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<== Date ==> <== Thread ==>

Subject: Re: Questions regarding CA protocol specification and phylosophy
From: Michael Davidsaver <mdavidsaver@gmail.com>
To: Diego Sanz <dshernan80@gmail.com>, Dirk Zimoch <dirk.zimoch@psi.ch>
Cc: EPICS Tech Talk <tech-talk@aps.anl.gov>
Date: Wed, 13 Sep 2017 10:45:20 -0500
On 09/13/2017 10:05 AM, Diego Sanz wrote:
> First of all, thanks a lot
> 
> Starting for the configuration: the 2 IOCs and the EPICS client is in
> the same Host, no firewall...
> If I understood correctly, every IOC, shall be working in different IPs
> on different subnetworks? e.g., 
> 
> IOC1 on 192.168.0.2 
> 
> IOC2 on 192.168.1.3
> 
> and client shall have access to booth IPs....
> 
> So then, the configuration as follows is not correct:
> 
> all of them working on 127.0.0.1

FYI, by default 127.0.0.1 (aka. the loopback interface) isn't used.  By
this I mean that beacons and searches will not be sent to 127.0.0.1.
However, by default listening sockets are bound to 0.0.0.0 (aka wildcard
interface) which will receive UDP traffic sent to 127.0.0.1.

For this reason you'll sometimes see EPICS_CA_ADDR_LIST=127.0.0.1 given
as a workaround for CA issues when client and IOC are on the same host.
This sends unicast searches to localhost.  As this is unicast, it works
with only one IOC on the host (typical developer scenario).

A linux specific trick EPICS_CA_ADDR_LIST=127.255.255.255 works for many
IOC.  On linux the loopback interface supports broadcasts but doesn't
set the IFF_BROADCAST flag to advertise this fact.


> Is well understood?
> 
> Thanks a lot 
> 
> Diego
> 
> 
> 
> 2017-09-13 16:26 GMT+02:00 Dirk Zimoch <dirk.zimoch@psi.ch
> <mailto:dirk.zimoch@psi.ch>>:
> 
>     On 13.09.2017 16:03, Kasemir, Kay wrote:
> 
>         The main issue here is not TCP but UDP.
> 
> 
>     Just for completeness: TCP can be an issue as well if you have a
>     firewall between client and IOC. Even if if you tell the firewall to
>     allow the CA ports for UDP and TCP then the search broadcast may
>     pass, maybe even the reply reaches the client, but you still may not
>     be able to connect to the dynamically assigned TCP port of the
>     second IOC.
> 
>     Dirk
> 
> 


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

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