CCNA Tutorials

CCNA tutorials Part 1
Introduction to networking devices

HUB

Hubs connect computers together in a star topology network. Due to their design, they increase the chances for collisions. Hubs operate in the physical layer  of the OSI model and have no intelligence. Hubs flood incoming packets to all ports all the time. For this reason, if a network is connected using hubs, the chances of a collision increases linearly with the number of computers (assuming equal bandwidth use). Hubs pose a security risk since all packets are flooded to all ports all the time. If a user has packet sniffing software, they can extract data from the network and potentially decode it and use it. Hubs make it easy to "spy" on users on the same LAN as you.

REPEATER

A repeater is an electronic device that receives a signal and retransmits it at a higher level and/or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances without degradation. Because repeaters work with the actual physical signal, and do not attempt to interpret the data being transmitted, they operate on the physical Layer, the first layer of the OSI model. Repeaters are majorly employed in long distance transmission to reduce the effect of attenuation. It is important to note that repeaters do not amplify the original signal but simply regenerate it.

MODEM

Modem (from modulator-demodulator) is a device that turns the digital 1s and 0s of a personal computer into sounds that can be transmitted over the telephone lines of plane old telepnone system (POTS), and once received on the other side, converts those sounds back into a form used by a USB, Ethernet, serial, or network connection. Modems are generally classified by the amount of data they can send in a given time, normally measured in bits per second, or "bps".

Network Interface Card(NIC)

A network interface card is a computer hardware component designed to allow computers to communicate over a computer network. It is both an OSI layer 1 (Physical Layer) and layer 2 (data link layer) device, as it provides physical access to a networking medium and provides a low-level addressing system through the use of MAC address. It allows users to connect to each other either by using cables or wirelessly. Most motherboards today come equipped with a network interface card in the form of a controller, with the hardware built into the board itself, eliminating the need for a standalone card.

SWITCH

Switches are often confused with bridges because they also operate at the data link layer of the OSI model. Similar to a hub, switches provide a central connection between two or more computers on a network, but with some intelligence. They provide traffic control for packets; rather than forwarding data to all the connected ports, a switch forwards data only to the port on which the destination system is connected. They use a database of MAC address to determine where computers are located and very efficiently send packets only where they need to go. The database is created dynamically as computers communicate on the network. The switch simply watches the incoming packets and memorizes the MAC address and port a packet arrives on. If a packet arrives with a destination computer that the switch does not have an address for in its MAC address table, it will flood the packet out all connected ports. A switch creates separate collision domains for each physical connection. A switch will only create separate broadcast domains if separate VLANs(Virtual Local Area Networks) are assigned to different ports on the switch. Otherwise, a broadcast received on one port will be flooded out all ports except the one it came in on.

ROUTER

Routers operate at the network Layer of the OSI model and efficiently route information between LANs. Since routers operate in the third layer, the network layer, they must understand layer 3 addressing... such as TCP/IP. A router will divide a broadcast domain by not forwarding broadcasts on one connected network to another connected network. Routers operate in two different planes: the control plane, in which the router learns the outgoing interface that is most appropriate for forwarding specific packets to specific destinations, and the forwarding plane, which is responsible for the actual process of sending a packet received on a logical interface to an outbound logical interface.