Fwd: Wrong beacon source IP address

[Ralph Lange <ralph.lange@gmx.de>]

Dear colleagues,

I think Anze's got a point here.
What are the consequences? Are there any?

Cheers,
~Ralph


-------- Forwarded Message --------

Subject:	Wrong beacon source IP address
From:	Anze Zagar <anze.zagar@cosylab.com>

I was playing around with CA beacons a little bit, and observed some
surprising behaviour.

On my system I have three network interfaces:

eth0
  inet addr:10.5.4.190  Bcast:10.5.7.255  Mask:255.255.248.0

vmnet1
  inet addr:192.168.103.1  Bcast:192.168.103.255  Mask:255.255.255.0

vmnet8
  inet addr:172.16.209.1  Bcast:172.16.209.255  Mask:255.255.255.0


Now if I run EPICS IOC, it will send beacons to all three broadcast
addresses, however the source address (in the IP frame of the beacon UDP
packet) will in all three cases correspond to the IP address of the
first interface. Thus with EPICS_CA_AUTO_ADDR_LIST=yes, source IP is
always 10.5.4.190.

And if I configure, e.g.:

export EPICS_CA_AUTO_ADDR_LIST=no
export EPICS_CA_ADDR_LIST="192.168.103.255 172.16.209.255 10.5.7.255"

source IP is 192.168.103.1 for all three subnets (see also the attached
wireshark screenshot).

I noticed that this may impact some CA client implementations, because
they expect beacon to have the source address corresponding to existing
CA connections (which will obviously not be the case for second and
third subnet). Effectively, it will ignore all beacons and check for the
IOC availability by pinging them instead. Additionally, it will also not
reuse CA connections for multiple PVs hosted on the same server.

I observed this on EPICS 3.14.12.5. Do you know, if this is something
known or expected?

Attachment: wireshark.png
Description: PNG image