Chris Marget wrote:
For the exact same reason that replying to an ICMP Echo Request sent to your broadcast address is generally considered a Bad Idea.
The obvious solution is "Doctor, it hurts when I do that" "Don't do that anymore".
And, it implies that some ISPs will filter all the ICMPv6 PTB including those generated against unicast ones, which means PMTUDv6 won't work. Filtering ICMPv6 PTB generated against multicast packets but not unicast ones is not very easy.
It's not as obvious to me as it is to you. I mean, v6 *requires* exactly this behavior, so it can't be all that bad, can it?
Yes, of course. See https://en.wikipedia.org/wiki/Design_by_committee which is why we should avoid IPv6 entirely, especially because NAT, with its 48bit effective address space, is fair enough and, for theoretical purity, NAT can be modified to have full end to end transparency (https://tools.ietf.org/html/draft-ohta-e2e-nat-00), or, UPnP capable NAT already practically have the transparency.
I'll probably come around, but I've not yet concluded that "screw it, fragment my traffic, I don't care" is the stance that a conscientious application should be taking.
Don't you care, for routers, generating ICMP PTB is as burdensome as generating fragments? Masataka Ohta PS Pages 87-101 of ftp://chacha.hpcl.titech.ac.jp/2014/infra5.ppt is my presentation at APNIC32 on the problem.