IKE extension: exchange-ip-addrv4

This feature allows IKE to inject a custom /32 route on both sides of an IPsec tunnel:

In BGP on loopback design, we use it to provide loopback reachability without the use of additional routing protocols.

It injects the /32 loopback route both over static IPsec tunnels (Spoke-to-Hub) and over dynamic ADVPN shortcuts (Spoke-to-Spoke). As we will show in the Example of route resolution with BGP on loopback, it helps to resolve the advertised BGP routes. (Remember that the BGP NH is the loopback IP of the originating SD-WAN node.)