Comcast enables 6to4 relays

John Jason Brzozowski john_brzozowski at
Mon Aug 30 22:17:38 UTC 2010

I actually agree with the below.  Using whatever you learn "today" via BGP
does not appear to be a good plan.  6to4 in particular becomes very
unpredictable and does in fact contribute to brokenness.  I am not saying
deploying your own will make 6to4 good or great, it will however, help to
make it less broken and more controllable.

If operators deployed their own it would likely be beneficial to their
subscribers, particularly if there is a lot of 6to4.

I would also go out on a limb and say that absent and poorly deployed 6to4
relays collectively play hugely into the perception of brokenness.

There was a noticeable difference deploying our own 6to4 relays compared to
using the next or first available.  I am not saying the other relay was
poorly run, just saying it is different having one on-net versus off-net.


On 8/30/10 5:44 PM, "Jack Bates" <jbates at> wrote:

> Franck Martin wrote:
>> Is there a list of 6to4 relays?
>> I'm curious.
>> Also, I'm also curious to know if ISPs in Europe (which are more advanced in
>> IPv6 deployment) have experienced the same issues?
> Sprint has one which is absolutely horrible (or was a year or two ago).
> I'd recommend any and every ISP to setup a 6to4, even if it runs over a
> v6 tunnel to HE. Accidentally getting one from someone else can give you
> exceptionally broken 6to4 connectivity. Being anycast, I'd say
> routeviews might be a good place to check for some, but often times they
> are hidden within the networks they serve.
> That being said, 6to4 itself is often horrible. It works fine if you are
> talking 6to4 direct to the remote site (vs using a relay), but relays
> often break and are hard to troubleshoot due to their nature.
> In the last year, my 6to4 tunnel has peaked at 6.44mb/s (1day average)
> but more common peaks are 150-250kb/s (5min average).
> My tunnel to was running 4-8 times that including the 6to4 relay
> serving all my customers + native traffic for 15 hosts and 2 servers.
> It's hard to get accurate on recent traffic loads as much of my v6
> traffic shifted to dual stacked peers and I don't have a method of
> separating the v4/v6 traffic in the graphs (me thinks it's time to test
> ipv6 over mpls).
> Jack

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

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