10-wired.network

[Match]
Name=eth0

[Network]
Address=10.20.30.40/24
Address=10.20.30.135/24
Gateway=10.20.30.1
DNS=10.20.30.1
From=10.20.30.40

jailtransmission.sh

#!/usr/bin/env sh
# add the ip
# handled by systemd-networkd
# ip addr add 10.20.30.135/24 dev eth0

# change the default route to include standard src ip
# handled by systemd-networkd
# ip route change default via 10.20.30.1 src 10.20.30.40

# Create a new routing table 100 with other src ip
ip route add default via 10.20.30.1 src 10.20.30.135 table 100
ip route list table 100

# Make mark 33 use table 100
ip rule add fwmark 33 table 100

# Mark transmissions outgoing packets with 33
iptables -A OUTPUT -m cgroup --path /system.slice/transmission.service -j MARK --set-mark 33