to use larger network buffer sizes:

Solaris: ndd -set /dev/udp udp_max_buf {value}

Linux: sysctl -w net.core.rmem_max={value}
       sysctl -w net.core.wmem_max={value}

MacOSX / FreeBSD: sysctl -w kern.ipc.maxsockbuf={value}
(The actual maximum you can use is 8/9 of this value)

NetBSD: sysctl -w kern.sbmax={value}