Well-Known UDP Ports

Service	UDP Port Number	Description
echo	7	Echo
discard	9	Discard or null
systat	11	Users
daytime	13	Daytime
netstat	15	Network status
qotd	17	Quote of the Day
chargen	19	Character generator
time	37	Time server
name	42	Host Name server
domain	53	Domain name server (DNS)
nameserver	53	Domain name server (DNS)
bootps	67	Bootstrap protocol service/DHCP
bootpc	68	Bootstrap protocol client/DHCP
tftp	69	Trivial File Transfer Protocol
portmap	111
sunrpc	111	SUN RPC service
ntp	123	Network Time Protocol
nbname	137	NetBIOS name
nbdatagram	148	NetBIOS datagram
sgmp	153
snmp	161	Simple Network Management Protocol
snmp-trap	162	Simple Network Management Protocol trap

Well-Known TCP Ports

Service	TCP Port Number	Brief Description
tcpmux	1	TCP port service multiplexor
compressnet	2	Management utility
compressnet	3	Compression utility
echo	7	Echo
discard	9	Discard or null
systat	11	Users
daytime	13	Daytime
netstat	15	Network status
qotd	17	Quote of the Day
chargen	19	Character generator
ftp-data	20	File Transfer Protocol data
ftp	21	File Transfer Protocol control
telnet	23	Terminal network connection
smtp	25	Simple Mail Transport Protocol
nsw-fe	27	NSW user system
time	37	Time server
name	42	Host name server
domain	53	Domain name server (DNS)
nameserver	53	Domain name server (DNS)
DHCP	67	Dynamic Host Configuration Protocol
gopher	70	Gopher service
rje	77	Remote job entry
finger	79	Finger
http	80	WWW service
link	87	TTY link
supdup	95	SUPDUP protocol
hostnames	101	sri-nic host name server
iso-tsap	102	ISO-TSAP
x400	103	X.400 mail service
x400-snd	104	X.400 mail send
pop	109	Post Office Protocol
pop2	109	Post Office Protocol 2
pop3	110	Post Office Protocol 3
portmap	111
sunrpc	111	SUN RPC service
auth	113	Authentication service
sftp	115	Secure FTP
path	117	UUCP path service
uucp-path	117	UUCP path service
nntp	119	Usenet Network News Transfer Protocol
nbsession	139	NetBIOS session service
NeWS	144	News
tcprepo	158	TCP repository

Transport Layer Concepts

important concepts:

• Connection-oriented and connectionless protocols

• Ports and sockets

• Multiplexing

Connection-Oriented and Connectionless Protocols

• A connection-oriented protocol establishes and maintains a connection between communicating computers and monitors the state of that connection over the course of the transmission. In other words, each package of data sent across the network receives an acknowledgment, and the sending machine records status information to ensure that each package is received without errors, retransmitting the data if necessary. At the end of the transmission, the sending and receiving computers gracefully close the connection.

• A connectionless protocol sends a one-way datagram to the destination and doesn't worry about officially notifying the destination machine that data is on the way. The destination machine receives the data and doesn't worry about returning status information to the source computer.