Section A-3. IP Port Numbers

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A-3. IP Port Numbers

Transport layer protocols identify higher-layer traffic with 16-bit fields called port numbers. A connection between two devices uses a source port and a destination port, both contained in the protocol data unit. Figure A-3 shows the User Data Protocol (UDP) header format, with the source and destination port fields shaded. Figure A-4 shows the Transmission Control Protocol (TCP) header format, with the source and destination port fields shaded.

Figure A-3. UDP Datagram Format Showing Port Fields


Figure A-4. TCP Segment Format Showing Port Fields


Both UDP and TCP use port numbers that are divided into the following ranges:

  • Well-known port numbers (0 through 1023)

  • Registered port numbers (1024 through 49151)

  • Dynamic or private port numbers (49152 through 65535)

Usually, a port assignment uses a common port number for both UDP and TCP. A connection from a client to a server uses the well-known port on the server as a service contact port, while the client is free to dynamically assign its own port number. For TCP, the connection is identified by the source and destination IP addresses, as well as the source and destination TCP port numbers.

Cisco firewalls have keywords that can be used to specify certain IP ports in access lists. Table A-3 shows these keywords, along with the IP port numbers.

Table A-3. Cisco Firewall Keywords for IP Ports

Port

UDP-Applicable?

TCP-Applicable?

Firewall Keyword

UDP/TCP Protocol Description

7

Yes

Yes

echo

Echo

9

Yes

Yes

discard

Discard

13

No

Yes

daytime

Day time, RFC 867

19

No

Yes

chargen

Character generator

20

No

Yes

ftp-data

File Transfer Protocol (FTP), data port

21

No

Yes

ftp

File Transfer Protocol (FTP), control port

22

No

Yes

ssh

Secure Shell (SSH)

23

No

Yes

telnet

Telnet, RFC 854

25

No

Yes

smtp

Simple Mail Transport Protocol (SMTP)

37

Yes

No

time

Time protocol

42

Yes

No

nameserver

Host Name Server

43

No

Yes

whois

Who Is

49

Yes

Yes

tacacs

Terminal Access Controller Access Control System Plus (TACACS+)

53

Yes

Yes

domain

Domain Name System (DNS)

67

Yes

No

bootps

Bootstrap Protocol (BOOTP) server

68

Yes

No

bootpc

Bootstrap Protocol (BOOTP) client

69

Yes

No

tftp

Trivial File Transfer Protocol (TFTP)

70

No

Yes

gopher

Gopher

79

No

Yes

finger

Finger

80

No

Yes

www

Hypertext Transfer Protocol (HTTP)

101

No

Yes

hostname

Host name server

109

No

Yes

pop2

Post Office Protocol (POP), version 2

110

No

Yes

pop3

Post Office Protocol (POP), version 3

111

Yes

Yes

sunrpc (rpc)

Sun Remote Procedure Call (RPC)

113

No

Yes

ident

Ident authentication service

119

No

Yes

nntp

Network News Transfer Protocol (NNTP)

123

Yes

No

ntp

Network Time Protocol (NTP)

137

Yes

No

netbios-ns

NetBIOS Name Service

138

Yes

No

netbios-dgm

NetBIOS Datagram Service

139

No

Yes

netbios-ssn

NetBIOS Session Service

143

No

Yes

imap4

Internet Message Access Protocol (IMAP), version 4

161

Yes

No

snmp

Simple Network Management Protocol (SNMP)

162

Yes

No

snmptrap

Simple Network Management Protocol (SNMP) trap

177

Yes

No

xdmcp

X Display Manager Control Protocol (XDMCP)

179

No

Yes

bgp

Border Gateway Protocol (BGP)

194

No

Yes

irc

Internet Relay Chat (IRC) protocol

195

Yes

No

dnsix

DNSIX Session Management Module Audit Redirector

389

No

Yes

ldap

Lightweight Directory Access Protocol (LDAP)

434

Yes

No

mobile-ip

MobileIP-Agent

443

No

Yes

https

Hypertext Transfer Protocol over SSL/TLS

496

Yes

Yes

pim-auto-rp

Protocol-Independent Multicast (PIM) autodiscovery

500

Yes

No

isakmp

Internet Security Association and Key Management Protocol (ISAKMP; UDP only)

512

Yes

No

biff

New mail notification for UNIX-based mail systems

512

No

Yes

exec

Remote process execution

513

No

Yes

login

Remote login

513

Yes

No

who

Who

514

No

Yes

cmd

Remote process execution with automatic authentication

514

Yes

No

syslog

System log

515

No

Yes

lpd

Line Printer Daemon (LPD)

517

Yes

Yes

talk

Talk

520

Yes

No

rip

Routing Information Protocol (RIP)

540

No

Yes

uucp

UNIX-to-UNIX Copy Program (UUCP)

543

No

Yes

klogin

KLOGIN

544

No

Yes

kshell

Korn Shell

636

No

Yes

ldaps

Lightweight Directory Access Protocol (LDAP) over SSL/TLS

750

Yes

Yes

kerberos

Kerberos

1352

No

Yes

lotusnotes

IBM Lotus Notes

1494

No

Yes

citrix-ica

Citrix Independent Computing Architecture (ICA)

1521

No

Yes

sqlnet

Structured Query Language (SQL) Network

1645

Yes

No

radius

Remote Authentication Dial-In User Service (RADIUS) authentication; obsolete; moved to 1812

1646

Yes

No

radius-acct

Remote Authentication Dial-In User Service (RADIUS) accounting; obsolete; moved to 1813

1720

No

Yes

h323

H.323 call signaling

1723

No

Yes

pptp

Point-to-Point Tunneling Protocol (PPTP)

2748

No

Yes

ctiqbe

Computer Telephony Interface Quick Buffer Encoding (CTIQBE)

5190

No

Yes

aol

America Online (AOL)

5510

Yes

No

secureid-udp

SecureID over UDP

5631

No

Yes

pcanywhere-data

pcAnywhere data

5632

Yes

No

pcanywhere-status

pcAnywhere status


    team bbl



    Cisco ASA and PIX Firewall Handbook
    CCNP BCMSN Exam Certification Guide (3rd Edition)
    ISBN: 1587051583
    EAN: 2147483647
    Year: 2003
    Pages: 120
    Authors: David Hucaby

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