option 212 for 6RD

Jeroen Massar jeroen at massar.ch
Mon Jan 14 20:43:47 CET 2013

On 2013-01-14 19:51, 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. 

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)

>> Any insights and thougts appreciated!
> I'd say you're safe enabling it, but be aware that you may get a few
> support call from people having "YouTube problems" on the short term. 

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.


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