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Ports

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.

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

PORT	LAYER	NAME	DESCRIPTION
1	TCP	tcpmux	TCP port service multiplexer
5	TCP	rje	Remote Job Entry
7	TCP	echo	Echo service
9	TCP	discard	Null service for connection testing
11	TCP	systat	System Status service for listing connected ports
13	TCP	daytime	Sends date and time to requesting host
17	TCP	qotd	Sends quote of the day to connected host
18	TCP	msp	Message Send Protocol
19	TCP	chargen	Character Generation service; sends endless stream of characters
20	TCP	ftp-data	FTP data port
21	TCP	ftp	File Transfer Protocol (FTP) port; sometimes used by File Service Protocol (FSP)
22	TCP	ssh	Secure Shell (SSH) service
23	TCP	telnet	The Telnet service
25	TCP	smtp	Simple Mail Transfer Protocol (SMTP)
37	TCP	time	Time Protocol
39	TCP	rlp	Resource Location Protocol
42	TCP	nameserver	Internet Name Service
43	TCP	nicname	WHOIS directory service
49	TCP	tacacs	Terminal Access Controller Access Control System for TCP/IP based authentication and access
50	TCP	re-mail-ck	Remote Mail Checking Protocol
53	TCP	domain	domain name services (such as BIND)
63	TCP	whois++	WHOIS++, extended WHOIS services
67	TCP	bootps	Bootstrap Protocol (BOOTP) services; also used by Dynamic  Host Configuration Protocol (DHCP) services
68	TCP	bootpc	Bootstrap (BOOTP) client; also used by Dynamic Host Control Protocol (DHCP) clients
69	TCP	tftp	Trivial File Transfer Protocol (TFTP)
70	TCP	gopher	Gopher Internet document search and retrieval
71	TCP	netrjs-1	Remote Job Service
72	TCP	netrjs-2	Remote Job Service
73	TCP	netrjs-3	Remote Job Service
73	TCP	netrjs-4	Remote Job Service
79	TCP	finger	Finger service for user contact information
80	TCP	http	HyperText Transfer Protocol (HTTP) for World Wide Web (WWW) services
88	TCP	kerberos	Kerberos network authentication system
95	TCP	supdup	Telnet protocol extension
101	TCP	hostname	Hostname services on SRI-NIC machines
102	TCP	iso-tsap	ISO Development Environment (ISODE) network applications
105	TCP	csnet-ns	Mailbox nameserver; also used by CSO nameserver
107	TCP	rtelnet	Remote Telnet
109	TCP	pop2	Post Office Protocol version 2
110	TCP	POP3	Post Office Protocol version 3
111	TCP	sunrpc	Remote Procedure Call (RPC) Protocol for remote command execution, used by Network Filesystem (NFS)
113	TCP	auth	Authentication and Ident protocols
115	TCP	sftp	Secure File Transfer Protocol (SFTP) services
117	TCP	uucp-path	Unix-to-Unix Copy Protocol (UUCP) Path services
119	TCP	nntp	Network News Transfer Protocol (NNTP) for the USENET discussion system
123	TCP	ntp	Network Time Protocol (NTP)
137	TCP	netbios-ns	NETBIOS Name Service used in Red Hat Enterprise Linux by Samba
138	TCP	netbios-dgm	NETBIOS Datagram Service used in Red Hat Enterprise Linux by Samba
139	TCP	netbios-ssn	NETBIOS Session Service used in Red Hat Enterprise Linux by Samba
143	TCP	IMAP	Internet Message Access Protocol (IMAP)
161	TCP	snmp	Simple Network Management Protocol (SNMP)
162	TCP	snmptrap	Traps for SNMP
163	TCP	cmip-man	Common Management Information Protocol (CMIP)
164	TCP	cmip-agent	Common Management Information Protocol (CMIP)
174	TCP	mailq	MAILQ email transport queue
177	TCP	xdmcp	X Display Manager Control Protocol (XDMCP)
178	TCP	nextstep	NeXTStep window server
179	TCP	bgp	Border Gateway Protocol
191	TCP	prospero	Prospero distributed filesystem services
194	TCP	irc	Internet Relay Chat (IRC)
199	TCP	smux	SNMP UNIX Multiplexer
201	TCP	at-rtmp	AppleTalk routing
202	TCP	at-nbp	AppleTalk name binding
204	TCP	at-echo	AppleTalk echo
206	TCP	at-zis	AppleTalk zone information
209	TCP	qmtp	Quick Mail Transfer Protocol (QMTP)
210	TCP	z39.50	NISO Z39.50 database
213	TCP	ipx	Internetwork Packet Exchange (IPX), a datagram protocol commonly used in Novell Netware environments
220	TCP	IMAP3	Internet Message Access Protocol version 3
245	TCP	link	LINK / 3-DNS iQuery service
347	TCP	fatserv	FATMEN file and tape management server
363	TCP	rsvp_tunnel	RSVP Tunnel
369	TCP	rpc2portmap	Coda file system portmapper
370	TCP	codaauth2	Coda file system authentication services
372	TCP	ulistproc	UNIX LISTSERV
389	TCP	ldap	Lightweight Directory Access Protocol (LDAP)
427	TCP	svrloc	Service Location Protocol (SLP)
434	TCP	mobileip-agent	Mobile Internet Protocol (IP) agent
435	TCP	mobilip-mn	Mobile Internet Protocol (IP) manager
443	TCP	https	Secure Hypertext Transfer Protocol (HTTP)
444	TCP	snpp	Simple Network Paging Protocol
445	TCP	microsoft-ds	Server Message Block (SMB) over TCP/IP
464	TCP	kpasswd	Kerberos password and key changing services
468	TCP	photuris	Photuris session key management protocol
487	TCP	saft	Simple Asynchronous File Transfer (SAFT) protocol
488	TCP	gss-http	Generic Security Services (GSS) for HTTP
496	TCP	pim-rp-disc	Rendezvous Point Discovery (RP-DISC) for Protocol Independent Multicast (PIM) services
500	TCP	isakmp	Internet Security Association and Key Management Protocol (ISAKMP)
535	TCP	iiop	Internet Inter-Orb Protocol (IIOP)
538	TCP	gdomap	GNUstep Distributed Objects Mapper (GDOMAP)
546	TCP	dhcpv6-client	Dynamic Host Configuration Protocol (DHCP) version 6 client
547	TCP	dhcpv6-server	Dynamic Host Configuration Protocol (DHCP) version 6 Service
554	TCP	rtsp	Real Time Stream Control Protocol (RTSP)
563	TCP	nntps	Network News Transport Protocol over Secure Sockets Layer (NNTPS)
565	TCP	whoami	whoami user ID listing
587	TCP	submission	Mail Message Submission Agent (MSA)
610	TCP	npmp-local	Network Peripheral Management Protocol (NPMP) local / Distributed Queueing System (DQS)
611	TCP	npmp-gui	Network Peripheral Management Protocol (NPMP) GUI / Distributed Queueing System (DQS)
612	TCP	hmmp-ind	HyperMedia Management Protocol (HMMP) Indication / DQS
631	TCP	ipp	Internet Printing Protocol (IPP)
636	TCP	ldaps	Lightweight Directory Access Protocol over Secure Sockets Layer (LDAPS)
674	TCP	acap	Application Configuration Access Protocol (ACAP)
694	TCP	ha-cluster	Heartbeat services for High-Availability Clusters
749	TCP	kerberos-adm	Kerberos version 5 (v5) ‘kadmin’ database administration
750	TCP	kerberos-iv	Kerberos version 4 (v4) services
765	TCP	webster	Network Dictionary
767	TCP	phonebook	Network Phonebook
873	TCP	rsync	rsync file transfer services
992	TCP	telnets	Telnet over Secure Sockets Layer (TelnetS)
993	TCP	IMAPS	Internet Message Access Protocol over Secure Sockets Layer (IMAPS)
994	TCP	ircs	Internet Relay Chat over Secure Sockets Layer (IRCS)
995	TCP	POP3s	Post Office Protocol version 3 over Secure Sockets Layer (POP3S)

