Multiple BMCs in a system: IPMB? Redfish? MCTP?
Thomaiyar, Richard Marian
richard.marian.thomaiyar at linux.intel.com
Sun May 10 06:07:46 AEST 2020
PICMG has defined certain specifications in this angle (HPM), but those
basically uses IPMI (PICMG group extension commands)
1. Physical interface (i2c/IPMB) - IPMI
2. LAN Channel - IPMI RMCP+ other Direct stuff for say console access etc.
PICMG started working with DMTF redfish for the purpose of IPMC to IPMC
communication few years before (but not sure where it stands now)
No one solution will fit for all, and need to consider based on 1.
Features required (ssh / serial console access / SOL / KVM etc.) and 2.
Physical interface between the controller (I2C/ LAN / others?) . Nancy /
Say, with i2c- anything related to SSH / KVM forwarding etc is going to
be a problem, but with LAN these can be addressed.
With i2c-> IPMB / PLDM (MCTP over smbus) (with IPMI moving out of
picture PLDM will be better alternative).
With LAN -> PLDM / Redfish. (Using Redfish has advantage over PLDM for
RDE, and still other features can be supported)
Apart from this, need to define fail-over management(PICMG defined some)
/ discovery(MCTP offers some) etc.
On 5/8/2020 10:48 PM, Vijay Khemka wrote:
> *From: *openbmc <openbmc-bounces+vijaykhemka=fb.com at lists.ozlabs.org>
> on behalf of Nancy Yuen <yuenn at google.com>
> *Date: *Thursday, May 7, 2020 at 12:47 PM
> *To: *Andrew Jeffery <andrew at aj.id.au>
> *Cc: *OpenBMC Maillist <openbmc at lists.ozlabs.org>
> *Subject: *Re: Multiple BMCs in a system: IPMB? Redfish? MCTP?
> On Mon, May 4, 2020 at 3:31 AM Andrew Jeffery <andrew at aj.id.au
> <mailto: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
> > > 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
> > 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
> I think this looks like the right approach. Certainly some thought
> would be
> required in designing the MCTP networks given the (intentionally)
> number of endpoint IDs.
> 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?
> What is connectivity between BMC1, BMC2 and BMC3. Are these exposing
> any out of band connections. For security reasons, aggregator should
> use inband connectivity between BMCs and as Deepak said MCTP is good
> option for inband.
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