Maximum segment lifetime
Maximum segment lifetime or MSL is the time a TCP segment can exist in the internetwork system. It was defined in 1981 to be 2 minutes.[1]
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 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:[2]
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 TCP_TIMEWAIT_LEN, hard-coded as 60 seconds. Linux implements several possible optimizations to shorten the TIME_WAIT state through recycling, down to a minimum of 3.5s in recent kernels.[3][4]
References
- ↑ "RFC 793". Transmission Control Protocol. http://www.rfc-editor.org/rfc/rfc793.txt. Retrieved December 5, 2006.
- ↑ "Tuning FreeBSD to serve 100-200 thousands of connections". http://rerepi.wordpress.com/2008/04/19/tuning-freebsd-sysoev-rit/.
- ↑ "Linux Kernel socket implementation". https://github.com/tinalinux/linux-3.10/blob/r40-v1.y/net/ipv4/inet_timewait_sock.c#L340.
- ↑ "Linux Kernel headers for TCP". https://github.com/torvalds/linux/blame/0983f6bf2bfc0789b51ddf7315f644ff4da50acb/include/net/tcp.h#L144.
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