Multiple ISP Load Balancing

Christopher Morrow morrowc.lists at
Wed Dec 14 19:34:46 UTC 2011

On Wed, Dec 14, 2011 at 2:28 PM, Drew Weaver <drew.weaver at> wrote:
> I've asked several times about this in the past; although I learned quickly to stop asking.
> It seems that the consensus has generally been that the best way to handle traffic engineering in networks where you have multiple full-feed up-streams is to do it manually (i.e. set preference for your top N AS/prefix destinations) or don't do it at all (let BGP figure it out..?).

seems the feeling is that if you have multiple full feeds and need to
loadshare, you really don't want (in most cases) ispa=500mbps +

you really want destinationA to be reached across the 'best path'
(best ... in some form, distance? packetdrop%? jitter? cost?)  you'll
most likely have to tweak things in order to achieve what you want
since only distance is really used in the stock bgp calculation
(distance by as-hops, presuming you don't listen to closely to med
from your providers)

> Suggesting that a "route optimization system" has any value generally makes people cranky.

ha! :)


> Thanks,
> -Drew
> -----Original Message-----
> From: Holmes,David A [mailto:dholmes at]
> Sent: Wednesday, December 14, 2011 2:07 PM
> To: nanog at
> Subject: Multiple ISP Load Balancing
> From time to time some have posted questions asking if BGP load balancers such as the old Routescience Pathcontrol device are still around, and if not what have others found to replace that function. I have used the Routescience device with much success 10 years ago when it first came on the market, but since then a full BGP feed has become much larger, Routescience has been bought by Avaya, then discontinued, and other competitors such as Sockeye, Netvmg have been acquired by other companies.
> Doing some research on how load balancing can be accomplished in 2011, I have come across Cisco's performance routing feature, and features from load balancing companies such as F5's Link Controller. I have always found BGP to be easy to work with, and an elegant, simple solution to load balancing using a route-reflector configuration in which one BGP client (Routescience Pathcontrol in my background) learns the best route to destination networks, and then announces that best route to BGP border routers using common and widely understood BGP concepts such as communities and local pref, and found this to lead to a deterministic Internet routing architecture. This required a knowledge only of IETF standards (common BGP concepts and configurations), required no specialized scripting, or any other knowledge lying outside IETF boundaries, and it seemed reasonable to expect that network engineers should eagerly and enthusiastically want to master this technology, just as any other technology must be mastered to run high availability networks.
> So I am wondering if anyone has experience with implementing load balancing across multiple ISP links in 2011, and if there have been any comparisons between IETF standards-based methods using BGP, and other proprietary methods which may use a particular vendor's approach to solving the same problem, but involves some complexity with more variables to be plugged in to the architecture.
> David
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