MTU handling in 6RD deployments

Mark Townsley mark at
Tue Jan 7 16:18:10 CET 2014

And generating stinkin' ICMPv6 too big messages ends up being perhaps the most significant scaling factor of a 6rd BR deployment...

- Mark

On Jan 7, 2014, at 3:59 PM, Simon Perreault wrote:

> Le 2014-01-07 08:46, Jean-Francois.TremblayING at a écrit :
>> In the list of "tricks", you might want to add:
>> * Slightly raise the ICMPv6 rate-limit values for your 6RD BR (we do 50/20)
> Yeah, this is really problematic. When IPv6 packets arrive at the BR from the Internet, the BR needs to send too bigs so that the remote node can do PMTUD correctly and figure out the 1480 MTU. If you rate-limit those too bigs, you create black holes. You need to expect a lot of too bigs to be generated by the BR in regular operation, even if the CPE uses tricks such as TCP MSS adjustment or advertising 1480 in RA, because we still need to live with non-TCP traffic and nodes that don't understand the MTU param in RAs.
> Simon
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