Create A Network Namespace Using a Bypass Gateway

netns.sh

#!/usr/bin/env sh

NAMESPACE=proxy
GATEWAY=172.16.1.15
STATIC_IP= #172.16.1.97/24
DNS_SERVER=172.16.1.1

# check root permission
if [ "$(id -u)" != "0" ]; then
    echo "Please run as root"
    exit 1
fi

# parse current network config
iname=$(ip -o link show | sed -rn '/^[0-9]+: en/{s/.: ([^:]*):.*/\1/p}') # enp34s0

on() {
	# create namespace
	ip netns add $NAMESPACE
	# create macvlan
	ip link add macvlan-$NAMESPACE link $iname type macvlan mode bridge
	# assign macvlan to the namespace
	ip link set macvlan-$NAMESPACE netns $NAMESPACE
	# make resolve.conf
	mkdir -p /etc/netns/$NAMESPACE
	touch /etc/netns/$NAMESPACE/resolv.conf
	# bring up the interfaces
	ip netns exec $NAMESPACE ip link set lo up
	ip netns exec $NAMESPACE ip link set macvlan-$NAMESPACE up
	# set IP address of the macvlan interface
	[ -z "$STATIC_IP" ] && ip netns exec $NAMESPACE dhclient macvlan-$NAMESPACE || ip netns exec $NAMESPACE ip addr add $STATIC_IP dev macvlan-$NAMESPACE
	sleep 1
	# add default route in the namespace
	[ -z "$STATIC_IP" ] && ip netns exec $NAMESPACE ip route del default
	ip netns exec $NAMESPACE ip route add default via $GATEWAY
	# custom dns
	[ -z "$DNS_SERVER" ] || echo "nameserver $DNS_SERVER" > /etc/netns/$NAMESPACE/resolv.conf

	echo "Namespace '$NAMESPACE' created with gateway '$GATEWAY'"
}

off() {
	ip netns del $NAMESPACE
	rm -rf /etc/netns/$NAMESPACE
}


if [ "$1" = "on" ]; then
	on
elif [ "$1" = "off" ]; then
	off
else
	echo -e "Invalid args! \nUsage: netns.sh [on|off]"
	exit 1
fi