Subject: Re: (ION) Non-member submission from ["Paul Henri" <[email-masked]>]

From: Joel Halpern <[email-masked]>
Date: Sun, 1 Nov 1998 15:07:03 -0500 (EST)

> From: "Paul Henri" <[email-masked]>
>
> Joel Halpern wrote:
> 
> > Sorry, I got lost in the (1)s and (2)s.  The intend was:
> >
> > If you request an answer of length x, you will never get an answer shorter
> > than length x.
> >
> > This is not so much for the originator  (he is probably only willing to
> > accept /32, or willing to accept anything), but for the progression.  It
> > is important that the match only get lengthened as it goes from router to
> > router.  If the mask got shortened, it could produce incorrect overlapping
> > resolutions.
> >
> 
> I am having trouble making sense of this. Barbara's response seems more
> logical to me. If the requestor is looking for a /24 (for reasons only it
> knows), it may be inappapropriate to respond with something which is
> represents a subset of the /24 (eg. /32). A superset (eg. /16) covers the
> request, and more.

There are two related issues, both of which drive us in the direction I
indicated:

1) If I request a /32, it is probably because I can not deal with a
prefix.  Therefore, giving the requestor a prefix when the requestor asked
for a /32 is not going to help any.

2) Suppose that we start with a /16.  This probably means that the
requestor has a table entry with a 16 bit prefix in it matching the
destination.  Hence, if you give the requestor anything shorter, he will
have to ignore it.  The intermediate version of this is the most important
part.  Suppose the request started out at /1 (really /0, but that is a
synonym for /32).  Suppose that some intermediate router had several table
entries which could match the request, and the longest one (after allowing
for overlaps) was /16.  If you ever shorten the prefix to /10 or
something, you will have incorrect routing.

Remember that the shortcuts must match routing.

Yours,
Joel M. Halpern                         [email-masked]
Newbridge Networks Inc.

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