Summary: How do you tune TCP/IP packet re-transmit timeout

From: David Gempton (
Date: Mon Sep 16 1996 - 18:58:20 CDT

Many thanks to:
Daniel Blander =8^)
Sr. Systems Engineer Applied Computer Solutions

His reply .......

/usr/sbin/ndd -set /dev/tcp tcp_deferred_ack_interval

You can use /usr/sbin/ndd /dev/tcp tcp_deferred_ack_interval
to see the current value......
The solution I used was based on his EM. I created a script in /etc/rc2.d with these entries:
# Alter the tcp/ip re-transmit interval.
/usr/sbin/ndd -set /dev/tcp tcp_deferred_ack_interval 500
/usr/sbin/ndd -set /dev/tcp tcp_rexmit_interval_initial 1500
/usr/sbin/ndd -set /dev/tcp tcp_rexmit_interval_min 600

This has dropped the retransmit rate from more that 25% to arround 3%.
Original Question.

Could someone tell me:

How to increase the timeout value for TCP/IP re-transmitting packets due to not receiving an "Ack" from the packet destination with in that timeout period.

The situation:
The network is a WAN consisting of 18 LAN's. These LAN's all access one server called "Server-X" via a Router called "Rout-X".

9 of the lans are PC networks & 9 of the lans are PC networks with a local Solaris 2.3 work station. Server-X is running Solaris 2.3.

I am having periods of poor responce times due to congestgion caused I believe by the re-transmitting of IP protocol packets.

What I want to do is increase the timeout on re transmitting packets. In the hope that given a little more time the ACK's will arrive.

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