Experimental Physics and
Industrial Control System

"Jeff Hill" <[email protected]> · Tue, 8 Jun 2004 16:37:22 -0600

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

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System