Re: aggregate6 - a fast versatile prefix list compressor

[Steve Atkins <steve () blighty com>]

> On Dec 1, 2017, at 2:16 AM, Elmar K. Bins <elmi () 4ever de> wrote:
>
> nanog () studio442 com au (Julien Goodwin) wrote:
>
> > > The first optimisation is to remove any supplied prefixes which are
> > > superfluous because they are already included in another supplied
> > > prefix. For example, 2001:67c:208c:10::/64 would be removed if
> > > 2001:67c:208c::/48 was also supplied.
> > >
> > > The second optimisation identifies adjacent prefixes that can be
> > > combined under a single, shorter-length prefix. For example,
> > > 2001:67c:208c::/48 and 2001:67c:208d::/48 can be combined into the
> > > single prefix 2001:67c:208c::/47. As an IPv4 exampl: 10.0.0.0/24 and
> > > 10.0.1.0/24 can be joined into 10.0.0.0/23.
> >
> > Will it catch cases like:
> > 10.0.0.0/24 10.0.1.0/24 10.0.2.0/23 -> 10.0.0.0/22
>
> I guess the developers will have implemented a loop that runs until no
> more optimizations have been found. Which would of course catch it as
>
> Iteration 1
> 10.0.0.0/24 + 10.0.1.0/24
> -> 10.0.0.0/23
>
> Iteration 2
> 10.0.0.0/23 + 10.0.2.0/23
> -> 10.0.0.0/22

The usual trick is to build a prefix tree then walk the tree, which catches
this sort of case in one step.

Cheers,
  Steve