Seven. This is a subjective view and may not agree with the authors of the
question. Read the justification below to understand the technology.
A collision domain is a logical network where data packets can collide with
one another when sent on a shared medium.
A broadcast domain is a logical network where any host can send broadcast
which will reach all other hosts in a domain.
A hub does not affect seperation of collision or broadcast domains.
An ethernet bridge seperates collision domains. The same can be said for
each standard interface of an ethernet switch.
A router seperates broadcast domains. A router also happens to seperate
collision domains, but this is hardly ever mentioned.
Examples of broadcasts include DHCP requests, ARP requests, and some other
forms of network traffic such as a Windows host broadcasting a NetBIOS node
name in order to elicit an IP response from the named host. These
broadcasts are blocked by routers from progressing further into the network.
Exceptions to this border of a broadcast domain are not in the default
configuration of routers and should not be taken into consideration, such as
using a router as a bridge or implementing technology such as aloowing a
router to forward DHCP requests.
Referecing the diagram:
(0) Hub1 does not seperate collision domains.
(3) Each connection out of Switch1 is a collision domain.
(2) Each connection out of Switch2 is a collision domain.
(2) Each connection out of Bridge1 is a collision domain.
Total = 7
Another way to state this exact same result:
Broadcast Domain #1
(1) Hub1 to Switch1 is part of the same collision domain as the other
connections out of Hub1
(1) Switch1 has a collision domain on its connection out the top of the
device in the diagram
(1) Switch1 to Router1 is a collision domain
Broadcast Domain #2
(1) Router1 to Switch2 is a collision domain
(1) Switch2 to Router2 is a collision domain
Broadcast Domain #3
(1) Router2 to Bridge1 is a collision domain
(1) Bridge1 has a collision domain on its connection out the right of the
device in the diagram
Total Broadcast Domains = 3
Total Collision Domains = 7
Remember: Bridge = Switch
The terms are interchangable. We only traditionally see a bridge as a two
interface device (like a highway road bridge with two ends) and a switch as
a multi-interface device. Technically a switch functions like a hub with a
mini-bridge on every port. If you hear of a Brouter, which is a router and
a switch in the same device, just consider it a layer 3 routing capable