Tuning TCP/IP performance

The IP protocol stack is configured to maximize performance on all supported network adapters. If desired, you can further adjust performance parameters for each network interface using the ifconfig(ADMN) command as described in ``Using ifconfig to change parameters for a network card''. This command allows you to adjust:

• The send and receive TCP window for an interface. These windows are used by two communicating systems to negotiate the amount of data that can be sent before an acknowledgement is required. The default values of these windows are set to optimize performance on a local area network (LAN). If you are using a high bandwidth, and high latency connection such as a satellite link, increase the values of these parameters to increase throughput on the link. The maximum value that you can set is 64KB.

• The maximum segment size (MSS) rounding parameter. This is a boolean value; if set to 1, TCP negotiates the largest segment size that can be transmitted in the maximum transmission unit of the physical network. This is also referred to as using full frames. If set to 0, the MSS is rounded down to the nearest power of 2. For Ethernet, this corresponds to 1KB.

  With modern Ethernet hardware, you should use full frames to maximize the amount of data per Ethernet frame. On older Ethernet cards with small buffers and narrow data paths, rounding down should be selected to enable the data in the Ethernet frame to be moved into the card's buffer more efficiently.

  Token Ring networks have a much larger MTU than Ethernet; full frames should always be used.

• One-packet mode. This should be set for older network adapters whose small buffers cannot handle back-to-back streams of packets.

• Time-to-live. If it is known that a substantial number of network hops will be necessary for a packet to reach its destination, increase this parameter.

Problems with TCP/IP may be experienced if:

• There are insufficient STREAMS resources. These may be investigated as described in ``STREAMS resources''.

• There is too much activity on the network. Break the network into smaller subnetworks, or move network-intensive client-server applications onto dedicated machines. These issues are considered further in ``Configuring network topology for performance''.

• There is intermittent loss of connection due to the network being incorrectly configured physically. See ``Testing network connectivity'' for ways of testing this.

• Using the Internet routing discovery daemon (irdd) instead of routed or gated as described in ``Configuring routing for performance''.

• Altering the functionality of the domain name server to decrease system load, or to balance the load between the network and the local machine as described in ``Configuring DNS name service for performance''.

• Ensuring that serial line communications (SLIP and PPP) operate at peak performance as described in ``Tuning SLIP performance'' and ``Tuning PPP performance''.

See also:

• ``Troubleshooting TCP/IP''