The IP address acts as a unique identifier for a computer connected to the internet. Using it, computers send data to each other. Internet is a type of network. In addition to the IP address of the remote system, an application also needs to know how to address the specific program that it wishes to communicate with. This is accomplished by specifying a service port, a 16-bit number that uniquely identifies an application running on the system. Instead of numbers, however, service names are usually used instead. Like hostnames, service names are usually matched to port numbers through a local file, commonly called services. This file lists the logical service name, followed by the port number and protocol used by the server. Cpanel : The Webhosting service provided by us has its own communication port which can be accessed by typing www.sitename.com/cpanel or sitename.com:portnumber.
The Default port for communication on the internet is port 80.
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Since Opaque started off with a good intro - I'll just add in a complete list of TCP/IP Service Ports (standardized by the IANA) for your future reference. Here goes:
QUOTE
Common Ports
This file was taken from the IANA website. It is a list of the well known port numbers.
# /etc/services:
# $Id: services,v 1.4 1997/05/20 19:41:21 tobias Exp $
#
# Network services, Internet style
#
# Note that it is presently the policy of IANA to assign a single well-known
# port number for both TCP and UDP; hence, most entries here have two entries
# even if the protocol doesn't support UDP operations.
# Updated from RFC 1700, ``Assigned Numbers'' (October 1994). Not all ports
# are included, only the more common ones.
tcpmux 1/tcp # TCP port service multiplexer
echo 7/tcp
echo 7/udp
discard 9/tcp sink null
discard 9/udp sink null
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 # message send protocol
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 # SSH Remote Login Protocol
telnet 23/tcp
# 24 - private
smtp 25/tcp mail
# 26 - unassigned
time 37/tcp timserver
time 37/udp timserver
rlp 39/udp resource # resource location
nameserver 42/tcp name # IEN 116
whois 43/tcp nicname
re-mail-ck 50/tcp # Remote Mail Checking Protocol
re-mail-ck 50/udp # Remote Mail Checking Protocol
domain 53/tcp nameserver # name-domain server
domain 53/udp nameserver
mtp 57/tcp # deprecated
bootps 67/tcp # BOOTP server
bootps 67/udp
bootpc 68/tcp # BOOTP client
bootpc 68/udp
tftp 69/udp
gopher 70/tcp # Internet Gopher
gopher 70/udp
rje 77/tcp netrjs
finger 79/tcp
www 80/tcp http # WorldWideWeb HTTP
www 80/udp # HyperText Transfer Protocol
link 87/tcp ttylink
kerberos 88/tcp kerberos5 krb5 kerberos-sec # Kerberos v5
kerberos 88/udp kerberos5 krb5 kerberos-sec # Kerberos v5
supdup 95/tcp
# 100 - reserved
hostnames 101/tcp hostname # usually from sri-nic
iso-tsap 102/tcp tsap # part of ISODE.
