[babel] Robert Wilton's Discuss on draft-ietf-babel-source-specific-07: (with DISCUSS and COMMENT)

Robert Wilton via Datatracker <noreply@ietf.org> Thu, 05 November 2020 13:08 UTC

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Subject: [babel] Robert Wilton's Discuss on draft-ietf-babel-source-specific-07: (with DISCUSS and COMMENT)
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Robert Wilton has entered the following ballot position for
draft-ietf-babel-source-specific-07: Discuss

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Please see the comment below for further description.

My specific discuss issue relates to clarifying the indexes of the 'source' and
'route' tables to indicate whether they are replacing the 'prefix-len' elements
of the existing 3 tuple indexes, or adding additional elements to the existing
index, effectively making them 5 tuple indexes.



Caveat, I'm not familiar with the Babel routing protocol, and I might be
getting the wrong end of the stick.

In some ways I found the content and concepts of this document easy to
understand, but the choice of particular terminology made is hard for me to
know for sure that I am correctly interpreting this document.  In particular, I
am confused between the definition of "source", "destination prefix" and
"source prefix" between this document and draft-ietf-babel-rfc6126bis.

I might be completely confused, but my understanding is that what is called the
"destination prefix" in this document, is effectively what is referred to as
the "source" in draft-ietf-babel-rfc6126bis (e.g., in the Route Table in
section 3.2.5), that also happens to be a prefix.  Is that right?

A further confusion is that this draft seems to sometimes describes prefixes
differently from how they are described in the Babel RFC that it is extending. 
E.g., it seems that in some cases the prefix-length is implicitly part of the
prefix, and in other cases it is described as a separate element (e.g., in the
'source' and 'route' table indexes).


    3.1.  The Source Table

       Every Babel node maintains a source table, as described in [BABEL]
       Section 3.2.5.  A source-specific Babel node extends this table with
       the following field:

       o  The source prefix specifying the source address of packets to
          which this entry applies.

       The source table is now indexed by triples of the form (prefix,
       source prefix, router-id).

According to 3.2.5 of draft-ietf-babel-rfc6126bis, the table is already index
by a triple, i.e. prefix, prefix-len, router-id.  Is the intention of this
document to remove prefix-len as one of the keys to the index?  I presume not,
and that the new table is really indexed by a 5-tuple, i.e., adding
source-prefix and source-prefix length to the existing keys.

       Note that the route entry contains a source (see sections 2 and 3.2.5
       of [BABEL]) which itself contains a source prefix.  These are two
       very different concepts that should not be confused.

Should this reference be to 3.2.6?  It may be helpful to expand on what the
original "source" in a route entry means to avoid any confusion.

If my understanding is right, then I think that this document would greatly
benefit from being very clear on the differences in terminology and probably be
very specific about what they mean in the context of this document.