Comcast enables 6to4 relays

Jack Bates jbates at
Tue Aug 31 13:09:06 UTC 2010

Mikael Abrahamsson wrote:
> End users are using 6to4 and Teredo, if an ISP isn't providing their own 
> relays, someone else is and the performance might be good or bad.
Teredo usage isn't common enough on our network to warrant the work. 
Very few apps will activate it is my guess.

> Same logic applies to Teredo as to 6to4 and why if you're an ISP who 
> cares, you should run your own. Your customers are using both, whether 
> they know it or not.

A customer is more likely (not always) to know when teredo has been 
activated. I've considered putting it in, but it is not friendly in many 
ways. 6to4 is usually running on routers in various pops. Teredo, I'd 
have to back feed to a server farm. This doesn't make for ideal traffic 
patterns even with bandwidth being so low.

Then there is the "customer is unaware" fact. If the customer is unaware 
that their NAT is being pierced for IPv6 communication, then we have 
contributed to decreasing their security. For this reason, it might not 
be completely unwarranted for an ISP to block teredo all together. 6to4 
doesn't suffer from this as there is no NAT traversal.


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