Prefix Flag Extension for OSPFv2 and OSPFv3
draft-ietf-lsr-ospf-prefix-extended-flags-07

Thank you for a clearly written and useful document. I have no substantive comments that have not alreadyy been highlighted by other reviewers.

Hi Ran, Detao, Peter, Ketan, and Liyan, 

Thank you for the effort put into this specification. This is an important piece of work.

I definitely support this. I have some few comments that I’d like to be addressed, especially the first three comments and the comment in Section 3.

# General

## Should we have a recommendation whether the remaining flags are assigned first vs. use of the sub-TLV? I think we need a guidance (not rigid, though).

## Not sure if this is assumed, but is it allowed that a group of bits (e.g., 2 bits) may be allocated for one single purpose? The current description seems to assume that flags will be allocated individually.

## Should we have configuration parameters to control the use of the flags (e.g., rfc8362#appendix-A)?

## (nit) Please use terms to be consistent with the use in RFC8362 (sub-TLV, etc.).

## (nit) Use explicit references (with sections) to help readers to find where to look.

## (nit) Be consistent with the IANA registry names

# Abstract: Please indicate that the sub-TLV applies for both versions

OLD:
   Each OSPF prefix can be advertised with an 8-bit field to indicate
   specific properties of that prefix.  However, all the OSPFv3 Prefix
   Options bits have already been assigned and only a few bits remain
   unassigned in the flags field of the OSPFv2 Extended Prefix TLV.

   This document solves the problem of insufficient prefix options bits
   by defining variable-length Prefix Attribute Flags Sub-TLV for OSPF.

NEW:
   Each OSPF prefix can be advertised with an 8-bit field to indicate
   specific properties of that prefix.  However, all the OSPFv3 Prefix
   Options bits have already been assigned and only a few bits remain
   unassigned in the flags field of the OSPFv2 Extended Prefix TLV.

   This document solves this problem by defining variable-length Prefix
   Attribute Flags sub-TLV for OSPF. This sub-TLV is applicable to OSPFv2
   and OSPFv3.

# Section 2:

## (nits) Fix several nits

OLD: 
   This document defines variable-Length Prefix Attribute Flags Sub-TLVs
   for OSPFv2 and OSPFv3.  These Sub-TLVs specify the variable-flag
   fields to advertise additional attributes associated with OSPF
   prefixs i.e., the advertisement and processing of the existing fixed-
   size prefix attribute flags remains unchanged.

NEW:
   This document defines variable-Length Prefix Attribute Flags sub-TLV
   for OSPFv2 and OSPFv3.  Such Sub-TLV specifies the variable-flag
   fields to advertise additional attributes associated with OSPF
   prefixes. The advertisement and processing of the existing fixed-
   size prefix attribute flags remain unchanged.

## (nit) Add caption  and call them in the text. For example,  

OLD: 
   The format of OSPFv2/OSPFv3 Prefix Attribute Flags Sub-TLVs 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             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     //                 Prefix Attribute Flags (Variable)           //
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

NEW:
   The format of OSPFv2/OSPFv3 Prefix Attribute Flags sub-TLV is shown in Figure 1.

      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             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     //                 Prefix Attribute Flags (Variable)           //
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Format of OSPFv2/OSPFv3 Prefix Attribute Flags Sub-TLV 

## I don’t parse what is meant by “defined prefix flags” in the following:

CURRENT:
   Defined prefix flags that are not
   transmitted due to being beyond the transmitted length MUST be
   treated as being set to 0. 

# Should the event covered in this part be logged?

CURRENT:
   When multiple instances of an OSPFv2/OSPFv3 Prefix Attribute Flags
   Sub-TLVs are received within the same TLV, an implementation MUST use
   only the first occurrence of the Sub-TLV and MUST ignore all
   subsequent instances of the Sub-TLV.

(nit) Maybe better to reword as follows: 

NEW:
   When multiple instances of the OSPFv2/OSPFv3 Prefix Attribute Flags
   sub-TLV are received within the same TLV, an implementation MUST use
   only the first occurrence of the sub-TLV and MUST ignore all
   subsequent instances of the sub-TLV.

# Section 3: MUST seems redundant with “Unrecognized TLVs and sub-TLVs are ignored” stated in rfc8362#section-6

CURRENT:
   The Prefix Attribute Flags Sub-TLVs defined in this document does not
   introduce any backward compatibility issues.  An implementation that
   does not recognize the OSPFv2/OSPFv3 Prefix Attribute Flags Sub-TLV
   MUST ignore the Sub-TLV.

(nit) We may consider: s/The Prefix Attribute Flags Sub-TLVs defined in this document/The Prefix Attribute Flags sub-TLV does not

# Section 5: We may add subsections for each OSPF version to better organize the actions (and also avoid orphan subsections):

OLD: 
     5.1.  OSPFv2 Prefix Attribute Flags Sub-TLV Registry
       5.1.1.  OSPFv2 Prefix Extended Flags Field Registry
     5.2.  OSPFv3 Prefix Attribute Flags Sub-TLV Registry
       5.2.1.  OSPFv3 Prefix Extended Flags Field Registry

NEW
     5.1.  OSPFv2
       5.1.1.  OSPFv2 Prefix Attribute Flags Sub-TLV Registry
       5.1.2.  OSPFv2 Prefix Extended Flags Field Registry
     5.2.  OSPFv3
       5.2.1. OSPFv3 Prefix Attribute Flags Sub-TLV Registry
       5.2.2. OSPFv3 Prefix Extended Flags Field Registry

# FWIW, the full review with other minor edits/nits can be found at: 

* pdf: https://github.com/boucadair/IETF-Drafts-Reviews/blob/master/2025/draft-ietf-lsr-ospf-prefix-extended-flags-06-rev%20Med.pdf 
* doc: https://github.com/boucadair/IETF-Drafts-Reviews/blob/master/2025/draft-ietf-lsr-ospf-prefix-extended-flags-06-rev%20Med.doc

Feel free to grab whatever useful there.

Cheers,
Med