Basic Hardware Components

All networks are made up of building blocks of basic equipment to interconnect the network nodes, such as network interface cards (NICs), bridges, hubs, switches and routers. In addition, a method of connecting these building blocks can be done in the form of galvanic cable (most commonly Category 5 cable). Less common are microwave links (as in IEEE 802.12) or optical cable ("optical fiber").

Network Adapters
A network card, network card or NIC (Network Interface Card) is a piece of hardware designed to allow computers to communicate over a computer network. It provides physical access to a network of support and often provides a low level to address the use of MAC addresses.
Each NIC has a unique identifier. What is written on a chip that is installed on the card.

Repeaters

A repeater is an electronic device that receives a signal that cleans unnecessary noise, regenerated and relayed to a higher energy level, on either side of an obstruction, so the signal can cover longer distances without degradation. In most configurations of Ethernet twisted pair, repeaters are necessary for the cable that goes over 100 yards. A repeater with multiple ports is known as a hub. Repeaters work at the physical layer of the OSI model. Repeaters require a small amount of time to regenerate the signal. This can cause a propagation delay that can affect network communication when multiple repeaters in a row. Many network architectures limit the number of repeaters that can be used in a row (eg, Ethernet 5-4-3 rule).

Bridges
Network bridge connects multiple network segments, the data link layer (layer 2) of the OSI model. Bridges will be sent to all ports except the port where the consignment has been received. However, the bridges do not promiscuously copy traffic to all ports, as hubs do, but MAC addresses are reachable through specific ports. When the bridge that connects the port and address, sends traffic to that port at that address only.

Bridges learn the association of ports and addresses by checking the source address of frames that it sees on various ports. When a frame arrives at a port, its source address is stored and the bridge assumes that MAC address associated with this port. The first time a previously unknown destination address is considered, the bridge forwards the frame to all ports except the frame was reached.

Bridges are three basic types:

Local bridges         : a direct connection to local area networks (LAN).

Remote bridges  : Can be used to create a WAN (wide area), LAN connection. Remote Bridges, which link is slower networks, largely have been replaced by routers.

Wireless bridges   : Can be used to join LANs or connect remote stations to a LAN.

Switches 

The power switch is a device that transmits and filters is based OSI layer 2 datagrams (blocks of data communication) between ports (connected cables) on the MAC addresses of packets. Switch differs from the node that transmits only the frames with the communication ports and all ports. Switch disconnects the collision domain, but represent themselves broadcast domain. Switches to make decisions on the basis of the MAC frame forwarding addresses. Switch is usually a number of ports, to facilitate the star topology equipment, and additional switches in cascade. Some switches can route based on Layer 3 addresses or other logical levels, these are called multi-layer switches. The switch term is used loosely to include the marketing of devices such as routers and bridges, as well as devices that can share the load of traffic or application content (for example, a Web URL identifier).

RoutersInternetworking router is a device that forwards packets between networks of information processing can be found in the datagram or packet (Internet protocol information on Level 3 of the OSI model). In many cases, this information will be treated together in the routing table (also known as the forwarding table). Routers use routing tables to which the user interface to forward packets (this may include "null" is also known as "black hole" because the user interface information can go there, but no further processing is done said the data).

Firewalls
Firewalls are the most important aspect of network security. A firewall does not have all data transfers interaction or supervised by a human, as automated processes can be put in place to help deny access requests from unsafe sources, and if the shares from them recognized. The crucial role of play in firewalls network security grows with the steady rise of "cyber attacks to steal / destroy data, plant viruses, etc.

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