What is the value of TCP's MSL variable on SLES

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Environment

SUSE Linux Enterprise Server 10
SUSE Linux Enterprise Server 11
SUSE Linux Enterprise Server 12

Situation

TCP by definition (RFC 793) has connection states.

They include LISTEN, ESTABLISHED, FIN-WAIT-1, FIN-WAIT-2, CLOSING, TIME-WAIT, CLOSE-WAIT, LAST-ACK, and the virtual state of CLOSED.

When a TCP connection has passed through an Active Close and is now in a TIME-WAIT state, it MUST remain in that state by TCP specification for 2*MSL.

That brings up the question,
What is the value MSL on a SLES server?

Resolution

It turns out that the value is hard coded in the kernel and 2*MSL = 60 seconds.
You can find where it is hard coded here:
$(kernel_code)/include/net/tcp.h:
 ...
#define TCP_TIMEWAIT_LEN (60*HZ) /* how long to wait to destroy TIME-WAIT
                                                                       * state, about 60 seconds     */
 ...

The sysctl -a | grep -i fin command at the terminal returns net.ipv4.tcp_fin_timeout = 60.
This would appear to be a way to access and alter this functionality.
But since it is hard coded in the kernel there is no way to change it at the terminal.

Cause

Additional Information

Sometimes the hyphenated states are given with underscores like this:
FIN_WAIT_1, FIN_WAIT_2, TIME_WAIT, CLOSE_WAIT, LAST_ACK

Disclaimer

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