> And don't even get me started on how evil extension headers are from a hardware point of view. > trying to argue for an IPv5 that was just an extended v4 with

> And don't even get me started on how evil extension headers are from a hardware point of view. > trying to argue for an IPv5 that was just an extended v4 without all this added complexity. > V6 is miserable in OSes because everything has to be done twice because you have two stacks (see my other post here regarding the PMTU locking issue in FreeBSD), On the other hand that flexibility may save us from going through that "we have to upgrade the whole Internet at once" pain again. In the end widespread v6 adoption is driven mostly by v4 address space exhaustion. At the time this got really severe some years ago the implementations in both hard and software were already pretty reasonable and widespread. Would we really be at a higher adoption rate right now with no additional reason to upgrade? (also IPv5 was already used in RFC 1819 for sth. different, that's why they jumped to 6 ;)) > The only good thing about the new V6 proto from a hardware perspective is the elimination of the header checksum (which was trivial anyway). What about fragmentation which is entirely left to the hosts in v6? > Even if you want to say that FreeBSD sucks, pretty much every innovation has some to V6 later than V4 on every OS I can think of. From simple things like TSO and checksum offload to RSS. There are examples of this on Linux, OSX and Windows. I don't think such optimizations coming a bit later had a significant negative impact in v6 adoption (and if v6 adoption would have been higher it would have been implemented more equally). Also bugs get found and sorted out a lot faster if someone is actually using the code.