Ports are simply a software abstraction, used to distinguish between communication channels. Similar to the way IP addresses are used to identify machines on networks, ports identify specific applications in use on a single machine. For example, your web browser will by default connect to TCP port 80 of machines in HTTP URLs. If you specify the secure HTTPS protocol instead, the browser will try port 443 by default. Nmap works with two protocols that use ports: TCP and UDP. A connection for each protocol is uniquely identified by four elements: source and destination IP addresses and corresponding source and destination ports. All of these elements are simply numbers placed in the headers of each packet sent between hosts. The protocol is an eight-bit field, which specifies what type of packet is contained in the IP data (payload) section.

Read:- what is ROM (Read Only Memory)

For example, TCP is protocol number six, and UDP is 17. IPv4 addresses have a length of 32-bits, while ports are 16-bits long. IPv6 addresses are 128-bits in length.


What Are the Most Popular Ports

The following two lists provide the top TCP and UDP ports as determined by our empirical scan data. The listed service is the one found in our nmap services file. We try to list the most common service for each port there, though of course it is possible for a port to be used for different things.

Top 20 (most commonly open) TCP ports

1. Port 80 (HTTP)—If you don’t even know this service, you’re reading the wrong book. This accounted for more than 14% of the open ports we discovered.

2. Port 23 (Telnet)—Telnet lives on (particularly as an administration port on devices such as routers and smart switches) even though it is insecure (unencrypted).

3. Port 443 (HTTPS)—SSL-encrypted web servers use this port by default.

4. Port 21 (FTP)—FTP, like Telnet, is another insecure protocol which should die. Even with anonymous FTP (avoiding the authentication sniffing worry), data transfer is still subject to tampering.

5. Port 22 (SSH)—Secure Shell, an encrypted replacement for Telnet (and, in some cases, FTP).

6. Port 25 (SMTP)—The Standard Mail Transfer Protocol (also insecure).

7. Port 3389 (ms-term-server)—Microsoft Terminal Services administration port.

8. Port 110 (POP3)—Post Office Protocol version 3 for email retrieval (insecure).

9. Port 445 (Microsoft-DS)—For SMB communication over IP with MS Windows services (such as file/printer sharing).

10. Port 139 (NetBIOS-SSN)—NetBIOS Session Service for communication with MS Windows services (such as file/printer sharing). This has been supported on Windows machines longer than 445 has.

11. Port 143 (IMAP)—Internet Message Access Protocol version 2. An insecure email retrieval protocol.

12 Port 53 (Domain)—Domain Name System (DNS), an insecure system for conversion between host/domain names and IP addresses.

13. Port 135 (MSRPC)—Another common port for MS Windows services.

14. Port 3306 (MySQL)—For communication with MySQL databases.

15. Port 8080 (HTTP-Proxy)—Commonly used for HTTP proxies or as an alternate port for normal web servers (e.g. when another server is already listening on port 80, or when run by unprivileged UNIX users who can only bind to high ports).

16. Port 1723 (PPTP)—Point-to-point tunneling protocol (a method of implementing VPNs which is often required for broadband connections to ISPs).

17. Port 111 (RPCBind)—Maps SunRPC program numbers to their current TCP or UDP port numbers.

18. Port 995 (POP3S)—POP3 with SSL added for security.

19. Port 993 (IMAPS)—IMAPv2 with SSL added for security.

20 Port 5900 (VNC)—A graphical desktop sharing system (insecure).

Top 20 (most commonly open) UDP ports

1. Port 631 (IPP)—Internet Printing Protocol.

2. Port 161 (SNMP)—Simple Network Management Protocol.

3. Port 137 (NETBIOS-NS)—One of many UDP ports for Windows services such as file and printer sharing.

4. Port 123 (NTP)—Network Time Protocol.

5. Port 138 (NETBIOS-DGM)—Another Windows service.

6. Port 1434 (MS-SQL-DS)—Microsoft SQL Server.

7. Port 445 (Microsoft-DS)—Another Windows Services port.

8. Port 135 (MSRPC)—Yet Another Windows Services port.

9. Port 67 (DHCPS)—Dynamic Host Configuration Protocol Server (gives out IP addresses to clients when they join the network).

