Experimental Physics and
Industrial Control System

"Jeff Hill" <[email protected]> · Fri, 15 Apr 2005 12:02:07 -0600

Kate,

What network interfaces are used is of course dependent on what
routes are configured. Without knowing the IP addresses involved
and the routes that are configured on the host for MEDM, the IOC,
and any intervening routers, it is difficult to draw specific
conclusions.

However, I can guess that the following scenario might occur.

o CA server receives UDP search message from IOC's interface
specified in EPICS_CA_ADDR_LIST
o Server responds back to the source of the search message
o IP kernel chooses default route using interface n.n.n.n
o IP kernel needs to supply the "from" address in the IP header
and it will choose the same n.n.n.n that it selected for routing
purposes
o CA client library builds TCP circuit to n.n.n.n using "from"
address in the search response
o The same network interface is used for the TCP circuits of both
MEDMs invariant of the address specified in EPICS_CA_ADDR_LIST,
and the interface where the UDP search messaged arrived.

PS: The CA server in the IOC is different from the "portable" CA
server that is used by the EPICS gateway and other programs
(applies to both R3.14 and R3.13). The "portable" CA server has
capabilities to bind itself to a specified set of network
interfaces. This facilitates configuring the server to not
receive UDP search messages and or connect TCP circuits destined
for other interfaces. This capability is unfortunately not yet
supported by EPICS IOC's.

Jeff

> -----Original Message-----
> From: [email protected] [mailto:[email protected]] On
> Behalf Of Kate Feng
> Sent: Friday, April 15, 2005 11:28 AM
> To: [email protected]
> Subject: CA for IOCs w/ dual NICs
> 
> Hi,
> 
> There are two network interfaces (N.I.) on my IOC, each
> attached
> to  a  different  IP address. I  thought one could  decide
> which medm
> clients  "Channel Accessing"  which  N.I. by opening two
> windows.
> Both windows  are set with  EPICS_CA_AUTO_ADDR_LIST = NO.
> Window #1 is set with EPICS_CA_ADDR_LIST= IP1, while
> window #2  is set with  EPICS_CA_ADDR_LIST= IP2.
> 
> 
> Is ther any other better way ?   I wanted to make sure  that
> certain
> clients  CA the specified IP, instead of  the other one.  Thus,
> I
> disconnected
> one of the cable going to that specified N.I.  However, when I
> do that,
> all the medm clients on both windows  became disconnected from
> the IOC.
> 
> 
> Any pointer highly appreciated,
> Kate

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System