Re: nested prefixes in Internet

[joel jaeggli <joelja () bogus com>]

On 10/10/16 9:04 AM, Roy wrote:
> The solution proposed allows ISP-B to use both paths at the same time,
> needs ISP-C to minimal changes, and has low impact on the global
> routing tables..  I have successfully used it in the past and my old
> company is still using it today.

Having two parties in control of a prefix announcement is a bit of a
disaster. ISP A becomes partitioned from isp B isp B does not withdraw
the covering aggregate and black-holes the of ISP A that lands on it's 
edge. bummer.

> .On 10/9/2016 11:50 PM, Martin T wrote:
> > Florian:
> >
> > as I told in my initial e-mail, ISP-B is multi-homed, i.e connected to
> > ISP-A(who leases the /24 to ISP-B from their /19 block) and also to
> > ISP-C. ISP-B wants to announce this /24 both to ISP-A and ISP-C.
> > That's the reason why either solution 1 or 2 in my initial e-mail is
> > needed.
> >
> > However, I would like to hear from Roy and Mel why do they prefer a
> > third option where ISP A announces the /19 and the /24 while ISP B
> > does just the /24.
> >
> >
> > thanks,
> > Martin
> >
> > On Wed, Oct 5, 2016 at 11:50 PM, Florian Weimer <fw () deneb enyo de>
> > wrote:
> > > * Martin T.:
> > >
> > > > Florian:
> > > >
> > > > > Are the autonomous systems for the /19 and /24 connected directly?
> > > > Yes they are.
> > > Then deaggregation really isn't necessary at all.
> > >
> > > > > (1) can be better from B's perspective because it prevents certain
> > > > > routing table optimizations (due to the lack of the covering prefix)
> > > > What kind of routing table optimizations are possible if covering /19
> > > > prefix is also present in global routing table?
> > > The /24 prefix could arguably be dropped and ignored for routing
> > > decisions.

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