Experimental Physics and
Industrial Control System

"Jeff Hill" <[email protected]> · Mon, 19 May 2003 13:00:12 -0600

> > I am running a Linux IOC on a machine that is on multiple
> > networks.  I
> > Message: "Ambiguous channel host (multiple IOC's have a
> > channel by that name)"

If you have the common situation where your host has multiple
network interfaces each attached to a different IP subnet
(broadcast domain), then you will *not* see these messages. 

However, if you have an unusual situation where multiple network
interfaces are attached to the same IP subnet (to the same
broadcast domain) then there is the possibility of your IOC's
receiving the same broadcast message twice and replying twice
from different IP addresses (depending on your IP kernel). 

The EPICS_CAS_INTF_ADDR_LIST variable can be used with the
portable server library to bind the CA server to a limited set of
network interfaces. Unfortunately, the original server in iocCore
does not implement this feature set and probably will not until a
subsequent release.

In the short term you might decide to disable or disconnect the
redundant network interface which is attached to the same subnet
as another network interface. It probably isn't buying you much
other than possibly redundancy or load balancing. These features
are probably more likely to be necessary when there is a massive
client load and that situation is more common when running the CA
proxy gateway (which uses the portable server library and does
implement the EPICS_CAS_INTF_ADDR_LIST feature set).

I should add that if the client and servers are *not* both
running recent versions of EPICS R3.14 then it is possible for
unusual hosts configured like yours to detect (and possibly
produce depending on your IP kernel) false CA beacon anomalies.
This can result in increased broadcast traffic on your LAN. An
R3.14 program named casw can be used to detect false beacon
anomalies. The details are in the R3.14 CA reference manual.

Another possibility is that the net mask is incorrectly
configured for your network interfaces or you might have routing
configuration problems.

Jeff

> -----Original Message-----
> From: [email protected] [mailto:[email protected]] On
> Behalf Of Adam DeGrush
> Sent: Monday, May 19, 2003 12:20 PM
> To: [email protected]
> Subject: Re: Multiple Network quesion
> 
> Don't know if this went throught the first time...
> 
> Adam DeGrush wrote:
> 
> > Hi All,
> >
> > Basic Question:
> > I am running a Linux IOC on a machine that is on multiple
> networks.  I
> > do I deal with the fact that under this condition there
> appears to be
> > two sets of databases,  one for each network. This, of
course,
> gives
> > warning messages when monitoring channels such as:
> >
> > Message: "Ambiguous channel host (multiple IOC's have a
> channel by that
> > name)"
> >  Severity: "Warning" Context: "Channel.VAL Accepted:
> netcom1.edu:5064
> > Rejected: netcom2.edu:5064 "
> >
> > Although Channel.VAL is really on only one machine.
> >
> > One solution, at least in my case, is for the database to
> exist on a
> > single network for broadcasting purposes. Is this possible?
> Is there
> > something better?
> >
> > Cheers and Thanks,
> > Adam DeGrush

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System