Page 105 - DCAP104_EXPOSURE_TO_COMPUTER_DISCPLINES

Exposure to Computer Disciplines

Notes 5.4.3.1 Bridges come in three basic types
 Local bridges: Directly connect local area networks (LANs).

 Remote bridges: Can be used to create a wide area network (WAN) link between LANs.
Remote bridges, where the connecting link is slower than the end networks, largely
have been replaced with routers.

 Wireless bridges: Can be used to join LANs or connect remote stations to LANs.
5.4.4 Switches

A network switch is a device that forwards and filters OSI layer 2 datagrams (chunks of data
communication) between ports (connected cables) based on the MAC addresses in the packets.
A switch is distinct from a hub in that it only forwards the frames to the ports involved in
the communication rather than all ports connected. A switch breaks the collision domain but
represents itself as a broadcast domain. Switches make forwarding decisions of frames on the
basis of MAC addresses. A switch normally has numerous ports, facilitating a star topology
for devices, and cascading additional switches. Some switches are capable of routing based
on Layer 3 addressing or additional logical levels; these are called multi-layer switches. The
term switch is used loosely in marketing to encompass devices including routers and bridges,
as well as devices that may distribute traffic on load or by application content (e.g., a Web
URL identifier).

Figure 5.18: A Network Switch

5.4.5 Routers

A router is an internetworking device that forwards packets between networks by processing
information found in the datagram or packet (Internet protocol information from Layer 3 of the
OSI Model). In many situations, this information is processed in conjunction with the routing
table (also known as forwarding table). Routers use routing tables to determine what interface
to forward packets (this can include the “null” also known as the “black hole” interface because
data can go into it, however, no further processing is done for said data).

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