[191967] in North American Network Operators' Group
Re: nested prefixes in Internet
daemon@ATHENA.MIT.EDU (Martin T)
Wed Oct 5 03:45:26 2016
X-Original-To: nanog@nanog.org
In-Reply-To: <a4f809a2-7a0f-4071-8966-28f7f70b51f0@typeapp.com>
From: Martin T <m4rtntns@gmail.com>
Date: Wed, 5 Oct 2016 10:45:20 +0300
To: fw@deneb.enyo.de, r.engehausen@gmail.com, mel@beckman.org
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces@nanog.org
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 routin=
g 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 slig=
htly 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, =C3=A0 17:52, Mel Beckman <mel@beckman.org> a =C3=
=A9crit:
>>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
>>>
