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'''Maximum segment lifetime''' or '''MSL''' is the time a [[Transmission Control Protocol|TCP]] [[protocol data unit|segment]] can exist in the [[Internetworking|internetwork]] system.  It was defined in 1981 to be {{nowrap|2 minutes}}.<ref>{{cite web | title=RFC 793 | work=Transmission Control Protocol | url=http://www.rfc-editor.org/rfc/rfc793.txt | accessdate=December 5, 2006 }}</ref>
{{quote | For this specification the MSL is taken to be 2 minutes.  This is an engineering choice, and may be changed if experience indicates it is desirable to do so. }}

The specification calls for this value to be used for the "time-wait" interval, the minimum time a system must keep the socket in the {{mono|TIME_WAIT}} ''state'' before designating the socket closed, thus preventing the socket from being re-used before that interval.

== Values in various operating systems ==

The command that can be used on Solaris systems (prior to v11) to determine the time-wait interval is:

    ndd -get /dev/tcp tcp_time_wait_interval

60000 (60 seconds) is a common value.

On [[FreeBSD]] systems this description and value can be checked by the command [[sysctl]]:<ref>{{cite web | title=Tuning FreeBSD to serve 100-200 thousands of connections
 | url=http://rerepi.wordpress.com/2008/04/19/tuning-freebsd-sysoev-rit/ }}</ref>
    sysctl -d net.inet.tcp.msl
    sysctl net.inet.tcp.msl
which gets the result:
    net.inet.tcp.msl: Maximum segment lifetime
    net.inet.tcp.msl: 30000

In Linux, the time-wait interval is defined by the {{mono|TCP_TIMEWAIT_LEN}}, hard-coded as 60 seconds.  Linux implements several possible optimizations to shorten the {{mono|TIME_WAIT}} state through ''recycling'', down to a minimum of 3.5s in recent kernels.<ref>{{cite web |title=Linux Kernel socket implementation| url=https://github.com/tinalinux/linux-3.10/blob/r40-v1.y/net/ipv4/inet_timewait_sock.c#L340 }}</ref><ref>{{ cite web | title=Linux Kernel headers for TCP| url=https://github.com/torvalds/linux/blame/0983f6bf2bfc0789b51ddf7315f644ff4da50acb/include/net/tcp.h#L144}} </ref>

==References==

<references/>

[[Category:Transmission Control Protocol]]