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How To Test Linux Operating System for IPv6 Networking Support

Q. Before I can start using IPv6 on a Linux server, how do I test, whether my Linux server system is IPv6 ready or not? If not, how do I enable IPv6 support under Redhat Enterprise Linux version 5?

A. Linux kernel has IPv6 support since 1996. All you need to do is compile kernel with IPv6 networking support. However, there is easy way to find out if Linux kernel compiled with IPv6 or not.

Task: Check for IPv6 support in the current running kernel

To check, whether your current running kernel supports IPv6, take a look into your /proc-file-system. Following entry must exists:
$ cat /proc/net/if_inet6

00000000000000000000000000000001 01 80 10 80       lo
fe8000000000000002179afffe0af644 03 40 20 80      ra0
fe800000000000000219d1fffe2abaa8 02 40 20 80     eth0

IPv6 protocol stack for Linux via ipv6 module - Turn on IPv6 Support

ipv6 module has IPv6 protocol stack for Linux. If above cat command fails, it is quite likely, that the IPv6 module is not loaded. Just login as root and type the following command, enter:
# modprobe ipv6
Now test again, enter:
$ lsmod | grep ipv6

ipv6                  411425  18

Try following simple shell conditional code to display human readable output, enter:
$ [ -f /proc/net/if_inet6 ] && echo 'IPv6 ready system!' || echo 'No IPv6 support found! Compile the kernel!!'

IPv6 ready system!

Further readings:

{ 7 comments… add one }

  • blink4blog July 9, 2008, 2:37 am

    The last bash run have this output:

    bash: !": event not found

  • nixCraft July 9, 2008, 4:22 am


    The faq has been updated, it was a typo on my part. Try again and let me know..

  • blink4blog July 9, 2008, 5:28 am

    yeah its working now. thanks

  • fabio October 18, 2010, 4:50 am

    I’ve had the T400s for >1y, amazing keyboard, and 1.8kg
    you won’t play games on it, but man is it nice to type on.
    i am getting a Thinkpad T60…
    it’s free :) it’s either yes or no ;)
    no choice on the model
    one of those t60 pre Lenovo
    no need to play games other than chess/freecell or alike ;)
    might even install Windows 7 on it
    or something weird
    i need something weird for a change
    maybe FreeBSD
    at least I can use it to port kronosnet
    so far the major obstacle of sparc is done :)
    win7 might be too slow
    i was kidding about W7 :)
    need something unix like to travel
    either BSD or Debian or Fedora rawhide
    haven’t made up my mind yet
    want something bleeding edge
    Debian SID + experimental
    there is a difference between bleeding edge and pure idiocy :)
    ubuntu lands in the latter
    i am very disappointed with how one of my childred did grow
    and I am really sorry about it
    but Ubuntu is not going near any of my machines
    I guess I shouldn’t tell you what my daily OS is then. ;)
    <- ex. Canonical employee and founder
    i loved ubuntu, I gave it birth. i don’t like what is it turning into
    ever heard of the Super Secret Debian Startup? :)
    when Canonical was born, before it was even called CAnonical and Ubuntu was only a rumor on the internet (without a name)
    i was there :)
    that “entity” was called SSDS
    because all of a sudden, there were about 10 debian developers connecting from Mark’s house at the same time ;)
    the first 10 employees in Canonical
    people did notice and called us SSDS :)
    fun times
    the very first Warty Warthogs installation was done in Brazil, by me, on MArk’s laptop
    at some DEbConf 3 or 4.. can’t remember
    so what don’t you like about how it developed, if I may ask?
    quality has gone down a lot
    it used to be decently tested
    ah, that I can attest to.
    now it’s a hack after another
    10.04 was great, but I’ve had a few problems with 10.10. It feels rushed.
    not enough to roll back
    well the release after an LTS is always to avoid
    it’s the one where they push all the crack in one go
    but also, the last 2 LTS were really bad
    tons of unnoticed bugs
    basic stuff that should never break
    (speaking from a server side perspective)
    nfs mounts from fstab -> broken
    * sdake has quit (Ping timeout: 250 seconds)
    kernel FS corruption -> unfixed
    ah, I’d never consider ubuntu for server. ever
    on my laptop though, I must say that I like it.
    you’re right though, it’s not stable
    well I used to be server team leader for Dapper
    so yeah.. i have been using it on server and it did perform well for sometime
    but even on desktop, I run a Mythtv bunch of machines
    -> FS corruption in some conditions, still unfixed
    because they pushed some setups to an extreme
    time to get ready.. kids are about to wake up
    later :)
    but I am sorry to see it going downhill
    it’s still something I really enjoed to do for > 5 year

  • Nils Breunese September 26, 2011, 2:46 pm

    I have CentOS 5 systems with the ipv6 kernel module loaded, but /proc/net/if_inet6 doesn’t exist. I guess checking for /proc/net/if_inet6 isn’t a failsafe test?

    • Nishanth May 2, 2012, 2:48 pm

      Are you able to configure ipv6 on the interfaces?
      The module may be loaded with options ipv6 disable=1, disabling ipv6 support. Remove this option in your modprobe.conf, unload and load the module, then check whether /proc/net/if_inet6 exists.

  • Nisarg Shah June 10, 2014, 7:23 pm

    Thanks for the article. The last resort worked for me.

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