Network tuning and port allocation

[Peter Yandell]

Is there a simple way to check the proportion of available TCP ports 
currently in use for a particular address on a particular interface?

I'm testing some networking gear, and am using a few tools to generate 
large amounts of network traffic. One of the tuning issues in doing 
this is ensuring that enough TCP port numbers are available to support 
all the connections I want to make.

For most network tuning issues, there's a way to make a measurement and 
a way to make an adjustment. For example, I can check the mbuf usage 
using "netstat -m" and adjust my nmbclusters accordingly.

For TCP port usage I can make the adjustment through 
net.inet.ip.portrange.*, or by assigning more addresses to an interface 
and distributing traffic across them, but how do I measure the problem 
in the first place? At the moment, if I haven't got enough ports 
available, I usually discover it by noticing a slowdown in traffic and 
then eliminating all the other potential problems, or by just 
allocating more ports and seeing if it makes a difference. I'm hoping 
there's a better way.

Cheers,

Pete Yandell