Stanislav, 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 effective. - Serge Thus spake Stanislav Rost (stanrost@lcs.mit.edu):
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 <stanrost@lcs.mit.edu> Laboratory for Computer Science, MIT