option 212 for 6RD

[Daniel Roesen]

On Fri, Jan 18, 2013 at 01:16:52PM +0100, Mikael Abrahamsson wrote:
> On Fri, 18 Jan 2013, Daniel Roesen wrote:
>
>> How so? MTU is a property of a L2 domain, a "link". There is no such thing 
>> as a "default route MTU" or a "prefix MTU" in RAs.
>
> I disagree, at least when used with IPv6. My understanding is that if there 
> are two routers on the link, each advertising its own /64 using RA, clients 
> making GUA using SLAAC, I expect each of these /64 (and derived default 
> route) to have different MTU even though they are in the same L2 domain.
>
> Do you disagree?

Yes, I totally disagree.

http://tools.ietf.org/html/rfc4861#section-4.6.2
Nowhere any notion of a per-prefix MTU.

It's a link property:
http://tools.ietf.org/html/rfc4861#section-4.6.2

> Would probably make a nice test case for implementers to use though. But it 
> works currently, my ipv6 speakers at home use different ipv6 mtu and ipv4 
> mtu just based on the RAs.

Then, strictly speaking, you're operating your LAN in a broken way. With
most ethernet/IP stacks that usually works though as they don't derrive
ethernet MAC MTU from L3 MTU.

Best regards,
Daniel

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