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RE: Multiple ISP Load Balancing
From: Drew Weaver <drew.weaver () thenap com>
Date: Wed, 14 Dec 2011 14:44:27 -0500

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 + ispb=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)

Yes, but performance from your network to $destination_AS via $ISPx can be variable and how do you know when it changes 
before someone starts complaining?

There are traditionally two pieces involved with optimization.

1) "Cost" (Commitment/oversubscribe management and monitoring)
2) "Performance"

Usually "cost control" is #1 so systems like that are configured so that as long as the traffic isn't breaking your 
commits or filling your pipes they will then optimize X number of your top prefixes for performance (based on what the 
system can see).

The performance aspect is generally just sending basic probes in all directions towards a destination host and seeing 
which ones reply the fastest.

Although obviously this only impacts traffic outbound from your AS.


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