TCP services

There are standard TCP port numbers for common services, i.e.

Name	Port
HTTP	80
SMTP	25
SSH	22
FTP data	20
FTP control	21

A more complete list is in /etc/services.

How do programs set up TCP connections?

Servers:

1. Use socket(2) to create a socket
2. Use bind(2) to associate a local IP address and port number with the socket
3. Use accept(2) to wait for incoming connections
4. Usually, fork() a child to manage the file handle returned by accept()

Clients:

1. Use socket(2) to create a socket
2. Use bind(2) to associate a remote IP address (of the server host) and port number (of the desired service) with the socket
3. Use connect(2) to initiate the connection (obtaining a file handle)
4. read() and write() data

UDP sockets are also possible, but don't have guarantees about delivery and sequencing

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