network_namespaces.sh

#!/bin/bash

ip netns del one
ip netns del two
ip netns del three

ip link del name virtual-bridge type bridge

iptables -F POSTROUTING -t nat

ip netns add one
ip netns add two
ip netns add three

ip link add veth-one-in type veth peer name veth-one-out
ip link add veth-two-in type veth peer name veth-two-out
ip link add veth-three-in type veth peer name veth-three-out

ip link set veth-one-in netns one
ip link set veth-two-in netns two
ip link set veth-three-in netns three

ip netns exec one ip addr add 10.0.0.10/24 dev veth-one-in
ip netns exec two ip addr add 10.0.0.20/24 dev veth-two-in
ip netns exec three ip addr add 10.0.0.30/24 dev veth-three-in

ip link add name virtual-bridge type bridge

ip link set veth-one-out master virtual-bridge
ip link set veth-two-out master virtual-bridge
ip link set veth-three-out master virtual-bridge

ip link set virtual-bridge up

ip link set veth-one-out up
ip link set veth-two-out up
ip link set veth-three-out up

ip netns exec one ip link set dev veth-one-in up
ip netns exec two ip link set dev veth-two-in up
ip netns exec three ip link set dev veth-three-in up

ip netns exec one ip link set dev lo up
ip netns exec two ip link set dev lo up
ip netns exec three ip link set dev lo up

ip addr add 10.0.0.1/24 dev virtual-bridge

ip netns exec one ip route add default via 10.0.0.1
ip netns exec two ip route add default via 10.0.0.1
ip netns exec three ip route add default via 10.0.0.1

iptables -t nat -A POSTROUTING -s 10.0.0.0/24 -j MASQUERADE

sysctl -w net.ipv4.ip_forward=1