WWAN if public ip but gateway private

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”, and ISP can say “no you don’t, you have 2.64.x.x”. ISP peer can still say “I have” and you’d typically use that as a gateway.

In your routing tables, you’d have a directly attached route via ppp0 as well as a (default gateway) route via .

[well something along those lines anyway … ppp itself is dying … but you might end up having /32 on ethernet interfaces these days instead]

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Alright, thanks for enlightening me, this was new info :slight_smile: