Wireguard uses incorrect interface - routing issue

[Diyaa Alkanakre]

The better approach would be to exclude the IPs from your WireGuard AllowedIPs. I always exclude IPs if I can before doing policy based routing.

https://www.procustodibus.com/blog/2021/03/wireguard-allowedips-calculator/


Jun 21, 2024, 5:15 AM by nico.schottelius at ungleich.ch:

>
> Hello again,
>
> I'm sorry to flood the mailing list with wireguard bugs, but it seems
> there is yet another routing bug in wireguard - happy to be wrong, but
> here are my findings:
>
> a) system has source based routing on via ip rule:
>
> [11:07] server141.place10:~# ip rule ls
> 0:      from all lookup local
> 32765:  from 192.168.1.0/24 lookup 42
> 32766:  from all lookup main
> 32767:  from all lookup default
> [11:07] server141.place10:~# ip route sh table 42
> 194.5.220.0/24 via 192.168.1.254 dev eth1 proto bird metric 32 
> 194.187.90.23 via 192.168.1.254 dev eth1 proto bird metric 32 
> 212.103.65.231 via 192.168.1.254 dev eth1 proto bird metric 32 
> [11:08] server141.place10:~# 
>
> This should ensure that packets towards 194.187.90.23 travel via eth1.
>
> b) tcpdump for verification
>
> Using "tcpdump -ni any port 4000" I observe:
>
> 11:10:22.445638 eth0  Out IP 192.168.1.149.58591 > 194.187.90.23.4000: UDP, length 148
> 11:10:27.447026 eth0  Out IP 192.168.1.149.58591 > 194.187.90.23.4000: UDP, length 148
> 11:10:32.448329 eth0  Out IP 192.168.1.149.58591 > 194.187.90.23.4000: UDP, length 148
> 11:10:37.449719 eth0  Out IP 192.168.1.149.58591 > 194.187.90.23.4000: UDP, length 148
>
> c) Route in main table
>
> There is indeed a route in the main routing table that matches, too:
>
> [11:08] server141.place10:~# ip r get 194.187.90.23
> 194.187.90.23 via 10.5.2.123 dev eth0 src 192.168.1.149 uid 0 
>  cache 
>
> d) ip rule not working (?)
>
> So from what I can observe it is that ip rule does not work together
> with wireguard / wireguard routing takes the route from main fib instead
> of from the separate table.
>
> I am not sure if this is related at all to the IP address binding bug,
> but it appears in a similar context from our tests.
>
> BR,
>
> Nico
>
> -- 
> Sustainable and modern Infrastructures by ungleich.ch
>