Have people use sysctl to adjust somaxconn

# Network options. NMBCLUSTERS defines the number of mbuf clusters and

# defaults to 256. This machine is a server that handles lots of traffic,

# so we crank that value.

options         SOMAXCONN=256           # max pending connects

options         NMBCLUSTERS=4096        # mbuf clusters at 4096

#

options         OPEN_MAX=512            # maximum fds (breaks RPC svcs)

</PRE>

SOMAXCONN is not derived from maxusers, so you'll always need to increase

that yourself. We used a value guaranteed to be larger than Apache's

default for the listen() of 128, currently.

<P>

In many cases, NMBCLUSTERS must be set much larger than would appear

<P>

To increase the size of the <CODE>listen()</CODE> queue, you need to

adjust the value of SOMAXCONN. SOMAXCONN is not derived from maxusers,

so you'll always need to increase that yourself. We use a value guaranteed

to be larger than Apache's default for the listen() of 128, currently.

The actual value for SOMAXCONN is set in <CODE>sys/socket.h</CODE>.

The best way to adjust this parameter is run-time, rather than changing

it in this header file and thus hardcoding a value in the kernel and

elsewhere.  To do this, edit <CODE>/etc/rc.local</CODE> and add the

following line:

<PRE>

    /usr/sbin/sysctl -w kern.somaxconn=256

</PRE>

<P>

We used <CODE>256</CODE> but you can tune it for your own setup. In

many cases, however, even the default value of <CODE>128</CODE> (for

later versions of FreeBSD) is OK.

<P>

<STRONG>Caveats</STRONG>

<P>