The default initial retransmission timeout (RTO) value for a TCP connection in milliseconds. Refer to the following discussion of per route metrics for setting a different value on a per-route basis.

3 seconds

1 millisecond to 20 seconds

Yes

Do not change this value. Lowering the value can result in unnecessary retransmissions.

Unstable

The default maximum retransmission timeout value (RTO) in milliseconds. The calculated RTO for all TCP connections cannot exceed this value. See also "tcp_ip_abort_interval".

60 seconds

1 millisecond to 2 hours

Yes

Do not change the value in a normal network environment.

If in some special circumstances, the round trip time (RTT) for a connection is in the order of 10 seconds, you can change the value to a higher value. If you change this value, you should also change the tcp_ip_abort_interval parameter to match it. Change the value of tcp_ip_abort_interval to at least four times the value of tcp_rexmit_interval_max.

Unstable

The default minimum retransmission time-out (RTO) value in milliseconds. The calculated RTO for all TCP connections cannot be lower than this value. See also "tcp_rexmit_interval_max".

400 milliseconds

1 millisecond to 20 seconds

Yes

Do not change the value in a normal network environment.

TCP's RTO calculation should be able to cope with most RTT fluctuations. If in some very special circumstances such that the round trip time (RTT) for a connection is in the order of 10 seconds, change to a higher value. If you change this value, you should change the tcp_rexmit_interval_max parameter to match it. You should change the value of tcp_rexmit_interval_max to at least eight times the value of tcp_rexmit_interval_min.

Unstable

A constant added to the calculated retransmission time-out value (RTO) in milliseconds.

0 milliseconds

0 to 2 hours

Yes

Do not change the value.

When the RTO calculation fails to obtain a good value for a connection in some circumstances, you can change this value to avoid unnecessary retransmissions.

Unstable

If this parameter is set to 1, and the window scale option is enabled for a connection, TCP also enables the timestamp option for that connection.

1 (enabled)

0 (disabled), 1 (enabled)

Yes

Do not change this value. In general, when TCP is used in high-speed network, protection against sequence number wraparound is essential, thus you need the timestamp option.

Unstable

Controls the default minimum receive window size. The minimum is tcp_recv_hiwat_minmss times the size of maximum segment size (MSS) of a connection.

4

1 to 65,536

Yes

Do not change the value. If changing it is necessary, do not change the value lower than 4.

Unstable

If set to 1, protocol control blocks of TCP connections in TIME-WAIT state are compressed to reduce memory usage. If set to 0, no compression is done. See "tcp_time_wait_interval" also.

1 (enabled)

0 (disabled), 1 (enabled)

Yes

Do not turn off the compression mechanism.

Unstable

The default maximum UDP socket datagram size in bytes. For more information, see "udp_max_buf".

8192 bytes

4096 to 65,536

Yes

Note that an application can use setsockopt(3XNET) SO_SNDBUF to change the size for an individual socket. In general, you do not need to change the default value.

Unstable