Experimental Physics and
Industrial Control System

"Jeff Hill" <[email protected]> · Mon, 12 Mar 2007 11:33:27 -0600

> 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?

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
> -------------------------------------------------------------------

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System