We ran out of public IP addresses on our site where we map public IP addresses to services on internal servers via MIPs.

When we received more IP addresses in a different subnet I could not easily figure out how to use them until I ran across an article on the Juniper support site.

The solution was really simple:

1. Add a routing entry for the new subnet on the external interface (ethernet1) with “0.0.0.0″ as gateway
   Network -> Routing -> Destination -> New
2. Add MIPs using addresses in the new IP subnet

How simple and it works great!