Hi Frank,
thank you for sharing your points. Please find my notes in-line and tagged
GIM>>. I believe that this is very much relevant to work of other working
groups that directly work on the overlay encapsulations in the center of
the discussion and hence I've added them to the list. Hope we'll have more
opinions to reach the conclusion that is acceptable to all.


On Wed, Apr 11, 2018 at 12:02 PM, Frank Brockners (fbrockne) <
fbroc...@cisco.com> wrote:

> Back at the IPPM meeting in London, we discussed several drafts dealing
> with the encapsulation of IOAM data in various protocols
> (draft-brockners-ippm-ioam-vxlan-gpe-00, draft-brockners-ippm-ioam-geneve-00,
> draft-weis-ippm-ioam-gre-00). One discussion topic that we decided to take
> to the list was the question on whether draft-ooamdt-rtgwg-ooam-header
> could be leveraged.  After carefully considering 
> draft-ooamdt-rtgwg-ooam-header,
> I came to the conclusion that the “OOAM header” does not meet the needs of
> * Efficiency: IOAM adds data to live user traffic. As such, an
> encapsulation needs to be as efficient as possible. The “OOAM header” is 8
> bytes long. The approach for IOAM data encapsulation in the above mentioned
> drafts only requires 4 bytes. Using the OOAM header approach would add an
> unnecessary overhead of 4 bytes – which is significant.
GIM>> The difference in four octets is because OOAM Header:

   - provides more flexibility, e.g. Flags field and Reserved fields;
   - supports larger OAM packets than iOAM header;
   - is future proof by supporting versioning (Version field).

* Maturity: IOAM has several implementations, which were also shown at
> recent IETF hackathons – and we’re expecting additional implementations to
> be publicized soon. Interoperable implementations need timely
> specifications. Despite the question being asked, the recent thread on OOAM
> in the NVO3 list hasn’t revealed any implementation of the OOAM header. In
> addition, the thread revealed that several fundamental questions about the
> OOAM header are still open, such as whether or how active OAM mechanisms
> within protocols such as Geneve would apply to the OOAM header. This
> ultimately means that we won’t get to a timely specification.
GIM>> May I ask which encapsulations supported by the implementations you
refer to. Until very recently all iOAM proposals were to use meta-data TLV
in, e.g. Geneve and NSH. And if these or some of these implementations
already updated to the newly proposed iOAM shim, I don't see problem in
making them use OOAM Header. Would you agree?

> * Scope: It isn’t entirely clear to which protocols the OOAM header would
> ultimately apply to. The way the OOAM header is defined, OOAM uses a 8-bit
> field for “Next Prot”, the next protocol. Some protocols that IOAM data
> needs to be encapsulated into use 16-bits for their next protocol code
> points. See e.g. the GRE encapsulation – as specified in
> draft-weis-ippm-ioam-gre-00.
GIM>> The first paragraph of the Introduction section states:
   New protocols that support overlay networks like VxLAN-GPE
   [I-D.ietf-nvo3-vxlan-gpe], GUE [I-D.ietf-nvo3-gue], Geneve
   [I-D.ietf-nvo3-geneve], BIER [I-D.ietf-bier-mpls-encapsulation], and
   NSH [I-D.ietf-sfc-nsh] support multi-protocol payload, e.g.
   Ethernet, IPv4/IPv6, and recognize Operations, Administration, and
   Maintenance (OAM) as one of distinct types.  That ensures that
   Overlay OAM (OOAM)packets are sharing fate with Overlay data packet
   traversing the underlay.
I'm updating the OOAM Header draft and along with cleaning nits will update
reference to GUE. I think that the list and the statemnt are quite clear in
identifying the scope of networks that may benefit from using not only
common OOAM Header but common OOAM mechanisms, e.g. Echo Request/Reply

With the above in mind, I’d suggest that the WG moves forward with specific
> definitions for encapsulating IOAM data into protocols – per the above
> mentioned drafts.
> Regards, Frank
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