Computer Networking Devices
By Stephen Bucaro
Computer networking devices, also known as networking hardware or network equipment
are components connected to the network by network media that are used to divide
large networks in smaller subnetworks or to route data between networks.
A hub is a simple device that sends all data to all devices connected to the hub. A hub
provides no error checking, and no filtering, it simply forwards everything. Every device
connected to a hub shares the same broadcast domain and so is in the same collision domain.
Sometimes hubs are divided into passive and active. A passive hub does
nothing except provide a path for the data. An active hub regenerates the signal before
sending it along.
A bridge is used to connect two networks, and therefore has one port for each network.
A bridge operates at the Data Link layer (layer 2) of the OSI model; therefore, it can read
the MAC (Media Access Control) addresses in the data packets. A bridge has internal RAM.
When a bridge first starts up, it behaves like a hub. But as the bridge receives packets from
each network, it builds a table of the source MAC addresses on each segment.
When the bridge receives a data packet, it looks up the MAC address in the list stored in its
RAM to determine on which network the packet's destination resides. If the destination address
is not on the same network as the source, the bridge will forward the packet to the other network.
If the destination is on the same network as the source it will filter, or stop, the packet from
passing through to the other network.
The process of filtering packets results in each network segment carrying fewer packets.
Less traffic on each segment means fewer collisions. The network is divided into two separate
"collision domains", each with fewer collisions than the original single collision domain. Both
segments and the entire network operate with greater efficiency.
Network data packets can be either "unicast" or "broadcast". Unicast means the packet's
destination is a single device. At times it is desired to send a broadcast message to all nodes
on the network. This might be necessary, for example, to troubleshoot the network. Bridges
always forward all broadcast packets.
When a bridge forwards a packet, it copies it exactly, leaving the original source MAC address.
Bridges are said to be "transparent" or "invisible". Because a bridge does not require any configuration,
they are the easiest way to break a high traffic network into two segments in order to increase its efficiency.
Bridges cannot connect two segments with different access methods, such as Ethernet to
Token Ring, nor can they connect two different media types such as 10Base2 and 10BaseT.
This can be achieved with special transitional bridges, but these are rarely used because another method,
such as the use of a gateway device, is better. A bridge may be a stand-alone piece of equipment,
or it can be implemented as software installed on a server.