[AusNOG] Write up - Big ISP, little ISP, local internet exchanges

Campbell, Alex Alex.Campbell at ogilvy.com.au
Fri Sep 5 12:40:33 EST 2008

There was a very interesting NANOG presentation on these issues a few years ago:
(it seems to have recently disappeared from the NANOG site so I have temporarily re-posted it)

> Take an uplink which is also on the local internet exchange, advertise 
> your /24s to the local internet exchange and your big /21 to the uplink 
> provider. Why? Because the uplink provider will advertise your /21 to 
> the rest of the internet, while it will internally route it via the /24s to the 
> local internet exchange. Free inbound traffic! And if your port on the 
> local internet exchange is 100Mbps or 1000Mbps and the link towards 
> your uplink provider is less than 100Mbps, you will have a nice extra 
> speed increase with it too.

Making troubleshooting more difficult and creating unnecessary routing asymmetry just to save a few bucks on inbound traffic seems like a false economy to me (but perhaps our economic priorities are different to others).

> Some providers run their accounting systems based on all the IP 
> traffic going through their edge routers and will bill you for the 
> traffic even if it doesn't go over the physical wire. Check your terms 
> and conditions to see what you can do about this Layer 8 behaviour.

The blog post seems to be suggesting that you could use the terms and conditions to legitimise stealing free traffic from your provider.

Providers that do their traffic accounting at their border have already solved this problem.  We used to buy transit from Uecomm and also peer with them at an MLPA exchange - they didn't care how the last-hop traffic got to us but they would charge us for it either way (which I didn't have any issues with).

As the presentation above suggests, careful logging and/or rate-limiting of suspicious IX traffic can detect / prevent most of the common bandwidth stealing techniques.

I can't see many (any) big providers splitting up their network and adding a lot of complexity to solve a non-problem.


From: ausnog-bounces at lists.ausnog.net [mailto:ausnog-bounces at lists.ausnog.net] On Behalf Of Matthew Moyle-Croft
Sent: Friday, 5 September 2008 11:55 AM
To: Edwin Groothuis
Cc: ausnog at ausnog.net
Subject: Re: [AusNOG] Write up - Big ISP, little ISP,local internet exchanges

What you've described is much of the reasoning as to why most of the peering world doesn't like MLPAs - a lack of control and opportunities for transit theft.

Have you actually used your complex multiple ASes and IP-IP tunnels in practice?  It sounds fairly unwieldly compared to the various filtering and contractual options available.


On 05/09/2008, at 9:36 AM, Edwin Groothuis wrote:

Now that I have a lot more free time and as a result my mind is
settling and things start to fall in place and actually make sense,
I have time to write up ideas, stories and experiences in the field
of inter-networking.

One of the more interesting issues with internet exchanges is that
you sometimes get unexpected results with regarding to routing and
the possibilities it gives.

At http://www.mavetju.org/weblog/html/00247.html I have placed a
write up called "Big ISP, little ISP, local internet exchanges"
which is about the behaviour you initially don't expect, but is
perfectly explainable, when the local internet exchange gets hooked
up by both "edge ISPs" and "transit providers" and what transit
providers can do about it to overcome it.

Edwin Groothuis      |            Personal website: http://www.mavetju.org
edwin at mavetju.org    |              Weblog: http://www.mavetju.org/weblog/
AusNOG mailing list
AusNOG at lists.ausnog.net

Matthew Moyle-Croft Internode/Agile Peering and Core Networks
Level 4, 150 Grenfell Street, Adelaide, SA 5000 Australia
Email: mmc at internode.com.au    Web: http://www.on.net
Direct: +61-8-8228-2909		     Mobile: +61-419-900-366
Reception: +61-8-8228-2999        Fax: +61-8-8235-6909

More information about the AusNOG mailing list