csnet-ns 105/tcp cso-ns # also used by CSO name server
csnet-ns 105/udp cso-ns
# unfortunately the poppassd (Eudora) uses a port which has already
# been assigned to a different service. We list the poppassd as an
# alias here. This should work for programs asking for this service.
# (due to a bug in inetd the 3com-tsmux line is disabled)
#3com-tsmux 106/tcp poppassd
#3com-tsmux 106/udp poppassd
rtelnet 107/tcp # Remote Telnet
rtelnet 107/udp
pop2 109/tcp postoffice pop-2 # POP version 2
pop2 109/udp pop-2
pop3 110/tcp pop-3 # POP version 3
pop3 110/udp pop-3
sunrpc 111/tcp portmapper # RPC 4.0 portmapper TCP
sunrpc 111/udp portmapper # RPC 4.0 portmapper UDP
auth 113/tcp authentication tap ident
sftp 115/tcp
uucp-path 117/tcp
nntp 119/tcp readnews untp # USENET News Transfer Protocol
ntp 123/tcp
ntp 123/udp # Network Time Protocol
pwdgen 129/tcp # PWDGEN service
pwdgen 129/udp # PWDGEN service
netbios-ns 137/tcp # NETBIOS Name Service
netbios-ns 137/udp
netbios-dgm 138/tcp # NETBIOS Datagram Service
netbios-dgm 138/udp
netbios-ssn 139/tcp # NETBIOS session service
netbios-ssn 139/udp
imap2 143/tcp imap # Interim Mail Access Proto v2
imap2 143/udp imap
snmp 161/udp # Simple Net Mgmt Proto
snmp-trap 162/udp snmptrap # Traps for SNMP
cmip-man 163/tcp # ISO mgmt over IP (CMOT)
cmip-man 163/udp
cmip-agent 164/tcp
cmip-agent 164/udp
mailq 174/tcp # Mailer transport queue for Zmailer
mailq 174/udp # Mailer transport queue for Zmailer
xdmcp 177/tcp # X Display Mgr. Control Proto
xdmcp 177/udp
nextstep 178/tcp NeXTStep NextStep # NeXTStep window
nextstep 178/udp NeXTStep NextStep # server
bgp 179/tcp # Border Gateway Proto.
bgp 179/udp
prospero 191/tcp # Cliff Neuman's Prospero
prospero 191/udp
irc 194/tcp # Internet Relay Chat
irc 194/udp
smux 199/tcp # SNMP Unix Multiplexer
smux 199/udp
at-rtmp 201/tcp # AppleTalk routing
at-rtmp 201/udp
at-nbp 202/tcp # AppleTalk name binding
at-nbp 202/udp
at-echo 204/tcp # AppleTalk echo
at-echo 204/udp
at-zis 206/tcp # AppleTalk zone information
at-zis 206/udp
qmtp 209/tcp # The Quick Mail Transfer Protocol
qmtp 209/udp # The Quick Mail Transfer Protocol
z3950 210/tcp wais # NISO Z39.50 database
z3950 210/udp wais
ipx 213/tcp # IPX
ipx 213/udp
imap3 220/tcp # Interactive Mail Access
imap3 220/udp # Protocol v3
rpc2portmap 369/tcp
rpc2portmap 369/udp # Coda portmapper
codaauth2 370/tcp
codaauth2 370/udp # Coda authentication server
ulistserv 372/tcp # UNIX Listserv
ulistserv 372/udp
ldap 389/tcp # Lightweight Directory Access Protocol
ldap 389/udp # Lightweight Directory Access Protocol
https 443/tcp # MCom
https 443/udp # MCom
snpp 444/tcp # Simple Network Paging Protocol
snpp 444/udp # Simple Network Paging Protocol
saft 487/tcp # Simple Asynchronous File Transfer
saft 487/udp # Simple Asynchronous File Transfer
npmp-local 610/tcp dqs313_qmaster # npmp-local / DQS
npmp-local 610/udp dqs313_qmaster # npmp-local / DQS
npmp-gui 611/tcp dqs313_execd # npmp-gui / DQS
npmp-gui 611/udp dqs313_execd # npmp-gui / DQS
hmmp-ind 612/tcp dqs313_intercell# HMMP Indication / DQS
hmmp-ind 612/udp dqs313_intercell# HMMP Indication / DQS
ipp 631/tcp # Internet Printing Protocol
ipp 631/udp # Internet Printing Protocol
#
# UNIX specific services
#
exec 512/tcp
biff 512/udp comsat
login 513/tcp
who 513/udp whod
shell 514/tcp cmd # no passwords used
syslog 514/udp
printer 515/tcp spooler # line printer spooler
talk 517/udp
ntalk 518/udp
route 520/udp router routed # RIP
timed 525/udp timeserver
