Repeaters, Hubs, Bridges, Switches and Routers
To pass you CCENT and CCNA test, you should be able to recognize the common network devices in the network physical documentation.
In the above exhibit, A is a bridge, B is a hub, C is a router and D is a switch.
- Repeater and Hub are layer 1 devices. Repeater address the issue of attenuation. Attenuation is the loss of signal over distance. Repeater rebuilt the electrical signal that comes in and send it out to other side. Hub is a multi-port repeater. Electrical signal came into any one hub port will be repeated on all other ports.The layer 1 devices are dumb, they have no decision making abilities. Hubs do not read any of the data passing through them, and they are not aware of the source or destination of the frame. All the devices attached to a hub are belong to one collision domain, which means if two hosts try to send data at the same time, a collision will occur. All the devices attached to a hub are also belong to one braoadcast domain, that is, broadcast frame sent by one host will be received by all other hosts in the network.
- Bridge and Switch are layer 2 devices. They can make decisions about to which port the frames will go, based on MAC Addresses. Bridges and switches help avoid frame collision by breaking down one collision domain to two or more smaller collision domains, then buffer and forward frames between them. Nowadays, a switch can be configured to allow each connected host to have its own individual collision domain. As a result, all the hosts can trasnmit data simultaneously without collision, because they no longer share the bandwidth with each other. It is important to notice hosts attached to bridge or switch still belong to the same broadcast domain.
- Router is layer 3 device. The purpose of router is to route packets from one broadcast domain to another. Router maintains a routing table. The routing table contains ip addresses associated with interfaces, out of which the packet will be forward to.
Collision Domains – A collision domain is defined as a network segment that shares bandwidth with all other devices on the same network segment. Generally speaking, A Collision Domain includes all of the Ethernet segments between a pair of bridges or other layer 2 devices. When two hosts on the same network segment transmit at the same time, the resulting digital signals will fragment or collide, hence the term collision domain.
Broadcast Domain – A broadcast domain is defined as all devices on a network segment that hear broadcasts sent on that segment.
All devices plugged into a hub are in the same collision domain and the same broadcast domain.
All devices plugged into a switch are in separate collision domains but the same broadcast domain. Although, you can buy special hardware to break up broadcast domains in a switch, or use a switch capable of creating VLANs. VLANs breakup broadcast domains.
Hubs and Repeaters extend collision and broadcast domains.
Switches, Bridges and Routers break up collision domains.
Routers (and Switches using VLANs) break up broadcast domains.
Bridging vs. LAN Switching
Layer 2 switches are just bridges with a lot more ports, more advanced functionality, and higher speed. They both forward layer 2 broadcasts, learn MAC addresses by examining the source address of each frame received and make forwarding decisions based on layer 2 addresses.
There are some important differences between bridge and LAN switch:
- Bridges are software based, while switches are hardware based because they use ASIC chips to help make filtering decisions.
- There can be only one spanning-tree instance per bridge, while switches can have many.
- Switches have a higher port density than most bridges.
- Switches have larger frame buffers.
- Switches support for mixed media rates.
- Switches support dedicated communication between devices.
- Switch ports can run in full-duplex mode. In full-duplex mode the collision counter is inactive. If FCS, CRC errors increment then the most likely cause is a duplex mismatch. Other causes can be a faulty cable, a faulty switch port or hardware/software issues with NIC.