[AusNOG] What Transit Providers Would You Pair Together

[Andrew McLeod]

Hi James,



Achieving near 50/50 load balancing will be very tough unfortunately!



[Balancing Problems]



Let's say that for example, you were to choose two different Go4 providers with very similar path costs to popular destinations (Australia and the USA for example).



On the surface, it might seem like the ideal way to get the desired 50/50 balance but in practice if there are two identical cost paths than only one of those paths will be chosen, and the path that's chosen will be the one that's had the best uptime (least recent flapping event).



So let's say you started your prefix advertisements on provider [A], and then immediately turn on provider [B], the upstream routers will first choose the one with the shortest path, and if they see two equal cost paths they will chose provider [A] since it's been up the longest.



The end result is that most traffic ends up coming down provider [A], until such a time that this link goes down, and then the traffic will flick over to provider [B].



When provider [A] comes back online, the shortest path decision will happen of course, but where there's equal cost paths the traffic will stay on [B]. So you end up finding that one provider gets the most traffic until it goes down, and then the other provider ends up with the most traffic, rinse and repeat.



[Provider Choice]



Obviously the key is choosing providers that utilize different domestic and international paths, as others have suggested to do some research by utilizing http://bgp.he.net, etc, etc.



But taking that another level, as far as domestic paths go, if you're already with a Go4 provider than generally they don't peer with other providers, so when it comes to choosing a non-Go4 just make sure you choose one that peers extensively (PipeIX, WAIX, etc) as this will help considerably with your balancing goals.



As far as international paths go, try and make sure they use different logical international paths at a minimum, and preferably different physical paths as well (if it's possible to ascertain). This will also help with the balancing goals.



--



Just my 2c, but I hope this all makes sense.


Cheers,
[cid:image001.png at 01CED6F8.4309EB00]



-----Original Message-----
From: AusNOG [mailto:ausnog-bounces at lists.ausnog.net] On Behalf Of James Mcintosh
Sent: Friday, 1 November 2013 6:20 AM
To: ausnog at ausnog.net
Subject: [AusNOG] What Transit Providers Would You Pair Together



Hi Noggers,



We're looking at adding a second transit provider for redundancy (and hopefully more-or-less even load balancing). I was wondering what transit providers people would recommend pairing together to get the most diverse set of routes. Obviously you don't want your two upstreams to have very similar routes and paths.



As a start I was thinking perhaps a Gang of Four provider plus a non-Go4 provider would make a good pairing but I'd really appreciate the comments of some of the more experienced BGP gurus on the list.





-James

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