Specifications

Chapter 1 Understanding Networking and IP Addressing
Networking using IP
Niagara Release 2.3
Niagara Networking & Connectivity Guide Revised: May 22, 2002
1–31
About Ports A port is a communication channel that allows different applications on the same
computer to use network resources without interfering with each other. For example,
on a multi-function server that runs Telnet, FTP, and web servers, each function uses
a different TCP port (typically ports 23, 21, and 80, respectively) for clients to talk
to. They are used in TCP/IP networking for long term conversations between two
hosts (such as a client accessing a web page on a server).
To go back to the telephone analogy used previously, a port is like a telephone
extension in an office environment. While the main telephone number (the IP
address) is used to direct a call (the data) to the particular company (the computer),
the extension (the port) directs the call to the particular person (the application).
In IP networking, ports can be assigned from 0 to 65535, and many popular
applications have default ports, which are assigned or registered by IANA. Many
applications (such as Niagara) allow you to change the default port of a particular
function (such as the web server). For more information about Niagara ports, see
“Default Niagara Port Numbers,” page 6-7.
Note When the client initiates a conversation with the server it randomly chooses a
client-side port (greater than 1024) that is not currently in use. The client uses this
port to connect to the server on the server-side port (such as HTTP standard port 80).
For examples of this, review the “netstat” section on page 2-25.
Table 1-10 lists common IP networking functions and their default TCP ports.
Table 1-10 Common well-known TCP ports.
Port Function
21 FTP (file transfer protocol)
23 Telnet
25 SMTP (simple mail transfer protocol)
37 Time Protocol
53 DNS (domain name service)
80 HTTP (hypertext transfer protocol)
107 Rtelnet (remote telnet)
110 POP3 (post office protocol version 3)
119 NNTP (network news transfer protocol)
123 NTP (network time protocol)
143 IMAP (Internet message access protocol)
161 SNMP (simple network management protocol)
194 IRC (Internet relay chat protocol)
389 LDAP (lightweight directory access protocol)
401 UPS (uninterruptible power supply)
443 HTTPS (HTTP over TLS/SSL)
447 SNNP (simple network paging protocol)
563 NNTPS (NNTP over TLS/SSL)
636 LDAPS (LDAP over TLS/SSL)