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

Subject: Re: Why do I need to prevent looping when deploying CA gateway
From: Andrew Johnson <anj@aps.anl.gov>
To: <tech-talk@aps.anl.gov>
Date: Mon, 24 Jul 2017 16:50:30 -0500
Hi Lin,

On 07/24/2017 10:43 AM, Wang, Lin wrote:
> When I was deploying CA gateways for our facility recently according
> the users guide [1], I was confused about the motivation for
> preventing looping mentioned in the document. Does CA gateway looping
> affect anything? Will CA gateways work improperly when looping
> happens?
> 
> For example, when I create two CA gateways (gateway1 and gateway2) in
> one PC with eth0 and eth1 connecting to NetA and NetB respectively.
> Gateway1 binds eth0 as CA server IP and adds eth1/NetB to
> EPICS_CA_ADDR_LIST, whereas gateway2 binds eth1 as CA server IP and
> adds eth0/NetA to EPICS_CA_ADDR_LIST. This way, there is a loop and
> the internal PVs inside both gateway1 and gateway2 can be accessed
> from both NetA and NetB. However, I cannot see anything abnormal, the
> two CA gateways still work properly. Even if I capture UDP/TCP
> packets using Wireshark with cashark plugin, I still cannot see
> excessive packets.
> 
> Any hints or answers are appreciated. Thanks.

I haven't experienced this myself, but try stopping, turning off or
disconnecting one of the IOCs while monitoring the network traffic. I
suspect that's when looping might start to have an effect. Make sure you
have active client connections (MEDM/EDM/CSS-BOY) both going through the
gateway(s) and local to that IOC while you do that.

If you're using the -signore option or setting the environment variable
EPICS_CAS_IGNORE_ADDR_LIST correctly you should be protected against
loops though.

HTH,

- Andrew

-- 
Arguing for surveillance because you have nothing to hide is no
different than making the claim, "I don't care about freedom of
speech because I have nothing to say." -- Edward Snowdon

References:
Why do I need to prevent looping when deploying CA gateway Wang, Lin

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