I have a Ubuntu linux server that has 1 main and 5 other network interfaces.
I’m trying to setup a proxy server using 3proxy.
My issue is I cannot use internet connection when I specify internal server as main ip and external as one of those other 5 network interfaces.
I tried to use same setup on Windows and it works.
Im using netplan to configure network interfaces and I did set the metric low for main and higher for other network interfaces.
I currently can fix the problem by changing metric to be lower for that external ip network interface but this is not a healthy solution since I cannot use the internet connection of the main network interface anymore.
Any suggestions?
My config.cfg file:

system "echo Proxy is running!"

nserver 1.1.1.1
nserver 1.0.0.1

nscache 65536

timeouts 1 5 30 60 180 1800 15 60

#My other external network interface ip.
external 192.168.2.100 

#My main network interface ip
internal 192.168.0.1

log ./logs/3proxy.log D
logformat "- +_L%t.%. %N.%p %E %U %C:%c %R:%r %O %I %h %T"

rotate 365

auth none

deny * * 127.0.0.0/8
deny * * 192.168.0.0/8
allow * * * 80-88,8080-8088 HTTP
allow * * * 443,8443 HTTPS

proxy -n -p3128 -a

flush
auth iponly strong cache
allow * * 127.0.0.0/8
allow admin * 10.0.0.0/8
admin

I have tried to change metric and it works but I need more elegant solution.