nested prefixes in Internet

Martin T m4rtntns at
Mon Oct 10 06:50:39 UTC 2016


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

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.


On Wed, Oct 5, 2016 at 11:50 PM, Florian Weimer <fw at> 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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