UNIX-Specific Port

PORT	LAYER	NAME	DESCRIPTION
512	TCP	exec	Authentication for remote process execution
512	UDP	biff [comsat]	Asynchrous mail client (biff) and service (comsat)
513	TCP	login	Remote Login (rlogin)
513	UDP	who [whod]	whod user logging daemon
514	TCP	shell [cmd]	Remote shell (rshell) and remote copy (rcp) with no logging
514	UDP	syslog	UNIX system logging service
515		printer [spooler]	Line printer (lpr) spooler
517	UDP	talk	Talk remote calling service and client
518	UDP	ntalk	Network talk (ntalk) remote calling service and client
519		utime [unixtime]	UNIX time (utime) protocol
520	TCP	efs	Extended Filename Server (EFS)
520	UDP	router [route, routed]	Routing Information Protocol (RIP)
521		ripng	Routing Information Protocol for Internet Protocol version 6 (IPv6)
525		timed [timeserver]	Time daemon (timed)
526/	TCP	tempo [newdate]	Tempo
530	TCP	courier [rpc]	Courier Remote Procedure Call (RPC) protocol
531	TCP	conference [chat]	Internet Relay Chat
532		netnews	Netnews newsgroup service
533	UDP	netwall	Netwall for emergency broadcasts
540	TCP	uucp [uucpd]	UNIX-to-UNIX copy services
543	TCP	klogin	Kerberos version 5 (v5) remote login
544	TCP	kshell	Kerberos version 5 (v5) remote shell
548		afpovertcp	Appletalk Filing Protocol (AFP) over Transmission Control Protocol (TCP)
556		remotefs [rfs_server, rfs]	Brunhoff’s Remote Filesystem (RFS)

