8

I want to create a custom table using iptables so that I can add my custom chains in it. But I doesn't see any option to do that. I tried to search for it but didnt found anything. Please Help.

16

I think you are looking for creating a chain, not a table.

   -N, --new-chain chain
          Create a new user-defined chain by the given name.  There must be no target of that name already.

Example (-t filter is implied):

iptables -N Services
iptables -A INPUT -j Services
iptables -A Services -m tcp -p tcp --dport 80 -j ACCEPT

Tables can be selected with the -t option:

iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

And if you are using iptables-restore, the above two rules can be combined to:

*nat
-A POSTROUTING -j MASQUERADE
COMMIT

*filter
:Services -
-A INPUT -j Services
-A Services -m tcp -p tcp --dport 80 -j ACCEPT
COMMIT
  • Thanks for the reply but I'm looking to create a different table for my custom chains. Creating a different table is not possible? – Tarun Jul 6 '13 at 8:26
  • 1
    Why do you want to create a different table? To be able to group your chains? Unless you write your own kernel module, you won't be able to insert new chains. See this picture about the packet flow to understand what the different tables are used for. – Lekensteyn Jul 6 '13 at 12:47
  • Ok I didn't knew that. Thanks for the help. – Tarun Jul 6 '13 at 13:59
5

Creating a table is done at the kernel level; normally there is no need to create a new one unless one is adding to the kernel's TCP/IP capabilities.

What you likely want to do is create a new chain in one of the existing tables, which is done with the -N flag.

  • "normally there is no need to..." - but custom chains make things so much neater. For example adding a custom chain to an interface. – Konrad Gajewski May 25 at 13:06

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