option 212 for 6RD

Jean-Francois.TremblayING at videotron.com Jean-Francois.TremblayING at videotron.com
Mon Jan 14 21:38:12 CET 2013

Jeroen Massar <jeroen at massar.ch> a écrit sur 14/01/2013 02:43:47 PM :

> Wouldn't the CPE (that terminates the 6rd tunnel and routes a /64 out of
> the delegated prefix to the LAN side) send PTB's already?
> At least, that is how I have been doing IPv6 for years now.... (some
> device makes a tunnel with MTU of <1500, LAN has 1500)

In our experience, there are number of cases where the first large 
packet is sourced from the content provider rather the client. In that
scenario, it's the 6RD relay that sends back the PTB and the content 
who has to adjust. My 6RD relays ICMP stats seem to tell that story at 
> Google handles PMTUD properly afaik... but yes, there will be others who
> will send packets with size == 1500 even though the tunnel endpoint
> sends a PTB to them that that packet size really won't fit.

I still have to debug this in details. It's an on-going project to 
characterize the PTB destinations and their exact content. For now, 
all I can tell is that we had a number of support calls related to 
this, all with YouTube. 


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