10. Port 53 (Domain)—Domain Name System (DNS) server.

11. Port 139 (NETBIOS-SSN)—Another Windows Services port.

12 Port 500 (ISAKMP)—The Internet Security Association and Key Management Protocol is used to set up IPsec VPNs.

13. Port 68 (DHCPC)—DHCP client port.

14. Port 520 (Route)—Routing Information Protocol (RIP).

15. Port 1900 (UPNP)—Microsoft Simple Service Discovery Protocol, which enables discovery of Universal plug-and-play devices.

16. Port 4500 (nat-t-ike)—For negotiating Network Address Translation traversal while initiating IPsec connections (during Internet Key Exchange).

18. Port 162 (SNMPTrap)—Simple Network Management Protocol trap port (An SNMP agent typically uses 161 while an SNMP manager typically uses 162).

19. Port 69 (TFTP)—Trivial File Transfer Protocol.

20. Port 49152 (Varies)—The first of the IANA-specified dynamic/private ports. No official ports may be registered from here up until the end of the port range (65536). Some systems use this range for their ephemeral ports, so services which bind a port without requesting a specific number are often allocated 49152 if they are the first program to do so.

Red Hat Enterprise Linux depends on access to many TCP and UDP ports to function. RHEL also includes numerous software programs that require access to these communication ports.

