Display the Natted / Routed Connections on a Linux Iptable Firewall

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Q. I’ve Linux box acting as software router (natted) for over 100 computer connected via LAN. Regular netstat command is not displaying the list of all natted connections. How do I find out connections managed by netfilter / iptables which comes with the Debian 4.x system?

A. You cannot use regular netstat command to display NAT connections managed by iptables. You need to use netstat-nat command. You can also use /proc/net/ip_conntrack or /proc/net/nf_conntrack, which is the temporary conntrack storage of netfilter.

Install netstat-nat

Use apt-get command under Debian / Ubuntu Linux, enter:
$ sudo apt-get install netstat-nat

Source code / RPM file

If you are using Suse / Redhat Linux, grab source code or RPM file here:

How do I use netstat-nat command?

Login as root user and type the following to display list of all natted connections:
# netstat-nat -n
To display NAT connections with protocol selection, enter:
# netstat-nat -np
To display all connection by source IP called 192.168.1.100
# netstat-nat -s 192.168.1.100
To display all connections by destination IP/hostname called laptop, enter:
# netstat-nat -s laptop
To display SNAT connections, enter:
# netstat-nat -S
To display DNAT connections, enter:
# netstat-nat -D
To display only connections to NAT box self i.e. doesn’t show SNAT & DNAT, enter:
# netstat-nat -L
To display help, enter:
$ netstat-nat -h
$ man netstat-nat

Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin and a trainer for the Linux operating system/Unix shell scripting. He has worked with global clients and in various industries, including IT, education, defense and space research, and the nonprofit sector. Follow him on Twitter, Facebook, Google+.

5 comment

  1. I’ve been using iptstate at home to look at connections, but it’s more like top for network connections through IPTables.

    netstat-nat is a lot more flexible — especially when I have people over who are IMing and surfing all over the place.

    Thanks for the info.

  2. You can use the conntrack command as well (in fedora it is in the conntrack-tools package ).
    It has a nice feature to watch the events in “real-time”…

  3. basura, netstat-nat is outdated crap:

    # netstat-nat
    Could not read info about connections from the kernel, make sure netfilter is enabled in kernel or by modules.
    open(“/proc/net/nf_conntrack”, O_RDONLY) = -1 ENOENT (No such file or directory)

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