Comcast's 6to4 Relays

Owen DeLong owen at
Wed Apr 20 20:41:51 UTC 2011

Sent from my iPad

On Apr 20, 2011, at 4:09 PM, Doug Barton <dougb at> wrote:

> On 04/20/2011 12:50, Owen DeLong wrote:
>> Turnning off the servers will not reduce the brokenness of 6to4, it will increase it.
> Depends on your definitions of "increase" and "broken." If all the relays disappeared tomorrow then the failure rate would be 100%, sure. But that would mean a single, (more or less) instant, deterministic failure that any modern OS ought to be able to handle intelligently; rather than the myriad of ways that 6to4 can half-succeed now. To me, that's a win.
Uh, no. It would, indeed, be a single deterministic failure. However, most OS are coded that if there isn't native, they'll try 6to4 if it's turned on. Many OS have it turned on by default.
As such, it would simply be a 100% failure, not one that was automatically dealt with in a
rational or useful manner. It would require manual intervention on a large number of hosts.

To me, that's not a win. That's a loss.

The success rate for 6to4 today in most environments is close to 90%. There are many environments in widespread use today (hotel networks and airports come to mind) where IPv4 does not enjoy that level of success.


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