Why does OpenBMC use Avahi mDNS instead of SSDP?

Why does OpenBMC use Avahi mDNS instead of SSDP?

[Joseph Reynolds]

Redfish specifies SSDP [1] [2] as the standard discovery service but 
OpenBMC uses the Avahi mDNS discovery service [3].  I asked Redfish to 
add mDNS to the spec [4] but they don't want to, and pointed to their spec.

I want to allow the BMC admin to enable and disable the mDNS discovery 
service.  How can this be done?  Options:
1. Implement ManagerNetworkProtocol.Oem.OpenBMC.mDNS.
2. Move OpenBMC to SSDP and away from mDNS.
3. Re-ask Redfish to add a ManagerNetworkProtocol.mDNS protocol.

What is best for the project?

- Joseph

[1]: Redfish spec DSP0266 version 1.9.0 section 5.6.4 "Service Discovery".
[2]: Redfish ManagerNetworkProtocol.SSDP version 1.4.2
[3]: 
https://github.com/openbmc/docs/blob/master/designs/management-console/service_discovery.md
[3]: https://redfishforum.com/thread/267/add-avahi-managernetworkprotocol

Note: This email refreshes a previous thread archived here:
https://lists.ozlabs.org/pipermail/openbmc/2020-April/021170.html

Re: Why does OpenBMC use Avahi mDNS instead of SSDP?

[Patrick Williams]

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On Tue, Apr 07, 2020 at 09:58:15AM -0500, Joseph Reynolds wrote:
> Redfish specifies SSDP [1] [2] as the standard discovery service but 
> OpenBMC uses the Avahi mDNS discovery service [3].  I asked Redfish to 
> add mDNS to the spec [4] but they don't want to, and pointed to their spec.

Avahi is a particular implementation of mDNS.  We implement mDNS using
Avahi.  MacOS also uses mDNS with an entirely different implementation.

mDNS is used more in the UNIX world, SSDP is used more in Windows.

I don't see any reason why we couldn't support both.  We initially
supported mDNS because OpenBMC is Linux and OpenPOWER machines were
likely running Linux, which more likely had the mDNS software installed.

> I want to allow the BMC admin to enable and disable the mDNS discovery 
> service.  How can this be done?  Options:
> 1. Implement ManagerNetworkProtocol.Oem.OpenBMC.mDNS.
> 2. Move OpenBMC to SSDP and away from mDNS.
> 3. Re-ask Redfish to add a ManagerNetworkProtocol.mDNS protocol.

I don't see a strong reason to "move away" from mDNS, but I certainly
think that *any* network service should be able to be disabled by an
administrator to reduce the security footprint if the service is unused.

So, either #1 or #3 seems best to me.  Adding optional SSDP support would
be reasonable, but likely only to be added by someone who cares about
discovery in a Windows environment.

-- 
Patrick Williams

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Re: Why does OpenBMC use Avahi mDNS instead of SSDP?

[Joseph Reynolds]

On 4/7/20 10:46 AM, Patrick Williams wrote:
> On Tue, Apr 07, 2020 at 09:58:15AM -0500, Joseph Reynolds wrote:
>> Redfish specifies SSDP [1] [2] as the standard discovery service but
>> OpenBMC uses the Avahi mDNS discovery service [3].  I asked Redfish to
>> add mDNS to the spec [4] but they don't want to, and pointed to their spec.
> Avahi is a particular implementation of mDNS.  We implement mDNS using
> Avahi.  MacOS also uses mDNS with an entirely different implementation.
>
> mDNS is used more in the UNIX world, SSDP is used more in Windows.
>
> I don't see any reason why we couldn't support both.  We initially
> supported mDNS because OpenBMC is Linux and OpenPOWER machines were
> likely running Linux, which more likely had the mDNS software installed.

Thanks for explaining that.

>> I want to allow the BMC admin to enable and disable the mDNS discovery
>> service.  How can this be done?  Options:
>> 1. Implement ManagerNetworkProtocol.Oem.OpenBMC.mDNS.
>> 2. Move OpenBMC to SSDP and away from mDNS.
>> 3. Re-ask Redfish to add a ManagerNetworkProtocol.mDNS protocol.
> I don't see a strong reason to "move away" from mDNS, but I certainly
> think that *any* network service should be able to be disabled by an
> administrator to reduce the security footprint if the service is unused.
>
> So, either #1 or #3 seems best to me.  Adding optional SSDP support would
> be reasonable, but likely only to be added by someone who cares about
> discovery in a Windows environment.

I've appended the thread to re-ask Redfish if they would support 
ManagerNetworkProtocol.mDNS.
https://redfishforum.com/thread/267/add-avahi-managernetworkprotocol

I don't need this function right away and can wait for a spec change.  
(That is, help make it happen.)
So I am backing off my request for 
ManagerNetworkProtocol.Oem.OpenBMC.mDNS art this time.

