Re: EPICS_CA_MCAST_TTL equivalent for pvAccess

[James G Smedinghoff via Tech-talk <tech-talk@aps.anl.gov>]

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