option 212 for 6RD

[Ole Troan]

Mikael,

>> 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?

that would result in hosts switching from one MTU to the other. and the routers reporting inconsistent information being advertised on the link.
RFC4861, 6.2.7.

MTU is a link property, not a per prefix property.

> 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.

btw, the simplest 6rd deployment would be to be able to carry 1500 byte IPv6 packets across the 6rd domain.
barring that, one should advertise in RAs the WAN IPv4 MTU - 20 on the LAN.

cheers,
Ole