Re: [RTG-DIR] Rtgdir telechat review of draft-ietf-babel-rfc6126bis-11

[Juliusz Chroboczek <[e-mail]>]

Dear Mr Qu,

Thank you for your review.

> The description about packet trailer is in RFC 7557 section 2.5, but not
> included in the bis version. Considering this document will obsolete RFC 7557,
> I suppose it should be self-complete, so readers don’t need to go back to RFC
> 7557 for more information.

The packet trailer is described in Section 4.2.

> There are multiple places in the document about TLV/Sub-TLV being
> “self-terminating”, but I didn’t find what it means. Maybe I’m missing
> something here?

This is defined in Section 4.4.  I have checked that all uses of
self-terminating occur after its definition.

> Section 1.1
> “unmanaged and wireless environment”, what does “unmanaged” mean here?

Not being actively managed by a human administrator.  This is a non-normative
section.  Please let me know if I'm using this term badly.

> Section 3.2.3
> The interface Hello seqno is changed to outing multicast hello seqno, however
> there is no description about unicast hello at all.

Unicast Hellos are per-neighbour, so they appear in Section 3.2.4 (Section
3.2.3 describes per-interface data structure while 3.2.4 describes
per-neighbour structures).  Both kinds of Hellos are described in more
detail in Section 3.4.1.

> While I was reading it, I kept thinking what if it’s unicast hello? Is
> there a unicast hello timer needed?

There is one, see Section 3.2.4, penultimate paragraph.

> From later sections, I realized there are unicast hellos. So I’d suggest
> add some descriptions to avoid the confusion.

Sections 3.2.4 and 3.4.1.

> Section 3.2.4
> There is “the expected incoming Unicast Hello sequence number” and “the
> outgoing Unicast Hello sequence number”, but it was not mentioned in section
> 3.2.3 (related with previous comment).

That's right.  Section 3.2.3 describes per-interface data.  Section 3.2.4
describes per-neighbour data.  Multicast Hellos are per-interface.
Unicast Hellos are per-neighbour.

> Section 3.8.1.1
> After a node receives a route request, if the given prefix doesn’t exist in its
> route table, it MUST send a retraction for that prefix. So my question is
> whether a node is allowed to send multiple explicit requests for a given
> prefix?

There's nothing forbidding it.  It may send multiple requests to different
neighbours (over unicast), or multiple requests on different interfaces
(over multicast).  There's also nothing forbidding a node from sending
multiple requests to the same destination, e.g. to compensate for packet
loss.

(Our implementation experience shows that, at least over 802.11, such
aggressive behaviour is not useful, it increases noise without having
a measurable effect on convergence time, hence the SHOULD in Section
3.8.2.3 which only requires a single request.  However, further research
might yield new insights, which is why this document does not explicitly
disallow such behaviour.)

> If so, what happens if both retractions and updates are received?

The procedure described in Section 3.5.4 is run for each received update
or retraction, which results in the construction of the data structures
used as input for the precedure described in Section 3.6.

> 1616    4.4.  Sub-TLV Format

> This section is about Sub-TLV, however the description language in this
> paragraph is mainly about TLV.

Good catch, thanks.  I'll fix that.

> Section 4.5
> it says that “an implementation may choose to use a dedicated stateless parser
> to parse the packet trailer”. Will the packet trailer be able to use the state
> parser if there are state there useful or just for implementation purpose?

I do not understand this comment.  Please clarify.

> Although there is no packet trailer defined at this moment.

Section 4.2.

> Section 4.5
> 1674       parsing a TLV MUST update the parser state even if the TLV is
> 1675       otherwise ignored due to an unknown mandatory sub-TLV.

I believe you may have forgotten to write your comment.

> Section 4.6.5
> 1805                 send a new scheduled Hello TLV with the same setting of the
> 1806                 Unicast flag.  If this is 0, then this Hello represents an
> I’d suggest changing the text to “the same setting of flags” instead of “the
> same setting of the Unicast flag”, considering the flags will be extended later.

I disagree.  This paragraph is about the multicast/unicast dichotomy, not
about future flags of an informative nature.

> Nits:

> 1049       metric) from a neighbour neigh with a link cost value equal to cost,
> 1050       it checks whether it already has a route table entry indexed by
> [neighbour neigh] => [neighbour]

I disagree.  We're defining the variable neigh, which we use in the next
sequence.

Regards,

-- Juliusz Chroboczek