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Useful iptables Information

Many a nerd has written an article or two about iptables but I thought I would write a few pages, I don't want to feel left out.

iptables will increase your network security!

You remember Mr McKittrick and Paul, I think, from WarGames? Unfortunately I cannot take the credit for this cool idea... it was on a blog by dediserve that is not available anymore. I thought it would be a shame to lose this masterpiece so I recreated it :-).

Visualising the IP filtering mechanism

This diagram is just fantastic to help you diagnose problems and create your rules. I do not know who created it but it is in one of the Linux documentation project documents I think, if I find a link I will put it here.

really useful chart

Interacting with iptables

The iptables command is how we interact with IPv4 iptables. To look at rules for IPv6 iptables (if you have the tool installed and your kernel has IPv6 support) the command is ip6tables.

gre and iptables

I use a Raspberry Pi for routing some traffic and I wanted to get my PPTP VPN for work working over the Raspberry Pi router. This took me longer than I thought because GRE packets are not handled like I thought they would be. Anyway to get this working one must add the MASQUERADE match as you would normally:

Chain POSTROUTING
  432691 28991316 MASQUERADE  all  --  *      ppp0    0.0.0.0/0            0.0.0.0/0

And load some modules into your kernel:

Module                  Size  Used by
nf_nat_pptp             2444  0
nf_nat_proto_gre        1311  1 nf_nat_pptp
nf_conntrack_pptp       4172  1 nf_nat_pptp
nf_conntrack_proto_gre     3803  1 nf_conntrack_pptp
ip_gre                 10648  0
gre                     1633  1 ip_gre
ip_tunnel              13258  1 ip_gre

I don't know if you actually need ALL those modules but nf_conntrack_proto_gre looks quite important!

Lazy Ben...

Until I have some time to update this page, please see an interesting article on the same thing (or similar) for routing a specific user's traffic via a dedicated routing table on my Freenet Routing Fu page.

Useful iptables commands

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