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Posted by stephen on April 16, 2008, 5:35 pm
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> > What is your understanding of the 20/80 rule? I have seen it as 20% of
> > traffic is one the local subnet, 80% is remote, but have also seen it
the
> > other way, 80% local, 20% remote.
> >
> > My frickin' BCMSN study guide shows it both ways at different spots in
the
> > book. Also, it's not clear to me if this is intended as a design
guideline
> > or a "fact of life" to be dealt with.
> >
> > Thanks.
> >
>
> My understanding of the 80/20 (20/80) rule is that it is one of those
> networking myths that some marketer used in a presentation somewhere and
it
> then became embedded in networking folklore - of course I don't have
> references for this so this maybe just a myth I've created.
>
> I would say that pre-Internet (and remember most "traditional" network
> design had it's origins solely within the Enterprise) the original idea
> would have been to design your network/internetwork so that as much
traffic
> as possible was kept local. Enterprise WAN bandwidth was scarce and
> expensive. And operationally this made sense too - servers and printers,
> etc, were all on the local network with the WAN used for interbranch
> communications (internal email say) and perhaps nightly backups to a
central
> archive or some such.
it actually goes all the way back to bridging, and it cam out of local
campus design.
WANs to LANs even now have a much bigger difference in performance - very
few people (or company offices) have an Internet feed that has 20% of the
performance of their local 10/100 or 1000 Mbps LAN.
the idea was that most traffic stays in 1 collision domain and only 20%
crosses a bridge to go somewhere else.
this was when bridges (= 2 port switches) were software driven beasties and
couldnt cope with a full 10 Mbps thruput.
and even if they could handle "wire speed", with the same speed LANs
everywhere and 2 port bridges, if your design has 100% remote traffic over a
bridge hop or 2 the aggregate thruput of your campus drops to 10 Mbps or
even less.
it went out of the window when multiport bridges and then switches became
available.
Plenty of big sites ended up with large central star switches or even
routers with just about every LAN hooked up.
>
> The Internet and the Web changed all that.- now it was possible for
> customers and the public generally to access the services you made
available
> to them. Also the Internet made bandwidth available for internal
> communciations via VPN, etc.
>
> So the balance has shifted, but to say it's 80/20 or 60/40 or 50/50 and in
> which direction, is a guess - each enterprise and system has its own
> characteristics which means initial network design analysis is more
critical
> then ever - generalisations don't help and in my view should be avoided.
>
> And besides I think you'd be very unlucky to have this a question in any
> cert exam.
>
> Aubrey
--
Regards
stephen_hope@xyzworld.com - replace xyz with ntl
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