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

[Andrew Jeffery]

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