第二章 课后题答案

1. 参见 https://www.iana.org/assignments/version-numbers/version-numbers.xhtml#version-numbers-1
2. 参见https://tools.ietf.org/html/rfc1819
3. ip minimum packet size is 576B, minus fixed ip header(20B) and tcp header(20B), then max mss is 536B, 参见https://tools.ietf.org/html/rfc6691
4. 如下:
   
   1. client: SYN i
   2. server: SYN j, ACK i+1
   3. client: ACK j+1
   4. server: response data(26B)
   5. client: ACK i+2, FIN m (client socket status: FIN_WAIT_1)
   6. server: ACK m+1, FIN n (client socket status: FIN_WAIT_2, server socket status: CLOSE_WAIT)
   7. client: ACK n+1 (client socket status: TIME_WAIT, server socket status: CLOSED)
5. no mss options specified, then user max mss 536B
6. 89, 参见https://www.iana.org/assignments/protocol-numbers/protocol-numbers.xhtml#protocol-numbers-1, also https://tools.ietf.org/html/rfc2328#page-42
7. no yet knows