Internet Sharing Ubuntu 16.04 – Systemd style

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Checklist:

Setup interfaces

Setup dhcp server

Enable routing

Setup iptables script

Setup service to start iptable script on startup.

 

Install DHCP server

apt install isc-dhcp-server

 

/etc/dhcp/dhcpd.conf

default-lease-time 600;

 max-lease-time 7200;
 log-facility local7;

 allow booting;
 allow bootp;
subnet 192.168.52.0 netmask 255.255.255.0 {
 range 192.168.52.10 192.168.52.30;
 
option broadcast-address 192.168.52.255;
 option routers 192.168.52.1;
option domain-name-servers 8.8.8.8;
 filename "pxelinux.0";

 next-Server 192.168.52.1;
 }

Start service and enable at boot

systemctl start isc-dhcp-server6.service

systemctl enable isc-dhcp-server6.service

 

Test by typing

sudo netstat -uap

 

 

/etc/sysctl.conf

net.ipv4.ip_forward = 1
net.ipv4.conf.default.rp_filter = 1
Restart to take affect.
sudo systemctl restart systemd-sysctl.service

Creating iptable script

/etc/myiptable.sh

#!/bin/bash
iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT ACCEPT
iptables -I INPUT -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
iptables -A INPUT -i wlan0 -j ACCEPT
iptables -A INPUT -i lo -j ACCEPT
iptables -A INPUT -i eth0 -p tcp -m tcp --dport 22 -j ACCEPT
iptables -I FORWARD -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -s 192.168.0.0/24 -i wlan0 -j ACCEPT
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
chmod a+x /etc/myiptable.sh

Create service to start script on bootup:

/etc/systemd/system/mynetwork.service
[Unit]
Description= Internet sharing script to enp17s
After=network.target
[Service]
Type=forking
User=root
ExecStart=/etc/myiptable.sh
[Install]
WantedBy=multi-user.target