When you’re studying to pass the CCNA exam and earn your certification, you’re introduced to a great many terms that are either totally new to you or seem familiar, but you’re not quite sure what they are. The term “collision domain” falls into the latter category for many CCNA candidates.
What exactly is “colliding” in the first place, and why do we care? It’s the data that is being sent out onto an Ethernet segment that we’re concerned with here. Ethernet uses Carrier Sense Multiple Access / Collision Detection (CSMA/CD) to avoid collisions in the first place. CSMA/CD is a set of rules dictating when hosts on an Ethernet segment can and cannot transmit data. Basically, a host that wants to transmit data will “listen” to the ethernet segment to see if another host is currently transmitting. If no one else is transmitting, the host will go forward with its own transmission.
This is an effective way of avoiding a collision, but it is not foolproof. If two hosts follow this procedure at the exact same time, their transmissions will collide on the Ethernet segment and both transmissions will...