Experimental Physics and
Industrial Control System

Burkhard Kolb <[email protected]> · Tue, 13 Mar 2007 14:33:50 +0100

Jeff Hill wrote:

I use the same list of IOCs on other linux boxes and have no problem
there.

This might be because what UDP responses are discarded off the end of the
finite length UDP queue might be highly dependent on what hosts manage to
jamb their responses in first - and therefore on the topology of the
network.
Anyhow this IOC is in the list but is actually really down - on purpose.

So, I still think it would be good idea to peek under the hood at the ICMP
traffic in case something unusual is going on (its not hard to do), but this
may only reveal that there is one ICMP response reflected off of each host
that isn't currently available.
We run a flat switched network.

This probably means of course that the control system is all contained
within one subnet? If so then perhaps you can get by using ordinary
broadcasted search requests? Listing each host in the EPICS_CA_ADDR_LIST
certainly does have the disadvantage of competition from ICMP responses when
the routing system knows that the host that is being sent a search message
is unreachable. One wouldn't generally have that specific problem with
broadcast based search messages.
Do you have an important reason to list the hosts individually in the
EPICS_CA_ADDR_LIST?
Well...

As our network people still refuse to have routed networks here we have
one large switched network with several thousand nodes. Many of them
constantly produce broadcast messages contributing to quite some load.

My concern was really the difference between Macs and the standard linux
boxes here, where I don't see this behaviour.

Maybe some of the Mac enthusiasts out there have an idea?
Are you listing specific hosts in the EPICS_CA_ADDR_LIST in order to avoid

contacting certain hosts on the network? If so, one solution might be to use

a different UDP port for a subsystem of the overall control system. You

could possibly also use a ca gateway to selectively couple between control

subsystems operating on different ports. This might transparently provide

the appearance of one control system operating on a single port to certain

clients even though there are actually multiple underlying control systems

operating on independent ports. 
Multicast groups might provide a better way to manage grouping of hosts
independent of subnets - in contrast to using different UDP ports. This
isn't implemented yet but it's probably not a large amount of programming to
add that feature. The primary benefit would be avoidance of configuration
complexity - especially if the control system crosses over multiple subnets.
Jeff
-----Original Message-----
From: Burkhard Kolb [mailto:[email protected]]
Sent: Friday, March 09, 2007 2:02 AM
To: Jeff Hill
Cc: [email protected]
Subject: Re: Darwin and EPICS_CA_AUTO_ADDR_LIST issue
Jeff Hill wrote:

On my MAC (OSX 10.4.8), EPICS base-3.14.9, medm 3.11:
When I set EPICS_CA_AUTO_ADDR_LIST to NO and have the

EPICS_CA_ADDR_LIST

pointing to the list of IOCs medm does not find all PVs. Sometimes the
connections work for a short time then several IOCs are not seen

anymore.

If I set it to YES, medm finds them always.
In the xterm window I get some error messages from really not existing
IOCs:
CAC: error = "Host is down" sending UDP msg to 140.181.98.50:5064
But the lost ones are not reported!
I use the same list of IOCs on other linux boxes and have no problem

there.
What is the response to "ping -s 140.181.98.50"?

ping: invalid packet size: `140.181.98.50'
Did you mean -R or -r?
Anyhow this IOC is in the list but is actually really down - on purpose.
But most of the other ones are VxWorks 68040 cpus all running the same
kernel, same setup...
What bothers me most, is that sometimes when I start a medm with a
screen where vxStats infos from the IOCs is displayed, the IOCs show up
and then drop out - in the case when EPICS_CA_AUTO_ADDR_LIST=NO.

PS: Behavior is known to vary between IP kernels for such unicast

addresses

if there are two or more daemons (in this case two or more CA UDP

servers)

listening to the same {IP address, port} tuple on the same host. The

typical

behavior difference is that on certain IP kernels only one daemeon

listening

on UDP port 5064 will receive a UDP message with a unicast destination
address, but in contrast on other IP kernels all daemeons listening on

UDP

port 5064 will receive such messages. In my experience UDP frames with
broadcast address destinations always go to all registered listeners
listening on UDP port 5064 - a uniform behavior across IP kernel
implementations.
PPS: One possible workaround to the above dilemma is to use directed
broadcast addresses (router forwarded broadcast addresses) in the
EPICS_CA_ADDR_LIST. This sometimes requires enabling of "broadcast
forwarding" features in your routers. We might also add support for
multicasting to future versions of CA.
We run a flat switched network.
Jeff
-----Original Message-----
From: Burkhard Kolb [mailto:[email protected]]
Sent: Thursday, March 08, 2007 9:28 AM
To: '[email protected]'
Subject: Darwin and EPICS_CA_AUTO_ADDR_LIST issue
On my MAC (OSX 10.4.8), EPICS base-3.14.9, medm 3.11:
When I set EPICS_CA_AUTO_ADDR_LIST to NO and have the

EPICS_CA_ADDR_LIST

pointing to the list of IOCs medm does not find all PVs. Sometimes the
connections work for a short time then several IOCs are not seen

anymore.

If I set it to YES, medm finds them always.
In the xterm window I get some error messages from really not existing
IOCs:
CAC: error = "Host is down" sending UDP msg to 140.181.98.50:5064
But the lost ones are not reported!
I use the same list of IOCs on other linux boxes and have no problem

there.

Any idea?
--
-------------------------------------------------------------------
Dr. Burkhard Kolb
GSI mbH  |   KP1   |  Planckstr. 1  |  D-64291 Darmstadt
Email: [email protected]                |  Tel.: +49 (0)6159 / 71 2667
-------------------------------------------------------------------

--
-------------------------------------------------------------------
Dr. Burkhard Kolb
GSI mbH  |   KP1   |  Planckstr. 1  |  D-64291 Darmstadt
Email: [email protected]                |  Tel.: +49 (0)6159 / 71 2667
-------------------------------------------------------------------

--
-------------------------------------------------------------------
Dr. Burkhard Kolb
GSI mbH  |   KP1   |  Planckstr. 1  |  D-64291 Darmstadt
Email: [email protected]                |  Tel.: +49 (0)6159 / 71 2667
-------------------------------------------------------------------

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System