From: Chris Higgins (chris.higgins at domain horizon.ie)
Date: Fri 10 Aug 2001 - 14:00:29 IST
> > If you build the network as it is below, with no intelligence, then it
> > can be horrible. What you have in effect is one large LAN (albeit switched).
> > Any broadcast packets from one machine goes to *every* port on that network.
> > Which (if you have a large number of machines) can cause loads of problems.
> This is more out of sheer curiosity itself, rather than anything work
> related (and would be overkill regarding a HAN no doubt), but are there
> any docs out 'there'  on proper network design?
OOoohhh 'proper network design'... what an excellent topic for
a war :)
In true networking fashion, the answer is really "it depends"... and
which of these variables are involved and what their relative
importance should be - is where most arguments start.
As soon as someone gives a 'for example', or 'rule of thumb', someone
else will be right back in there complaining that it doesn't work on
their particular network.
BUT - to answer your question.. in a way..
For proper network design - you chuck out ethernet and go for
something a bit faster - like myrinet. However given that most people
are going to be in the ethernet class LAN networks for a while
let's stick there...
Building a network is the same as building a linux server - the
same principles apply - you first need to understand what your
requirements are, and then you can apply different design models
For example: Building an office network for file/print sharing is
a lot more straight forward than building one that will have
broadcast TV and requirements for guaranteed end-to-end performance.
Building a linux box to serve static WWW pages is substantially
different to building a linux box to host databases. Anyone who
says 'but - you just install your distro, and then the application'
is missing the point.
The things you want to avoid in the network design are the obvious
things that you want to avoid anywhere else - single points of
failure... ie: any one thing that could happen which would render
the network useless. This may be hardware failure (so you get
spare power supplies, redundant blades in routers/switches,
run HSRP between routers), or it may be software failure
(some nitwit with a virus flooding the network with ARP requests)
Either way - you need to build the network to be resiliant to
those failures... one class of problem with plain old ethernet
segments is broadcast storms - usually seen with broken bridges,
but can be created by dying network stacks ( I had an ethernet
segment filled with broadcasts from a sunos 4.1.1 machine back
in the early 90's that got stuck in a kernel loop pushing
packets - it brought the network to a halt. ).
Having separate broadcast domains in your network lets you limit
the damage a single broadcast storm can have. So in the example
posed at the start of the thread - if you have 4 labs, and each
is it's own LAN (VLAN / Broadcast domain), then a broadcast storm
(or game of doom / quake / whatever) is contained within that
particular network segment/lan/vlan/broadcast domain.
I have seen a large company (who *SHOULD* really have
known better) try bridge their entire network (including
regional offices) onto one network... There were a couple
of us 'router' people who didn't see the point of the non-routable
protocols , we tried to convince them that routing the traffic
was better than bridging it.. but they wouldn't listen..
A while later (8-9 months) the network was falling apart and
we heard that they had consultants in doing a complete audit
and moving away from bridged to routed networks. :)
As to reference material - Cisco have some good stuff on
their site - look for a document called
"LAN Design Guide for the Midmarket"
Then there are bits like
They do tend to look to places most networks aren't considering - so
they discuss moving your office voice systems to the network, and
the designs (and demands on the network) reflect this.
I don't think you'll find a good general purpose 'this is how you should
design a network' document, but you will find lots of
'whatever you do - don't try this'.
 Just watch the war start :)
>  - on the net
>  - as opposed to just buying some cat5,a hub etc and hoping for the
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-- ** Chris Higgins e: chris.higgins at horizon.ie ** ** Technical Business Development tel: +353-1-6204916 ** ** Horizon Technology Group fax: +353-1-6204949 **
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