Wireguard uses incorrect interface - routing issue

[Nico Schottelius]

Diyaa,

this is about the *outside* tunnel IP address that wireguard uses to
establish connection, not about inside routing.

BR,

Nico


Diyaa Alkanakre <diyaa at diyaa.ca> writes:

> 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
>>
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