udp2raw masked site-to-site tunnel and cloudfare warp

[TomHsiung]

192.168.0.0/24 (sun) === 0.0.0.0/0 (moon) tunnel works no matter cloudflare warp (via wireguard) is up or down.

192.168.1.0/24 (sun) > udp2raw (client) === fake tcp === udp2raw (server) < 0.0.0.0/0 (moon) only works if cloudflare warp (vai wireguard) is up.

ip route get 192.168.1.35 when warp is down

192.168.1.35 dev lo table 220 src public.ip.x.x uid 1000
cache

and

4 packets transmitted, 0 received, 100% packet loss, time xxxxxms

ip route get 192.168.1.35 when warp is up

192.168.1.35 via public.gateway.x.x dev eth1 src private.ip.x.x uid 1000
cache

and

2 packets transmitted, 2 received, 0% packet loss, time xxxxxms

Finally, the tricky is this, which solved the problem.

ip rule add pref 100 lookup main suppress_prefixlength 0

Actually, the wg-quick up syntax has a line:

[#] ip -4 rule add table main suppress_prefixlength 0

I think this case is interesting and I want to understand the logic behind. However, it's a little complex for me. Thanks.