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Subject: Re: Questions regarding CA protocol specification and phylosophy
From: "Kasemir, Kay" <kasemirk@ornl.gov>
To: Diego Sanz <dshernan80@gmail.com>, EPICS Tech Talk <tech-talk@aps.anl.gov>
Date: Wed, 13 Sep 2017 14:03:43 +0000
1. Theoretically, I can run 2 or more IOCs in the same host for the same IP. The first IOC takes CA-1-TCP for PV values data transmission with the clients, and the second one must take another port (e.j., 33003) so 33003-TCP for the same purpose. Besides  both IOCs will be listening on the same UDP port CA-1. Now I lunch a #caget PVname where the EPICS_CA_ADDR_LIST is the same IP, and it works for one of the IOCs and not for the other. I do the same with CSS, and occurs the same... only one of the IOC PVs are  reachable. Is there any other configuration regarding this issue?

--------

The main issue here is not TCP but UDP.
Both IOCs are listening on UDP 5064 for name searches.
So they should both see the "caget" looking for the PV name, right?
Unfortunately, due some some quirk in most network kernels, only the IOC started _last_ will actually receive UDP search requests that are sent to that computer, port 5064. As a workaround, you need to configure the EPICS_CA_ADDR_LIST to use the broadcast address of the respective subnet. 

See https://wiki-ext.aps.anl.gov/epics/index.php/How_to_Configure_Channel_Access,
https://wiki-ext.aps.anl.gov/epics/index.php/How_to_Make_Channel_Access_Reach_Multiple_Soft_IOCs_on_a_Linux_Host.

-Kay

Replies:
Re: Questions regarding CA protocol specification and phylosophy Dirk Zimoch
References:
Questions regarding CA protocol specification and phylosophy Diego Sanz

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