Common/Popular IANA Registered Port

1TCPtcpmuxTCP port service multiplexer
5TCPrjeRemote Job Entry
7TCPechoEcho service
9TCPdiscardNull service for connection testing
11TCPsystatSystem Status service for listing connected ports
13TCPdaytimeSends date and time to requesting host
17TCPqotdSends quote of the day to connected host
18TCPmspMessage Send Protocol
19TCPchargenCharacter Generation service; sends endless stream of characters
20TCPftp-dataFTP data port
21TCPftpFile Transfer Protocol (FTP) port; sometimes used by File Service Protocol (FSP)
22TCPsshSecure Shell (SSH) service
23TCPtelnetThe Telnet service
25TCPsmtpSimple Mail Transfer Protocol (SMTP)
37TCPtimeTime Protocol
39TCPrlpResource Location Protocol
42TCPnameserverInternet Name Service
43TCPnicnameWHOIS directory service
49TCPtacacsTerminal Access Controller Access Control System for TCP/IP based authentication and access
50TCPre-mail-ckRemote Mail Checking Protocol
53TCPdomaindomain name services (such as BIND)
63TCPwhois++WHOIS++, extended WHOIS services
67TCPbootpsBootstrap Protocol (BOOTP) services; also used by Dynamic  Host Configuration Protocol (DHCP) services
68TCPbootpcBootstrap (BOOTP) client; also used by Dynamic Host Control Protocol (DHCP) clients
69TCPtftpTrivial File Transfer Protocol (TFTP)
70TCPgopherGopher Internet document search and retrieval
71TCPnetrjs-1Remote Job Service
72TCPnetrjs-2Remote Job Service
73TCPnetrjs-3Remote Job Service
73TCPnetrjs-4Remote Job Service
79TCPfingerFinger service for user contact information
80TCPhttpHyperText Transfer Protocol (HTTP) for World Wide Web (WWW) services
88TCPkerberosKerberos network authentication system
95TCPsupdupTelnet protocol extension
101TCPhostnameHostname services on SRI-NIC machines
102TCPiso-tsapISO Development Environment (ISODE) network applications
105TCPcsnet-nsMailbox nameserver; also used by CSO nameserver
107TCPrtelnetRemote Telnet
109TCPpop2Post Office Protocol version 2
110TCPPOP3Post Office Protocol version 3
111TCPsunrpcRemote Procedure Call (RPC) Protocol for remote command execution, used by Network Filesystem (NFS)
113TCPauthAuthentication and Ident protocols
115TCPsftpSecure File Transfer Protocol (SFTP) services
117TCPuucp-pathUnix-to-Unix Copy Protocol (UUCP) Path services
119TCPnntpNetwork News Transfer Protocol (NNTP) for the USENET discussion system
123TCPntpNetwork Time Protocol (NTP)
137TCPnetbios-nsNETBIOS Name Service used in Red Hat Enterprise Linux by Samba
138TCPnetbios-dgmNETBIOS Datagram Service used in Red Hat Enterprise Linux by Samba
139TCPnetbios-ssnNETBIOS Session Service used in Red Hat Enterprise Linux by Samba
143TCPIMAPInternet Message Access Protocol (IMAP)
161TCPsnmpSimple Network Management Protocol (SNMP)
162TCPsnmptrapTraps for SNMP
163TCPcmip-manCommon Management Information Protocol (CMIP)
164TCPcmip-agentCommon Management Information Protocol (CMIP)
174TCPmailqMAILQ email transport queue
177TCPxdmcpX Display Manager Control Protocol (XDMCP)
178TCPnextstepNeXTStep window server
179TCPbgpBorder Gateway Protocol
191TCPprosperoProspero distributed filesystem services
194TCPircInternet Relay Chat (IRC)
199TCPsmuxSNMP UNIX Multiplexer
201TCPat-rtmpAppleTalk routing
202TCPat-nbpAppleTalk name binding
204TCPat-echoAppleTalk echo
206TCPat-zisAppleTalk zone information
209TCPqmtpQuick Mail Transfer Protocol (QMTP)
210TCPz39.50NISO Z39.50 database
213TCPipxInternetwork Packet Exchange (IPX), a datagram protocol commonly used in Novell Netware environments
220TCPIMAP3Internet Message Access Protocol version 3
245TCPlinkLINK / 3-DNS iQuery service
347TCPfatservFATMEN file and tape management server
363TCPrsvp_tunnelRSVP Tunnel
369TCPrpc2portmapCoda file system portmapper
370TCPcodaauth2Coda file system authentication services
389TCPldapLightweight Directory Access Protocol (LDAP)
427TCPsvrlocService Location Protocol (SLP)
434TCPmobileip-agentMobile Internet Protocol (IP) agent
435TCPmobilip-mnMobile Internet Protocol (IP) manager
443TCPhttpsSecure Hypertext Transfer Protocol (HTTP)
444TCPsnppSimple Network Paging Protocol
445TCPmicrosoft-dsServer Message Block (SMB) over TCP/IP
464TCPkpasswdKerberos password and key changing services
468TCPphoturisPhoturis session key management protocol
487TCPsaftSimple Asynchronous File Transfer (SAFT) protocol
488TCPgss-httpGeneric Security Services (GSS) for HTTP
496TCPpim-rp-discRendezvous Point Discovery (RP-DISC) for Protocol Independent Multicast (PIM) services
500TCPisakmpInternet Security Association and Key Management Protocol (ISAKMP)
535TCPiiopInternet Inter-Orb Protocol (IIOP)
538TCPgdomapGNUstep Distributed Objects Mapper (GDOMAP)
546TCPdhcpv6-clientDynamic Host Configuration Protocol (DHCP) version 6 client
547TCPdhcpv6-serverDynamic Host Configuration Protocol (DHCP) version 6 Service
554TCPrtspReal Time Stream Control Protocol (RTSP)
563TCPnntpsNetwork News Transport Protocol over Secure Sockets Layer (NNTPS)
565TCPwhoamiwhoami user ID listing
587TCPsubmissionMail Message Submission Agent (MSA)
610TCPnpmp-localNetwork Peripheral Management Protocol (NPMP) local / Distributed Queueing System (DQS)
611TCPnpmp-guiNetwork Peripheral Management Protocol (NPMP) GUI / Distributed Queueing System (DQS)
612TCPhmmp-indHyperMedia Management Protocol (HMMP) Indication / DQS
631TCPippInternet Printing Protocol (IPP)
636TCPldapsLightweight Directory Access Protocol over Secure Sockets Layer (LDAPS)
674TCPacapApplication Configuration Access Protocol (ACAP)
694TCPha-clusterHeartbeat services for High-Availability Clusters
749TCPkerberos-admKerberos version 5 (v5) ‘kadmin’ database administration
750TCPkerberos-ivKerberos version 4 (v4) services
765TCPwebsterNetwork Dictionary
767TCPphonebookNetwork Phonebook
873TCPrsyncrsync file transfer services
992TCPtelnetsTelnet over Secure Sockets Layer (TelnetS)
993TCPIMAPSInternet Message Access Protocol over Secure Sockets Layer (IMAPS)
994TCPircsInternet Relay Chat over Secure Sockets Layer (IRCS)
995TCPPOP3sPost Office Protocol version 3 over Secure Sockets Layer (POP3S)

