The PhoneBoy Blog


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Your ISP May be Trialing IPv6 Already!

I’ve been playing with IPv6 a bit on my home network and experimenting with different access methods. While I love the folks at Hurricane Electric and their Tunnel Broker service, it turns out that both Comcast and CenturyLink (I use both of them) are already providing 6to4 Anycast relay service using the 192.88.99.1 address! It’s not native IPv6 yet–Comcast is trialing dual-stack IPv4 and IPv6 in a few areas as well as other access methods per their Comcast IPv6 Information Center–but I feel somewhat better using a service my ISP is using.

The way it works is pretty simple: the IPv6 prefix 2002::/16 is allocated specifically to 6to4 tunneling. If you set up a tunnel to 192.88.99.1 (which is an anycast IP address), you will be able to use 2002:xxxx:xxxx/48 as IP address space (where xxxx is your public IPv4 address in hex). So for example if your public IPv4 IP is 192.0.2.240, you will have 2002:c000:02f0::/48 as publicly routable IP address space!

I found a great site that explains how to configure this kind of 6to4 tunnel on various operating systems. It tells you what your current IP is and tells you how to configure the tunnel based on that IP. You can also specify an IP to use.

Using this, I experimented with both Comcast and CenturyLink and found CenturyLink’s 6to4 relay to have significantly lower latency. I also discovered, from traceroutes, that CenturyLink appears to be using a 6to4 relay at Hurricane Electric!

The nice thing about this is that you don’t have to sign up for account or anything. You just configure it properly and it works. With a /48 all to yourself.

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