Strange routing issue, may be related to VPN #465
Description
My Environment
Oneplus9 pro Android 14
Unlock root. Run Ubuntu in super administrator mode, ssh remote login.
Problem Brief
After using AnLinux + termux to install Ubuntu, network anomalies occurred after a while. However, everything is normal outside the Ubuntu system (including termux and the Android system).
Connecting to any VPN (enabled on the Android system) resolves the issue. However, the network access speed is very slow.
The problem reappeared after turning off the VPN again.
Specific description of the problem
Installed Ubuntu using AnLinux + Termux.
In the Ubuntu system
Everything was normal at first, but after a while, strange routing issues would occur.
Specifically, it manifests as an error when using curl to access any address: Could not resolve host xxx
For example
curl www.baidu.com
Could not resolve host www.baidu.com
It can be determined that it is not related to a specific domain name, as accessing any domain name is the same.
Connecting to any VPN on the Android system will restore normal access, but the access speed is noticeably slow
Problem Troubleshooting
Install iproute2.
Comparison of IP router with and without VPN
apt install iproute2
When there is a VPN
root@localhost:~# ip route
26.26.26.0/30 dev tun0 proto kernel scope link src 26.26.26.1
192.168.31.0/24 dev wlan0 proto kernel scope link src 192.168.31.230
Without VPN
root@localhost:~# ip route
192.168.31.0/24 dev wlan0 proto kernel scope link src 192.168.31.230
Based on this result, ChatGPT suggests that I execute
ip route add default via 192.168.31.1
The IP 192.168.31.1 is my home router.
The problem has been solved.
Problem Impact
Although ip route add default via 192.168.31.1 can solve the problem, I cannot keep adding this route manually.
How else can I continue to investigate this issue?