tempo 526/tcp newdate
courier 530/tcp rpc
conference 531/tcp chat
netnews 532/tcp readnews
netwall 533/udp # -for emergency broadcasts
gdomap 538/tcp # GNUstep distributed objects
gdomap 538/udp # GNUstep distributed objects
uucp 540/tcp uucpd # uucp daemon
afpovertcp 548/tcp # AFP over TCP
afpovertcp 548/udp # AFP over TCP
remotefs 556/tcp rfs_server rfs # Brunhoff remote filesystem
klogin 543/tcp # Kerberized `rlogin' (v5)
kshell 544/tcp krcmd # Kerberized `rsh' (v5)
nntps 563/tcp snntp # NNTP over SSL
nntps 563/udp snntp # NNTP over SSL
ldaps 636/tcp # LDAP over SSL
ldaps 636/udp # LDAP over SSL
tinc 655/tcp # tinc control port
tinc 655/udp # tinc packet port
kerberos-adm 749/tcp # Kerberos `kadmin' (v5)
#
webster 765/tcp # Network dictionary
webster 765/udp
rsync 873/tcp # rsync
rsync 873/udp # rsync
ftps-data 989/tcp # FTP over SSL (data)
ftps 990/tcp # FTP over SSL
telnets 992/tcp # Telnet over SSL
telnets 992/udp # Telnet over SSL
imaps 993/tcp # IMAP over SSL
imaps 993/udp # IMAP over SSL
ircs 994/tcp # IRC over SSL
ircs 994/udp # IRC over SSL
pop3s 995/tcp # POP-3 over SSL
pop3s 995/udp # POP-3 over SSL
#
# From ``Assigned Numbers'':
#
#> The Registered Ports are not controlled by the IANA and on most systems
#> can be used by ordinary user processes or programs executed by ordinary
#> users.
#
#> Ports are used in the TCP [45,106] to name the ends of logical
#> connections which carry long term conversations. For the purpose of
#> providing services to unknown callers, a service contact port is
#> defined. This list specifies the port used by the server process as its
#> contact port. While the IANA can not control uses of these ports it
#> does register or list uses of these ports as a convienence to the
#> community.
#
socks 1080/tcp # socks proxy server
socks 1080/udp # socks proxy server
lotusnote 1352/tcp lotusnotes # Lotus Note
lotusnote 1352/udp lotusnotes # Lotus Note
ingreslock 1524/tcp
ingreslock 1524/udp
prospero-np 1525/tcp # Prospero non-privileged
prospero-np 1525/udp
datametrics 1645/tcp old-radius # datametrics / old radius entry
datametrics 1645/udp old-radius # datametrics / old radius entry
sa-msg-port 1646/tcp old-radacct # sa-msg-port / old radacct entry
sa-msg-port 1646/udp old-radacct # sa-msg-port / old radacct entry
radius 1812/tcp # Radius
radius 1812/udp # Radius
radius-acct 1813/tcp radacct # Radius Accounting
radius-acct 1813/udp radacct # Radius Accounting
rtcm-sc104 2101/tcp # RTCM SC-104 IANA 1/29/99
rtcm-sc104 2101/udp # RTCM SC-104 IANA 1/29/99
cvspserver 2401/tcp # CVS client/server operations
cvspserver 2401/udp # CVS client/server operations
venus 2430/tcp # codacon port
venus 2430/udp # Venus callback/wbc interface
venus-se 2431/tcp # tcp side effects
venus-se 2431/udp # udp sftp side effect
codasrv 2432/tcp # not used
codasrv 2432/udp # server port
codasrv-se 2433/tcp # tcp side effects
codasrv-se 2433/udp # udp sftp side effect
mon 2583/tcp # MON
mon 2583/udp # MON
dict 2628/tcp # Dictionary server
dict 2628/udp # Dictionary server
gds_db 3050/tcp # InterBase server
gds_db 3050/udp # InterBase server
icpv2 3130/tcp icp # Internet Cache Protocol (Squid)
icpv2 3130/udp icp # Internet Cache Protocol (Squid)
mysql 3306/tcp # MySQL
mysql 3306/udp # MySQL
rfe 5002/tcp # Radio Free Ethernet
rfe 5002/udp # Actually uses UDP only
cfengine 5308/tcp # CFengine
cfengine 5308/udp # CFengine
x11 6000/tcp x11-0 # X windows system
