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Re: [RRG] thoughts on the design space 3: caching
Jari,
It is not at all clear if it is a problem. In fact, I'll argue on some
points it could be a feature.
Sure. I don't want to make an argument that the delay/drop
characteristics of caching are horrible.
In fact, while I know this is
an issue, I do not have any information about whether it is of
significant practical consequence. This why I'm asking you to find a
test for this in EXPLISP.
I'm also not convinced that the mapping delay matters on real networks
provided that the granularity of the mapping replies is sufficiently
large. In this case, the mapping service is only contacted once for the
first packet towards the corresponding EID prefix. In most networks,
most of the traffic is sent towards a small number of prefixes, see e.g.
http://inl.info.ucl.ac.be/publications/implications-topological-properties-i
http://inl.info.ucl.ac.be/publications/implications-interdomain-traffic-char
Thus, the ratio ( number of packets waiting for mapping reply) / (total
number of packets) will be very low
We did simulations based on Netflow traces on a 1Gbps link connecting
10.000 users and assuming that the mapping replies are for BGP prefixes,
the amount of mapping request is reasonable. See e.g.
http://inl.info.ucl.ac.be/publications/cost-caching-locatorid-mappings
The only case where you would detect problems with mapping are when a
single host is opening a single TCP connection. In this case, the SYN
packet will be delayed by the mapping. Note that using the DNS also
causes such a delay...
If EXPLISP needs to perform an evaluation, I would suggest to perform
the evaluation based on packet traces or netflow traces as we did and
not only on lab experiments with limited traffic.
Olivier
--
http://inl.info.ucl.ac.be , UCLouvain, Belgium
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