switch speed question

[tvarriale at comcast.net (Tony Varriale)]

That isn't always true.  Some switches are already speced as full.  It's 
best to read the product docs or speak with a rep to be sure.

tv
----- Original Message ----- 
From: "Eric Gearhart" <eric at nixwizard.net>
To: "NANOG list" <nanog at nanog.org>
Sent: Tuesday, February 24, 2009 9:51 AM
Subject: Re: switch speed question


> On Tue, Feb 24, 2009 at 2:33 AM, Bruce Grobler <bruce at yoafrica.com> wrote:
>> Hi,
>>
>> It depends on how heavily loaded your switch is expected to be, for 
>> instance
>> two machines using the switch will be able to get a full 1Gbps, however
>> depending on the backplane (switching fabric), it limits how many ports 
>> will
>> receive full 1Gbps when the switch is congested, e.g. a 2 gig backplane
>> against a 24 gig.
>>
>> Regards,
>>
>> Bruce
>
> Note that the traffic to a switch is bi-directional (full duplex) - so
> a 24 port gigabit switch can max out its 32 Gig backplane, if all 24
> ports have a gig coming in and going out (24 X 2 is 48, more than the
> 32 gig backplane).
>
> This isn't immediately apparent - the other day someone at my work
> asked the exact question "Why's the 32 gig backplane > the 24 ports on
> the switch?"
>
> --
> Eric
> http://nixwizard.net
>