#!/bin/bash

ip link add name hv type bridge
ip addr add 192.168.200.1/24 dev hv
ip addr add 192.168.100.1/24 dev hv
ip link set hv up

sysctl -w net.ipv4.ip_forward=1

iptables-save | grep -q -- '-A POSTROUTING -o hv -j MASQUERADE' && exit 0

iptables-restore <<EOF
*mangle
:PREROUTING ACCEPT [:]
:INPUT ACCEPT [:]
:FORWARD ACCEPT [:]
:OUTPUT ACCEPT [:]
:POSTROUTING ACCEPT [:]
COMMIT
*nat
:PREROUTING ACCEPT [:]
:INPUT ACCEPT [:]
:OUTPUT ACCEPT [:]
:POSTROUTING ACCEPT [:]
-A POSTROUTING -o hv -j MASQUERADE
COMMIT
*filter
:INPUT ACCEPT [:]
:FORWARD ACCEPT [:]
:OUTPUT ACCEPT [:]
COMMIT
EOF