Switching Domains
Collision Domains
In legacy networks, hubs were used. Network devices needed to compete to access the shared medium. The network segments that share the same bandwidth between devices are well known as “Collision Domains”. When multiple devices within the same collision domain try to communicate at the same time, a collision will occur.
If a switch port is operating in Half-Duplex, each segment is in its own collision domain, therefore there are no collision domains when switch ports are operating in Full-duplex. As long as there is a single switch port operating in Half-Duplex, there will be a present collision domain.
Nowadays, by default switch ports will auto-negotiate Full-Duplex when the other device can also operate in Full-Duplex. If the port is connected to another device operating in Half-Duplex mode, then it will simply operate in Half-Duplex.
When a Half-Duplex connection is present, the switch port will become part of a collision domain.
Broadcast Domains
A group of interconnected switches will form a single broadcast domain. Only a network layer device like for example a Router is able to divide Layer 2 broadcast domains. Routers are in fact used to segment broadcast domains but they will also segment collision domains.
When a device sends a Layer 2 broadcast, the destination MAC address in the frame is set to all binary ones.
A Layer 2 broadcast domain is also known as a MAC broadcast domain. The MAC broadcast domain consists of all the devices present on the LAN that receive broadcast frames from a host
When a switch receives a broadcast frame, it will forward the frame out of each port except the port where the broadcast from was received (Ingres Port). All the devices connected to the switch will receive the frame and must process it.
Broadcasts are necessary to locate other devices but in the meantime, they reduce network efficiency. Too many broadcasts may result in traffic congestion which will slow down the network.
When a switch is connected to another switch. the broadcast domain is increased since the new switch and all the hosts connected to that new switch will become part of the same broadcast domain.