It's a bit sad that, as a result of the urgent pointer being useless, there are 16 zero bits sent in every TCP header. They can't even be repurposed - the specs

It's a bit sad that, as a result of the urgent pointer being useless, there are 16 zero bits sent in every TCP header. They can't even be repurposed - the specs say they're meaningful only when the URG bit is set, and leave their condition when URG is clear unspecified, but various middleboxes take a clear URG bit as licence to explicitly zero the urgent pointer on the way through. (And of course some clear it no matter what.) This is one of those areas where IPv6 could have been something quite different and amazing. Separating TCP and IP was, in hindsight, a mistake; some alternate universe out there had the IPv6 process focus on finding a better way of carving up the problem.