[Bug 1971737] Re: EPICS 3.13 clients cannot connect to EPICS 7 or 3.16

[Dirk Zimoch via Core-talk <core-talk at aps.anl.gov>]

I just read the tech-talk post. I have no package capture but I have
added printf debugging to camessage. I can see that the 3.14+ search
requests contain a CA_PROTO_VERSION message first before the
CA_PROTO_SEARCH. 3.13 host tools (ca_test) start straight with
CA_PROTO_SEARCH. Their requests get „silently ignored“. I plan to check
if a 3.13 IOC does the same. I guess so as the links never connect and
the EPICS 7 IOC prints no „to old“ message but stays silent.

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https://bugs.launchpad.net/bugs/1971737

Title:
  EPICS 3.13 clients cannot connect to EPICS 7 or 3.16

Status in EPICS Base:
  New

Bug description:
  Since commit 95fd255d "rsrv: ignore CA client version older than v4.4"
  from Jul 30 2016, EPICS 3.13 clients cannot connect any more, even
  though their CA version is V4.8.

  The reason is that camessage drops the incoming CA_PROTO_SEARCH
  messages because the 3.13 client has not yet sent a CA_PROTO_VERSION
  message and thus the code reads client->minor_version_number as 0.

  This is a huge hindrance for upgrading 3.14 IOCs to EPICS 7 when there
  are still 3.13 IOC (which cannot be upgraded yet) in the network which
  need to connect.

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