Comcast enables 6to4 relays

Franck Martin franck at
Sat Aug 28 22:06:32 UTC 2010

These are good news.

However, if Comcast provides native IPv6 to their customers, then the IPv6 native customers don't need these 6to4 relays?

Airport Extreme, Linksys and other user equipment, enable IPv6 by doing 6to4 tunnels, so what this press release says, is that there are many users who are already on IPv6 via Comcast network but not native? Providing relays close to them, is a good transition move. Alternatively, the measurement of this 6to4 bandwidth on IPv4 may give you an idea of the demand for IPv6 from your customers? May be you detected a non null number here?

I'm just trying to understand more IPv6 by the examples.

I'm personally using 6to4 at home, and experiencing some MTU issues, which seems related to some PTB packets suppressed on the way between some end points, and that can depend on which 6to4 relay I'm using. Still trying to debug this (I'm not too fanatic about it, but work on it when I have a bit of time). I thought I would mention that.
The WAND people have done some good studies:

At the office, I have a more classical tunnel with and do not have any issue there.

----- Original Message -----
From: "John Jason Brzozowski" <john_brzozowski at>
To: "NANOG" <nanog at>
Sent: Sunday, 29 August, 2010 5:49:30 AM
Subject: Comcast enables 6to4 relays

FYI - thought this would be of interest to some of you, there will be more
news on this front shortly.

6to4 Relays Activated
Tuesday, August 17, 2010

As we started our IPv6 trials, we began to observe an increase in 6to4 relay
traffic. 6to4 is a transition mechanism built into some operating systems
and home gateways. While it is not a transition technology that Comcast
planned to invest in due to limitations related to performance, we did
observe poor performance when 6to4 was used by our customers. In many cases,
these customers were not even aware that 6to4 was enabled by default or that
their device or operating system was attempting to use 6to4 to communicate
with IPv6 resources on the Internet.

More information about the NANOG mailing list