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<== Date ==> <== Thread ==>

Subject: Re: single IOC on Linux with two ports
From: Andrew Johnson <anj@aps.anl.gov>
To: Hovanes Egiyan <hovanes.egiyan@gmail.com>
Cc: "tech-talk@aps.anl.gov" <tech-talk@aps.anl.gov>
Date: Tue, 16 Jul 2013 10:23:34 -0500
Hi Hovanes,

On 07/16/2013 09:41 AM, Hovanes Egiyan wrote:
I would like to run one EPICS IOC on a Linux system configured with two
Ethernet interfaces connected to
two different networks. But I would like the IOC to respond to the
requests to only one of the interfaces,
and send the data using the same interface. Basically, I would like
EPICS IOC not to interfere with
the main traffic going through the other Ethernet port. Can this be
done? I know it can be done using a virtual
machine, but I would like to avoid doing it and consuming extra
resources since these are VME CPUs.

I tried running an IOC that I built using R3-14-12-3, and when I set
EPICS_CAS_INTF_ADDR_LIST
the IOC still responds to the requests sent to any of the two
interfaces. Actually, the CA manual page says that
/"In R3.14 and previous releases the CA server employed by iocCore does
not implement this feature./"
Is this feature going to be implemented for IOCs in the near-future
releases (3-15 for instance)?

Nobody in the core developers group is working on that at the moment so I think it unlikely, although we would be happy to review and accept patches to implement that often-requested functionality.

In the meantime you may be able to set up a firewall on your Linux system to prevent UDP packets for ports 5064 and 5065 from being sent or received on your second network interface -- you probably don't need to block any TCP packets, but it won't do any harm if you do them too.

And another
question is if eventually the IOC only responds to the requests
addressed to only one of its interfaces, will it
also transmit the data using that interface or the data will be routed
considering both Ethernet interfaces?

The IOC listens to UDP packets coming from CA clients doing name searches, and broadcasts a UDP beacon packets every 15 seconds. The IOC is also usually a CA client so it will send out UDP search request packets, and connects to the caRepeater program which is listening to beacon packets from other IOCs.

The route that TCP connections take to/from the IOC is controlled purely by the routing configuration of your interfaces and the IP subnets that they belong to. I would not recommend connecting two interfaces on the same machine to the same IP subnet unless you know what you're doing.

HTH,

- Andrew
--
Advertising may be described as the science of arresting the human
intelligence long enough to get money from it. -- Stephen Leacock

References:
single IOC on Linux with two ports Hovanes Egiyan

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