iptables-translate (II)

Hi all,

This is going to be one another post about the iptables-translate utility. This post is going to cover the importance of this tool and how it can be used to translate different kinds of targets and matches of iptables with examples.
The first translation that I provided was for the match “mark”. For those unfamiliar with iptables, you use this module to match the netfilter mark field associated with a packet.

In iptables, one writes a rule corresponding to this as simply as

# iptables -A FORWARD -m mark --mark 22 -j ACCEPT

However, in nftables, this rule turns out to be even simpler.

# nft add rule ip filter FORWARD mark 0x16 accept

Note that if a table is not specified in the beginning of any rule, the default table is taken to be ‘filter’ in case of iptables. However it is necessary to mention the type (ip, ip6, etc) and the table name in case of nftables.

See how the translation has taken place:

iptables nft
-A add rule
FORWARD ip filter FORWARD
-m mark –mark 22 mark 0x16
ACCEPT accept

Quite simple, right?

Now, see the iptables rule for routing realm. This module matches any given realm number. It is used in complex routing setups involving dynamic routing protocols like BGP.

# iptables -A PREROUTING -m realm --realm 4

Going by the aforementioned procedure, we can easily come up with nftables rule as

# nft add rule ip filter PREROUTING realm 0x4

Easiest stuff ever!
But wait. What is this weird message on my terminal?

c77024

Seems like things aren’t piece of cake. What do we do now? We have no information about routing realm.

People, hold your breaths. Here comes the savior…

iptables-translate

This utility will always come for rescue , I bet.*

*T&C: provided I have completed the translation corresponding to that module

So, now that we have our hero, all we have to do is

$ sudo iptables-translate -A PREROUTING -m realm --realm 4

and then we have on the terminal,

nft add rule ip filter PREROUTING rtclassid 0x4 counter

Try adding this rule to your chain. Congrats! No weird looking errors this time.

[iptables-translate: Oh, come on. There’s no need for claps. No. Seriously.]

So, this is why you are going to need this utility. There is a lot of change in the syntax which is actually better and more understandable but you need to know the exact keywords.

This tool is pretty good and very very easy to use. Try it out and report the bugs if you come across any.

Thanks for reading.

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8 thoughts on “iptables-translate (II)

  1. Hey
    I’m wondering how nft would deal with virtual interfaces, such as the tun (tunnel) that is created with openVPN connections, or ppp that is created with PPTP vpn.
    I find a lot of info about openvpn on a server — however — I’m a workstation. Currently I need to turn off nftables to connect to vpn.

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  2. Hi Shivani, I’ve been sieving through the iptables source code, but I cannot seem to build and/or find “iptables-translate” tool neither on iptables or nftables (searching around, my guess is in iptables/xtables area). Where and/or how can I get this tool (just a brief hint will do such as “make iptables with libXXX”, etc).

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    • Hello!
      iptables has not had a new release since iptables-translate was included, you can clone the git repository (git clone git://git.netfilter.org/iptables) and build from there to use iptables-translate as of now.

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      • Thanks for the reply, though I’ve git-cloned from netfilter.org before I’ve posted/inquired here. I’ve simply did ‘$find . -executable -name “*trans*”‘ (also “ip*”) in hopes to find the executable but to no avail. Compiled it on both Gentoo and Debian (Jessie). Tried different options on configure such as “–enable-devel” as well.

        Here’s a sample output snippets of configure (on Gentoo):
        [code]
        Iptables Configuration:
        IPv4 support: yes
        IPv6 support: yes
        Devel support: yes
        IPQ support: no
        Large file support: yes
        BPF utils support: no
        nfsynproxy util support: no
        nftables support: yes
        connlabel support: no

        Build parameters:
        Put plugins into executable (static): no
        Support plugins via dlopen (shared): yes
        Installation prefix (--prefix): /usr/local
        Xtables extension directory: /usr/local/lib/xtables
        Pkg-config directory: /usr/local/lib/pkgconfig
        Host: x86_64-pc-linux-gnu
        GCC binary: gcc
        [code]

        As you can see, I do have nftables support

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      • It turns out iptables-translate is a soft-link (ln -s) of “xtables-compat-multi” (similar to iptables{-save,-restore} are soft links to xtables-multi). Thanks!!

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  3. Also, I used the iptables-translate-restore -f /etc/iptables.up.rules which had statements like
    -A INPUT -m set –match-set level3 src -j DROP
    and these just got uncommented like this:
    # -t filter -A INPUT -m set –match-set level3 src -j DROP

    Do you know if the translation of a statement like that will be translatable soon?

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