RE: How many CA server tools per host?

[johill@lanl.gov (Jeff Hill)]

On Monday, November 16, 1998 3:01 PM, Guy Jennings [SMTP:jennings@anl.gov] wrote:
> 
> How many portable channel access server tools may be run on a given host
> at any one time?
> 

Guy,

Of course if all of the CA server tools are using different port numbers than you can 
have essentially an unlimited number of server tools per host. The C++ based CA server library
attempts to accommodate more than one server tool per host on the same port number, but
is restricted somewhat by limitations typically built into the IP kernels available today.
It turns out that if two processes are attached to the same CA UDP port and a broadcast or
multicast datagram addressed to that port arrives both processes will receive a copy of the message. 
However, unexpectedly, if a unicast datagram addressed to that port arrives then only one of the 
processes will receive a copy of the incoming message. A unicast datagram is a datagram sent to 
one IP host only. The bottom line is that you can use more than one server tool on the same port on the 
same host, but you will not be able to reliably connect to both of them using a unicast address
in EPICS_CA_ADDRESS_LIST. This is really a nuisance. I should at some point attempt to eliminate 
this inconsistency. One possible solution would be to allow port numbers to be specified with
the IP addresses in EPICS_CA_ADDRESS_LIST.

Jeff