Re: [Tsv-art] Tsvart last call review of draft-ietf-mpls-bfd-directed-27

[Lars Eggert <[e-mail]>]

Hi Greg,

On Apr 15, 2024, at 15:50, Greg Mirsky <[e-mail]> wrote:
> ### Section 3.1, paragraph 7
> ```
>      Reverse Path field contains none, one or more sub-TLVs.  Any non-
>      multicast Target FEC Stack sub-TLV (already defined, or to be defined
>      in the future) for TLV Types 1, 16, and 21 of MPLS LSP Ping
>      Parameters registry MAY be used in this field.  Multicast Target FEC
> ```
> I think you mean "no other sub-TLV than X, Y, Z MUST be used"?(The MAY
> makes anything allowed.)
> GIM>> I think that your suggestion is close but could the new wording be interpreted that some of sub-TLV MUST be present? Would the following update make the use of the normative language clear:
> OLD TEXT:
>    Reverse Path field contains none, one or more sub-TLVs.  Any non-
>    multicast Target FEC Stack sub-TLV (already defined, or to be defined
>    in the future) for TLV Types 1, 16, and 21 of MPLS LSP Ping
>    Parameters registry MAY be used in this field.  
> NEW TEXT:
>    Reverse Path field MAY contain none, one, or more sub-TLVs.  Only
>    non-multicast  Target FEC Stack- sub-TLVs (already defined, or to be
>    defined in the future) for  TLV Types 1, 16, and 21 of MPLS LSP Ping
>    Parameters registry MUST be used  in this field. 
> 
> WDYT?

WFM!

> ### Section 3.1, paragraph 6
> ```
>      MAY be included in the BFD Reverse Path TLV.  However, the number of
>      sub-TLVs in the Reverse Path field MUST be limited.  The default
>      limit is 128, but an implementation MAY be able to control that
> ```
> Why must it be limited? And what unit is the default of 128 expressed
> in, bytes (for the "length" field)? Or number of entries?
> GIM>> Yes, the concern is for the number of entries. That is the result of addressing the comments by Andrew Allston. As Andrew explained, the concern is not for the size of the TLV but about the possible impact on the control plane (sort of DoS attack).  

OK, then please make it clear(er) that the limit is in bytes and applies to the Length field?

> ### Section 3.1, paragraph 6
> ```
>      If the egress LSR cannot find the path specified in the Reverse Path
>      TLV it MUST send Echo Reply with the received BFD Discriminator TLV,
>      Reverse Path TLV and set the Return Code to "Failed to establish the
>      BFD session.  The specified reverse path was not found" Section 3.2.
> GIM>> Thank you for pointing that out to me. That must be a forward reference. Would enclosing Section 3.2 in parentheses help? 

Yes, that would have made it clear.

Thanks,
Lars