nested prefixes in Internet

Owen DeLong owen at delong.com
Wed Oct 19 16:50:48 UTC 2016


Assuming that there is a PNI A<->C assumes facts not in evidence.

Owen

> On Oct 19, 2016, at 11:27 AM, Martin T <m4rtntns at gmail.com> wrote:
> 
> Hi,
> 
> I made a drawing of those two best solutions: http://i.imgur.com/7NQVgUH.png
> 
> As much as I understand, both solutions require no special changes
> from "ISP C". Only advantage of solution B over solution A, that I can
> see, is that at the time when link between "ISP C" and "ISP B" is up,
> the traffic from Internet towards "ISP B" prefers the "ISP C"
> connection.
> 
> 
> In case the link between "ISP A" and "ISP B" goes down, then traffic
> from "ISP A" addressed to this /24 will use a private peering link
> between "ISP A" and "ISP C" so the transit costs are not an issue.
> 
> 
> thanks,
> Martin
> 
> On Wed, Oct 12, 2016 at 1:58 AM, Owen DeLong <owen at delong.com> wrote:
>> 
>>> On Oct 10, 2016, at 14:59 , Baldur Norddahl <baldur.norddahl at gmail.com> wrote:
>>> 
>>> 
>>> 
>>> Den 10/10/2016 kl. 22.27 skrev Owen DeLong:
>>>> Not true… There are myriad reasons that the /24 might not reach a network peered with ISP-A, including the possibility of being a downstream customer of a network peered with or buying transit from ISP-A. In the latter case, not an issue, since it’s paid transit, but in the former (peered, not transit), again, ISP-A is probably not super excited to carry traffic that someone isn’t paying them to carry.
>>>> 
>>> 
>>> But ISP-A is in fact being paid to carry the traffic. Supposedly ISP-B has a paid transit relation to ISP-A. In the case the transit link is down ISP-A might have to transport the traffic through a less profitable link however.
>> 
>> Which isn’t really in the agreement between ISP-B and ISP-A unless it was specifically (and unusually) negotiated.
>> 
>> Also, you’re assuming that the leased space came with a transit agreement. In many cases, address leases don’t, so consider the additional scenario where ISP-B leases addresses from ISP-A, but has transit contracts with ISP-C and ISP-D but no connection at all to ISP-A.
>> 
>>> I know that if ISP-A was my network I would be making money even with the transit link down. Yes I might have to transport something out of my network through one of my transits, but outbound traffic is in fact free for us because we are heavy inbound loaded.
>> 
>> Yes, but it doesn’t help if it also came in on a transit link. Any traffic you both receive and transmit on transit costs you money pretty much no matter who you are.
>> 
>> 
>> Owen
>> 



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