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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: Load balancing in routers
I don't think flow-caching is necessarily due to CEF. Even on dinky 2500 & 2600 series where you don't run CEF, load balancing over multiple links uses a flow-hashed method. If you want per-packet load distribution you have to specifically enable it by saying "no ip route-cache" on each interface. Paul's statement about CEF is interesting. It's probably the first public statement I've ever heard where someone was praising CEF. Usually discussions about CEF are accompanied by liberal amounts of swearing... Joe On 4/8/02 9:03 AM, "Iljitsch van Beijnum" <[email protected]> wrote: > > On 8 Apr 2002, Paul Vixie wrote: > >>> I seem to remember fast switching was per-destination, and CEF was >>> round robin. But it seems CEF is now per-destination as well in IOS 12.2. >>> Round robin is optional. > >> CEF is flow-hashed, and the hash seems to include both source and >> destination, and seems to include the port numbers. This is by observing >> the behaviour of flows hitting various members of the F.ROOT-SERVERS.NET >> set, each of whom sends F's address to several upstream routers using OSPF. >> CEF works like a charm -- the load is never split by more than 45-55 and >> that's damn good for wire speed hashing in my view. > >> We used CEF in 11.x and it behaved the same way. It was never round-robin >> in any way we could observe. > > You're right. I was thinking of process switching. > > According to: > http://www.ils.unc.edu/dempsey/186s00/reorderingpaper.pdf > > packet reordering at MAE East was extremely common a few years ago. Does > anyone have information whether this is still happening? > >
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