nested prefixes in Internet

Tue Sep 27 15:40:19 UTC 2016

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 at 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
> 