Network switch

The network switch, packet switch (or just switch) plays an integral part in the vast majority of current Ethernet local area networks or LANs. Mid-to-large sized LANs contain a number of linked managed switches. Soho or home networks typically use a single switch or simply an all-purpose device such as a DSL router , WiFi Router or Gateway which may include a small embedded Ethernet switch.

A switch is a data link layer networking device. Switches perform transparent bridgingnetwork segments with forwarding based on MAC addresses). Typical port speeds on an Ethernet switch are 10, 100, 1000 or 10000 megabits per second (Mbit/s), and half or full-duplex. Half-duplex means that the device can only send or receive at any given time, whereas full-duplex can send and receive at the same time. Addition of expansion cards makes it possible to connect different types of networks, for example Ethernet, Fibre Channel, ATM, and 802.11.

Hubs vs switches:

An Ethernet hub, or repeater, is a fairly unsophisticated broadcast device, and rapidly becoming obsolete. Hubs do not manage any of the traffic that comes through them. Any packet entering a port is broadcast out or "repeated" on every other port, save the port of entry. Since every packet is repeated on every other port, packet collisions result--which slows down the network.

A switch isolates ports, meaning that every received packet is sent out only to the port on which the target may be found (assuming the proper port can be found; if it is not, then the switch will broadcast the packet to all ports except the port from which the request originated). Since the switch intelligently sends packets where they need to go, the performance of the network can be greatly increased. Broadcast frames are also forwarded on all ports, which is normally fine, but in the case of IP multicast this causes inefficient use of bandwidth. To work around this problem some switches implement IGMP snooping.^[2]

More expensive switches can also do several other operations, such as isolating ports from each other by placing them in different VLANs, or allowing snooping by copying all packets on some set of ports to a special "sniffer" port.

This leaves the question of when a switch is most appropriate, versus a hub. If most of the network traffic involves only a few ports, then there will be little performance gain achieved by upgrading from a hub to a switch. But if the traffic involves more than a few ports, using a switch can yield a significant improvement in performance. Also, modern Fast Ethernet switches designed for small office / home office (SOHO) use are priced comparably to hubs, making use of a hub somewhat pointless if new equipment must be purchased anyway.

Because data is routed through the correct ports and not broadcast indiscriminately as with hubs, switches are somewhat more secure. Were a user with the intent of capturing other users' data to run a packet sniffer while connected through a switch, they'd usually see only their own data. In contrast, a hub would broadcast all traffic to all users. This said, even the extra security provided by switches can still be breached with techniques such as MAC flooding and ARP spoofing.

(From Wikipedia)