Addresses

Internet addresses has three levels:

БNetwork Address (Net ID)
БHost on Network Address (Host ID)
БProcess in Host Address (port or process)

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

Б
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.

Chee YapБ

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