Subject: [babel] [PATCH 3/4] address IETF-97 slides section I point 3

From: Denis Ovsienko <[email-masked]>
Date: Sun, 11 Dec 2016 23:34:59 +0000

"The dependency of a valid neighbour entry on receiving both Hello and
IHU TLVs on time may not look obvious but is critical for a correct
implementation."

This change in the middle of "Neighbour Acquisition" adds a paragraph to
clarify that.
---
 draft-ietf-babel-rfc6126bis/draft-ietf-babel-rfc6126bis.xml | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/draft-ietf-babel-rfc6126bis/draft-ietf-babel-rfc6126bis.xml b/draft-ietf-babel-rfc6126bis/draft-ietf-babel-rfc6126bis.xml
index d4dd853..4cab5d1 100644
--- a/draft-ietf-babel-rfc6126bis/draft-ietf-babel-rfc6126bis.xml
+++ b/draft-ietf-babel-rfc6126bis/draft-ietf-babel-rfc6126bis.xml
@@ -687,6 +687,10 @@ bidirectional reachability.  On unreliable media, neighbour acquisition
 additionally provides some statistics that MAY be used in link quality
 computation.</t>
 
+<t>For the avoidance of doubt, for a neighbour to remain in a stable
+bidirectional reachability state it is essential that it keeps sending both
+Hello and IHU TLVs on time as specified below.</t>
+
 <section title="Reverse Reachability Detection">
 
 <t>Every Babel node sends periodic Hellos over each of its interfaces.
-- 
2.7.4

-- 
    Denis Ovsienko

---

From: Juliusz Chroboczek <[email-masked]>
Date: Mon, 12 Dec 2016 17:57:45 +0100

> +Hello and IHU TLVs on time as specified below.</t>

I don't understand this sentence.  Is it an additional requirement for
implementations (in which case it should be stated in terms of MUST), or
is it just rephrasing what the document already says?

-- Juliusz

---

From: Denis Ovsienko <[email-masked]>
Date: Mon, 12 Dec 2016 18:14:05 +0000

---- On Mon, 12 Dec 2016 16:57:45 +0000 Juliusz Chroboczek  wrote ---- 
>is it just rephrasing what the document already says? 

It is the latter, as the commit message for this change hopefully says (the quoted text below is from the slides):

--------------------------------------------------
"The dependency of a valid neighbour entry on receiving both Hello and
IHU TLVs on time may not look obvious but is critical for a correct
implementation."

This change in the middle of "Neighbour Acquisition" adds a paragraph to
clarify that.
--------------------------------------------------

Saying the same in other words would be:

The stated dependency can be _derived_ from the current document if the reader knows what they are looking for (as I did to produce the FSM diagram). But if they don't look for it on purpose they can make an implementation mistake. This way this statement in this section
to me looks as a simple way to avoid a possible waste of time.

-- 
    Denis Ovsienko

---

From: Juliusz Chroboczek <[email-masked]>
Date: Wed, 14 Dec 2016 01:07:24 +0100

> It is the latter,

I see.  Denis, I agree with you that 3.4.1 and 3.4.2 are badly written.
However, the correct fix is to fix 3.4.1 and 3.4.2, not to add an
additional paragraph that basically says "3.4.1 and 3.4.2 are badly
written, so read them carefully".

-- Juliusz