Technical data

Tuning Techniques
2.1 Subsystem Attributes
Table 2–4 (Cont.) TCP Keepalive Options
Option Description
tcp_keepintvl Specifies the amount of time, in seconds, between retransmission of
keepalive probes. The default interval is 75 seconds.
tcp_keepcnt Specifies the maximum number of keepalive probes that are sent before
the connection is dropped. The default is 8 probes.
tcp_keepinit Specifies the maximum amount of time, in seconds, before an initial
connection attempt times out. The default is 75 seconds.
2.1.6.7 Increasing the Timeout Rate for TCP Connection Context
The TCP protocol includes a concept known as the Maximum Segment Lifetime
(MSL). When a TCP connection enters the TIME_WAIT state, it must remain in
this state for twice the value of the MSL; otherwise, undetected data errors on
future connections can occur. The
inet subsystem attribute tcp_msl determines
the maximum lifetime of a TCP segment and the timeout value for the
TIME_WAIT
state.
In some situations, the default timeout value for the TIME_WAIT state (60 seconds)
is too large, thereby reducing the value of the tcp_msl attribute frees connection
resources sooner than the default setting.
Performance Benefits and Tradeoffs
You can decrease the value of the tcp_msl attribute to make the TCP connection
context time out more quickly at the end of a connection. However, this will
increase the chance of data corruption.
You can modify the
tcp_msl attribute without rebooting the system.
When to Tune
Usually, you do not have to modify the timeout limit for the TCP connection
context.
Recommended Values
The value of the
tcp_msl attribute is set in units of 0.5 second. The default value
is 60 units (30 seconds), which means that the TCP connection remains in TIME_
WAIT state for 60 seconds, or twice the value of the MSL.
Do not reduce the value of the tcp_msl attribute unless you fully understand
the design and behavior of your network and the TCP protocol. It is strongly
recommended that you use the default value; otherwise, there is the potential for
data corruption.
2.1.6.8 Disabling Delayed Acknowledgment
The TCP/IP software can send an acknowledgment packet for every frame
received over the network. However, this is an inefficient mode of operation.
The
tcp_nodelack attribute controls the delay of acknowledgment messages.
When this attribute is set to 0 (the default), network traffic is greatly reduced. If
you set this attribute to 1, an acknowledgment message is sent for every frame
received, increasing network traffic and impacting the performance of the network
server.
Tuning Techniques 2–13