Hello,
Here are some additional comments on the above draft. Section 4 suggests
the utilisation of a hash to perform the load balancing based on the
source-address/flow label pair. Hash functions are often used in load
balancing applications. I think that it could be useful to point the
advantages and the drawbacks of using hash functions for load balancing
purposes.
The main advantage of hash functions is that they usually exhibit the
avalanche effect, i.e. a small change in the input causes a large change
in the output of the function. Simulations show that this effect is
important to correctly balance real traffic.
However, with hash functions, this advantage comes with a drawback. It
is difficult to predict the set of inputs that would provide a specific
output. Being able to predict which decision will be taken by a load
balancer is important for monitoring applications for example. If a
network operator wants to verify the round-trip-time between two hosts
when there is a load balancer in between, he/she should take into
account this load balancing when defining his/her probes. A similar
situation happens when a network operator wants to use traceroute to
detect block holes on a load-balanced path.
It should be noted that there exist functions that exhibit the avalanche
effect without being one-way functions like the classical hash
functions. If used in load-balancers, these functions would provide both
good load balancing and predictibility which is desired for many
monitoring applications. A recent paper shows how such load-balancing
can be performed efficiently by using block ciphers instead of hash
functions. The solution proposed in this paper could be adapted to
utilise the IPv6 flow label :
http://inl.info.ucl.ac.be/publications/revisiting-flow-based-load-balancing-stateless-path-selection-data-center-networks
Best regards,
Olivier Bonaventure
--
INL, ICTEAM, UCLouvain, Belgium, http://inl.info.ucl.ac.be
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