Re: Communication error

[Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov>]

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.