[NTLUG:Discuss] Router or switch?

[Darin W. Smith]

On Mon, 05 May 2003 14:25:24 -0500, Greg Edwards <greg at nas-inet.com> wrote:
> You may pay a little more for a smart hub but if you run very much data 
> they're worth it.  I run the 3Com OfficeConnect hubs and they have smarts 
> that direct traffic to only the addressed port rather than broadcasting 
> across all ports.  If the destination port is not on the same hub then no 
> data is passed to the other machines on that hub.  Only to the port (up 
> or down link) that falls in the route needed to get to the destination 
> gets traffic.
>

Wait, isn't this the real difference between a hub and a switch?

A hub is a "repeater"...i.e., all traffic goes out all ports.  If two 
stations transmit simultaneously, then there is a collision and both must 
wait a random period before retransmitting.  Plus, every machine has to 
look at all the ethernet frames.

A switch, by definition, should build an internal table of the MAC 
addresses (hardware ethernet addresses) it sees attached to each of its 
ports, only passing traffic destined to the particular port, or broadcast 
frames (things like ARP will mark their frames as broadcast)--note this is 
on the ethernet frame layer.  Most modern switches additionally incorporate 
a spanning-tree algorithm, which helps shut down the source of a loop on 
your network (for example, using a cross-over cable to directly connect two 
ports on a switch or hub).  The ability to only forward appropriate traffic 
is what makes a switched network:
a) collision-free by definition
b) therefore much faster
c) less burdensome to the individual stations

In my experience, the "smart" in "smart hubs" and "smart switches" meant 
"management capable."  In other words, you could remotely manage them using 
SNMP or some-such.  Some allow you to activate/deactivate particular ports. 
 That is a nice feature if you run a large installation and wire up 
everything in the building.  You can then only turn on the room jacks that 
you want turned on.

I would recommend a switch.  The only two useful features I'd look for on 
one beyond being a 100BaseTX switch are:
1) Ability to run full duplex
2) Auto-MDIX

Auto-MDIX is a great thing!  When I wired up my house last year, I used 
cheapo Fry's palm-sized switches that are full-duplex capable and support 
auto-MDIX.  I just plugged everything together and was done.  No more "do I 
need a crossover cable?"  It just figures it out, and does it a heck of a 
lot faster than I can think "I only need a crossover cable if I'm going 
NIC-to-NIC or switch-to-switch (non-uplink)".

-- 
D!
Darin W. Smith
AIM: JediGrover

"For want of a nail, the shoe was lost:
For want of the shoe, the horse was lost;
For want of the horse, the rider was lost;
For want of the rider, the battle was lost;
For want of the battle, the kingdom was lost,
And all for the want of a nail."

The moral of the story: details matter.