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Tuesday, July 31, 2012

Makeshift Mobile IPv6

For all its benefits, IPv6 also has increased support for mobility. This is due to the header structure of IPv6 accommodating extension headers - one of which is a mobility header.

However, given the slow adoption and limited deployment of IPv6, use of the mobility header isn't really prevalent and mobility of IPv6 nodes - my computer in this example - leaves a lot to be desired.

In fact, the only reason I have IPv6 working at home isn't from the forethought of my Internet Service Provider - Comcast, but because I'm tech-savvy and configured a Hurricane Electric 6in4 tunnel through their Tunnel Broker service.

NOTE: Comcast is very far ahead of many ISPs when it comes to IPv6 support including dual-stack support to end customers - unfortunately, just not in my area.

While the HE 6in4 tunnel works fine from my home - terminating on my home router with DD-WRT and providing all equipment in my home network with IPv4/IPv6 support - it doesn't help me when I'm not at home. When I take my computer anywhere - even into the office - I no longer can use IPv6, unless of course the network I connect to has IPv6 deployed (not likely).

My solution albeit not a very elegant one is to use another of the 5 free 6in4 tunnels HE provides me with. The first is for my home network and that stays static. The second one I have configured to a random endpoint which changes based on my location. HE offers a web-based update both manually and via a simple GET URL to change the local endpoint IP address of any of your 6in4 tunnels. The HE server examines the IP address from which it sees your request come from and adjusts the tunnel configuration on the server side. I even wrote a simple batch script to call the HE URL and configure the local tunnel interface on my computer. This works great ...

... but of course there's a catch. HE requires that the local IP address to terminate the tunnel be reachable via Ping. Therefore, if ICMP echo-requests are blocked or echo-replies are not sent, the tunnel won't get built. This is an issue as many sites prevent ICMP for security purposes - in fact, most all home routers disable ICMP from the Internet by default. For my home router, I can change the setting to have the tunnel built, but when I'm travelling, I'm relying on the network to allow ICMP so my mobile IPv6 tunnel can be built. Again, not the most elegant solution.

There are other options. SixXS offers a tunnel broker service and a client AICCU that provides AYIYA (Anything In Anything) support. This may provide a client-based alternative that doesn't rely on a provider network to support IPv6 or ICMP to build a 6in4 tunnel. I may test this next time I'm away.

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