Collision domain
A collision domain, as the name implies, is the part of a network where packet collisions can occur. A collision occurs when two devices simultaneously send a packet in the shared network segment. Packages collide and both devices must retransmit packets, which reduces network performance. Collisions are often in a hub environment because each port of a hub is in the same collision domain. In contrast, each port is on a bridge, a power switch, or a router in a separate collision domain.
The following examples illustrate collision domains:
Collision domains
In the above example we have 6 collision domains.
NOTE
Note that each port of a hub is in the same collision domain. Each port on a bridge, power switch, or router is in a separate collision domain.
Broadcast domain
A broadcast domain is the domain to which a broadcast is routed. A broadcast domain contains all devices that can broadcast over the data link layer (OSI Layer 2). All ports on a hub or switch are in the same broadcast domain by default. All ports of a router are in the different shipping domains, and routers do not send mail from one sending domain to another.
The following example illustrates the concept:
Broadcast domains
In the screenshot above, we have three broadcast domains because all ports on a hub or switch are in the same broadcast domain and all ports on a router are in a different broadcast domain.
