Why does OpenBMC use Avahi mDNS instead of SSDP?

[Gunnar Mills]

On 4/16/2020 7:42 PM, Richard Hanley wrote:
>
>     > The members on the call really wanted to encourage OpenBMC to
>     implement
>     > SSDP instead.
>
>     It probably isn't a bad thing to be able to support SSDP, don't get me
>     wrong, but "instead"?  Why would we want to take away service
>     advertisement functionality, unless someone wants to explicitly
>     disable it?
>
>     I can understand if they don't want to document, in the standard,
>     a way to
>     advertise the Redfish service over mDNS, but isn't that a different
>     problem from what we're asking for?  Aren't we asking for a method to
>     manage the enablement of services on the BMC, specifically our mDNS
>     service?  So, if we still have mDNS, don't we need a way to
>     configure it
>     through Redfish?
>
> I see your point here.  I guess there might be some implicit 
> assumption that adding it to a schema implies endorsement elsewhere.

Yeah, from Jeff's reply on the thread, "The concern is if we add this to 
ManagerNetworkProtocol, it would seem to indicate that Redfish supports 
mDNS/DNS-SD for discovery of Redfish services, which it does not (SSDP 
is the standard discovery mechanism). "

> Discovery is probably an area where supporting a diversity of 
> protocols is better than making a single choice.

A bit over my head here, but I believe Redfish's interoperability 
concern about supporting a second discovery protocol comes from then all 
Redfish implementations need to implement both otherwise different 
Redfish implementations aren't discoverable. This can be expanded to 
OpenBMC's use of mDNS vs Redfish's SSDP and hence the ask for OpenBMC to 
implement SSDP. A concern of compatibility of OpenBMC-based Redfish 
implementations vs other Redfish implementations.

These are all good questions. Anyone can sign up for an account and post 
to the Redfish forum if you are interested in pursuing.
https://redfishforum.com/thread/267/add-avahi-managernetworkprotocol

Forum posts, along with new issues and proposals, are discussed on the 
main Redfish calls, Tuesday at 1:00 PM CT and Thursday at 2:00 PM CT if 
your company is a supporting member of Redfish.

Thanks,
Gunnar

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