Comcast enables 6to4 relays

John Jason Brzozowski john_brzozowski at
Sat Aug 28 17:49:30 UTC 2010

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.

In most cases, we observed that 6to4-enabled operating systems and devices
were attempting to use a 6to4 relay infrastructure hosted by a midwestern
university. In order to improve the Internet experience for Comcast
customers who are using 6to4, whether knowingly or not, we have decided to
operate 6to4 relays on a temporary, trial basis.

Comcast has decided to deploy 6to4 relays in five locations around our
network to improve performance and predictability, as compared to operating
relays from a single location. These 6to4 relays are available via the
standard 6to4 Anycast IP address, according to RFC 3068, which is Devices attempting to use 6to4 within our network should
automatically discover and utilize these new 6to4 relays, without end user
intervention or configuration.

The first pair of these relays was activated today. We plan to activate the
remaining three within the next seven to ten days. We plan to monitor the
performance of the 6to4 relays, to measure any beneficial effects resulting
from adding these elements to our network. As our IPv6 trials evolve and we
develop our plans for 2011 and beyond, we will assess our plans to support
6to4 moving forward.

John Jason Brzozowski
Comcast Cable
e) mailto:john_brzozowski at

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