Ephemeral Source Port Selection Strategies

Thanks to all those who contribute updates and corrections to this page! If you would like to be acknowledged publicly for your contributions, please indicate so when you contact us and we will list your name here.

Jon Zeolla for verifying the Microsoft Windows 8 port number range

Introduction

This page enumerates a variety of default ephemeral port usage and source port selection strategies known to be used by a variety of systems. We rely on community feedback to help us improve the accuracy and completeness of this page. Please send us your updates and corrections.

The table below summarizes the default ephemeral source port selection range and strategy used by modern systems. The strategy column denotes whether the values are derived from a global, system pool of values or a local, typically flow-specific pool based on some set of the 5-tuple (IP source address, IP destination address, protocol, source port and destination port) socket detail. It also denotes how subsequent values are chosen (e.g. sequential versus random). Following the table we discuss additional details about various implementations that cannot be easily summarized in the table with pointers and references to additional information.

Ephemeral Source Port Strategy Listing

System	Port Number Range	Selection Strategy
AIX	32768 - 65535	N/A
Android	N/A	N/A
Apple iOS 7	49152 - 65535	global, sequential (TCP), random (UDP)
Apple OS X 10.9	49152 - 65535	global, sequential (TCP), random (UDP)
BlackBerry OS	N/A	N/A
BSD/OS	49152 - 65535	N/A
HP-UX	49152 - 65535	N/A
IRIX	1024 - 65535	N/A
Linux	32768 - 61000	local, random
FreeBSD 10.0	10000 - 65535	global, random
Microsoft Windows 2000	1024 - 5000	global, sequential
Microsoft Windows ME	N/A	N/A
Microsoft Windows XP	1024 - 5000	global, sequential
Microsoft Vista	49152 - 65535	N/A
Microsoft Windows 7	49152 - 65535	N/A
Microsoft Windows 8	49152-65535	N/A
Microsoft Windows 8.1	N/A	N/A
Microsoft Windows 10	N/A	N/A
Microsoft Server 2003	1024 - 5000	global, sequential
Microsoft Server 2008	49152 - 65535	N/A
Microsoft Server 2012	N/A	N/A
Microsoft Server 2016	N/A	N/A
NetBSD	49152 - 65535	N/A
OpenBSD	1024 - 49151	global, random
QNX	N/A	N/A
Solaris	32768 - 65535	N/A
Symbian	N/A	N/A
HP Tru64 UNIX	1024 - 5000	N/A

System-specific Notes

Apple OS X

Mac OS X has leveraged some of the FreeBSD networking stack, so in this regard Mac OS X and FreeBSD are similar. However, FreeBSD changes may not find their way into Mac OS X at the same pace, if at all as is the case with ephemeral source port selection. As of this writing, the current version of OS X implements a slightly different default and older version of ephemeral source port selection strategy from an earlier release of FreeBSD. At a Mac OS X terminal prompt run sysctl -a | grep port to see the current settings (net.inet.ip.portrange.first and net.inet.ip.portrange.last are the default port range settings and the OS X specific option net.inet.udp.randomize_ports option is enabled by default, while the TCP equivalent is disabled).

FreeBSD

As of FreeBSD 10.0 the default ephemeral port range is between 10,000 and 65,535 inclusive, but applications that utilize the socket functions can alter the ephemeral port range by setting the socket option to one of the non-default values. The default value is specified by the macro IP_PORTRANGE_DEFAULT (10000 - 65535) and defined in /usr/include/netinet/in.h. There are also the IP_PORTRANGE_HIGH (49152-65535) and IP_PORTRANGE_LOW (0-1023) macros, but the last one requires root privileges.

Microsoft

In Microsoft Server 2000 and Windows XP the upper range of ephemeral source ports can be configured by setting the MaxUserPort value in the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters to an integer between 5000 and 65534.

NetBSD

As of NetBSD 6.1.5 the default ephemeral port range is between 49152 and 65535 inclusive, but applications that utilize socket functions can alter the ephemeral range by setting the socket option to one of the non-default values. The default minimum value is specified by the macro IPPORT_ANONMIN, while the maximum is specified by the macro IPPORT_ANONMAX both defined in /src/sys/netinet/in.h.

OpenBSD

As of OpenBSD 5.5 the default ephemeral port range is between 1024 and 49,151 inclusive, but applications that utilize the socket functions can alter the ephemeral port range by setting a socket option to one of the non-default values much like FreeBSD. The default value is specified by the macro IP_PORTRANGE_DEFAULT (1024-49151) and defined in /usr/include/netinet/in.h. There are also the IP_PORTRANGE_HIGH (49152-65535) and IP_PORTRANGE_LOW (0-1023) macros, but the last one requires root privileges.