Re: Communication error

[Francisco Ramos via Tech-talk <tech-talk at aps.anl.gov>]

Hi Michel, 

     First of all, thank you for your reply, it has been very helpful and has even allowed me to go deeper into the problem.

The longer story goes back to 2017 and:
https://code.launchpad.net/~epics-core/epics-base/camodern/+merge/306371

     We have tested and analyzed both solutions. The first one only works in one direction, as you explained (Note that this is only needed in one direction.  New (>=3.14) clients can still connect to any CA server version). It would work for us as well but I would have to make some changes in the schematics. However, with the second option, using the gateway (https://epics.anl.gov/extensions/gateway/index.php), it worked very well. The changes to be made are trivial and it has allowed us to move forward with the migration. I hope that once the heavy block of the migration is finished we will also have time to migrate these subsystems that are working with the old versions.

     Thank you very much for the information and your response has been very helpful in moving forward. 

Regards!!

El mar, 15 mar 2022 a las 19:40, Matt Rippa (<matt.rippa at noirlab.edu>) escribió:

Thanks for this Michael. Francisco is out on leave but the team is following up with your recommendation.

Cheers,

Matt

On Sat, Mar 12, 2022, 3:27 PM Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov> wrote:

On 3/10/22 08:43, Francisco Ramos via Tech-talk wrote:
> ...
> I don't know if EPICS 7 should be compatible with version ( 3.13.9 ), if not, I would appreciate if you could guide us on how to fix it. Right now we are not planning to migrate the subsystems we have compiled with that version of EPICS.

The short answer is to recommend putting a cagateway built against Base <= 3.15
in between any <= 3.13 clients and >=3.14 servers.

Note that this is only needed in one direction.  New (>=3.14) clients can still
connect to any CA server version.


The longer story goes back to 2017 and:

https://code.launchpad.net/~epics-core/epics-base/camodern/+merge/306371

Where I was removing support for CA protocol versions circa Base <=3.12 which
depend on handling of UDP broadcasts which these days seem like an invitation
for abuse.

However, it seems that this change also effected 3.13.x era protocol versions.
This wasn't noticed at the time, and I and others only came to suspect it
last year.

https://github.com/epics-base/epics-base/pull/141/files/29f9d4db197487f9d81a52e5b5f3235532990172#r602439829

Which is what prompted me to put at a call for information.

https://epics.anl.gov/tech-talk/2021/msg00484.php

The response wasn't overwhelming.  I did get one sample, which wasn't by
itself conclusive for me.  (cf. ca-search-3.13.pcapng.gz)  Also, the site
which provided this sample wasn't reporting any problems.  With no urgency,
I stopped looking into this.

https://github.com/mdavidsaver/cashark/tree/master/test


I guess one moral of this story is that none of the Base developers test with
Base < 3.14 anymore (I never have).  I don't expect this to change, which makes
situations like this seem inevitable.