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22336 posts

Uber Geek


# 41968 26-Sep-2009 16:37
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need to get something on my firewall machine that is between my lan and my flatmates.

3 active nics in it now, one to the adsl router, one to my PC's, one to my flatmates lan.

Its the default gateway for my lan, and is natting everything to the adsl router as that is the degault gateway.

I need it to just route between my network and the flatmates, a static route willbe made on his machines to my machine

eth0  - my internal lan

eth2 - my adsl router
gateway is (my adsl router)

eth3 - on flatmates lan -

no gateway or all my traffic goes on his internet.

I have a file from iptables-save that I pipe to iptables-resore

# Generated by iptables-save v1.2.11 on Tue May 16 22:13:55 2006
:PREROUTING ACCEPT [67917:13329159]
:OUTPUT ACCEPT [12676:1026290]

:PREROUTING ACCEPT [3927:262748]
:OUTPUT ACCEPT [158:10907]

(whole heap of portfowards)


# Completed on Tue May 16 22:13:55 2006
# Generated by iptables-save v1.2.11 on Tue May 16 22:13:55 2006
:PREROUTING ACCEPT [67918:13329251]
:INPUT ACCEPT [12931:2572624]
:FORWARD ACCEPT [54977:10755022]
:OUTPUT ACCEPT [12676:1026290]
:POSTROUTING ACCEPT [67653:11781312]
# Completed on Tue May 16 22:13:55 2006
# Generated by iptables-save v1.2.11 on Tue May 16 22:13:55 2006
:INPUT ACCEPT [12931:2572624]
:FORWARD ACCEPT [54977:10755022]
:OUTPUT ACCEPT [12676:1026290]
# Completed on Tue May 16 22:13:55 2006

Im assuming that I need to change the line in bold to something else or put something ahead of it to say not to nat stuff to the range, but am not sure what exactly.


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7 posts

Wannabe Geek

  # 259263 29-Sep-2009 09:01

-A POSTROUTING -s -d ! -j MASQUERADE -o eth2
-A FORWARD -i eth0 -o eth3 -s -d -j ACCEPT

I'm far from an expert but does this work? (Replacing the line in bold)

894 posts

Ultimate Geek


  # 259907 30-Sep-2009 22:43
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How did you go with this? I'm not much of a fan of iptables-save/restore.  Prefer to see rules through iptables -L and setting them up in scripts.

One thing to make sure is you have enabled ip_forwarding otherwise traffic from one lan, destined for another will not be forwarded regardless of rules.

I've made a very basic quick firewall script you may be able to use if you want. Completely untested so your mileage may vary :)

Also if your linux box is the default gateway for all machines on either network, then there is no need for static routes :) as each pc will send data to the linux box as the default gateway which then will forward to the correct network.


22336 posts

Uber Geek


  # 263179 10-Oct-2009 21:49
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I finally got around to trying that, it failes on line 63 which is

-A FORWARD -i eth0 -o eth3 -s -d -j ACCEPT

Seems to be happy with this lot however and it seems to do what I want, havent checked that there is no internet access from the flatmates side yet.



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