UNIX-Specific Port

512TCPexecAuthentication for remote process execution
512UDPbiff [comsat]Asynchrous mail client (biff) and service (comsat)
513TCPloginRemote Login (rlogin)
513UDPwho [whod]whod user logging daemon
514TCPshell [cmd]Remote shell (rshell) and remote copy (rcp) with no logging
514UDPsyslogUNIX system logging service
515printer [spooler]Line printer (lpr) spooler
517UDPtalkTalk remote calling service and client
518UDPntalkNetwork talk (ntalk) remote calling service and client
519utime [unixtime]UNIX time (utime) protocol
520TCPefsExtended Filename Server (EFS)
520UDProuter [route, routed]Routing Information Protocol (RIP)
521ripngRouting Information Protocol for Internet Protocol version 6 (IPv6)
525timed [timeserver]Time daemon (timed)
526/TCPtempo [newdate]Tempo
530TCPcourier [rpc]Courier Remote Procedure Call (RPC) protocol
531TCPconference [chat]Internet Relay Chat
532netnewsNetnews newsgroup service
533UDPnetwallNetwall for emergency broadcasts
540TCPuucp [uucpd]UNIX-to-UNIX copy services
543TCPkloginKerberos version 5 (v5) remote login
544TCPkshellKerberos version 5 (v5) remote shell
548afpovertcpAppletalk Filing Protocol (AFP) over Transmission Control Protocol (TCP)
556remotefs [rfs_server, rfs]Brunhoff’s Remote Filesystem (RFS)
IANA Network Community
1080socksSOCKS network application proxy services
1236bvcontrol [rmtcfg]Remote configuration server for Gracilis Packeten network switches
1300h323hostcallscH.323 telecommunication Host Call Secure
1433ms-sql-sMicrosoft SQL Server
1434ms-sql-mMicrosoft SQL Monitor
1494icaCitrix ICA Client
1512winsMicrosoft Windows Internet Name Server
1524ingreslockIngres Database Management System (DBMS) lock services
1525prospero-npProspero non-privileged
1645datametrics [old-radius]Datametrics / old radius entry
1646sa-msg-port [oldradacct]sa-msg-port / old radacct entry
1649kermitKermit file transfer and management service
1701l2tp [l2f]Layer 2 Tunneling Protocol (LT2P) / Layer 2 Forwarding (L2F)
1718h323gatediscH.323 telecommunication Gatekeeper Discovery
1719h323gatestatH.323 telecommunication Gatekeeper Status
1720h323hostcallH.323 telecommunication Host Call setup
1758tftp-mcastTrivial FTP Multicast
1759UDPmtftpMulticast Trivial FTP (MTFTP)
1789helloHello router communication protocol
1812radiusRadius dial-up authentication and accounting services
1813radius-acctRadius Accounting
1911mtpStarlight Networks Multimedia Transport Protocol (MTP)
1985hsrpCisco Hot Standby Router Protocol
1986licensedaemonCisco License Management Daemon
1997gdp-portCisco Gateway Discovery Protocol (GDP)
2049nfs [nfsd]Network File System (NFS)
2102zephyr-srvZephyr distributed messaging Server
2103zephyr-cltZephyr client
2104zephyr-hmZephyr host manager
2401cvspserverConcurrent Versions System (CVS) client/server operations
2430TCPvenusVenus cache manager for Coda file system (codacon port)
2430UDPvenusVenus cache manager for Coda file system (callback/wbc interface)
2431TCPvenus-seVenus Transmission Control Protocol (TCP) side effects
2431UDPvenus-seVenus User Datagram Protocol (UDP) side effects
2432UDPcodasrvCoda file system server port
2433TCPcodasrv-seCoda file system TCP side effects
2433UDPcodasrv-seCoda file system UDP SFTP side effect
2600hpstgmgr [zebrasrv]Zebra routing
2601discp-client [zebra]discp client; Zebra integrated shell
2602discp-server [ripd]discp server; Routing Information Protocol daemon (ripd)
2603servicemeter [ripngd]Service Meter; RIP daemon for IPv6
2604nsc-ccs [ospfd]NSC CCS; Open Shortest Path First daemon (ospfd)
2605nsc-posaNSC POSA; Border Gateway Protocol daemon (bgpd)
2606netmon [ospf6d]Dell Netmon; OSPF for IPv6 daemon (ospf6d)
2809corbalocCommon Object Request Broker Architecture (CORBA) naming service locator
3130icpv2Internet Cache Protocol version 2 (v2); used by Squid proxy caching server
3306mysqlMySQL database service
3346trnsprntproxyTransparent proxy
4011pxePre-execution Environment (PXE) service
