Subject: [rbridge] Ambiguous tie break algorithm in 4.5.1

From: "Cornelius Kraemer" <[email-masked]>
Date: Tue, 20 Apr 2010 09:19:37 +0200

Hi all,

In 4.5.1 Distribution Tree Calculation of draft-ietf-trill-rbridge-protocol-16.txt, it is stated:

   When building the tree number j, remember all possible equal cost
   parents for node N. After calculating the entire "tree" (actually,
   directed graph), for each node N, if N has "p" parents, then order
   the parents according to 7-octet IS-IS ID. For tree j, choose N's
   parent as choice j mod p.

I am convinced that this will lead to incompatible implementations, and 
that some clarification in the text is needed.

1. It should read "then order the parents in ascending order according to 
7-octet IS-IS ID."
2. j mod p has values 0, 1, 2, ..., p-1. So it should be made clear that 
the first position in the ordered list of IS-IS IDs is given by j mod p = 
0.
3. Since some parameters in TRILL have possible values 0, 1, 2, ... it is 
not self-explaining if parameter j (tree number) has the possible values 
0, 1, 2, ... or 1, 2, 3, ... . This is the worst problem with the above 
paragraph.

I have posted these remarks earlier, but received no reply. Maybe I am 
wrong, but I think these issues should be fixed.

Best regards,

   Cornelius

Dr. Cornelius Krämer
Head of Product Management
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---

From: "David Michael Bond" <[email-masked]>
Date: Tue, 20 Apr 2010 10:55:44 -0400

Hi Cornelius,

I believe the first question is addressed by this thread:

http://www.postel.org/pipermail/rbridge/2010-January/003866.html

Will this updated text be included through the RFC  Editor review?

I agree with the other two points.

-David

 

 

From: [email-masked] [mailto:[email-masked]] On
Behalf Of Cornelius Kraemer
Sent: Tuesday, April 20, 2010 3:20 AM
To: [email-masked]
Subject: [rbridge] Ambiguous tie break algorithm in 4.5.1

Hi all, 

In 4.5.1 Distribution Tree Calculation of
draft-ietf-trill-rbridge-protocol-16.txt, it is stated: 

I am convinced that this will lead to incompatible implementations, and that
some clarification in the text is needed. 

1. It should read "then order the parents in ascending order according to
7-octet IS-IS ID." 
2. j mod p has values 0, 1, 2, ..., p-1. So it should be made clear that the
first position in the ordered list of IS-IS IDs is given by j mod p = 0. 
3. Since some parameters in TRILL have possible values 0, 1, 2, ... it is
not self-explaining if parameter j (tree number) has the possible values 0,
1, 2, ... or 1, 2, 3, ... . This is the worst problem with the above
paragraph. 

Best regards, 

   Cornelius 

Dr. Cornelius Krämer

ExperTeach GmbH
Waldstr. 94
63128 Dietzenbach

---

From: Donald Eastlake <[email-masked]>
Date: Tue, 20 Apr 2010 12:13:03 -0400

Hi Cornelius and David,

It's good to know that people are really looking at the document closely.

I agree that these changes would be an improvement. In fact, David, I
thought I had make your suggested change, as noted in my reply where
you point in the mail archives. But I consider them to be editorial.
When it says "order X according to Y", at least in English, the
default is ascending. And, since j mod p takes on values from zero to
p-1, it does not seem hard to deduce that tree numbers must start at
zero.

Hopefully this change can be done during the RFC Editor process and
AUTH48 on the document. But in any case, there should probably be an
"Implementation Notes" draft, or the like, to accumulate any notes or
more lengthy explanations that people feel would be helpful to
implementers.

Cornelius: Sorry I missed your previous mail.

Thanks,
Donald (document editor)
=============================
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