I am using udp as communication protocol. I know that udp is connection 
less and may lose datagrams, but i expected this only on real networks 
or buffer overflows, not when using the loopback interface.

My application performs an handshaking over udp, the client sends an 
request and the server ansers with an ack. Fairly simple, but when 
running on max speed with no wait states, some datagrams are lost.
But why? Sending request-response is a form of flow-control, so the 
network buffers for udp should not overflow.

Is thery any way to reduce the discardment of datagrams, possibly a 
socket option or solaris kernel parameters? The problem occurs on real 
network connections (not loopback), too.
I used the option SO_DEBUG with my socket, but it seems there's no 
debug-log written to the syslog.
Are there any other tuning parameters!?

regards, markus

Markus Breuer <markus.breuer@gmx.de> writes:

>My application performs an handshaking over udp, the client sends an 
>request and the server ansers with an ack. Fairly simple, but when 
>running on max speed with no wait states, some datagrams are lost.
>But why? Sending request-response is a form of flow-control, so the 
>network buffers for udp should not overflow.

If you do request response I would not expecting packetloss; if you
are sending as fast as you can and you're not waiting for responses
then the kernel will not flow control UDP buffers will overflow
and packets will be dropped.

>Is thery any way to reduce the discardment of datagrams, possibly a 
>socket option or solaris kernel parameters? The problem occurs on real 
>network connections (not loopback), too.
>I used the option SO_DEBUG with my socket, but it seems there's no 
>debug-log written to the syslog.


You can increase the udp buffer size using setsockopt() and the
max buffer size using ndd -set /dev/udp.

For loopback, you can use AF_UNIX, SOCK_SEQPACKET

Casper
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Expressed in this posting are my opinions.  They are in no way related
to opinions held by my employer, Sun Microsystems.
Statements on Sun products included here are not gospel and may
be fiction rather than truth.