4.1. IPv6-ready kernel

4.1.1. 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:

/proc/net/if_inet6
   

A short automatical test looks like:

# test -f /proc/net/if_inet6 && echo "Running kernel is IPv6 ready"
   

If this fails, it is quite likely, that the IPv6 module is not loaded.

4.1.2. Try to load IPv6 module

You can try to load the IPv6 module executing

# modprobe ipv6
   

If this is successful, this module should be listed, testable with following auto-magically line:

# lsmod |grep -w 'ipv6' && echo "IPv6 module successfully loaded"
   

And the check shown above should now run successfully.

Note: unloading the module is currently not supported and can result, under some circumstances, in a kernel crash.

alias net-pf-10 ipv6  # automatically load IPv6 module on demand
    

alias net-pf-10 off   # disable automatically load of IPv6 module on demand
    

4.1.3. Compile kernel with IPv6 capabilities

If both above shown results were negative and your kernel has no IP6 support, than you have the following options:

• Update your distribution to a current one which supports IPv6 out-of-the-box (recommended for newbies), see here again: IPv6+Linux-Status-Distribution

• Compile a new vanilla kernel (easy, if you know which options you needed)

• Recompile kernel sources given by your Linux distribution (sometimes not so easy)

• Compile a kernel with USAGI extensions

If you decide to compile a kernel, you should have previous experience in kernel compiling and read the Linux Kernel HOWTO.

A mostly up-to-time comparison between vanilla and USAGI extended kernels is available on IPv6+Linux-Status-Kernel.

4.1.4. IPv6-ready network devices

Not all existing network devices have already (or ever) the capability to transport IPv6 packets. A current status can be found at IPv6+Linux-status-kernel.html#transport.

A major issue is that because of the network layer structure of kernel implementation an IPv6 packet isn't really recognized by it's IP header number (6 instead of 4). It's recognized by the protocol number of the Layer 2 transport protocol. Therefore any transport protocol which doesn't use such protocol number cannot dispatch IPv6 packets. Note: the packet is still transported over the link, but on receivers side, the dispatching won't work (you can see this e.g. using tcpdump).