Comcast enables 6to4 relays

John Jason Brzozowski john_brzozowski at
Sun Aug 29 17:27:05 UTC 2010

Before we turned up our own relays the closest 6to4 relay was a single relay
hosted by a mid-western university.  Regardless where the next closest
relays are located deploying our own resulted in improvements (as you
pointed out below).


On 8/29/10 12:24 PM, "Joel Jaeggli" <joelja at> wrote:

> On 8/29/10 6:25 AM, John Jason Brzozowski wrote:
>> Franck,
>> As you know 6to4 is enabled by default in many cases and is used perhaps
>> more than folks realize.  Because of this and other observations we decided
>> to deploy our own relays.
> Right prior to this the nearest 6to4 relay router from the vantage-point
> of comcast customers was at AMSIX. It's a given that you're going to
> have path asymmetry, in this case however it was frequently worse in one
> direction than in the other.
> This ought greatly improve the performance of existing devices located
> at comcast's customers.
>> This does not alter our plans for our native dual stack trials, in fact, I
>> hope to have more news on this front soon.
>> It is true that 6to4 has challenges, some of these may be related to how
>> 6to4 relays have been deployed.  Others may be related to the protocol
>> itself.  Either way, by deploying our own we observed an improvement, we
>> hope others have as well.
>> John
>> On 8/28/10 6:06 PM, "Franck Martin" <franck at> wrote:
>>> 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:
>>> nt
>>> s_of_IPv6_Path_MTU_Discovery_Behaviour.pdf
>>> 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.
>> =========================================
>> John Jason Brzozowski
>> Comcast Cable
>> e) mailto:john_brzozowski at
>> o) 609-377-6594
>> m) 484-962-0060
>> w)
>> =========================================

John Jason Brzozowski
Comcast Cable
e) mailto:john_brzozowski at
o) 609-377-6594
m) 484-962-0060

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