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Ethernet Switches and Crossover Cables

February 29 2012 , Written by Cisco & Cisco Router, Network Switch Published on #Cisco Switches - Cisco Firewall

Ethernet Switch

A switch is something that is used to turn various electronic devices on or off. However, in computer networking, a switch is used to connect multiple computers with each other. Since it is an external device it becomes part of the hardware peripherals used in the operation of a computer system. This connection is done within an existing Local Area network (LAN) only and is identical to an Ethernet hub in terms of appearance except with more intelligence. These switches not only receive data packets, but also have the ability to inspect them before passing them on to the next computer. That is, they can figure out the source, the contents of the data, and identify the destination as well. As a result of this uniqueness, it sends the data to the relevant connected system only, thereby using less bandwidth at high performance rates.ethernet-switches-copy-1.jpg


Ethernet Switches and Crossover Cables

The wires in a crossover cable are “crossed” so that output signals from the transmitting device are properly sent as input signals to the receiving end. An Ethernet switch can be thought of as a device that makes temporary crossover cable connections between computers that want to communicate. Just like crossover cables, switches do not suffer from collision problems.

However, it should be noted that the actual cables used are “straight through.” The crossover function is done inside of the switch.


Since separate wires are used for sending and receiving, switches support operation in full duplex mode. This mode allows devices to send and receive data at the same time.


Advantages over Hubs

As mentioned above, switches are intelligent devices that can read the data packets that pass through them. By storing each host’s MAC address and its corresponding port in a table, switches ensure that bandwidth is not wasted by intelligently directing traffic. Hubs are dumb devices that do not do any processing.


Unlike hubs, switches are modern, fast, and support full duplex operation. In short, they are much better.


...To be continued...


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Just a correction for a "typo" in my previous post<br /> <br /> I meant to say simplify instead of "simply", in the first sentence.
I'm not sure if you were trying to simply things for people that are COMPLETELY unfamiliar with networking, switching, routing, hubs, crossover/straight cables, etc., but this was over-simplified<br /> to the point of being incorrect in a few areas.<br /> <br /> 1. Switches are not necessarily hardware-based. Think of something like VMWare ESX/ESXi and the fact that you create virtual switches inside of it (based on different subnets/vlans, interfaces on<br /> the physical server (whether one's in a DMZ and another may not be), etc).<br /> <br /> 2. Switches can use either straight OR crossover cables depending on the configuration of the interface, specifically whether automatic duplexing is enabled or not (potentially forcing the<br /> interface to be in "uplink" mode). Some endpoints won't function correctly if automatic duplexing is enable on the switch's interface, so you'd have to disable it and use a crossover cable<br /> instead).<br /> <br /> 3. Switches CAN suffer from collision problems - depending on the type of collision you're referring to. If you're using spanning-tree for example on 2 switches within the same LAN, and your VLANs<br /> share the same priority, you will have a collision in terms of the switches fighting for which is to be the VLAN root and which is to be the designated forwarder.