Experimental Physics and
Industrial Control System

"Jeff Hill" <[email protected]> · Thu, 29 Mar 2001 12:16:24 -0700

> 
> Our network masks are now set at FFFFFF00.  We spent a day last week
> upgrading to this more restrictive mask on all our iocs when our hosts
> changed to the same mask for security reasons.
> 

I'm am guessing that your problem is that there are large numbers of 
machines on your network that have not yet configured to the new netmask.
They are all replying to every CA broadcast with "ICMP destination unreachable"
and this is swamping the client's UDP input queue. This can result in very 
unreliable behavior that strongly depends on network topology (the responses 
that arrive first get through and all others are discarded). As I mentioned, 
you can use snoop (or some other sniffer) to obtain a list of hosts that must 
be fixed. You may also decide to place your control system behind a firewall.

Jeff

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System