switch, hub and host

[sarahr202]

hi every body

Let say we have a layer 2 switch connected to two host h1 and h2 via hub. My question is will switch be able to realize it has to use half duplex or wehave  to configure it explicitly ?

At  work this is the set up:

    ethernet -------computer1   then second computer is simply daisy chained without hub. The result is  there  are two computers  connected to switch without hub over single ethernet.

i understand this the worst design but that is what  they have right now.  My question is     will switch need to be configured half duplex or it can decide via auto  to use half duplex ?

thanks

[thiland · Accepted solution]

If the switchport is configured for "auto" the behavior is to fallback to half-duplex mode if it does not receive autonegotation frames from the remote link.

So if you plug a L2 switchport (configured for auto) into a hub, auto-negotiation will fall and the switch will use half-duplex.  Alternately, you could configure the switchport for 10/half or 100/half depending on the hub link speed.

This applies to a diagram like this:

Switch --> Hub --> Computer1

Are you saying that a single 4-pair Cat5E cable has been split so it can connect to 2 computers?  I don't understand your diagram.

See this table for other autonegotiation options:

http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a00800a7af0.shtml#auto_neg_valid

[Leo Laohoo · Accepted solution]

Let say we have a layer 2 switch connected to two host h1 and h2 via hub. My question is will switch be able to realize it has to use half duplex or wehave  to configure it explicitly ?

Nice.  Absolutely nice.  A topic that will result in a knife-fight in  a phone booth. 

My answer is:  Depends on the switch.  1st generation of (dumb) switches, like the 2900XL/3500XL, will require you to set the speed and duplex (in cases I've seen).  But nowadays, you don't.

It also depends on the hub too.  Early generation of hubs were really downright pathetic.  But nowadays they are slightly better.