On Sat, Apr 16, 2022 at 9:31 PM Thomas Fossati via Datatracker <noreply@xxxxxxxx> wrote:
Reviewer: Thomas Fossati
Review result: Ready
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Document: draft-ietf-idr-bgp-ls-sbfd-extensions-??
Reviewer: Thomas Fossati
Review Date: 2022-04-16
IETF LC End Date: 2022-04-27
IESG Telechat date: Not scheduled for a telechat
This document is compact and well written. I think it is ready for
publication. Thank you editors, and all the people involved in its
drafting. I have left a few small editorial suggestions (caveat: I am
completely unfamiliar with the subject matter) in case you may find them
useful.
## Section 3, first para:
OLD
The BGP-LS [RFC7752] specifies the Node NLRI for the advertisement of
nodes and their attributes using the BGP-LS Attribute.
NEW
BGP-LS [RFC7752] specifies the Node NLRI for the advertisement of
nodes and their attributes using the BGP-LS Attribute.
## Section 3, second para:
I had to jump a couple of times between the textual definition and the
TLV layout to understand how the two actually match. Specifically, I
think it's the "Length: variable." bit that triggered my confusion.
So, I have an editorial suggestion that would have saved me from a
(very) mild cognitive dissonance:
OLD
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Discriminator 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Discriminator 2 (Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Discriminator n (Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: S-BFD Discriminators TLV
where:
o Type: 1032 (early allocation by IANA)
o Length: variable. It MUST be a minimum of 4 octets and increments
of 4 octets for each additional discriminator.
o Discriminator n: 4 octets each, carrying an S-BFD local
discriminator value of the node. At least one discriminator MUST
be included in the TLV.
NEW
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=4*n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Discriminator 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Discriminator 2 (Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Discriminator n (Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where Type is 1032, Length is 4*n, and n is the number of S-BFD local
discriminator values of the node carried in the TLV. n MUST be at least
1.
KT> I believe the existing text is quite simple and aligned to existing conventions for BGP-LS TLV description.
## Section 3, ignorant hat on:
I am not sure what is the typical number of discriminators expected in a
TLV? It looks to me that ~65K/4 is a decent magnitude. What is the
expectation in case the number of discriminators is higher than the
maximum allowed by the TLV encoding? Is this a valid scenario? If so,
how is overflow handled?
KT> The overflow is not really valid. The info is sourced from IGPs and there the size for ISIS is much lower while for OSPF is the same as BGP-LS. Therefore, I don't see the the
possibility of overflow.
## Section 4, Table 1:
The structure doesn't seem to match the layout of the "BGP-LS Node
Descriptor, etc." IANA registry. In particular:
* The length field seems spurious?
* The IS-IS TLV/Sub-TLV is missing — but I guess this can be skipped, so
not a problem;
* The first column heading should be "TLV Code Point";
* The Reference column is missing.
OLD
+---------------+--------------------------+----------+
| Code Point | Description | Length |
+---------------+--------------------------+----------+
| 1032 | S-BFD Discriminators TLV | variable |
+---------------+--------------------------+----------+
NEW
+----------------+--------------------------+-----------+
| TLV Code Point | Description | Reference |
+----------------+--------------------------+-----------+
| 1032 | S-BFD Discriminators TLV | RFCthis |
+----------------+--------------------------+-----------+
## Section 5, first sentence:
OLD
The new protocol extensions introduced in this document augment the
existing IGP topology information that was distributed via [RFC7752].
NEW
The new protocol extensions introduced in this document augment the
existing IGP topology information that was distributed via BGP-LS
[RFC7752].
## Section 6, first para:
OLD
The new protocol extensions introduced in this document augment the
existing IGP topology information that can be distributed via
[RFC7752].
NEW
The new protocol extensions introduced in this document augment the
existing IGP topology information that can be distributed via BGP-LS
[RFC7752].
# Section 5, third sentence:
Typo: "now encompasses" should be "now encompass"
