Experimental Physics and
Industrial Control System

Jameson Graef Rollins <[email protected]> · Tue, 09 Jul 2013 11:42:05 -0700

On Tue, Jul 09 2013, "Kasemir, Kay" <[email protected]> wrote:
> The first IOC will serve on TCP port 5065.
> The second one can't do that, so you get the warning Configured TCP port was unavailable, ...Using dynamically assigned TCP port 34497.
> Both will try to listen to UDP search requests on the same port, then reply with the TCP port that they actually use, so all should be fine.
>
> BUT: Because of a quirk in most network kernels only one of them will actually see those UDP search requests. For me it's usually the IOC started _last_.
>
> If you want your clients to send search requests to all IOCs that are listening on the UDP port, you need to send a broadcast. Search requests sent to a specific IP address will only reach one of the IOCs listening on that IP.
>
> You can try setting the EPICS_CA_ADDR_LIST=255.255.255.255.
> With localhost, that may not be possible, so you'll have to setup some network interface, maybe leave it disconnected, but it must have an IP address and most important a broadcast address.

Hi, Kay.  Thanks for the suggestion.  This is a possibility that I
considered, but since it requires administrative privileges to create
and configure the dummy interface it's less than ideal for a generic
testing infrastructure.

That said, I did give it a try and it does sort of work.  The dummy
interface is 127.2.0.1, and both servers bind to it.  However, the
client access is very slow:

0$ time EPICS_CA_ADDR_LIST=127.255.255.255 EPICS_CA_AUTO_ADDR_LIST=NO caget -t TEST0:FOO
0

real	0m6.292s
user	0m0.000s
sys	0m0.012s
0$

The initial response is fairly quick, but there's a long delay before
process returns.  Is using a broadcast address know to introduce a
noticeable delay like this?

jamie.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System