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North American Network Operators Group

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Re: Aggregate traffic management

  • From: Serge Maskalik
  • Date: Wed Jan 29 02:55:08 2003


  It depends what control mechanism you are using: 

   o routes learned via an IGP - ECMP would work and if it's a single 
     destination host, per-packet loadbalancing between the outgoing 
     links is your only practical choice; rest of ECMP schemes work 
     by distributing flows or routes amongst links

   o learned via BGP and the traffic consists of a variety of flows 
     that all use the same reachability information (BGP route); you 
     could de-aggregate the announcement locally if you have an idea 
     how the per-flow volume maps into the route; BGP Multipath feature
     set exists in most router implementations, but the distribution 
     methods are statistically different

  For the latter, several systems exist in the market place that try 
  to automate TE for BGP-learned routes, one of which is ours. These 
  system require a closed feedback loop for traffic volume per flow 
  and link mappings; this needs to occur close to real time to be 
  	- Serge  

Thus spake Stanislav Rost (

> Dear NANOGers,
> I have a very hands-on question:
> Suppose I am a network operator for a decent-sized ISP, and I decide
> that I want to "divide" aggregate traffic flowing through a router
> toward some destination, in order to then send some of it through one
> route and the remainder through another route.  Thus, I desire to
> enforce some traffic engineering decision.
> How would I be able to accomplish this "division"?  What technologies
> (even if vendor-specific) would I use?  
> I can think of some methods like prefix-matching classification and
> ECMP, but I am still not sure exactly how the latter works in practice
> (at the router level) and how one may set them up to achieve such
> load-sharing.
> Thank you for your expertise and lore,
> -- 
> Stanislav Rost <>
> Laboratory for Computer Science, MIT

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