[TriLUG] OT - gigabit switches

[Greg Brown]

Good questions!  Here is a basic run-down of Layers 1, 2, and 3 from a
network standpoint (where I spend most of my time).

Layer 1 refers to the physical wiring or lack there of.  Fiber optic and
Cat6 copper cables are most popular for Gig speeds though Cat5e is
technically rated for Gig though I have never used it for such a purpose.

Layer 2 regards information at the MAC address layer and it is called the
"Data Link Layer".  Switching occurs at Layer 2.  Therefore a layer2 switch
is a device that uses the unique MAC address that is burned into every card
to determine if a packet should or should not be sent to a particular port.
Broadcasts and multicasts are sent to every port within a single collision
domain (layer 2 switch or groups of switches).

Layer 3 refers to network protocol information and is called the "network
layer".  Routing occurs at Layer 3.  Packets are sent to and from ports
based on things like IP Address ranges, Appletalk Zones, and whatever other
kinds of protocols in the mix.  Thankfully today it is almost all TCP/IP
which makes the world a much more simple place to play.

So what is "Layer 3 switching"?  It is a term that makes my skin crawl.  It
used to be said, back in the days of the Cisco AGS and other old routers,
that routers were slow and you didn't want them in the core of the network
(at least some people said that).  Routers got faster and they wanted a term
to reflect this so someone put forth "Layer 3 switching" and it suck.  Layer
3 is routing, not switching.  The closest pure thing to L3 switching was
Virtual Link State Protocol buried in Cabletron gear and nobody uses that
anymore.  Whenever you hear "layer 3 switch" think router.

I don't have much experience with Dell gig switch gear as I mostly use Cisco
at my present employer.  We have 48 port POE Gig blades in our 65xx big guns
and a few gig blades in our 45xx devices.  In addition we have 48 port gig
switches with 10 gig uplinks.  They are hot stuff and we use them to
interconnect some or our blade servers.

You mentioned that some of your gear will have dual ports and that is a
whole other ball of wax.  We have many servers in the data center with a
primary gig port and a 10/100 control network port on different ranges.  We
also have F5 load balancers with multiple gig connections, etc.

Gig is sweet.  Deploy wisely and upgrade the switch-to-server cables to Cat6
if possible.  Some of the more inexpensive gig switches give you a lot of
bang for the buck but avoid the commodity stuff as even though they say they
are gig they have little more then 250 meg of throughput.

Greg


On 9/20/06, Christopher L Merrill <chris at webperformance.com> wrote:
>
> We would like to upgrade our testlab to a gigabit switch.  I'm not an
> expert in this area (I spend most of my time at level 7). Maybe some of
> you network gurus can set me straight.
>
> In our lab we'll have 10-25 machines (some with dual NICs) mostly fast
> ethernet but we're moving machines to GigE. We currently have a Dell 2324
> with 2 GigE ports.  Performance between the machines connected directly
> to the switch is the only real goal.  Management functions are not
> important, beyond the desire for simple plug-n-play management that we
> have today (in other words...no management - just plug them in).  Note
> that we do load-testing in the lab, so for a network with only a handful
> of machines, they run a LOT of traffic between them - frequently to the
> CPU/NIC limit of each machine.
>
> I've read a little on layer-2 and layer-3 switches and think I grasp the
> differences, but it is not clear to me if there would be any performance
> benefit for US with a layer-3 switch.  Budget is obviously a concern so
> a $2000 switch will take some selling.  Under what kind of situations
> would
> we see a difference in the total throughput rates on, for example, a Dell
> 2724 (layer 2, <$300), a Dell 5324 (layer 2/3, $750) and a 6024 (layer 3,
> $2000)???  What about an older Dell 5224 (layer2/3, ebay $300)?  What does
> "layer 2/3" mean?
>
> Any recommendations or pointers for some good reading would be much
> appreciated.
>
> p.s. We have lots of Linux boxes in the lab  :>
>
> TIA,
> C
>
>
>
> --
> ------------------------------------------------------------------------ -
> Chris Merrill                           |  Web Performance, Inc.
> chris at webperformance.com                |  http://webperformance.com
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>
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