Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Fri, 24 Sep 2010 12:37:36 -0500

On Friday 24 September 2010 12:01:07 Matthieu Bec wrote:
> > It is a simple matter to add multicast support to the
> > ca server, and that will address this issue.
>
> Of the different options I heard, it seems most transparent.

I'm not convinced it's quite as simple as Jeff makes out, and since this idea 
was first discussed in 1995 I wouldn't hold your breath waiting for it.

> Would it be backward compatible for older CA clients/servers trying to
> connect the single-host multiple IOCs?

It would need new versions of both the CA client and server code, plus you 
would have to configure the multicast group(s) that your IOCs and clients 
should use (probably through EPICS_CA_ADDR_LIST as Jeff suggests).  I don't 
know whether you also have to configure these in your network switches or 
routers as well.  Wikipedia says this about IP Multicast:

    There are at least two primary factors for the lack of widespread
    deployment, both somewhat related to the other. On the one hand,
    forwarding multicast traffic, particularly for two-way communication,
    requires a great deal of protocol complexity.  On the other hand,
    there are a number of additional operational concerns in being able to
    run a multicast network successfully, largely stemming from the
    complexity of a widely-deployed implementation, not the least of which
    is the enabling of additional avenues of failure, particularly from
    denial-of-service attacks.

- Andrew
-- 
The best FOSS code is written to be read by other humans -- Harald Welte

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System