We have some networking issue on a Raspberry Pi and a 4G dongle. The same buildroot image on other Raspberry Pi with another 4G dongle is working fine. However on this Raspberry Pi + dongle setup:
- PPP can establish connection and create a ppp0 interface
- Can ping 8.8.8.8
- When ping google.com, it can find IP address, but ping cannot go through, with 100% failure.
- Directly ping the found google.com IP also failed. Tried other domain names and IP as well. Internet like HTTP are also not working.
- In /etc/resolv.conf, the nameserver looks correct, it is in same network as the ppp0 IP assigned by ISP. Anyway if the "ping google.com" can find IP address, I think the DNS is working fine.
- routing table is also correct, there is only ppp0 routes in the table.
My question is, what could be the root cause of this issue and how to solve it? Or what test do you suggest for me to identify the root cause? Thanks!
It terms out that the APN we use is a Shared Internet APN rather than a public APN, which means The service provider only whitelists some IP addresses for us to access with this APN.