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TCP/IP Application Assignments and Server Port Number Ranges: Well-Known, Registered and Dynamic/Private Ports
(Page 2 of 2)
TCP/UDP Port Number Ranges
For this system to work well, universal
agreement on port assignments is essential. Thus, this becomes another
situation where a central authority is needed to manage a list of port
assignments that everyone uses. For TCP/IP, it is the same authority
responsible for the assignment and coordination of other centrally-managed
numbers, including IP addresses, IP Protocol numbers and so forth:
Assigned Numbers Authority (IANA).
As we have seen, there are 65,536
port numbers that can be used for processes. But there are also a fairly
large number of TCP/IP applications, and the list grows every year.
IANA needs to carefully manage the port number address space
to ensure that port numbers are not wasted on protocols that won't be
widely used, while also providing flexibility for organizations that
need to make use of obscure applications. To this end, the full spectrum
of TCP and UDP port numbers is divided into three ranges, as shown in
The existence of these ranges ensures
that there will be universal agreement on how to access a server process
for the most common TCP/IP protocols, while also allowing flexibility
for special applications. Most of the TCP/IP applications and application
protocols use numbers in the well-known port number range for their
servers. These port numbers are not generally used for client processes,
but there are some exceptions. For example, port 68 is reserved for
a client using the Boostratp
Protocol (BOOTP) or Dynamic
Host Configuration Protocol (DHCP).
Table 144: TCP and UDP Port Number Ranges
(Privileged) Port Numbers
0 to 1,023
These port numbers are managed
by IANA and reserved for only the most universal TCP/IP applications.
The IANA assigns these port numbers only to protocols that have been
standardized using the TCP/IP
RFC process, that are in the process of
being standardized, or that are likely to be standardized in the future.
On most computers, these port numbers are used only by server processes
run by system administrators or privileged users. These generally correspond
to processes that implement key IP applications, such as Web servers,
FTP servers and the like. For this reason, these are sometimes called
system port numbers.
(User) Port Numbers
There are many
applications that need to use TCP/IP but are not specified in RFCs,
or are not so universally used that they warrant a worldwide well-known
port number. To ensure that these various applications do not conflict
with each other, IANA uses the bulk of the overall port number range
for registered port numbers. Anyone who creates a viable TCP/IP server
application can request to reserve one of these port numbers, and if
approved, the IANA will register that port number and assign it to the
These port numbers are generally accessible by any user on a system
and are therefore sometimes called user port numbers.
49,152 to 65,535
These ports are neither reserved
nor maintained by IANA. They can be used for any purpose without registration,
so they are appropriate for a private protocol used only by a particular
Key Concept: Port numbers assignments are managed by IANA to ensure universal compatibility around the global Internet. The numbers are divided into three ranges: well-known port numbers used for the most common applications, registered port numbers for other applications, and private/dynamic port numbers that can be used without IANA registration.
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Version 3.0 - Version Date: September 20, 2005
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