Multiple BMCs in a system: IPMB? Redfish? MCTP?

[Nancy Yuen]

On Mon, May 4, 2020 at 3:31 AM Andrew Jeffery <andrew at aj.id.au> wrote:

>
>
> On Thu, 30 Apr 2020, at 17:08, Deepak Kodihalli wrote:
> > On 30/04/20 4:21 am, Nancy Yuen wrote:
> > > I've talked with some people a while back (long while back) about
> > > multiple BMCs in a system.  Either for redundancy or managing separate
> > > parts of a system.   I'm wondering what other people are thinking in
> > > this area if at all.
> > >
> > > We are considering similar designs and I'm looking into options for
> > > BMC-BMC communications.  Some BMCs may not be externally
> > > accessible. Here are some options that we've looked at:
> > >
> > >  1. i2c/IPMB
> > >  2. usbnet/Redfish
> > >  3. i2c/MCTP/PLDM or something else?
> > >  4. internal network via switch chip/Redfish or MCTP
> > >
> > >   I'd like to reduce our use of IPMI so I want to avoid (1).
> > >
> > > ----------
> > > Nancy
> >
> > Hi Nancy,
> >
> > I think it depends on whether the BMCs need to talk to each other for
> > platform management, or if they manage their own hosts and we need one
> > of the BMCs to broadcast out of band requests and aggregate responses.
> >
> > For the former I think PLDM over MCTP could be a good fit. This is more
> > of an "inband" use-case in my opinion so I'm not sure if Redfish is well
> > suited. For the latter, a Redfish based aggregation is a good option.
>
> I think this looks like the right approach. Certainly some thought would be
> required in designing the MCTP networks given the (intentionally) limited
> number of endpoint IDs.
>
> Andrew
>

Hi Andrew, Deepak,

Sorry for the delayed response!

For the purposes of this discussion I have BMCs managing their own host:
BMC3<--->BMC2<--->BMC1/controller<--> external.  I wrote BMC1 but there
maybe some other controller there that isn't strictly a BMC.  BMC2 would be
"passing through" information between BMC1 and BMC3.  But I don't
necessarily want BMC2 to do any form of aggregation from information from
BMC3.  For BMC1/Controller and BMC 2 we are thinking Redfish.

In my case I'm interested in what ways people are thinking BMC2 and BMC3
should be connected and speaking to each other. Is MCTP/PLDM where everyone
is leaning?
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