[NTLUG:Discuss] home networking question

[Bug Hunter]

On Mon, 20 Mar 2000, Richard Cobbe wrote:

> Lo, on Sunday, 19 March, 2000, Robert Barker did write:
> 
> > I'm getting DSL any day now and not knowing too much about how to go
> > about it, I want to build a home network behind a firewall.  Currently,
> > the plan is to create the firewall from an old P90 I have (no Xwindows -
> > just the basics), the firewall connects to a switch and the 3-4 pcs all
> > connect to the switch in turn.  I guess it would look something like
> > this:
> > 
> >   internet ----  dsl modem ----  firewall  -----  switch ----- pcs 
> > 
> > My questions are these:
<snip> > 
> 
> > The internal network is primarily for me, so I can diddle with a
> > php/mysql/webserver development box.  Also, I'm showing a switch over a
> > hub for performance.
> 
> Really?  Hadn't heard about this.  I was planning on moving to a situation
> not unlike this in the near future.  Do you have pricing info on switches?
> And how big is the performance difference?
> 
> Richard

  It varies between "wow!" and "ho hum!"

  If you have a lightly loaded network, switches will not make any
difference that you can tell.

  If you have a heavily loaded network -- say more than 10 pc's, then a
switch will make a difference, IF and ONLY IF, you have tons of traffic
between two or more pc's.

  Every Internet network packet is eventually sent to a MAC address on an
ethernet segment.  This MAC address is hard wired into the card.  It is
guaranteed unique by the manfuacturer, which gets a unique range of
addresses from a central source. (Linux can change its MAC address
via software, so you can spoof as another machine on the network).

  A switch knows which MAC address is on which port.  It sends the message
packets for that MAC address to only that wire.  A hub does not know, and
sends all packets on all wires.  Ethernet protocol has collision detection
on transmission.  (Collision occurs when two ethernet devices transmit
data packets at the same time on the same wire.)  It will wait a random
amount of time before it resends packets back out if it detects a
collision of a transmitted data packet. On a heavily loaded network, this
can cause data to be transmitted slowly due to very high occurence of 
delayed re-transmission of packets.

  switches tend to avoid collision of data packets, since traffic to a
machine is not put on the same wire as traffic for other machines.  It is
a traffic cop.  It can slow traffic down on a lightly loaded network, due
to the switching overhead.  Therefore, on lightly loaded networks,
switches can cause performance loss.