Re: [LARTC] many ways to do load balancing (or not?)

[Ashok N N <nalkunda@cse.msu.edu>]

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hi,
   since my masters thesis is also concerned with this, i thought of taking 
this opportunity to clarify/get clarified some of my own thougths. please see 
inline.

On Thursday 21 November 2002 07:19 am, Andreas Hasenack wrote:
> I'm a little confused about the many ways I've read that can be used
> for traffic load balancing, that is, two or more interfaces to the
> outside world being used transparently and efficiently by the internal
> machines.
> 
> I heard about:
> a) netfilter SNAT to more than one IP. If I'm correct, this is only
> a round robin, that is, one connection goes here, the other goes there,
> then the next goes here again, etc without much thought.
> 

i believe that SNAT is for connections initiated from outside world towards 
the internal network. and this would be reverse of what is intended here, 
that of using the links to the outside world efficiently. moreover if setup 
properly, the packets will go out back on the interface they came in.

> b) multipath default route. Seems to do something similar, but it "caches"
> routes. What exactly does this mean in the long run?
> 

i'm still looking at the code here. AFAIK, the when you have multipath option 
set, then when looking up for a route to an address, among the multiple equal 
cost paths, one is selected according to some criteria (i read random 
somewhere in the kernel but am not able to locate it now). but once the route 
is found, it is cached in the route cache and all packets will follow that 
route. so it is kind of a route-based load-balancing.

> c) multipath default route, but with the equalize option. Again, seems to
> work, but the best description I could find about it was something along
> the lines of "packet randomization", whatever that means. What does it do
> in the long run? Is it better/worse than b)?
> 

i read in one of the threads that 'equalize' causes per-packet load balancing, 
i.e looks up the route for each packet. but i am doubtful about the 
performance when each packet causes a route-lookup in the FIB.
(http://www.uwsg.iu.edu/hypermail/linux/net/0107.3/0028.html)

> d) OSPF. I read in the RFC that OSPF can do "load balancing", but I failed
> to understand how (no, I didn't read that RFC thoroughly, it's really high
> tech for me at this point). Does it use multipath routes to accomplish this?
> 
> Any help is appreciated, thanks.

ashok
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