- Joseph

Re: Why does OpenBMC use Avahi mDNS instead of SSDP?

[Gunnar Mills]

On 4/8/2020 3:27 PM, Joseph Reynolds wrote:
> On 4/7/20 10:46 AM, Patrick Williams wrote:
>> On Tue, Apr 07, 2020 at 09:58:15AM -0500, Joseph Reynolds wrote:
>>> Redfish specifies SSDP [1] [2] as the standard discovery service but
>>> OpenBMC uses the Avahi mDNS discovery service [3].  I asked Redfish to
>>> add mDNS to the spec [4] but they don't want to, and pointed to 
>>> their spec.
>>
>> mDNS is used more in the UNIX world, SSDP is used more in Windows.
>>
Was on the Redfish call earlier and this forum thread was discussed. The 
Redfish members on the call did not totally agree with this statement. 
They believe SSDP has a wider adaption than just Windows. A wider 
adaption than mDNS.  Since SSDP is already in the Redfish specification 
and has been adapted by Redfish implementations, adding a 2nd discovery 
service would damage interoperability in Redfish.
The members on the call really wanted to encourage OpenBMC to implement 
SSDP instead.
Posted the same to the forum thread.


>
>>> I want to allow the BMC admin to enable and disable the mDNS discovery
>>> service.  How can this be done?  Options:
>>> 1. Implement ManagerNetworkProtocol.Oem.OpenBMC.mDNS.
>>> 2. Move OpenBMC to SSDP and away from mDNS.
>>> 3. Re-ask Redfish to add a ManagerNetworkProtocol.mDNS protocol.
>> I don't see a strong reason to "move away" from mDNS, but I certainly
>> think that *any* network service should be able to be disabled by an
>> administrator to reduce the security footprint if the service is unused.
>>
>> So, either #1 or #3 seems best to me.  Adding optional SSDP support 
>> would
>> be reasonable, but likely only to be added by someone who cares about
>> discovery in a Windows environment.
>
> I've appended the thread to re-ask Redfish if they would support 
> ManagerNetworkProtocol.mDNS.
> https://redfishforum.com/thread/267/add-avahi-managernetworkprotocol
>
If think we are down to #1 or #2.

Thanks,
Gunnar

Re: Why does OpenBMC use Avahi mDNS instead of SSDP?

[Richard Hanley]

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>
>
> Was on the Redfish call earlier and this forum thread was discussed. The
> Redfish members on the call did not totally agree with this statement.
> They believe SSDP has a wider adaption than just Windows. A wider
> adaption than mDNS.  Since SSDP is already in the Redfish specification
> and has been adapted by Redfish implementations, adding a 2nd discovery
> service would damage interoperability in Redfish.
> The members on the call really wanted to encourage OpenBMC to implement
> SSDP instead.
> Posted the same to the forum thread.
>

Well that is unfortunate.

>
> >>> I want to allow the BMC admin to enable and disable the mDNS discovery
> >>> service.  How can this be done?  Options:
> >>> 1. Implement ManagerNetworkProtocol.Oem.OpenBMC.mDNS.
> >>> 2. Move OpenBMC to SSDP and away from mDNS.
> >>> 3. Re-ask Redfish to add a ManagerNetworkProtocol.mDNS protocol.
> >> I don't see a strong reason to "move away" from mDNS, but I certainly
> >> think that *any* network service should be able to be disabled by an
> >> administrator to reduce the security footprint if the service is unused.
> >>
> >> So, either #1 or #3 seems best to me.  Adding optional SSDP support
> >> would
> >> be reasonable, but likely only to be added by someone who cares about
> >> discovery in a Windows environment.
> >
> > I've appended the thread to re-ask Redfish if they would support
> > ManagerNetworkProtocol.mDNS.
> > https://redfishforum.com/thread/267/add-avahi-managernetworkprotocol
> >
> If think we are down to #1 or #2.
>

I'm trying to put myself in the mind of an administrator here, and I'd
expect most are relatively inflexible. Most hyperscalars probably have
their own discovery system, and are likely supporting that regardless of
our decision here.  Likewise smaller operations probably aren't super
interested in migrating here.

Can anyone speak to the merits of the two protocols? Is there are
technical benefit to moving to SSDP.

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Re: Why does OpenBMC use Avahi mDNS instead of SSDP?