x11 6000/udp x11-0 # X windows system
x11-1 6001/tcp # X windows system
x11-1 6001/udp # X windows system
x11-2 6002/tcp # X windows system
x11-2 6002/udp # X windows system
x11-3 6003/tcp # X windows system
x11-3 6003/udp # X windows system
x11-4 6004/tcp # X windows system
x11-4 6004/udp # X windows system
x11-5 6005/tcp # X windows system
x11-5 6005/udp # X windows system
x11-6 6006/tcp # X windows system
x11-6 6006/udp # X windows system
x11-7 6007/tcp # X windows system
x11-7 6007/udp # X windows system
afs3-fileserver 7000/tcp bbs # file server itself
afs3-fileserver 7000/udp bbs # file server itself
afs3-callback 7001/tcp # callbacks to cache managers
afs3-callback 7001/udp # callbacks to cache managers
afs3-prserver 7002/tcp # users & groups database
afs3-prserver 7002/udp # users & groups database
afs3-vlserver 7003/tcp # volume location database
afs3-vlserver 7003/udp # volume location database
afs3-kaserver 7004/tcp # AFS/Kerberos authentication
afs3-kaserver 7004/udp # AFS/Kerberos authentication
afs3-volser 7005/tcp # volume managment server
afs3-volser 7005/udp # volume managment server
afs3-errors 7006/tcp # error interpretation service
afs3-errors 7006/udp # error interpretation service
afs3-bos 7007/tcp # basic overseer process
afs3-bos 7007/udp # basic overseer process
afs3-update 7008/tcp # server-to-server updater
afs3-update 7008/udp # server-to-server updater
afs3-rmtsys 7009/tcp # remote cache manager service
afs3-rmtsys 7009/udp # remote cache manager service
font-service 7100/tcp xfs # X Font Service
font-service 7100/udp xfs # X Font Service
wnn6 22273/tcp # wnn6
wnn6 22273/udp # wnn6
#=========================================================================
# The remaining port numbers are not as allocated by IANA.
#
# Kerberos (Project Athena/MIT) services
# Note that these are for Kerberos v4, and are unofficial. Sites running
# v4 should uncomment these and comment out the v5 entries above.
#
kerberos4 750/udp kerberos-iv kdc # Kerberos (server) udp
kerberos4 750/tcp kerberos-iv kdc # Kerberos (server) tcp
kerberos_master 751/udp # Kerberos authentication
kerberos_master 751/tcp # Kerberos authentication
passwd_server 752/udp # Kerberos passwd server
krb_prop 754/tcp # Kerberos slave propagation
krbupdate 760/tcp kreg # Kerberos registration
kpasswd 761/tcp kpwd # Kerberos "passwd"
swat 901/tcp # swat
kpop 1109/tcp # Pop with Kerberos
knetd 2053/tcp # Kerberos de-multiplexor
zephyr-srv 2102/udp # Zephyr server
zephyr-clt 2103/udp # Zephyr serv-hm connection
zephyr-hm 2104/udp # Zephyr hostmanager
eklogin 2105/tcp # Kerberos encrypted rlogin
# Hmmm. Are we using Kv4 or Kv5 now? Worrying.
# The following is probably Kerberos v5 --- ajt@debian.org (11/02/2000)
kx 2111/tcp # X over Kerberos
#
# Unofficial but necessary (for NetBSD) services
#
supfilesrv 871/tcp # SUP server
supfiledbg 1127/tcp # SUP debugging
#
# Datagram Delivery Protocol services
#
rtmp 1/ddp # Routing Table Maintenance Protocol
nbp 2/ddp # Name Binding Protocol
echo 4/ddp # AppleTalk Echo Protocol
zip 6/ddp # Zone Information Protocol
#
# Services added for the Debian GNU/Linux distribution
#
linuxconf 98/tcp # LinuxConf
poppassd 106/tcp # Eudora
poppassd 106/udp # Eudora
imsp 406/tcp # Interactive Mail Support Protocol
imsp 406/udp # Interactive Mail Support Protocol
ssmtp 465/tcp smtps # SMTP over SSL
nqs 607/tcp # Network Queuing system
moira_db 775/tcp # Moira database
moira_update 777/tcp # Moira update protocol.
