Experimental Physics and
Industrial Control System

"Jeff Hill" <[email protected]> · Thu, 10 Jun 2004 08:54:29 -0600

> On modern Linux kernels, it is also possible to create 
> "virtual network interfaces", i.e. to assign more that one 
> IP address to the same physical network interface. It should 
> be possible to run every IOC with its own virtual 
> interface/addess/hostname. But I have not tried that yet.
> 

An interesting idea. Please send a summary of your experiences if you try
this.

Thanks,

Jeff

> Dirk
> 
> 
> 
> Jeff Hill wrote:
> > Hi Mike,
> >
> > There is a way to do this, but there are also some significant
> limitations.
> > They are documented in the CA reference manual, and I have attached an
> > excerpt. A possible solution to this problem would be to add
> multicasting
> > support to the CA server. This probably isn't going to be that hard to
> do,
> > but so far there haven't been that many requests for multiple servers
> on the
> > same system.
> >
> > Of course, another possibility will be to just combine N IOCs into one.
> >
> > Jeff
> >
> > Unicast Addresses in the EPICS_CA_ADDR_LIST Does not Reliably Contact
> > Servers Sharing the Same UDP Port on the Same Host
> >
> > Two servers can run on the same host with the same server port number,
> but
> > there are restrictions. If the host has a modern IP kernel it is
> possible to
> > have two or more servers share the same UDP port. It is not possible
> for
> > these servers to run on the same host using the same TCP port. If the
> CA
> > server library detects that a server is attempting to start on the
> same port
> > as an existing CA server then both servers will use the same UDP port,
> and
> > the 2nd server will be allocated an ephemeral TCP port. Clients can be
> > configured to use the same port number for both servers. They will
> locate
> > the 2nd server via the shared UDP port, and transparently connect to
> the 2nd
> > server's ephemeral TCP port. Be aware however that If there are two
> server's
> > running on the same host sharing the same UDP port then they will both
> > receive UDP search requests sent as broadcasts, but unfortunately (due
> to a
> > weakness of most IP kernel implementations) only one of the servers
> will
> > typically receive UDP search requests sent to unicast addresses (i.e.
> a
> > single specific host's ip address).
> >
> >
> >
> >>-----Original Message-----
> >>From: Laznovsky, Michael [mailto:[email protected]]
> >>Sent: Tuesday, June 08, 2004 3:56 PM
> >>To: tech talk
> >>Subject: multiple virtual IOCs with single CA server?
> >>
> >>Greetings- when running multiple virtual (i.e. target=solaris) IOCs on
> >>one host, is it possible to configure a single channel access server
> to
> >>provide all the PVs, rather than having multiple servers all using
> >>different ports?
> >>
> >>I can see that difficulties, given that the IOCs run as independent
> Unix
> >>processes... might an alternative be to daisy-chain the CA servers
> >>somehow
> >>on the same ports?  Just speculating here.
> >>
> >>thanks,
> >>Mike
> >>
> >>-----
> >>Michael P. Laznovsky
> >>mailto:[email protected]
> >>Application Software Developer, ESD                     ofc: (650)
> 926-
> >>2924
> >>Stanford Linear Accelerator Center, MS-46               fax: (650)
> 926-
> >>3515
> >>2575 Sand Hill Road, Menlo Park CA 94025 USA
> >>http://www.slac.stanford.edu
> >
> >
> >
> 
> 
> --
> Dr. Dirk Zimoch
> Swiss Light Source
> Paul Scherrer Institut
> Computing and Controls
> phone +41 56 310 5182
> fax   +41 56 310 4413

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System