Appendix C. TCPIP Ports


Appendix C. TCP/IP Ports

When your web browser or email program connects to another computer on the Internet, it does so through a TCP/IP port. If you have a web server or FTP server running on your computer, it opens a port to which other computers can connect. Port numbers are used to distinguish one network service from another.

Mostly, this is done invisibly behind the scenes. However, knowing which programs use a specific port number becomes important when you start considering security. A firewall uses ports to form its rules about which types of network traffic to allow and which to prohibit. And the Active Connections utility (netstat.exe), used to determine which ports are currently in use, allows you to uncover vulnerabilities in your system using ports. Ports, firewalls, and the Active Connections utility are all discussed in Chapter 7.

Some firewalls make a distinction between TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) ports, which is usually unnecessary. In most cases, programs that use the more common TCP protocol will use the same port numbers as their counterparts that use the less-reliable UDP protocol.

Ports are divided into three ranges:

Well-known ports: 0-1023
Registered ports: 1024-49151
Dynamic and/or private ports: 49152-65535

Since a complete port listing would consume about a hundred pages of this book, only the most commonly used ports are listed here. For a more complete listing, see any of these resources:

http://www.portsdb.org/
http://www.iana.org/assignments/port-numbers
http://www.faqs.org/rfcs/rfc1700.html

Table C-1 lists the more commonly used TCP/IP ports.

Those ports marked with an in Table C-1 are commonly exploited by worms and other types of remote attacks. Unless you specifically need them, you should block them in your firewall or router.


Table C-1. Commonly used TCP/IP Ports and how they're used

Port number

Description

21

FTP (File Transfer Protocol)

22

SSH (Secure Shell)

23

Telnet

25

SMTP (Simple Mail Transfer Protocol), used for sending email

43

WhoIs

50-51

IPSec (PPTP Passthrough for VPN, Virtual Private Networking)

53

DNS (Domain Name Server), used for looking up domain names

69

TFTP

70

Gopher

79

Finger

80

HTTP (Hypertext Transfer Protocol), used by web browsers to download standard web pages

81

Kerberos

110

POP3 (Post Office Protocol, version 3), used for retrieving email

119

NNTP (Network News Transfer Protocol), used for newsgroups

123

NTP (Network Time Protocol), used for XP's Internet Time feature

135

RPC (Microsoft Windows Remote Procedure Call)

139

NETBIOS Session Service

143

IMAP4 (Internet Mail Access Protocol version 4)

161, 162

SNMP (Simple Network Management Protocol)

220

IMAP3 (Internet Mail Access Protocol version 3)

443

HTTPS (HTTP over TLS/SSL), used by web browsers to download secure web pages

445

File sharing for Microsoft Windows networks

500

IPSec (PPTP Passthrough for VPN, Virtual Private Networking)

563

NNTPS (Network News Transfer Protocol over SSL), used for secure newsgroups

593

RPC (Microsoft Windows Remote Procedure Call) over HTTP

1026

Windows Messenger - pop-ups (spam)

1352

Lotus Notes mail routing

1503

Windows Messenger - application sharing and whiteboard

1701

VPN (Virtual Private Networking) over L2TP

1723

VPN (Virtual Private Networking) over PPTP

1863

Windows Messenger - instant messenging

3389

Remote Desktop Sharing (Microsoft Terminal Services), used for remote control

4444

W32.BLASTER.WORM virus

5004 and up

Windows Messenger - audio and video conferencing (port is chosen dynamically)

5010

Yahoo! Messenger

5190

AOL Instant Messenger

5631, 5632

pcAnywhere, used for remote control

5800, 58015900, 5901

VNC (Virtual Network Computing), used for remote control

6699

Peer-to-peer file sharing, used by Napster-like programs

6891-6900

Windows Messenger - file transfer

7648, 7649

CU-SeeMe video conferencing




    Windows XP Annoyances For Geeks
    Fixing Windows XP Annoyances
    ISBN: 0596100531
    EAN: 2147483647
    Year: 2003
    Pages: 97
    Authors: David A. Karp

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