job screening question

Thu Jul 5 19:39:02 UTC 2012

On Thu, Jul 05, 2012 at 01:45:54PM -0400, Derek Ivey wrote:
> This is exactly the issue comcast6.net is currently experiencing :).
> They seem to be blocking ICMP completely and that is causing my HE
> IPv6 tunnel to be unable to access their site from a browser. 

I've recently came across a dualstacked website which fails behind a
SixXS tunnel (MTU=1280) but works fine with a native connection
(MTU=1500). Having contacted their technical staff, we have diagnosed
the issue down to the dualstacked load balancer (pretty well-known brand)
SOMETIMES not reacting on ICMPv6 PTB errors.

It's not always as easy as "blocks all ICMPv6". For all the cases I've
hunted down to root cause in the last decade, it was never a firewall
blocking ICMPv6, but most times misbehaving load balancers, either due
to bugs or plain not having implemented PMTUD on IPv6.

Best regards,
Daniel

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