I’ve noticed on a pfSense with an LTE modem that the ppp0 interface has a public IP 2.46.X.Y while the gateway is a private 10.64.A.B, what is this called and how does this work?
Normally the if and gw are on the same network but this is different. The netmask is also a /32 on the if.
That’s ok, look at the routing tables.
PPP is weird if you’re used to LAN and ethernet addressing. There’s only a single IP on the other side, and peers are originally meant to be symmetrical and not really ask for IPs using DHCP - instead, they’d just announce what IPs they have using IPCP and expect the other side to ack.
Then the whole ip address discovery thing was bolted on, so you as a peer can say, “I have 0.0.0.0”, and ISP can say “no you don’t, you have 2.64.x.x”. ISP peer can still say “I have 10.64.64.0” and you’d typically use that as a gateway.
In your routing tables, you’d have a directly attached 10.64.64.0/32 route via ppp0 as well as a 0.0.0.0/0 (default gateway) route via 10.64.64.0/32 .
[well something along those lines anyway … ppp itself is dying … but you might end up having /32 on ethernet interfaces these days instead]
Alright, thanks for enlightening me, this was new info 
