Re: [mpls] Adam Roach's Discuss on draft-ietf-mpls-spring-lsp-ping-11: (with DISCUSS and COMMENT)

"Carlos Pignataro (cpignata)" <cpignata@cisco.com> Thu, 12 October 2017 00:42 UTC

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From: "Carlos Pignataro (cpignata)" <cpignata@cisco.com>
To: Adam Roach <adam@nostrum.com>
CC: The IESG <iesg@ietf.org>, "draft-ietf-mpls-spring-lsp-ping@ietf.org" <draft-ietf-mpls-spring-lsp-ping@ietf.org>, Loa Andersson <loa@pi.nu>, "mpls-chairs@ietf.org" <mpls-chairs@ietf.org>, "mpls@ietf.org" <mpls@ietf.org>
Thread-Topic: Adam Roach's Discuss on draft-ietf-mpls-spring-lsp-ping-11: (with DISCUSS and COMMENT)
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Date: Thu, 12 Oct 2017 00:42:32 +0000
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Subject: Re: [mpls] Adam Roach's Discuss on draft-ietf-mpls-spring-lsp-ping-11: (with DISCUSS and COMMENT)
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Hi, Adam,

You found a nice bug. Thank you! Please see inline.

> On Oct 11, 2017, at 6:44 PM, Adam Roach <adam@nostrum.com> wrote:
> 
> Adam Roach has entered the following ballot position for
> draft-ietf-mpls-spring-lsp-ping-11: Discuss
> 
> When responding, please keep the subject line intact and reply to all
> email addresses included in the To and CC lines. (Feel free to cut this
> introductory paragraph, however.)
> 
> 
> Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html
> for more information about IESG DISCUSS and COMMENT positions.
> 
> 
> The document, along with other ballot positions, can be found here:
> https://datatracker.ietf.org/doc/draft-ietf-mpls-spring-lsp-ping/
> 
> 
> 
> ----------------------------------------------------------------------
> DISCUSS:
> ----------------------------------------------------------------------
> 
> Section 5.3 indicates that "Advertising Node Identifier" and "Receiving Node
> Identifier" are "4 or 6 octets." There are two issues that arise with the way
> this is currently specified, both of which can lead to a lack of
> interoperability:

Indeed. This text, which is included both in the Advertising and Receiving Node ID, needs fixing. In summary, Protocol 0 needs specification of the length and value, and Protocol 1 needs to disambiguate the length.

> 
> 1. While implementors might infer that "Protocol=1" results in a 4-byte value,
> and that "Protocol=2" results in a 6-byte value, it's a bit unclear what length
> is to be used here for "Protocol=0.”

Indeed. For Protocol=0, there’s little we can glean. See text below.

> 
> 2. The descriptions for both of these fields include: "When Protocol is set to
> 1, then the 32 rightmost bits represent OSPF Router ID."  This implies that the
> field is *wider* than 32 bits when Protocol=1, which leaves deep ambiguity
> about the circumstances under which the field is allowed to be 4 octets.

Correct. Meaning, you are correct and the text is incorrect. Protocol=1, 4-octet field, 32-bit OSPF Router-ID. Will fix. See below.

> 
> I would strongly recommend that this section add clear language that
> unambiguously spells out how implementations are expected to select the field
> width for the four variable-width fields in this Sub-TLV (the two I cite above
> as well as the interface ID fields).
> 

Yes. New text:

   Local Interface ID

      An identifier that is assigned by the local LSR for a link to
      which Adjacency Segment ID is bound.  This field is set to a local
      link address (IPv4 or IPv6).  For IPv4, this field is 4 octets;
      for IPv6, this field is 16 octets.  In case of unnumbered, this
      field is 4 octets and includes a 32 bit link identifier as defined
      in [RFC4203], [RFC5307].  If the Adjacency Segment ID represents
      parallel adjacencies ([I-D.ietf-spring-segment-routing]), this
      field is 4 octets and MUST be set to 4 octets of zeroes.
…
   Advertising Node Identifier

      It specifies the advertising node identifier.  When Protocol is
      set to 1, then this field is 4 octets and carries the 32-bit OSPF
      Router ID; if Protocol is set to 2, then this field is 6 octets
      and carries the 48-bit ISIS System ID; if Protocol is set to 0,
      then this field is 4 octets, and MUST be set to zero.

   Receiving Node Identifier

      It specifies the downstream node identifier.  When Protocol is set
      to 1, then this field is 4 octets and carries the 32-bit OSPF
      Router ID; if Protocol is set to 2, then this field is 6 octets
      and carries the 48-bit ISIS System ID; if Protocol is set to 0,
      then this field is 4 octets, and MUST be set to zero.


Thoughts? Other comments?

> 
> ----------------------------------------------------------------------
> COMMENT:
> ----------------------------------------------------------------------
> 
> Sections 5.1, 5.2, and 5.3 define "Reserved" fields without indication of how
> these fields should be treated. Recommend each of these be defined to "MUST be
> set to 0 on send, MUST be ignored on receipt" -- this is the scheme that
> maximizes the ability to use them in the future.
> 

Correct. New text:

   Reserved

      MUST be set to 0 on send, and MUST be ignored on receipt.

In the three sections.

> Section 5.3 sefines three values for "Adj Type": 0, 4, and 6. Please either
> state that all other values are and will always be an error, or create an IANA
> registry for this field.

Done as per Alvaro’s COMMENT.

> 
> Section 5.3 sefines three values for "Protocol": 0, 1, and 2. Please either
> state that all other values are and will always be an error, or create an IANA
> registry for this field.
> 
> 

Done as per Alvaro’s COMMENT.

Thanks,

— Carlos.