Re: [nvo3] [Int-area] [ippm] encapsulation of IOAM data in various protocols - follow up from WG discussion in London

["Carlos Pignataro (cpignata)" <[e-mail]>]

Hi, Greg,

Thanks for the quick response — Frank provided answers to your points, but I do have one question about your response (and I will squeeze in a couple of additional comments).

Please see inline.

On Apr 12, 2018, at 12:54 PM, Greg Mirsky <[e-mail]<mailto:[e-mail]>> wrote:

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.

Regards,
Greg

On Wed, Apr 11, 2018 at 12:02 PM, Frank Brockners (fbrockne) <[e-mail]<mailto:[e-mail]>> 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 IOAM:
* 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).

Comment: engineering is usually about making trade-offs. Having Reserved fields, unnecessary (and over-generalized) Flags, and a Version field for this extra OOAM header does not seem to justify the ROI in adding an extra header and extra parsing. This goes back to ‘what problem?'. Having a lot of extra fields to parse adds overhead, not only in size, but also in complexity tax. Please see Fundamental Truths (6a), (10), and (12) [RFC 1925].
* 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.

Question: The “like” in the first sentence, basically implies “not all encapsulations”. Therefore, https://xkcd.com/927/.

Further, what are “protocols that support overlay networks”, and how are you choosing your examples?

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<https://tools.ietf.org/html/draft-ooamdt-rtgwg-demand-cc-cv-03>.


Question: I do not think this is quite clear as you state, given the fact that the word “like” adds imprecision and ambiguity. IP-in-IP? L2TPv3? Etc?

Thank you for considering these questions!
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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Thanks,

— Carlos Pignataro