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WAN and VLAN Solutions

Foundation concepts



Local area networks


LAN (local area network)
According to Cisco, a LAN is a network of computers and other components located relatively close together in a limited area.

VLAN (virtual LAN)
According to Cisco, a VLAN is a single broadcast domain.




Switching versus routing


According to Cisco, a switch creates a network and a router connects networks. What is the difference between switching and routing?




Names, addresses and routes


In computer networks, a source process inspects a string of bits in order to make decisions about how to reach a destination process. In this context, the string of bits could be one of the following:




Ethernet address vs. IP address


Ethernet addresses use a flat hierarchy design to satisfy the primary design objective of autoconfiguration.

IP addresses use a hierarchical design to satisfy a key design goal of aggregation.




Devices according to complexity of forwarding decisions






Devices at each layer


Repeater – Layer 1 device that regenerates the electrical signal from one network segment to another network segment. This was often used with bus topology networks.

Hub – An improved repeater device with multiple ports which was particularly suited for star topology networks.

Bridge – Layer 2 device that stores and forward frames between different network segments. Key functions of bridges are:
  1. Flooding frames
  2. Forwarding frames
  3. Discarding frames

Router – Layer 3 device that stores and forward packets with consideration for transit hops.

Switch – A device with multiple ports that combined the functions of a hub and a bridge.




Everything is switching


  1. Layer 1 switching is performed by repeaters and hubs
  2. Layer 2 switching is performed by bridges and switches
  3. Layer 3 switching is performed by routers or multilayer switches




The success of computer networks has narrowed the meaning of switching to be fast frame forwarding.

Previously, switching had a more general meaning of making a connection between two endpoints.



Forwarding by broadcast reduces capacity




Forwarding in parallel increases capacity






Service models


Using a connectionless service model, Layer n-1 offers two functions to Layer n above it:
  1. accept data from Layer n
  2. deliver data to Layer n

Using a connection-oriented service model, Layer n-1 must offer more functions to Layer n above it:
  1. connection setup
    1. connection initiated by Layer n
    2. connection initiated by a remote peer
  2. accept data from Layer n
  3. deliver data to Layer n
  4. connection release
    1. connection released by Layer n
    2. connection released by a remote peer