IANA Network Community

PORT	LAYER	NAME	COMMENT
1080		socks	SOCKS network application proxy services
1236		bvcontrol [rmtcfg]	Remote configuration server for Gracilis Packeten network switches
1300		h323hostcallsc	H.323 telecommunication Host Call Secure
1433		ms-sql-s	Microsoft SQL Server
1434		ms-sql-m	Microsoft SQL Monitor
1494		ica	Citrix ICA Client
1512		wins	Microsoft Windows Internet Name Server
1524		ingreslock	Ingres Database Management System (DBMS) lock services
1525		prospero-np	Prospero non-privileged
1645		datametrics [old-radius]	Datametrics / old radius entry
1646		sa-msg-port [oldradacct]	sa-msg-port / old radacct entry
1649		kermit	Kermit file transfer and management service
1701		l2tp [l2f]	Layer 2 Tunneling Protocol (LT2P) / Layer 2 Forwarding (L2F)
1718		h323gatedisc	H.323 telecommunication Gatekeeper Discovery
1719		h323gatestat	H.323 telecommunication Gatekeeper Status
1720		h323hostcall	H.323 telecommunication Host Call setup
1758		tftp-mcast	Trivial FTP Multicast
1759	UDP	mtftp	Multicast Trivial FTP (MTFTP)
1789		hello	Hello router communication protocol
1812		radius	Radius dial-up authentication and accounting services
1813		radius-acct	Radius Accounting
1911		mtp	Starlight Networks Multimedia Transport Protocol (MTP)
1985		hsrp	Cisco Hot Standby Router Protocol
1986		licensedaemon	Cisco License Management Daemon
1997		gdp-port	Cisco Gateway Discovery Protocol (GDP)
2049		nfs [nfsd]	Network File System (NFS)
2102		zephyr-srv	Zephyr distributed messaging Server
2103		zephyr-clt	Zephyr client
2104		zephyr-hm	Zephyr host manager
2401		cvspserver	Concurrent Versions System (CVS) client/server operations
2430	TCP	venus	Venus cache manager for Coda file system (codacon port)
2430	UDP	venus	Venus cache manager for Coda file system (callback/wbc interface)
2431	TCP	venus-se	Venus Transmission Control Protocol (TCP) side effects
2431	UDP	venus-se	Venus User Datagram Protocol (UDP) side effects
2432	UDP	codasrv	Coda file system server port
2433	TCP	codasrv-se	Coda file system TCP side effects
2433	UDP	codasrv-se	Coda file system UDP SFTP side effect
2600		hpstgmgr [zebrasrv]	Zebra routing
2601		discp-client [zebra]	discp client; Zebra integrated shell
2602		discp-server [ripd]	discp server; Routing Information Protocol daemon (ripd)
2603		servicemeter [ripngd]	Service Meter; RIP daemon for IPv6
2604		nsc-ccs [ospfd]	NSC CCS; Open Shortest Path First daemon (ospfd)
2605		nsc-posa	NSC POSA; Border Gateway Protocol daemon (bgpd)
2606		netmon [ospf6d]	Dell Netmon; OSPF for IPv6 daemon (ospf6d)
2809		corbaloc	Common Object Request Broker Architecture (CORBA) naming service locator
3130		icpv2	Internet Cache Protocol version 2 (v2); used by Squid proxy caching server
3306		mysql	MySQL database service
3346		trnsprntproxy	Transparent proxy
4011		pxe	Pre-execution Environment (PXE) service
4321		rwhois	Remote Whois (rwhois) service
4444		krb524	Kerberos version 5 (v5) to version 4 (v4) ticket translator
5002		rfe	Radio Free Ethernet (RFE) audio broadcasting system
5308		cfengine	Configuration engine (Cfengine)
5999		cvsup [CVSup]	CVSup file transfer and update tool
6000	TCP	x11 [X]	X Window System services
7000		afs3-fileserver	Andrew File System (AFS) file server
7001		afs3-callback	AFS port for callbacks to cache manager
7002		afs3-prserver	AFS user and group database
7003		afs3-vlserver	AFS volume location database
7004		afs3-kaserver	AFS Kerberos authentication service
7005		afs3-volser	AFS volume management server
7006		afs3-errors	AFS error interpretation service
7007		afs3-bos	AFS basic overseer process
7008		afs3-update	AFS server-to-server updater
7009		afs3-rmtsys	AFS remote cache manager service
9876		sd	Session Director for IP multicast conferencing
10080		amanda	Advanced Maryland Automatic Network Disk Archiver (Amanda) backup services
11371		pgpkeyserver	Pretty Good Privacy (PGP) / GNU Privacy Guard (GPG) public keyserver
11720		h323callsigalt	H.323 Call Signal Alternate
13720		bprd	Veritas NetBackup Request Daemon (bprd)
13721		bpdbm	Veritas NetBackup Database Manager (bpdbm)
13722		bpjava-msvc	Veritas NetBackup Java / Microsoft Visual C++ (MSVC) protocol
13724		vnetd	Veritas network utility
13782		bpcd	Veritable Net Backup
13783		vopied	Veritas VOPIE authentication daemon
22273		wnn6 [wnn4]	Kana/Kanji conversion system
26000		quake	Quake (and related) multi-player game servers
26208		wnn6-ds	Wnn6 Kana/Kanji server
33434		trace route	Traceroute network tracking tool

