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Subject: Re: EPICS_CA_MCAST_TTL equivalent for pvAccess
From: James G Smedinghoff via Tech-talk <[email protected]>
To: Michael Davidsaver <[email protected]>, Denise S Finstrom <[email protected]>, "[email protected]" <[email protected]>
Date: Wed, 22 Jan 2020 20:52:36 +0000
On 1/22/2020 1:24 PM, Michael Davidsaver wrote:
On 1/22/20 8:18 AM, Denise Finstrom via Tech-talk wrote:
Hello,

Is there an equivalent to EPICS_CA_MCAST_TTL for the pvAccess protocol?
There isn't one.  PVA doesn't (yet) support search by mcast.

Were you able to make this work with CA?  What does your network topology look
like?  (how many hops)  Did you encounter any problems?
Yes, I was able to use multicasts for CA search and beacons by defining environment variables.
On the client:
EPICS_CA_ADDR_LIST=<multicast address1>
EPICS_CA_AUTO_ADDR_LIST=NO
EPICS_CA_MCAST_TTL=20

On the IOC:

EPICS_CAS_INTF_ADDR_LIST=<multicast address1>
EPICS_CAS_BEACON_ADDR_LIST=<multicast address2>
EPICS_CAS_AUTO_BEACON_ADDR_LIST=NO
EPICS_CA_MCAST_TTL=20
caRepeater did not join the beacon IGMP multicast group, so I used a multicast address for the
beacons which the client node was already listening to.

The control system has a large central router which is connected to about a dozen 256 address subnets.
Each subnet is only 1 hop from the others. More hops would be needed to get to non-controls subnets
or the internet.

Jim
Adding this was a project of mine a few years ago.  I've actually never been
certain that it would work at scale since I don't have access to a large
network with mcast routing enabled for testing.  Nor have I had any feedback
from users until now.  So adding this feature to the PVA protocol code hasn't
been a priority for me.


We are attempting to use multicast for PV search and haven't found a way to change TTL values when using pvAccess. When we set EPICS_PVA_ADDR_LIST to a multicast address, the multicast goes out with a TTL of one and doesn't get routed to other subnets. We are successfully using multicast for PV search with the CA protocol and EPICS_CA_MCAST_TTL. We are looking to do the same with pvAccess, but the EPICS_PVA_MCAST_TTL environment variable doesn't seem to exist. We are using base-7.0.3.1. Any advice would be appreciated.

Thanks,

Denise



Replies:
Re: EPICS_CA_MCAST_TTL equivalent for pvAccess Michael Davidsaver via Tech-talk
References:
EPICS_CA_MCAST_TTL equivalent for pvAccess Denise Finstrom via Tech-talk
Re: EPICS_CA_MCAST_TTL equivalent for pvAccess Michael Davidsaver via Tech-talk

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