About the Internet 123

How computers are identified on the Internet

Well-known ports

Following are some of the most common well-known ports.

Default port

Service name

Program

 

 

 

20

ftp-data

FTP (File Transfer Protocol) data

 

 

 

21

ftp

FTP (File Transfer Protocol) control

 

 

 

23

telnet

Telnet terminal handler

 

 

 

25

smtp

SMTP (Simple Mail Transfer Protocol)

 

 

 

53

domain

DNS (Domain Name Service) lookup

 

 

 

79

finger

Finger

 

 

 

80

http

HTTP (Hypertext Transfer Protocol)

 

 

 

110

pop3

POP3 (Post Office Protocol 3)

 

 

 

113

auth

Ident Authentication Service

 

 

 

119

nntp

NNTP (Network News Transfer Protocol)

 

 

 

137

nbname

NetBIOS name (Microsoft Networking)

 

 

 

138

nbdatagram

NetBIOS datagram (Microsoft

 

 

Networking)

 

 

 

139

nbsession

NetBIOS session (Microsoft Networking)

 

 

 

143

imap

IMAP (Internet Message Access Protocol)

 

 

 

194

irc

IRC (Internet Relay Chat)

 

 

 

389

ldap

LDAP (Lightweight Directory Access

 

 

Protocol)

 

 

 

443

https

HTTPS (Secure HTTP)

 

 

 

How computers are identified on the Internet

Millions of computers are connected to the Internet. When you are trying to identify computers, it is easier to work with groups of computers rather than having to identify each one individually. Subnet masks provide a way to identify a group of related computers, such as those on your local network.