Collision Domains & Broadcast Domains

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I seem to keep screwing up practice questions that have network
diagrams and you have to identify the number of collision and broadcast
domains.  Is there an easy way to tackle this type of question?

I've tried using this approach:

Count each interface on the router as 1 collision domain and 1
broadcast domain.

Count each connected interface (including interfaces between switches
and routers) on a switch as a collision domain and unless VLANS are
used, count each switch as a broadcast domain.  If VLANS are used count
1 broadcast domain per VLAN.

Count 1 collision domain and 1 broadcast domain for each hub

Is this the correct logic?  Like I said, I always seem to get the
number of collision or broadcast domains wrong. I suspect becuase the
way the design is interconnected; hence my question on a way to
consistently get the right answer.

Thanks,

RB



Re: Collision Domains & Broadcast Domains


A router can break collision domains and broadcast domains.
Therefore, count each interface of a router as 1 collision domain and
1 broadcast domain.

A switch or bridge can only break collision domains, but not broadcast
domains unless VLANs are used.  Therefore, count each interface of a
switch as 1 collision domain, and each VLAN as 1 broadcast domain.

A hub or repeater cannot break collision domains and broadcast
domains.  Therefore, no need to consider hubs and repeaters when
counting collision domains or broadcast domains.

KPLAB
http://www.kp-lab.com - Free CCNA Study Guide


rb33339@yahoo.com.au wrote in message
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Re: Collision Domains & Broadcast Domains


just don't forget that connected elements should only be counted once.
For example, a 10 port switch connected to a 1 port router only has 10
collision domains; two routers connected to three networks (only one in
common) only have three broadcast domains.



Re: Collision Domains & Broadcast Domains


I'm with you on the first 2 points.  However don't you still have to
count a hub as one collision domain and one broadcast domain if it
happens to be sitting on the other side of a router?



Re: Collision Domains & Broadcast Domains


You only need to count the router interface.  For example, if the
router interface is connected to a hub which connects 5 hosts, all the
5 hosts are sharing the same collision domain and broadcast domain.
The number of collision domain and broadcast domain remain the same if
the router interface is connected to a host directly rather than
connected to the hub.


KPLAB
http://www.kp-lab.com - Free CCNA Study Guide


Re: Collision Domains & Broadcast Domains



kplab wrote:
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the
if

Gotcha.  Thanks for that!



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