Re: [sfc] #24 (nsh): -07 review (M. Boucadair)

["sfc issue tracker" <[e-mail]>]

#24: -07 review (M. Boucadair)


Comment (by [e-mail]):

 Updating the tracker to record the pending points:

 ==
 (1) Section 2: I suggest to delete the following sentence:

     NSH is designed to be easy to implement across a range of devices,
     both physical and virtual, including hardware platforms.

  Reason: the use of "easy to implement" should be justified if that text
 is
  maintained. Otherwise, this is subjective.

  or to reword it as follows:

     "NSH can be implemented in both physical and virtual platforms."

  (2) Section 2.3: CLOSED

  (3) Section 2.3- Not sure I would maintain this text:

     5.  NSH offers a common and standards-based header for service
         chaining to all network and service nodes.

  "to all" is not accurate as "legacy" nodes are still there.

  (4) Section 2.3: CLOSED

  (5) Section 3.2:

     NSH implementations MUST support MD-Type = 0x1, and SHOULD support
     MD- Type = 0x2.

  Because:
  * of potential interoperability issues.
  * MD#2 is more compact when no metadata is to be supplied
  * MD#2 allows to convey more information compared to MD#1

  I suggest we revisit that sentence to have MD#2 be mandatory to be
  supported (my favorite option), or at least require that both MDs defined
  in this spec MUST be supported.

  (6) Section 3.2:

     C bit: Indicates that a critical metadata TLV is present.  This bit
     acts as an indication for hardware implementers to decide how to
     handle the presence of a critical TLV without necessarily needing to
     parse all TLVs present.  For an MD Type of 0x1 (i.e. no variable
     length metadata is present), the C bit MUST be set to 0x0.

  6.1. What is the behavior of the implementation if C-bit is set but not
  critical metadata is found in the payload?
  6.2. What is the behavior of the implementation if C-bit is unset but a
  critical metadata is found in the payload?
  6.3. What is the behavior of the implementation with regards to this bit
  if a critical metadata is added in-path?
  6.4. What is the behavior of the implementation with regards to this bit
  if a critical metadata is stripped in-path?
  6.5. Should the specification recommend an order of metadata so that
  critical metadata are always positioned first?

  (7) Section 3.3: CLOSED

  (8) Section 3.4:

  8.2. The specification does not forbid that all context headers are set
 to
  zero. Otherwise, MD#2 should be used instead.
  8.3. The specification does not specify how these context headers are to
  be validated.
  8.4. I still don't understand why four headers are chosen.

  (9) Section 3.5.1:

  The length of "Metadata Class" is over-dimensioned. I suggest to reduce
  the length of this field and increase the length of "Type".

  For example, let's consider the proposal in https://tools.ietf.org/html
  /draft-napper-sfc-nsh-broadband-allocation-00#section-4.2:

      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     TLV Class = 3GPP          |C|    Type     |R|R|R|   Len   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Data ...
     +-+-+-+-+-+-+-+-+

                           Figure 5: TLV Allocation

     The intended use of the header is for TLVs associated with 3GPP Radio
     Access Networks as described in [TS.29.230].  This TLV can be used by
     3GPP to extend the metadata as per use cases.  Having this TLV helps
     to carry more information that does not fit within the MD Type 0x01.

  The list of codes in Table 7.1 of TS.29.230 cannot be conveyed with a
  "Type" field of 7 bits.

  (10) Section 4:

  OLD:

  +---------------+------------------+-------+----------------+---------+
   |                |  Insert         |Select |   Update       |Service  |
   |                |  or remove NSH  |Service|    NSH         |policy   |
   |                |                 |Function|               |selection|
   | Component      +--------+--------+Path   +----------------+         |
   |                |        |        |       | Dec.   |Update |         |
   |                | Insert | Remove |       |Service |Context|         |
   |                |        |        |       | Index  |Header |         |
   +----------------+--------+--------+-------+--------+-------+---------+
   |                |   +    |   +    |       |        |   +   |         |
   |Classifier      |        |        |       |        |       |         |
   +--------------- +--------+--------+-------+--------+-------+---------+
   |Service Function|        |   +    |  +    |        |       |         |
   |Forwarder(SFF)  |        |        |       |        |       |         |
   +--------------- +--------+--------+-------+--------+-------+---------+
   |Service         |        |        |       |   +    |   +   |   +     |
   |Function  (SF)  |        |        |       |        |       |         |
   +--------------- +--------+--------+-------+--------+-------+---------+
   |SFC Proxy       |   +    |   +    |       |   +    |       |         |
   +----------------+--------+--------+-------+--------+-------+---------+

  NEW:

  +---------------+------------------+-------+----------------+---------+
   |                |  Insert         |Select |   Update       |Service  |
   |                |  or remove NSH  |Service|    NSH         |policy   |
   |                |                 |Function|               |selection|
   | Component      +--------+--------+Path   +----------------+         |
   |                |        |        |       | Dec.   |Update |         |
   |                | Insert | Remove |       |Service |Context|         |
   |                |        |        |       | Index  |Header |         |
   +----------------+--------+--------+-------+--------+-------+---------+
   |                |   +    |   +    |       |        |   +   |         |
   |Classifier      |        |        |       |        |       |         |
   +--------------- +--------+--------+-------+--------+-------+---------+
   |Service Function|        |   +    |  +    |        |       |         |
   |Forwarder(SFF)  |        |        |       |        |       |         |
   +--------------- +--------+--------+-------+--------+-------+---------+
   |Service         |        |        |       |   +    |   +   |   +     |
   |Function  (SF)  |        |        |       |        |       |         |
   +--------------- +--------+--------+-------+--------+-------+---------+
   |SFC Proxy       |   +    |   +    |       |   +    |   +   |         |
   +----------------+--------+--------+-------+--------+-------+---------+

  (11) Section 7.2: CLOSED.

-- 
-------------------------------------+-------------------------------------
 Reporter:                           |       Owner:  draft-ietf-sfc-
  [e-mail]       |  [e-mail]
     Type:  defect                   |      Status:  new
 Priority:  major                    |   Milestone:
Component:  nsh                      |     Version:
 Severity:  -                        |  Resolution:
 Keywords:                           |
-------------------------------------+-------------------------------------

Ticket URL: <https://trac.tools.ietf.org/wg/sfc/trac/ticket/24#comment:1>
sfc <https://tools.ietf.org/sfc/>