moira_ureg 779/udp # Moira user registration.
omirr 808/tcp omirrd # online mirror
omirr 808/udp omirrd # online mirror
customs 1001/tcp # pmake customs server
customs 1001/udp # pmake customs server
rmiregistry 1099/tcp # Java RMI Registry
skkserv 1178/tcp # skk jisho server port
predict 1210/udp # predict -- satellite tracking
rmtcfg 1236/tcp # Gracilis Packeten remote config server
xtel 1313/tcp # french minitel
xtelw 1314/tcp # french minitel
support 1529/tcp # GNATS
sieve 2000/tcp # Sieve mail filter daemon
cfinger 2003/tcp lmtp # GNU Finger / Local Mail Transfer Protocol
ndtp 2010/tcp # Network dictionary transfer protocol
ninstall 2150/tcp # ninstall service
ninstall 2150/udp # ninstall service
zebrasrv 2600/tcp # zebra service
zebra 2601/tcp # zebra vty
ripd 2602/tcp # RIPd vty
ripngd 2603/tcp # RIPngd vty
ospfd 2604/tcp # OSPFd vty
bgpd 2605/tcp # BGPd vty
ospf6d 2606/tcp # OSPF6d vty
afbackup 2988/tcp # Afbackup system
afbackup 2988/udp # Afbackup system
afmbackup 2989/tcp # Afmbackup system
afmbackup 2989/udp # Afmbackup system
xtell 4224/tcp # xtell server
fax 4557/tcp # FAX transmission service (old)
hylafax 4559/tcp # HylaFAX client-server protocol (new)
pcrd 5151/tcp # PCR-1000 Daemon
noclog 5354/tcp # noclogd with TCP (nocol)
noclog 5354/udp # noclogd with UDP (nocol)
hostmon 5355/tcp # hostmon uses TCP (nocol)
hostmon 5355/udp # hostmon uses UDP (nocol)
postgres 5432/tcp # POSTGRES
postgres 5432/udp # POSTGRES
mrtd 5674/tcp # MRT Routing Daemon
bgpsim 5675/tcp # MRT Routing Simulator
canna 5680/tcp # cannaserver
sane 6566/tcp saned # SANE network scanner daemon
ircd 6667/tcp # Internet Relay Chat
ircd 6667/udp # Internet Relay Chat
ircd-dalnet 7000/tcp # IRC - Dalnet
ircd-dalnet 7000/udp # IRC - Dalnet
webcache 8080/tcp # WWW caching service
webcache 8080/udp # WWW caching service
tproxy 8081/tcp # Transparent Proxy
tproxy 8081/udp # Transparent Proxy
omniorb 8088/tcp # OmniORB
omniorb 8088/udp # OmniORB
mandelspawn 9359/udp mandelbrot # network mandelbrot
amanda 10080/udp # amanda backup services
kamanda 10081/tcp # amanda backup services (Kerberos)
kamanda 10081/udp # amanda backup services (Kerberos)
amandaidx 10082/tcp # amanda backup services
amidxtape 10083/tcp # amanda backup services
smsqp 11201/tcp # Alamin SMS gateway
smsqp 11201/udp # Alamin SMS gateway
xpilot 15345/tcp # XPilot Contact Port
xpilot 15345/udp # XPilot Contact Port
isdnlog 20011/tcp # isdn logging system
isdnlog 20011/udp # isdn logging system
vboxd 20012/tcp # voice box system
vboxd 20012/udp # voice box system
binkp 24554/tcp # Binkley
binkp 24554/udp # Binkley
asp 27374/tcp # Address Search Protocol
asp 27374/udp # Address Search Protocol
dircproxy 57000/tcp # Detachable IRC Proxy
tfido 60177/tcp # Ifmail
tfido 60177/udp # Ifmail
fido 60179/tcp # Ifmail
fido 60179/udp # Ifmail
Source: http://www.pantz.org/networking/tcpip/ports.shtml