4321rwhoisRemote Whois (rwhois) service
4444krb524Kerberos version 5 (v5) to version 4 (v4) ticket translator
5002rfeRadio Free Ethernet (RFE) audio broadcasting system
5308cfengineConfiguration engine (Cfengine)
5999cvsup [CVSup]CVSup file transfer and update tool
6000TCPx11 [X]X Window System services
7000afs3-fileserverAndrew File System (AFS) file server
7001afs3-callbackAFS port for callbacks to cache manager
7002afs3-prserverAFS user and group database
7003afs3-vlserverAFS volume location database
7004afs3-kaserverAFS Kerberos authentication service
7005afs3-volserAFS volume management server
7006afs3-errorsAFS error interpretation service
7007afs3-bosAFS basic overseer process
7008afs3-updateAFS server-to-server updater
7009afs3-rmtsysAFS remote cache manager service
9876sdSession Director for IP multicast conferencing
10080amandaAdvanced Maryland Automatic Network Disk Archiver (Amanda) backup services
11371pgpkeyserverPretty Good Privacy (PGP) / GNU Privacy Guard (GPG) public keyserver
11720h323callsigaltH.323 Call Signal Alternate
13720bprdVeritas NetBackup Request Daemon (bprd)
13721bpdbmVeritas NetBackup Database Manager (bpdbm)
13722bpjava-msvcVeritas NetBackup Java / Microsoft Visual C++ (MSVC) protocol
13724vnetdVeritas network utility
13782bpcdVeritable Net Backup
13783vopiedVeritas VOPIE authentication daemon
22273wnn6 [wnn4]Kana/Kanji conversion system
26000quakeQuake (and related) multi-player game servers
26208wnn6-dsWnn6 Kana/Kanji server
33434trace routeTraceroute network tracking tool
Red Hat Enterprise Linux (RHEL) Port
15tcpnetstatNetwork Status (netstat)
98tcplinuxconfLinuxconf Linux administration tool
106poppassdPost Office Protocol password change daemon (POPPASSD)
465tcpsmtpsSimple Mail Transfer Protocol over Secure Sockets Layer (SMTPS)
616tcpgiiGated (routing daemon) Interactive Interface
808omirr [omirrd]Online Mirror (Omirr) file mirroring services
871tcpsupfileservSoftware Upgrade Protocol (SUP) server
901tcpswatSamba Web Administration Tool (SWAT)
953rndcBerkeley Internet Name Domain version 9 (BIND 9) remote configuration tool
1127tcpsupfiledbgSoftware Upgrade Protocol (SUP) debugging
1178tcpskkservSimple Kana to Kanji (SKK) Japanese input server
1313tcpxtelFrench Minitel text information system
1529tcpsupport [prmsd, gnatsd]GNATS bug tracking system
2003tcpcfingerGNU finger
2150ninstallNetwork Installation Service
2988afbackupafbackup client-server backup system
3128tcpsquidSquid Web proxy cache
3455prsvpRSVP port
5432postgresPostgreSQL database
4557tcpfaxFAX transmission service (old service)
4559tcphylafaxHylaFAX client-server protocol (new service)
5232sgi-dglSGI Distributed Graphics Library
5354noclogNOCOL network operation center logging daemon (noclogd)
5355hostmonNOCOL network operation center host monitoring
5680tcpcannaCanna Japanese character input interface
6010tcpx11-ssh-offsetSecure Shell (SSH) X11 forwarding offset
6667ircdInternet Relay Chat daemon (ircd)
7100tcpxfsX Font Server (XFS)
7666tcptircproxyTircproxy IRC proxy service
8008http-altHypertext Tranfer Protocol (HTTP) alternate
8080webcacheWorld Wide Web (WWW) caching service
8081tproxyTransparent Proxy
9100tcpjetdirect [laserjet, hplj]Hewlett-Packard (HP) JetDirect network printing service
9359mandelspawn [mandelbrot]Parallel mandelbrot spawning program for the X Window System
10081kamandaAmanda backup service over Kerberos
10082tcpamandaidxAmanda index server
10083tcpamidxtapeAmanda tape server
20011isdnlogIntegrated Services Digital Network (ISDN) logging system
20012vboxdISDN voice box daemon (vboxd)
22305tcpwnn4_KrkWnn Korean input system
22289tcpwnn4_CncWnn Chinese input system
22321tcpwnn4_TwtWnn Chinese input system (Taiwan)
24554binkpBinkley TCP/IP Fidonet mailer daemon
27374aspAddress Search Protocol
60177tfidoIfmail FidoNet compatible mailer service
60179fidoFidoNet electronic mail and news network

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