January 14, 2012

1.1.3 Switches

Switches are multiport devices that improve network efficiency. Using switches improves network efficiency over hubs because of the virtual circuit capability. Switches also improve network security because the virtual circuits are more difficult to examine with network monitors.

A switch is a network device used to segment networks into smaller, more manageable sections and relays packets between the segments. Switches can be used for security, load balancing and performance improvements in a network.

A switch is able to inspect network packets and determine the source and destination to provide more efficient network flow and prevent network packets from one segment, from passing on to other network segments and causing network collisions.

Mastering the hula hoop (picture on right) requires an ability to switch the hips from one side to another in a rhythmic fashion. Now you will not forget what a switch is.

Switches map the Ethernet addresses of the nodes residing on each network segment and then allow only the necessary traffic to pass through the switch. When a packet is received by the switch, the switch examines the destination and source hardware addresses and compares them to a table of network segments and addresses. If the segments are the same, the packet is dropped ("filtered"); if the segments are different, then the packet is "forwarded" to the proper segment.

Switches can connect different networks types (such as Ethernet and Fast Ethernet) or networks of the same type.

A network switch or switching hub is a computer networking device that connects network segments.
An Ethernet switch operates at the data link layer of the OSI model to create a separate collision domain for each switch port. With 4 computers (e.g., A, B, C, and D) on 4 switch ports, A and B can transfer data back and forth, while C and D also do so simultaneously, and the two conversations will not interfere with one another.

A switch serves as a controller, enabling networked devices to talk to each other efficiently.
Switches create (or extend) a network. Routers connect networks.

Think of a switch as a traffic light (or traffic policeman) at a four-way intersection. The traffic light allows east-west (and west-east) traffic to move while holding back north-south (and south-north) traffic. And at an appropriate time the traffic light stops east-west (and west-east) traffic and allows north-south (and south-north) traffic to flow; analogous to how a switch operates.

References:
http://www.technick.net/public/code/cp_dpage.php?aiocp_dp=guide_networking_switching
http://en.wikipedia.org/wiki/Network_switch
CompTIA Security+ Study Guide: Exam SY0-301, Fifth Edition by Emmett Dulaney
Mike Meyers' CompTIA Security+ Certification Passport, Second Edition by T. J. Samuelle

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