Debian Setup als Router

eth0 = WAN eth1 = LAN

1. Open a new Putty Terminal and connect to server
2. Enter following command to edit interfaces file:

   # vim /etc/network/interfaces

3. Edit the file with the following lines: (add your netmask and gateway)

   /etc/network/interfaces

   auto lo 
   iface lo inet loopback
    
   auto eth0
   iface eth0 inet dhcp
    
   auto eth1
   iface eth1 inet static 
   address 172.168.1.1
   netmask 255.255.255.0

4. Now edit /etc/sysctl.conf and uncomment:

   # net.ipv4.ip_forward=1>

   so that it reads: net.ipv4.ip_forward=1

   and save it by entering

   :wq

5. To enable IP masquerading, enter following set of commands in terminal:

   # iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
   # iptables -A FORWARD -i eth1 -o eth0 -m state --state RELATED,ESTABLISHED -j ACCEPT
   # iptables -A FORWARD -i eth1 -o eth0 -j ACCEPT 

Update: Fix strange “-–state” causing command to fail and fix nat MASQUERADE to eth0 (wan interface)

# apt‐get install iptables‐persistent
# iptables-save > /etc/iptables/rules.v4

https://askubuntu.com/questions/590920/ubuntu-14-04-as-a-gateway-router-and-a-firewall

Bessere Lösung → https://gridscale.io/community/knowledgebase/tutorial-debian-routergateway-in-10-minuten/

Tutorial_ Debian Router_Gateway in 10 Minuten einrichten