Network Devices

Network Devices:

In a typical LAN, there are various types of network devices available as outlined below.

• Hub
•  Repeat signals received on each port by broadcasting to all the other connected ports.
• Repeaters
•  Used to connect two or more Ethernet segments of any media type, and to provide signal amplification for a segment to be extended. In a network that uses repeater, all members are contending for transmission of data onto a single network. We like to call this single network a collision domain. Effectively, every user can only enjoy a percentage of the available bandwidth. Ethernet is subject to the "5-4-3" rule regarding repeater placement, meaning we can only have five segments connected using four repeaters with only three segments capable of accommodating hosts.
• Bridge
•  A layer 2 device used to connect different networks types or networks of the same type. It maps the Ethernet addresses of the nodes residing on each segment and allows only the necessary traffic to pass through the bridge. Packet destined to the same segment is dropped. This "store-and-forward" mechanism inspects the whole Ethernet packet before making a decision. Unfortunately, it cannot filter out broadcast traffic. Also, it introduces a 20 to 30 percent latency when processing the frame. Only 2 networks can be linked with a bridge.
• Switch
•  Can link up four, six, eight or even more networks. Cut-through switches run faster because when a packet comes in, it forwards it right after looking at the destination address only. A store-and-forward switch inspects the entire packet before forwarding. Most switches cannot stop broadcast traffic. Switches are layer 2 devices.
• Routers
•  Can filter out network traffic also. However, they filter based on the protocol addresses defined in OSI layer 3(the network layer), not based on the Ethernet packet addresses. Note that protocols must be routable in order to pass through the routers. A router can determine the most efficient path for a packet to take and send packets around failed segments.
• Brouter 
• Has the best features of both routers and bridges in that it can be configured to pass the unroutable protocols by imitating a bridge, while not passing broadcast storms by acting as a router for other protocols.
• Gateway
•  Often used as a connection to a mainframe or the internet. Gateways enable communications between different protocols, data types and environments. This is achieved via protocol conversion, whereby the gateway strips the protocol stack off of the packet and adds the appropriate stack for the other side. Gateways operate at all layers of the OSI model without making any forwarding decisions.

The goal of LAN segmentation is to effectively reduce traffic and collisions by segmenting the network. In a LAN segmentation plan, we do not consider the use of gateways and hubs at all and the focus turns to device such as switches and routers.