Collision and broadcast domains

[abdullahvu20]

How many active CDs and BDs exist?

[Kasun Bandara]

if there is no VLANs configured, it is 3 BD and 12 CDs. if this is kind of assignment, you should understand the definition of BD and CD. dont go blind.

[abdullahvu20]

not going blindly. I am new to CCNA, and Got mixed up after watching
some Videos on youtube.

[Richard Burts]

We do not know how the switches are configured. Especially we do not know if each switch has a single vlan or multiple vlans. We do not know if the switch to router connections are access ports (single vlan) or are trunk ports (multiple vlans). And we do not know how the routers are configured which might impact the answer.

And it looks to me like there are 13 collision domains and at least 4 broadcast domains.

Essentially each active switch interface is a separate collision domain. The number of broadcast domains on a switch should be equal to the number of vlans on that switch. On a router the number of broadcast domains is a bit more complicated. Would you count the serial connection between routers as a broadcast domain? One simple approach for a router is to say that number of broadcast domains is the number of subnets. But that is problematic if you think about the possibility of secondary addressing which puts several different subnets all in the same broadcast domain.

[Joseph W. Doherty]

Number of CDs also depend on how switch ports are configured.  If full-duplex, there's no CD.  If half-duplex, there's no physical CD but there's a logical CD, the latter creating CD behavior.

BTW, on a twisted pair Ethernet hub, again, there's no physical CD, but the logical CD extends across multiple hub ports.