Docker Container Traffic Not Routing Through VPN Tunnel: Routing and IP Rules Issue

I’m trying to route traffic from a Docker container through a VPN tunnel on my Ubuntu server, but I'm encountering issues with routing. Here’s the setup and what I’ve tried so far:

Setup:

• Docker Container IP Address:172.20.0.2

• Docker Custom Bridge Network Subnet:172.20.0.0/16

• VPN Interface:vti1

• VPN Local IP Address:192.168.200.1

• VPN Peer IP Address:10.129.20.2

• Default Route:default via 142.93.128.1 dev eth0

• Routing Table vpn:default via 192.168.200.1 dev vti1

Current Routing and IP Rules:

$ ip route show

default via 192.168.200.1 dev vti1172.20.0.0/16 via 192.168.200.1 dev vti1root@dockeronubuntu2204-s-1vcpu-1gb-ams3-01:~# ip route showdefault via 142.93.128.1 dev eth0 proto static10.18.0.0/16 dev eth0 proto kernel scope link src 10.18.0.510.110.0.0/20 dev eth1 proto kernel scope link src 10.110.0.210.129.20.0/27 dev vti1 scope link142.93.128.0/20 dev eth0 proto kernel scope link src 142.93.141.70172.17.0.0/16 dev docker0 proto kernel scope link src 172.17.0.1172.18.0.0/16 dev br-db5a54d34c53 proto kernel scope link src 172.18.0.1 linkdown172.20.0.0/16 dev br-60ce34a14131 proto kernel scope link src 172.20.0.1192.168.200.0/24 via 192.168.200.1 dev vti1

$ ip route show table vpn

default via 192.168.200.1 dev vti1172.20.0.0/16 via 192.168.200.1 dev vti1

$ ip rule show

0:      from all lookup local216:    from 172.20.0.0/16 lookup vpn217:    from 172.18.0.0/16 lookup vpn218:    from 192.168.96.0/20 lookup vpn220:    from all lookup 22032766:  from all lookup main 32767:  from all lookup default

ip addr show vti1 gives:

18: vti1@NONE: <POINTOPOINT,NOARP,UP,LOWER_UP> mtu 1480 qdisc noqueue state UNKNOWN group default qlen 1000    link/ipip 192.168.200.1 peer 10.129.20.2    inet 192.168.200.1/24 scope global vti1       valid_lft forever preferred_lft forever    inet 192.168.200.2/24 scope global secondary vti1       valid_lft forever preferred_lft forever    inet6 fe80::5efe:c0a8:c801/64 scope link       valid_lft forever preferred_lft forever

Issue: When I attempt to ping 192.168.200.1 from the container with IP 172.20.0.2, the traffic doesn’t seem to be routing through the VPN, I checked using tcpdump -i vti1. On the other hand, trying to ping 192.168.200.0, I do see the traffic going through vti1, and the ping returns: From 192.168.200.1 icmp_seq=1 Destination Host Unreachable.

Does anyone know what I am missing? It seems to me that the vpn interface is not properly configured to handle traffic through 192.168.200.0/24, although I am very new into IT and do not know where to look anymore to solve the problem.

Additional Information:

• I’m using Ubuntu 22.04 on the server.

• The Docker container is connected to a custom bridge network.