Interface IP in public range, incorrect IP sent to noip

Question

RPi3 is connected to internet via 3G dongle. wwan0 interface IP is in public range, is accessible from outside and hasn't changed since I got the SIM. So far so good, right?

What worries me, is that a probably NAT-ed IP is sent to noip, not the interface one, making the site served by RPi inaccessible, unless the IP is known. Is there a way to send the "correct", wwan0 interface IP to noip?

Second worry is that when RPi will be moved off-site (to measure indoor temp), the dongle will use a different mobile mast and probably the IP of the wwan0 iface will change. My fear is that I will have to do a custom script to notify noip about the interface IP when IP changes or some sort of other notification.

Any feedback is appreciated!

Answer 1

Based on your story, my guess is that your operator has a proxy in place for mobile data speed optimization (something that reduces image sizes for example). This means your HTTP traffic will go through a proxy on the operator side, which could well be NAT'ed.

One way to avoid this is sending an explicit IP to noip (from their documentation):

curl http://username:[e-mail]/nic/update?hostname=mytest.example.com&myip=1.2.3.4

This could easily be integrated into a shell script:

#!/bin/bash

IP=$(/sbin/ip -4 a l wwan0 | grep 'inet ' | grep -oP '(?<=inet\s)\d+(\.\d+){3}')

curl "http://username:[e-mail]/nic/update?hostname=mytest.example.com&myip=${IP}"

Make this script executable and run it from cron every 10 minutes or so:

chmod 755 /home/user/update_noip.sh
crontab -e
# Add:
*/10 * * * * /home/user/update_noip.sh >/dev/null 2>&1