Re: [tlug] Class B Hubs not suitable for data center use?

["Jonathan Q" <jq@example.com>]

On 8/28/2002, "Jean-Christian Imbeault" <jean_christian@example.com>
wrote:

>I'm in need of some technical advice and suggestions concerning a
hub/switch
>I am using.
>
>At the data center we are using we have connected  two of our server
>together using a 3Com Office Connect Switch 8, and then from the hub to
the
>Data Center 100Mbps pipe. However those two servers have have been
showing
>problems with connections speeds.
>
>While looking into the problem the Data Center techies sent us this
email:
>
>"The hub you are using is a Class B device and not suitable for use in a
>100Mbps/sFull Data Center environment. We suggest you replace the hub with
a
>more suitable device"

What a load of crap.  An FCC class B device means that it is certified for
residential use.  An FCC class A device is certified only for office use. 
Class B has stricter RC emission requirements, such that it cannot produce
interference that affects other devices.  If it does, it will get a Class A
rating.

That doesn't mean the Office Connect is not a problem (but it also doesn't
mean that it is a problem).  The 3Com Office Connect series is a line of
entry-level SOHO products and is not intended for enterprise use, they are
correct about that. I would have used a Cisco 1912 or similar.  However, I
do rather suspect that they gave you a boilerplate answer without really
looking very closely at it.  Ask them how they know that it's the problem
and see if they give a solid answer or not.

>I checked with the 3Com web site and their sales material says this is
>"ideal for high-speed servers, backbones, ...".

That was obviously written by a marketer who probably doesn't even know
what a backbone is.  

>Could it be true that a Class B device would be unsuitable for a Data
>Center? Could there be so much interference in the DC that the hub is
>failing to transfer packets?

No.  As noted above, Class A and Class B are standards of radiation you
produce, not standards of radiation you receive.

I have a question about the description of your network architecture.  You
say that you're connecting two servers together with the Office Connect 8,
and then from the hub to the data center 100 mbps link.  Does this mean you
have the Office Connect 8 plugged into a hub and then the hub is connected
to the 100 mbps link?  Or are you mixing and matching terminology (note: a
hub and a switch are *not* the same thing and the terms are not
interchangeable)?

If you do have a hub standing between the Office Connect and the uplink,
get rid of it and plug the uplink into the Office Connect.  Having a hub in
the way is 

Next question: Is the 100 mpbps auto-negotiated or is it locked at 100
mpbs?  If it is auto-negotiated, try locking the port at 100 mbps and
having the data center people also lock their port at 100 mpbs. 
Auto-negotiating can sometimes cause problems.  If your switch will not do
this, you might want to look at getting one that does.  Two Cisco models to
look at are the 1912 (12 10 mbps ports and two 100 mpbs uplinks) and the
2912 (12 10/100 ports).  Even if (or maybe especially if :-p) the data
center side switch is a Cisco, locking the port speed at 100-full duplex
rather than auto-negotiating is still recommended.


Finally, can you be more specific about the problems with connection speeds
that you are seeing?  Do you mean they are having auto-negotiation trouble,
or long response times, or something else?  Are these the same servers that
you recently wrote about which are using only a fraction of the bandwidth
available?  How do you know the problem is the network and not the servers?
 
Do you have quality NICs or budget NICs?  There can be a huge throughput
difference between them.

Jonathan