nested prefixes in Internet

Mon Oct 10 06:50:39 UTC 2016

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 at 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.