Multiple ISP Load Balancing

Drew Weaver drew.weaver at
Wed Dec 14 19:44:27 UTC 2011

>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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