Why does UDP have a length field in the header and TCP does not?
问题 Why does UDP have a length field in the header and TCP does not? I am guessing that the length of the segment in TCP is inferred from the IP header but one should be able to do the same for a UDP datagram 回答1: According to TCP/IP Illustrated Volume 1 , the length field is redundant. That's all Stevens says on the matter. I personally believe it was to make the UDP header length (in bits) divisible by 32 :) 回答2: There is a 96 bit pseudo header conceptually prefixed to the TCP header that