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f5n00bie_77440's avatar
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Nov 24, 2010

Link Controller - outbound load balancing




I am new to F5s and implementing link controllers and trying to design a solution to meet the customers requirement of outbound link selection based on best performance, for a specific URL.




The closest article I could find on link selection based on performance was here:




Basically this article talks mainly about inbound load balancing and virtual server selection based on link performance characteristics. This selection of VS would ultimately influence the ISP link chosen to carry the traffic.




Is it possible to dynamically perform outbound traffic ISP link selection based on the best performance characteristics to a specific URL with a link controller?




Thanks for reading


3 Replies

  • You could certainly use tcp::rtt to look at the round trip time to the destination through 2 different pool members. The real question is, how often do you care about performance? If Link B is 5 ms faster than Link A, do you want to use Link B every single time even though the client would never notice?
  • Thanks and agreed, I find the requirement quite feckless. However, if packetloss could be monitored, that may provide some tangible benefit.



    Another concept I need to understand is how the default-gateway route is chosen by the link controller for outbound traffic by default.



    As far as I can see default-gateway load balancing is performed by round robin by default, even when dynamic ratio is applied (unless you change the ratios from 1:1) is this correct?



  • f5noobie - I assume you've got a pool which contains your routers? Depending on the load balancing algorithm for that pool, you may or may not use round robin. Least connections for instance would use the link with, well, the least connections. :-P