2008 April 14th Monday (四月 十四日 月曜日）

This moring I got a mail that tell me how to set my mail box which is used to communicate with Japanese customers.  After tring again and again, it still can not be used.  It was delayed about one week.  The skype also can not be used.  Until now I can apply an account for myself.   Why after a server program reboot can not bind its own local address?  It is the root of 2MSL.  An application based on TCP/IP will be at 2MSL(TIME_WAIT) time out state when it close a connection actively.  At 2MSL state TCP layer will wait the Last Ack from its peer.  The MSL(Maximum Segment Lifetime) is a segment maximum live time.  Double that is for the peer to can resend the Last Ack so as to lost it.   So, when an application was shutdwon, the local addresss and port used is still at 2MSL state.  It usually is 1~4 minutes.  At 2MSL, the socket pair(client and server addresses and ports) can not be reused.  As a rule, local address and port is prohibitted from reusing unless time out.  It can approach the TCP requiremenet of 2MSL.