Experimental Physics and
Industrial Control System

Andrew Johnson via Tech-talk <tech-talk at aps.anl.gov> · Fri, 16 Sep 2022 10:28:37 -0500

If the epics clients use the broadcast address, wont that allow multiple IOCs to listen on the same host on windows?

It's the other case (unicast to a host running multiple IOCs) where we have a workaround for a Linux host and it would be interesting to have something similar for Windows hosts.

Yes, you can use broadcasts.
The options in this example include

set EPICS_CA_ADDR_LIST=ca_gateway.bessy.de 
set EPICS_CA_AUTO_ADDR_LIST=NO 
-> You get PVs from the gateway, assuming the gateway hears you because it's the only CA server on that host.

set EPICS_CA_ADDR_LIST=my_computer.bessy.de 
set EPICS_CA_AUTO_ADDR_LIST=NO 
-> You get PVs from the IOC started last, since unicasts are only received by the listener registered last (or the one first for windows hosts??).

set EPICS_CA_ADDR_LIST=broadcast_address_of_the_subnet
set EPICS_CA_AUTO_ADDR_LIST=NO 
-> All CA servers on the subnet get it, which might be both my_computer.bessy.de and ca_gateway.bessy.de. So you can't avoid the gateway. A gateway is often configured to be read-only, so depending on luck you might get a read-only PV via the gateway or a writable PV from the actual IOC. Ask me how many confused emails that has caused.

One solution to this is to run the gateway on a non-standard port like 5099, so then you can  use

set EPICS_CA_ADDR_LIST=broadcast_address_of_the_subnet
set EPICS_CA_AUTO_ADDR_LIST=NO 
-> All servers on the subnet get it, including multiple IOCs on my_computer.bessy.de, but not the gateway

set EPICS_CA_ADDR_LIST=ca_gateway.bessy.de:5099
set EPICS_CA_AUTO_ADDR_LIST=NO 
-> Only the gateway will reply

.. or you get into the IP packet rewrite tricks mentioned earlier.

-- 
Complexity is free, it's Simplicity that takes work.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System