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| <== Date ==> | <== Thread ==> |
|---|
| Subject: | Re: [EXTERNAL] Re: EPICS_CA_MCAST_TTL equivalent for pvAccess |
| From: | "Kasemir, Kay via Tech-talk" <[email protected]> |
| To: | Michael Davidsaver via Tech-talk <[email protected]>, Denise Finstrom <[email protected]> |
| Cc: | Jim Smedinghoff <[email protected]> |
| Date: | Wed, 22 Jan 2020 20:10:02 +0000 |
|
PV Access _is_ using multicasts internally, basically as a replacement of the ca repeater.
When multiple servers and/or clients run on the same host, they pass the UDP messages which would by default only reach one of them to each other via a multicast.
For that, it makes sense to have a TTL of 1.
Would it hurt to send those with a larger TTL, when that enables using multicasts beyond localhost?
-Kay
From: Tech-talk <[email protected]> on behalf of Michael Davidsaver via Tech-talk <[email protected]>
Sent: Wednesday, January 22, 2020 2:24 PM To: Denise Finstrom <[email protected]> Cc: Jim Smedinghoff <[email protected]>; [email protected] <[email protected]> Subject: [EXTERNAL] Re: EPICS_CA_MCAST_TTL equivalent for pvAccess 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? 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 |