Greg,
The 'O' bit does not override or interact with the Protocol Type
field, so there is no issue with precedence. It is possible to
implement OAM on Geneve using options, in which case the payload could
be a stub of a packet to ensure consistent behavior between OAM and
data packets as has been done with other protocols. In this situation,
the Protocol Type would still indicate the type of the stub packet as
usual. It is also possible to implement OAM using the payload of the
packet as you describe and the Protocol Type would indicate that using
an EtherType assigned for this purpose.
In either case, the meaning of the 'O' bit is the same and it only
affects the behavior of endpoint devices processing OAM. Most devices
are oblivious to this and will simply use the Protocol Type field to
process the payload as usual. The appropriate behavior for 'O' bit
flagged packets is described in the draft:
Endpoints MUST NOT forward the payload and
transit devices MUST NOT attempt to interpret or process it.
Since these are infrequent control messages, it is RECOMMENDED
that endpoints direct these packets to a high priority control
queue (for example, to direct the packet to a general purpose CPU
from a forwarding ASIC or to separate out control traffic on a
NIC). Transit devices MUST NOT alter forwarding behavior on the
basis of this bit, such as ECMP link selection.
The 'O' bit does not otherwise change the interpretation of the packet.
Jesse
On Mon, Oct 15, 2018 at 6:01 PM Greg Mirsky <[email protected]> wrote:
>
> Dear All,
> I am concerned that the current definition of O-bit contradicts the
> definition of the Protocol Type field. Consider that O-bit defined as:
> O (1 bit): OAM packet. This packet contains a control message
> instead of a data payload.
> My interpretation, please correct me if it is wrong, is that the O-bit
> indicates that a message that immediately follows the Geneve header is
> OAM command or data. But that is what the Protocol Type field is for:
> Protocol Type (16 bits): The type of the protocol data unit
> appearing after the Geneve header.
> What is the precedence processing O-bit and the Protocol Type values? Should
> the specification explain how to interpret the value of the Protocol type
> field when O-bit is set? If the value of the Protocol Type field is
> equivalent to None, i.e., no message following the Geneve header, can O-bit
> be set to indicate that one of TLVs includes OAM? If that is the valid case,
> then the current definition of O-bit is not complete as it does not mention
> OAM in TLV case.
>
> And I have to point to an overall lack of discussion of OAM in the
> specification.
>
> Regards,
> Greg
>
> On Tue, Oct 9, 2018 at 2:08 AM Bocci, Matthew (Nokia - GB)
> <[email protected]> wrote:
>>
>> This email begins a two-week working group last call for
>> draft-ietf-nvo3-geneve-08.txt.
>>
>> Please review the draft and post any comments to the NVO3 working group
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>>
>>
>>
>> We are also polling for knowledge of any undisclosed IPR that applies to
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>> This poll will run until Friday 26th October.
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>> Regards
>>
>>
>>
>> Matthew and Sam
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