TCP and UDP ports

Protocols TCP and UDP act as port managers for user applications.

Some ports listed in /etc/services:


systat          11/tcp          users
daytime         13/tcp
daytime         13/udp
netstat         15/tcp
qotd            17/tcp          quote
msp             18/tcp         # message send protocol
msp             18/udp
chargen         19/tcp          ttytst source
chargen         19/udp          ttytst source
ftp-data        20/tcp
ftp             21/tcp
fsp             21/udp          fspd
ssh             22/tcp         # SSH Remote Login Protocol
ssh             22/udp
telnet          23/tcp
smtp            25/tcp          mail

Ports under 1024 are privileged ports.

Socket = Port + IP address.
Any new connection opens a new socket.

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