[NTLUG:Discuss] Re: Switch Question -- guidelines, access v. distribution, routers v. NAT, etc...

[Bryan J. Smith]

On Thu, 2004-11-11 at 23:45, Kipton Moravec wrote:
> server and about 16 computers.
> 8 are networked together and 8 are not.
> test area ... one computer on the network and 4 not
> machine setup area .. 3 non-networked computers within 6 feet of each
> Server is next to a 10/100 16 port switch.

First off, do you have a dedicated wiring closet, even for just phone?
Secondly, in case the server is no where near that, it should basically
be considered your data closet for now.

A centralized closet is really just a consideration if you decide to get
formal with some wiring runs for future expansion/consideration. 
Especially if you look to 1000Base where EMI becomes a real
consideration (if you're using copper).

> The reason the other computers are not on the network is because
> running the wires is a pain because of the high ceiling (the wires run
> across the drop ceiling) and it is a little over 100 feet of wire from
> the switch to each of the two areas.

That is still within specifications.  Cat-5 and below can run typically
85m (around 300 feet) and still be within specifications.

There are additional considerations for Cat-5e/6 if you are going to be
signaling 1000Base-T[4] (Copper UTP Gigabit Ethernet, GbE), but
typically not too much in such a basic environment.

> Most of the computers have 100 MB cards, but some of the ones that are not 
> yet hooked up have 10 MB cards in them.

Either should do fine.

> What I think I want to do is keep the server switch and add another switch 
> in the test area and another switch in the machine setup area.  These two 
> mini-switches will hook into the 16 port switch.

Cross-over cable or uplink should do fine on each.  At 100Base-T using
Cat-5, there should be any signaling or noise issues.  Of course you
don't want to be doing some major traffic over a single 100Base-T uplink
from each location though.

> The network is not very busy.
> I remember reading here not too far back that it was a bad idea to connect 
> switches to switches.  But I do not remember the details.

Er, there are _some_ considerations, but here are the general rules:  

 10Base-T Hub:  No more than 4 hops between any 2 nodes
100Base-T Hub:  No more than 1 hop between any 2 nodes
Any L2 Switch:  No more than 7 hops between any 2 nodes

For hubs, when I say "hop" I mean how many hub/switches a packet must
travel through to reach the other node.  If you use a transceiver, that
also counts as a "hop" (hence why a 100Base-T Hub with two different
types of media should _never_ be connected to anything but an uplink to
a switch).  E.g., for cascading 10Base-T hubs, this means that really no
more than 2 levels of hubs should be used -- because a node might travel
up 2 levels and then back down 2 levels.

For switches, it's the general rule in case various 802.1 protocols are
implemented.  The most common issue is for 802.1d Spanning Tree Protocol
(STP).  Although many companies don't utilize STP, the 7 hop rule
throughout an entire Layer 2 Switch is a highly recommended and general
guidelines.  You'd be surprised how many other 802.1 protocols have
similar limitations.

And if you need to 

> So the question is what is the down side of hooking the two areas the way I 
> propose? (The mini switches have uplink ports). If the switches should not 
> be chained like that what is the other method of using 1 wire to connect 
> two areas together?

No, it will work fine.  Just connect a crossover or uplink on each of
the local 10/100 "workgroup/desktop" (access) L2 switches in each area
to their own port on the 10/100 "backbone" (distribution) L2 switch.

Consider a better "backbone" L2 switch with GbE if and when you are
finding contention at the "workgroup" L2 switches.  And if you do, spend
a few extra bucks to get at least a _real_ "managed" L2 GbE switch. 

Don't guy a "workgroup" L2 GbE switch as your "backbone"
(distribution).  Trust me on this.  ;-ppp

> It seems overkill (to me) to have two extra routers. 

Do you mean "real" routers?
Or 1-to-many NAT devices aka "routers" (but not "real" routers ;-)?
_Never_ use those 1-to-many NAT devices internally on a network.  ;->

> Is that the preferred solution?

It depends on size.  In your case, I wouldn't worry about it.

The general, 5-year old Cisco model** is:  
 - Access
 - Distribution
 - Core

If every node in your network can reach every other note by going
through less than 5 L2 switches, then I wouldn't worry about using this
model.  But if you find there could be more than 5 switches between one
node and another, then I'd consider looking at the "core down" design
(and using "real" routing in some places).

**NOTE:  This model is no longer considered "current" by Cisco,
obsoleted by its "AAVID" model.  But that's more marketing because the
new model was introduced for real-time A/V-telephony.  Although it is
excellent if you are doing such, the old model is perfectly fine for
data-only designs.

> To make it more interesting, they also own another building across the 
> parking lot.  How do you connect the two buildings together? They have not 
> expanded operations into there yet, but I do not think it will be long 
> before they do. The buildings are only about 100 feet apart in the back but 
> the server is near the front of the main building, so it may be a 300-400 
> feet of wire from server to middle of the second building. Any ideas?

1000Base-SX (Multimode Fiber) GbE is the cheapest option and typically
an option for any GBIC slot/port on any modern L2 Switch today.  It will
give you around 250-400m of length.

You can and should always consider 1000Base-SX GbE for:  
A.  Runs from the "closet" to remote GbE switches
B.  GbE Servers in the "noisy closet"
C.  Generally when more than twelve (12) 1000Base-T[4] (Copper GbE) runs
would be within a few meters of each other (hence A & B, among others)

If you need longer, 1000Base-LX (Singlemode Fiber) GbE is an option for
anywhere from 450-2,000m (yes, upto about 1.2 miles).  Otherwise, you
want to start talking to your local telco.**

-- Bryan, CCDP (not that it matters)

**NOTE:  Many telco's can provide "raw" broadcast multiple access
Ethernet access between locations.  In a nutshell, they hide the
non-broadcast multiple access (NBMA) aspects typical of a Frame or Cell
(ATM) Relay setup.  Although many companies go this route, they still
must be wary of the 7 hop guideline if L2 switching is still used
throughout.  I.e., you must consider the number of hops in _all_
buildings, unless you introduce routing.  Typically it is much safer
(and more efficient) to put in a real router, and configure the NBMA
paths to each building for frame/cell relay.


-- 
Bryan J. Smith                                  b.j.smith at ieee.org 
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