[Patrick Williams]

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On Thu, Apr 16, 2020 at 03:02:46PM -0500, Gunnar Mills wrote:
> On 4/8/2020 3:27 PM, Joseph Reynolds wrote:
> > On 4/7/20 10:46 AM, Patrick Williams wrote:
> >> On Tue, Apr 07, 2020 at 09:58:15AM -0500, Joseph Reynolds wrote:

> >> mDNS is used more in the UNIX world, SSDP is used more in Windows.
> >>
> Was on the Redfish call earlier and this forum thread was discussed. The 
> Redfish members on the call did not totally agree with this statement. 
> They believe SSDP has a wider adaption than just Windows. A wider 
> adaption than mDNS.  Since SSDP is already in the Redfish specification 
> and has been adapted by Redfish implementations, adding a 2nd discovery 
> service would damage interoperability in Redfish.

I'm not really interested in a debate on this point, but I'm not finding
much evidence to back it up.  Can anyone point to well-used OSS
implementation of SSDP?  The only thing I can find is gssdp, which seems
to require a lot of Gnome components; not something we could easily pull
in on the BMC.

> 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?

-- 

Patrick Williams

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Re: Why does OpenBMC use Avahi mDNS instead of SSDP?

[Richard Hanley]

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>
>
> > >> mDNS is used more in the UNIX world, SSDP is used more in Windows.
> > >>
> > Was on the Redfish call earlier and this forum thread was discussed. The
> > Redfish members on the call did not totally agree with this statement.
> > They believe SSDP has a wider adaption than just Windows. A wider
> > adaption than mDNS.  Since SSDP is already in the Redfish specification
> > and has been adapted by Redfish implementations, adding a 2nd discovery
> > service would damage interoperability in Redfish.
>
> I'm not really interested in a debate on this point, but I'm not finding
> much evidence to back it up.  Can anyone point to well-used OSS
> implementation of SSDP?  The only thing I can find is gssdp, which seems
> to require a lot of Gnome components; not something we could easily pull
> in on the BMC.
>
> The only thing besides gssdp is this
https://github.com/troglobit/ssdp-responder, but that's only one
(presumably easier) half.


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

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Re: Why does OpenBMC use Avahi mDNS instead of SSDP?

[Gunnar Mills]

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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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Re: Why does OpenBMC use Avahi mDNS instead of SSDP - proposal

[Joseph Reynolds]

On 4/17/20 11:44 AM, Gunnar Mills wrote:
> On 4/16/2020 7:42 PM, Richard Hanley wrote:
>>
>>     > The members on the call really wanted to encourage OpenBMC to
>>     implement
>>     > SSDP instead.
>>

Thanks for helping to move this forward.  IMHO, Redfish has given us 
enough direction to move forward with OpenBMC.  I understand the debate, 
but don't have any insight or energy to contribute.  So on a purely 
practical level...

I hereby propose implementing ManagerNetworkProtocol.Oem.OpenBMC.mDNS.
Its schema would either be "Protocol" or a new "mDNSProtocol" modeled 
after SSDProtocol.
The only property I need to be readwrite is ProtocolEnabled.
This allows the BMC admin to enable and disable OpenBMC's Avahi-based 
mDNS discovery service.

- Joseph

>>
>>     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
>

Re: Why does OpenBMC use Avahi mDNS instead of SSDP - proposal

[Joseph Reynolds]

On 4/17/20 3:02 PM, Joseph Reynolds wrote:
> On 4/17/20 11:44 AM, Gunnar Mills wrote:
>> On 4/16/2020 7:42 PM, Richard Hanley wrote:
>>>
>>>     > The members on the call really wanted to encourage OpenBMC to
>>>     implement
>>>     > SSDP instead.
>>>
>
> Thanks for helping to move this forward.  IMHO, Redfish has given us 
> enough direction to move forward with OpenBMC.  I understand the 
> debate, but don't have any insight or energy to contribute. So on a 
> purely practical level...
>
> I hereby propose implementing ManagerNetworkProtocol.Oem.OpenBMC.mDNS.
> Its schema would either be "Protocol" or a new "mDNSProtocol" modeled 
> after SSDProtocol.
> The only property I need to be readwrite is ProtocolEnabled.
> This allows the BMC admin to enable and disable OpenBMC's Avahi-based 
> mDNS discovery service.

Who can effectively ask DMTF Redfish to add a new "mDNSProtocol"? Some 
of the reasons stated in this email thread [1] seem compelling:

1. Installations can be locked into a specific discovery protocol. Some 
use SSDP and some use mDNS.  It would take effort for these 
installations to support an additional discovery protocol.  --> Given 
that real Redfish server implement mDNS Discovery, can we add a Redfish 
capability to control this service?

2. If we wanted to use SSDP discovery of our FOSS Linux-based project, 
what implementation can we use?

I tried, but my knowledge is limited.  You can respond to this email or 
participate in the Redfish discussion here: 
https://redfishforum.com/thread/267/add-avahi-managernetworkprotocol

- Joseph

[1]: You can review the OpenBMC mDNS email discussion thread here:
https://lists.ozlabs.org/pipermail/openbmc/2020-April/

> - Joseph
>
>>>
>>>     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
>>
>