Re: [OSPF] Suresh Krishnan's Discuss on draft-ietf-ospf-encapsulation-cap-06: (with DISCUSS and COMMENT)

[Suresh Krishnan <[e-mail]>]

Hi Acee,
  Thanks for the quick reply. Please find comments inline.

> On Aug 31, 2017, at 5:50 AM, Acee Lindem (acee) <[e-mail]> wrote:
> 
> Hi Suresh, 
> 
> On 8/30/17, 10:49 PM, "Suresh Krishnan" <[e-mail] <mailto:[e-mail]>> wrote:
> 
> Suresh Krishnan has entered the following ballot position for
> draft-ietf-ospf-encapsulation-cap-06: Discuss
> 
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> Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html <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-ospf-encapsulation-cap/ <https://datatracker.ietf.org/doc/draft-ietf-ospf-encapsulation-cap/>
> 
> 
> 
> ----------------------------------------------------------------------
> DISCUSS:
> ----------------------------------------------------------------------
> 
> * There seems to be an difference between this document's definition of
> sub-TLVs (with 2 octet types and lengths) and those of RFC5512 (with 1 octet
> types and lengths). So I am surprised to see the document point to the RFC5512
> based TLVs for both syntax and semantics (Sections 5.1, 5.2, 5.3 ...) . Can you
> please explain how these sub-TLVs are encoded on the wire to be compatible with
> this draft?
> 
> I can answer this one since I specifically told the authors to use this format. If you look at RFC 7770, you’ll see that all OSPF Router Information (RI) LSA TLVs and Sub-TLVs have 2 octet types and lengths. 
> 
> 2.3. OSPF Router Information LSA TLV Format
> 
> The format of the TLVs within the body of an RI LSA is the same as
> the format used by the Traffic Engineering Extensions to OSPF [TE].
> The LSA payload consists of one or more nested Type/Length/Value
> (TLV) triplets. The format of each TLV is:
> 
>  0 1 2 3
>  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
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> | Type | Length |
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> | Value... |
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> 
> Figure 3. TLV Format
> 
> 
> Additionally, if you look at https://www.ietf.org/id/draft-ietf-idr-tunnel-encaps-07.txt <https://www.ietf.org/id/draft-ietf-idr-tunnel-encaps-07.txt> (which obsoletes RFC 5512), you’ll see that the 1 octet length with insufficient. 
> 
>    Each sub-TLV consists of three fields: a 1-octet type, a 1-octet or
>    2-octet length field (depending on the type), and zero or more octets
>    of value.  A sub-TLV is structured as shown in Figure 2:
> 
>                    +-----------------------------------+
>                    |      Sub-TLV Type (1 Octet)       |
>                    +-----------------------------------+
>                    |     Sub-TLV Length (1 or 2 Octets)|
>                    +-----------------------------------+
>                    |     Sub-TLV Value (Variable)      |
>                    |                                   |
>                    +-----------------------------------+
> 
>                Figure 2: Tunnel Encapsulation Sub-TLV Format
> 
>    o  Sub-TLV Type (1 octet): each sub-TLV type defines a certain
>       property about the tunnel TLV that contains this sub-TLV.
> 
> 
> 
> 
> 
> Rosen, et al.           Expires January 18, 2018                [Page 7]
> 
> Internet-Draft       Tunnel Encapsulation Attribute            July 2017
> 
> 
>    o  Sub-TLV Length (1 or 2 octets): the total number of octets of the
>       sub-TLV value field.  The Sub-TLV Length field contains 1 octet if
>       the Sub-TLV Type field contains a value in the range from 1-127.
>       The Sub-TLV Length field contains two octets if the Sub-TLV Type
>       field contains a value in the range from 128-254.
> 
>    o  Sub-TLV Value (variable): encodings of the value field depend on
>       the sub-TLV type as enumerated above.  The following sub-sections
>       define the encoding in detail.
I did read the draft-ietf-idr-tunnel-encaps-07 draft (following it from the references) and I do understand why the document made the switch to 2 octets for the length. The part that threw me off is that this document (ospf-encapsulation) mandates *2 Octet* sub-TLV types which are not even mentioned in draft-ietf-idr-tunnel-encaps-07. Similarly this document mandates 2 octet lengths without nuancing the length based on sub-TLV type (>127 or not). And then it states that the syntax is specified in the documents that use 1 octet types. This is the discrepancy that needs addressing.

Thanks
Suresh