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Addresses

Internet addresses has three levels:

The Net ID and Host ID is combined into a 32-bit value. The port or process is a 16-bit integer.

Well-known ports. In TCP/IP, the port numbers 1-255 is reserved for "well-known ports" (corresponding to standard services).

SERVICE TCP PORT UDP PORT
echo 7 7
daytime 13 13
netstat 15
ftp-data 20
ftp 21
telnet 23
smtp 25
time 37 37
domain 53 53
finger 79
http 80
pop-2 109
pop 101
sunrpc 111 111
uucp-path 117
nntp 119
talk 517

In some systems, ports 1-1023 are reserved.


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