Experimental Physics and
Industrial Control System

Mark Rivers via Tech-talk <tech-talk at aps.anl.gov> · Wed, 17 Jun 2020 19:24:21 +0000

> My understanding is that EPICS_CA_ADDR_LIST will let me access other subnets but only if if multicast packets are passed between the subnets or if there is a cagateway running.  Is that correct? 

I don't think that is correct.  If you set EPICS_CA_ADDR_LIST to a specific machine IP then I don't think it sends a multicast UDP message, it sends a TCP message directly to that machine.

> Is EPICS_CA_ADDR_LIST supposed to include all of subnet B (subnetB.255) or just the IP of the gateway?

I am not sure about gateways.  But EPICS_CA_ADDR_LIST can be set either to the broadcast address of the other network, or to the IP address of a specific EPICS IOC machine or machines.  There are some limitations:

- For broadcasts to work the router must be configured to allow directed broadcasts.  We do that on our beamline network at the APS.
- If you set EPICS_CA_ADDR_LIST to the specific IOC machine then by default it will not work if that machine is running more than one IOC.  But there are ways to work around that.

Mark

-----Original Message-----
From: Tech-talk <tech-talk-bounces at aps.anl.gov> On Behalf Of Randall Cayford via Tech-talk
Sent: Wednesday, June 17, 2020 2:10 PM
To: tech-talk at aps.anl.gov
Subject: EPICS across subnets

I’m trying to understand what the options are for working with EPICS across subnets and for remote access.

We have some IOCs running on subnet A.  We also need access to a few PVs from IOCs running on network B.  I would like to access PVs on both A and B from subnet C.  Subnets are separated by multiple layers of routers.  Subnet A is on the experimental floor and is pretty locked down to control network traffic. 

My understanding is that EPICS_CA_ADDR_LIST will let me access other subnets but only if if multicast packets are passed between the subnets or if there is a cagateway running.  Is that correct? 

If cagateway is running on subnet B does it pass only the packets requested by a client on subnet A or does it pass all the broadcast traffic from subnet B?

Is EPICS_CA_ADDR_LIST supposed to include all of subnet B (subnetB.255) or just the IP of the gateway?

What router access rules are needed to allow connections to PVs on B from clients on A or C?

Does PVaccess change any of this?

I’m sure this is all somewhere in the documentation but I haven’t been able to sort it out by reading.  This involves a lot of different people to set up so I’m looking for some clarity on what needs to be done and who needs to do it.

Randall

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System