Aggregate traffic management
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
From: "Stanislav Rost"
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.
To my knowledge it is somewhat vendor specific. I've used policy routes and tag switching in dividing and altering traffic flows. I do know that with some vendors, it is important to make sure you activate the optimizations for things such as policy routing to save mass amounts of cpu time. I'm still a neophyte when it comes to tag switching. Others might help better in that. Jack Bates BrightNet Oklahoma
It can be done several ways, but the question is "how are you differentiating"? This is an incomplete list of methods for differentiating, each of which is supported by one or more vendors or open-source solutions: - destination address - specific prefix matching - prefix length matching (.../23, /24, etc.) - destination AS # - destination AS path length - destination (fill in the blank for other BGP or IGP specific tricks) - source address (see "destination address" for list of possible match criteria) - protocol (UDP, TCP, ICMP) - port (source or destination) - ToS bits - URL for port 80 traffic - MAC address of source machine - amount of throughput to a particular source/destination path There are even some methods that don't differentiate, but do random traffic distribution (for some highly imperfect value of "random", which I won't debate here.) - round-robin gateway specification - DNS round-robin (limited use, usually for servers producing traffic) If you could be more specific on what your distinguishing method would be for choosing one path over the other, some specific examples could be distilled from this group, I'm sure. <sarcasm> Though, of course, we here in North America don't have to worry ourselves about these issues, and we route everything through our most congested peer. </sarcasm> Is this simply to get a survey of all possible routing decision concepts, or are you looking for answers only at one layer of the OSI model? You do say "router" in your description, but I'm still uncertain if that is a limiting factor in your question. JT
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
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
participants (4)
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Jack Bates -
John Todd -
Serge Maskalik -
Stanislav Rost