Re: nested prefixes in Internet

[Martin T <m4rtntns () gmail com>]

Florian:

> Are the autonomous systems for the /19 and /24 connected directly?

Yes they are.


> (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?


> But (1) can also be worse for B and A's other customers if /24s (and slightly shorter prefixes) in this part of the 
> IPv4 address space are commonly filtered.

Based on my experience /24 is allowed in prefix-filters.. Longer IPv4
prefixes are not.



Roy, Mel:

Could you please elaborate on that option. What kind of advantages
does this have compared to option 2?


thanks,
Martin


On Tue, Sep 27, 2016 at 8:52 PM, Michael Hallgren <mh () xalto net> wrote:
> Hi Martin,
>
> What do you want to do? Move from A to B or add A to B?
>
> Cheers,
> mh
>
>
>
> Le 27 sept. 2016 17:52, à 17:52, Mel Beckman <mel () beckman org> a écrit:
> > Precisely. This is how it's done by providers I've worked with.
> >
> > -mel beckman
> >
> > > On Sep 27, 2016, at 7:06 AM, Roy <r.engehausen () gmail com> wrote:
> > >
> > >
> > >
> > > Option 3?
> > >
> > > ISP A announces the /19 and the /24 while ISP B does just the /24
> > >
> > > > On 9/27/2016 4:20 AM, Martin T wrote:
> > > > Hi,
> > > >
> > > > let's assume that there is an ISP "A" operating in Europe region who
> > > > has /19 IPv4 allocation from RIPE. From this /19 they have leased
> > /24
> > > > to ISP "B" who is multi-homed. This means that ISP "B" would like to
> > > > announce this /24 prefix to ISP "A" and also to ISP "C". AFAIK this
> > > > gives two possibilities:
> > > >
> > > > 1) Deaggregate /19 in ISP "A" network and create "inetnum" and
> > "route"
> > > > objects for all those networks to RIPE database. This means that ISP
> > > > "A" announces around dozen IPv4 prefixes to Internet except this /24
> > > > and ISP "B" announces this specific /24 to Internet.
> > > >
> > > > 2) ISP "A" continues to announce this /19 to Internet and at the
> > same
> > > > time ISP "B" starts to announce /24 to Internet. As this /24 is
> > > > more-specific than /19, then traffic to hosts in this /24 will end
> > up
> > > > in ISP "B" network.
> > > >
> > > >
> > > > Which approach is better? To me the second one seems to be better
> > > > because it keeps the IPv4 routing-table smaller and requires ISP "A"
> > > > to make no deaggregation related configuration changes. Only bit
> > weird
> > > > behavior I can see with the second option is that if ISP "B" stops
> > for
> > > > some reason announcing this /24 network to Internet, then traffic to
> > > > hosts in this /24 gets to ISP "A" network and is blackholed there.
> > > >
> > > >
> > > > thanks,
> > > > Martin