TCP Multidata Transmit

Multidata transmit (MDT) is available only for systems that run a 64-bit kernel. This feature is new in the Solaris 9 8/03 release.

MDT enables the network stack to send more than one packet at one time to the network device driver during transmission. Use of this feature reduces the per-packet processing costs by improving the host CPU utilization or network throughput.

The multidata transmit feature is only effective for device drivers that support this feature.

The following parameter must be enabled in the /etc/system file to use the MDT parameter:

set ip:ip_use_dl_cap = 0x1

MDT is disabled by default. The TCP/IP stack can be instructed to enable MDT as follows:

# ndd -set /dev/ip ip_multidata_outbound 1

Review the following cautions before enabling MDT:

• Use of this feature might change the appearance of any packets between the IP layer and the DLPI provider. For example, a third-party STREAMS module might be dynamically inserted between the IP layer and the DLPI provider by using the ifconfig modinsert command. This module might not work. The ifconfig modinsert command does not “understand” the MDT STREAMS data type.

• Modules might be inserted between the IP and the DLPI provider with the autopush(1M) mechanism. These modules might not work as well in this case.

• Keep this feature disabled when a STREAMS module is not MDT aware. For example, the public domain utilities ipfilter and CheckPoint Firewall-1 are not MDT aware.

For more information, see the Solaris Tunable Parameters Reference Manual and the ip(7P) man page.