Sun Microsystems 1.0 - Manual (Page 55)

Improving Network Performance 29
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2. Use ndd —set to modify the current value of the TCP and UDP low water
marks ( tcp_xmit_lowat and udp_xmit_lowat ).
For optimum performance over FDDI connections, set the TCP and UDP
low water marks to 24 Kbytes.
Tuning the High and Low Water Marks at Boot Time
Each time you reboot your machine, the high and low water marks are reset to
their default values. If you want to configure your system so that the high
water marks are modified automatically each time you reboot the machine,
you must put these commands in a start-up script.
An example script is locate on the SunFDDI/P CD-ROM. Once installed on
your machine, this script sets the TCP and UDP high and low water marks
each time you reboot. The TCP and UDP high water marks are set to 32 Kbytes;
the TCP and UDP low water marks are set to 24 Kbytes. You can modify the
example script to enter your own values, if required.
Tuning the Socket Options
For applications that use Sockets, the application developer can make more
efficient use of the increased bandwidth provided by an FDDI connection by
increasing the size of the send and receive buffers used by a specific
application. This manipulation is restricted to applications and do not affect
the other socket connections.
Solaris 2.5.1 environments support program calls to getsockopt(3N) and
setsockopt(3N) . The options SO_SNDBUF and SO_RCVBUF are used to set
the size of the TCP send and receive buffers for a specified Socket. See the man
page for more detailed information.
To optimize performance, assign consistent values for the transmit and receive
buffers. The default value (4 Kbytes) assigned to these parameters is optimized
for transmitting across Ethernet connections. For applications running over
FDDI, the send and receive buffers should be set to 32 Kbytes.
# ndd —set /dev/tcp tcp_xmit_lowat 24576
# ndd —set /dev/udp udp_xmit_lowat 24576