Forgive my silly question.
I'm not quite understand what these mean.If anyone can explain it explicit.Thanks a lot.
Why does the TFTP client keep retransmitting its request when the ICMP messages are being ?returned? An element of network programming is occurring in which BSD systems don't notify user processes using UDP of ICMP messages that are received for that socket unless the process has issued a connect on that socket. The standard BSD TFTP client does not issue the connect, so it never receives the ICMP error notification.
TCP/IP illustrated Volume 1 Charter 6.5
preguntado el 28 de agosto de 12 a las 09:08
The ICMP messages aren't returned to the application unless it has issued a connect(), which it hasn't, so it doesn't know about them.
ICMP protocol is used for troubleshooting purpose, actually on most operating systems when you connect to a closed port on the server, the server will reply with
ICMP message type port unreachable.