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debian as a router

Fri Nov 15, 2013 7:31 pm

I am trying to get the feet wet, for the fun only.

Thist how-to is out of date, but easy to follow:
http://users.telenet.be/mydotcom/howto/ ... /linux.htm
This one is more elaborate (mainly on dnsmasq and iptables), but German:
http://wiki.ubuntuusers.de/Router
(there usually is an English version in the according ubuntu wiki too)

Here is my question:
The code block for interfaces :
Code:

   #loopback interface
   auto lo iface lo inet loopback

   # interface external network (internet), configured through dhcp
   auto eth0
   iface eth0 inet dhcp

   #interface network 1
   auto eth1
   iface eth1 inet static
           address 192.168.10.1
           netmask 255.255.255.0
           network 192.168.10.0
           broadcast 192.168.10.255

   #interface network 2
   auto eth2
   iface eth2 inet static
           address 192.168.20.1
           netmask 255.255.0.0
           network 192.168.20.0
           broadcast 192.168.20.255

speaks of 3 interfaces (besides loopback). eth0, eth1 and eth2.
I got it right:
eth0 is to connect the router to the modem and (in this case) to the internet.
eth1 is one internal network connected to the router.
eth2 is a second internal network connected to the router
?

That is:
If i have only 2 network cards, i use eth0 for the internet and eth1 for an internal network, but skip eth2 completely?
(If i had 3 cards i would make an according 4. entry) ?

Any other tips or experiences are welcome too.
I really need the most basic setup (for dnsmasq and iptables), to have something to start with. This will not be used in real life, it is a learning project (little problems in security don't matter right now, those questions come later).
I also need to be more clear about routing (the interfaces has no entry for gateway. How come?).

I did the best i could to explain what i want. If i could explain it better i wouldn't need to ask.
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