[191801] in North American Network Operators' Group
Re: nested prefixes in Internet
daemon@ATHENA.MIT.EDU (Mel Beckman)
Tue Sep 27 11:50:45 2016
X-Original-To: nanog@nanog.org
From: Mel Beckman <mel@beckman.org>
To: Roy <r.engehausen@gmail.com>
Date: Tue, 27 Sep 2016 15:40:19 +0000
In-Reply-To: <72a17413-8ccf-1425-4953-277322e161af@gmail.com>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces@nanog.org
Precisely. This is how it's done by providers I've worked with.=20
-mel beckman
> On Sep 27, 2016, at 7:06 AM, Roy <r.engehausen@gmail.com> wrote:
>=20
>=20
>=20
> Option 3?
>=20
> ISP A announces the /19 and the /24 while ISP B does just the /24
>=20
>> On 9/27/2016 4:20 AM, Martin T wrote:
>> Hi,
>>=20
>> 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:
>>=20
>> 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.
>>=20
>> 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.
>>=20
>>=20
>> 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.
>>=20
>>=20
>> thanks,
>> Martin
>=20
