Network

Source based routing

Tested on Debian 12

If your host have more than one NIC (in different nets), you maybe want to specify which traffic goes to which NIC. One use-case is, that you have a docker host, which should be accessible via NIC-1 (primary net) and the docker service should be accessible via another NIC-2 (secondary net). Therfore you have to create routing information for the traffic coming from the docker service.

(Ref: 1, 2, 3, 4)

Create a new table for the secondary net:
```
sudo nano /etc/iproute2/rt_tables
```
add at the end of this file:

Note: 200 must be a positive int and dmz can be any name you want
```
200    dmz
```

Create if-up script to make the routing information persistent (create routing information at every boot)

sudo nano /etc/network/if-up.d/docker_services_dmz

With the following content:

Note: enp6s19 is the NIC-2, 172.18.0.0/16 the docker service net and 10.0.0.1 the gateway from secondary net

#!/bin/sh

if [ "$IFACE" = "enp6s19" ]; then
    ip rule add from 172.18.0.0/16 table dmz
    ip route add default via 10.0.0.1 dev enp6s19 table dmz
fi

Make this script executable:

sudo chmod +x /etc/network/if-up.d/docker_services_dmz

Reboot or restart networking.service with sudo systemctl restart networking.service