Wireguard uses incorrect interface - routing issue

[Nico Schottelius <nico.schottelius@ungleich.ch>]

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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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