Re: [RRG] LISP-ALT (was: LISP-EMACS & LISP-ALT)

["Tom Petch" <nwnetworks@dial.pipex.com>]

----- Original Message -----
From: "Scott Brim" <swb@employees.org>
To: "Robin Whittle" <rw@firstpr.com.au>
Cc: "Routing Research Group list" <rrg@psg.com>
Sent: Friday, November 16, 2007 7:45 PM
Subject: Re: [RRG] LISP-ALT (was: LISP-EMACS & LISP-ALT)


<snip>
>
> > a separate ASN number space, completely unrelated to the current BGP
> > and ASN numbering systems.  The connectivity patterns of these
> > LISP-ALT routers is somehow determined by address structure, rather
> > than physical proximity as it is in the current Internet.
>
> Did you understand that part?  If you are responsible for 192.0.2.0/24
> you would say so to one or more parent nodes responsible for an
> including prefix, for example 192.0.0.0/18.
>
<snip>
>
> > Overall, I think the LISP proposals (not so much NERD) are hard to
> > understand, with terse, conceptual descriptions with many options
> > and not enough examples.
>
> And your feedback will help make future versions clearer.  Thank you.
>

I too struggle to understand these proposals.  I find the best approach is to
wait until there is a reply to Robin's questions, when things usually become
clearer:-)  Thus no, I did not understand responsibility for prefixes from the
references to 'a hierarchy which matches the EID prefix allocation' or to 'in a
tree-like fashion (with some meshiness), both with redundancy' if indeed that is
what they mean.  Yet your sentence above conveys the idea clearly and concisely;
worth deferring the reading of the I-D for.

Or look at s.3  ' LISP-ALT operates on two name spaces ' yes, which?  name space
( or namespace ) does not occur again.  Ditto 'introduces a new network element,
the EID Prefix Aggregators (see below)' well yes the term is below in 'Generic
Routing Encapsulation (GRE) tunnels between EID       Prefix Aggregators' but
only there - it is never defined, never explained.

It seems pertinent that [LISP] is an informative reference for this I-D and so
not necessary in order to understand it; presumably because ' Section 4 outlines
the basic LISP 1.5 model.' and so no more information on LISP is thought
necessary.

I struggle partly because of the grammar, which is not quite the English grammar
I learnt at school so that I find myself emending the text, but more because of
an absence of the big picture with the focus instead on a mass of incoherent (to
me) detail.  Ah well, as long as Robin keeps asking the questions, I'll be ok.

Two current questions.  What namespace are the GRE endpoint addresses in?  The
current IPv4 32 bit namespace or some other (in the way in which eg AS numbers,
OSPF router ids, OSPF area numbers are also 32 bit numbers but in different
namespaces).

And the description of BGP 'advertising summary prefixes to the LISP-ALT routers
logically "above" them'.  Does BGP also advertise downwards and sideways, as in
the BGP of the current Internet, so that everyone has a consistent view of the
topology, or are there unexplained mechanisms to restrict advertising?

Frustratedly,

Tom Petch

> Scott
>
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