option 212 for 6RD

Jeroen Massar jeroen at massar.ch
Mon Jan 14 22:04:36 CET 2013

On 2013-01-14 21:49, Jean-Francois.TremblayING at videotron.com wrote:
>>> The only recent issue we hit what with a specific brand of home 
> routers 
>>> that auto-detects native IPv6 vs 6RD. In some cases, they forget to 
>>> lower the IPv6 MTU in RAs to 1480. This issue will be fixed in their 
>>> future release. Leaving the LAN MTU at 1500 with 6RD causes PMTUD 
>>> problems with many content providers, especially YouTube, who doesn't 
>>> seem to process ICMP too bigs properly.
>> It would really help if you could share more specifics on this.
> Have a look at these threads: 
> http://forums.dlink.com/index.php?topic=50185.60
> http://forums.dlink.com/index.php?topic=51109.15
> Linksys also does 6RD "autodetection" I believe. Most of their routers
> lower the MTU to 1480, with the notable exception of the E4200v1 (which 
> is not autodetect, so less of a problem). 

Do you mean "lower the MTU to 1480" of the tunnel interface ("WAN") or
do you mean of the LAN?

As the tunnel should indeed be 1480 or lower, but the LAN can just stay
at 1500 and changing that would cause all kinds of other odd issues I
would think for hosts that don't take the info from the RA... and the
CPE should really be doing PTBs thus lowering the MTU is not needed as
it will send a PTB because of the tunnel interface having the lower MTU
(eg 1480).


PS: You might want to avoid cc'ing the ipv6-bounces+.... addresses, as
otherwise mailman might think that your mail is bouncing.

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