Red Hat Enterprise Linux (RHEL) Port

PORT	LAYER	NAME	COMMENT
15	tcp	netstat	Network Status (netstat)
98	tcp	linuxconf	Linuxconf Linux administration tool
106		poppassd	Post Office Protocol password change daemon (POPPASSD)
465	tcp	smtps	Simple Mail Transfer Protocol over Secure Sockets Layer (SMTPS)
616	tcp	gii	Gated (routing daemon) Interactive Interface
808		omirr [omirrd]	Online Mirror (Omirr) file mirroring services
871	tcp	supfileserv	Software Upgrade Protocol (SUP) server
901	tcp	swat	Samba Web Administration Tool (SWAT)
953		rndc	Berkeley Internet Name Domain version 9 (BIND 9) remote configuration tool
1127	tcp	supfiledbg	Software Upgrade Protocol (SUP) debugging
1178	tcp	skkserv	Simple Kana to Kanji (SKK) Japanese input server
1313	tcp	xtel	French Minitel text information system
1529	tcp	support [prmsd, gnatsd]	GNATS bug tracking system
2003	tcp	cfinger	GNU finger
2150		ninstall	Network Installation Service
2988		afbackup	afbackup client-server backup system
3128	tcp	squid	Squid Web proxy cache
3455		prsvp	RSVP port
5432		postgres	PostgreSQL database
4557	tcp	fax	FAX transmission service (old service)
4559	tcp	hylafax	HylaFAX client-server protocol (new service)
5232		sgi-dgl	SGI Distributed Graphics Library
5354		noclog	NOCOL network operation center logging daemon (noclogd)
5355		hostmon	NOCOL network operation center host monitoring
5680	tcp	canna	Canna Japanese character input interface
6010	tcp	x11-ssh-offset	Secure Shell (SSH) X11 forwarding offset
6667		ircd	Internet Relay Chat daemon (ircd)
7100	tcp	xfs	X Font Server (XFS)
7666	tcp	tircproxy	Tircproxy IRC proxy service
8008		http-alt	Hypertext Tranfer Protocol (HTTP) alternate
8080		webcache	World Wide Web (WWW) caching service
8081		tproxy	Transparent Proxy
9100	tcp	jetdirect [laserjet, hplj]	Hewlett-Packard (HP) JetDirect network printing service
9359		mandelspawn [mandelbrot]	Parallel mandelbrot spawning program for the X Window System
10081		kamanda	Amanda backup service over Kerberos
10082	tcp	amandaidx	Amanda index server
10083	tcp	amidxtape	Amanda tape server
20011		isdnlog	Integrated Services Digital Network (ISDN) logging system
20012		vboxd	ISDN voice box daemon (vboxd)
22305	tcp	wnn4_Kr	kWnn Korean input system
22289	tcp	wnn4_Cn	cWnn Chinese input system
22321	tcp	wnn4_Tw	tWnn Chinese input system (Taiwan)
24554		binkp	Binkley TCP/IP Fidonet mailer daemon
27374		asp	Address Search Protocol
60177		tfido	Ifmail FidoNet compatible mailer service
60179		fido	FidoNet electronic mail and news network

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