortiz]

Allows you to allocate a secondary subnet. Useful for subnet migration on LAN segments or additional non-contiguous internet subnet blocks on WAN interfaces.

There are other uses but those 2 come to mind.

[Andrew White]

Ah that makes sense as a while back we changed our IP range and I guess the ISP overlapped networks?

We have to change our ASA public IP range soon as we are changing ISP's much means I need to reconfigure all the NATs I wonder if the ASA can do secondary IPs and have some overlap rather than a 'big bang' approach?