Re: Is it really a HUB?

[kenw () kmsi net]

On Wed, 26 Nov 2003 13:49:00 -0500, you wrote:

> At 12:57 PM 11/26/2003, Petriz, Pablo wrote:
> ...
> > So i don't know if snort will see all the traffic on it...
>
> No, it won't...
>
> auto-bridging means that (at least) the transition between 10mbit and 
> 100mbit is switched.
>
> It is in fact IMPOSSIBLE to have a dual-speed hub which is a pure hub when 
> presented with mixed traffic speeds.. no.. really.. it's actually 
> impossible. If you tried every port would have to throttle down to 10mbit 
> and you'd have a 10mbit hub.
>
> Based on the description, which may differ from reality, all the 100mbit 
> ports might see each other's traffic, and all the 10mbit ports might see 
> each other's traffic, but they will definitely not see traffic from ports 
> of different speeds.

Up to this point, Matt is absolutely correct.  

> The problem is that the actual implementation may have more switching 
> behavior than advertized.. all they've guaranteed is that the 10/100 
> segments are bridged.. but that doesn't mean that the 100mbit ports can't 
> be fully switched with respect to each other too.

According to Cisco's literature, these hubs provide "100-Mbps peak
aggregate throughput".  That implies no switching on the 100Mbps side.

FWIW, I use a dual-speed hub (not this model) for network sniffing at
various sites.  In order to ensure that I'm connected the internal hub for
the speed-side I'm interested in, I often must manually set the sniffer
NIC's speed to that speed, rather than allowing it to auto-configure.

/kenw

Ken Wallewein CDP,CNE,MCSE,CCA,CCNA
K&M Systems Integration
Phone (403)274-7848
Fax   (403)275-4535
kenw () kmsi net
www.kmsi.net


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