[cisco-voip] 24 port switch question

[Mike Thompson]

Something that needs to be taken into consideration is the ASIC configuration.  The switch ASIC controls frame forwarding.  In many switches, a sing ASIC controls many ports.  Unless the switch is non-blocking for all 24 ports, you may not be able to concurrently put a frame on each port simultaneously. 

Sent from my phone, apologies for any typos.

On Sep 29, 2010, at 11:46 PM, Matthew Ballard <mballard at otis.edu> wrote:

> Agreed.  I think it is a badly worded question.  A follow up email from the original poster indicated it was a multiple choice question.  The keyword appears to be simultaneously, and collisions are really a non-factor.  If you’re looking at an exact snapshot of the shortest time possible, you can’t forward more than one frame per port (possibly 2 if you include duplex, one in each direction), but 24 was one of the answers,  and 48 was not.
> 
> Matthew
> 
> 
> 
> On 9/29/10 8:33 PM, "Norton, Mike" <mikenorton at pwsd76.ab.ca> wrote:
> 
> If you completely fill the MAC table of a switch, you’ll “turn it into a hub” in the sense that it would start forwarding traffic out all ports. But you still wouldn’t have collisions, because the ports would still all be full duplex.
> 
> If all ports are full duplex, there is no amount of traffic that could cause collisions. Collisions can only occur on shared media and shared media can only be half duplex. With enough traffic, you’ll start getting dropped/delayed frames - but that’s not a collision.
>  
> At least, that’s my take on it.
>  
> -- 
> Mike Norton
> I.T. Support
> Peace Wapiti School Division No. 76
> Helpdesk: 780-831-3080
> Direct: 780-831-3076
>  
> 
> From: cisco-voip-bounces at puck.nether.net [mailto:cisco-voip-bounces at puck.nether.net] On Behalf Of Lelio Fulgenzi
> Sent: September-29-10 6:07 PM
> To: Matthew Ballard
> Cc: cisco-voip at puck. net
> Subject: Re: [cisco-voip] 24 port switch question
> 
> 
> I recall a bug/exposure where one could turn a switch into a hub by flooding the switch with arp announcements or something like that. 
> 
> …
> 
> Don't look at me, my iPod maid that spilling mistake. 
> 
> 
> On 2010-09-29, at 5:57 PM, Matthew Ballard <mballard at otis.edu> wrote:
> 
> On a switch with all ports running full duplex, the collision domain is reduced down to the level of the individual port (which is one of the key benefits of a switch), so you should never see a collision if all ports are connected at full duplex to other switches and/or devices.
> 
> Beyond that, it depends on the switch, as you’ll hit either port capacity or forwarding limits of the switch before anything gets dropped.
> 
> Matthew Ballard
> Network Manager
> Otis College of Art and Design
> mballard at otis.edu
> 
> 
> On 9/29/10 1:41 PM, "Robert Shearrill" <rshearri at uchicago.edu> wrote:
> Hi, 
> 
> Can some answer this question for me, or tell me where i can find the reading on this question? I have looked and can find it no where.
> 
> Question:
> 
> How many frames can pass through a 24-port switch simultaneouly, without causing a collision and with using full duplex used on all ports?
> 
> Thanks
> 
> Robert
> 
> 
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