Network Topology

Topology in Network Design 
Think of a topology as a network's virtual shape or structure. This shape does not necessarily correspond to the actual physical layout of the devices on the network. For example, the computers on a home LAN may be arranged in a circle in a family room, but it would be highly unlikely to find a ring topology there.

 Network topologies are categorized into the following basic types:

• bus
• ring
• star
• tree
• mesh

Bus Topology

 Bus networks (not to be confused with the system bus of a computer) use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message.
      Ethernet bus topologies are relatively easy to install and don't require much cabling compared to the alternatives. 10Base-2  ("ThinNet") and 10Base-5 ("ThickNet") both were popular Ethernet cabling options many years ago for bus topologies



Ring Topology
 In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either "clockwise" or "counterclockwise"). A failure in any cable or device breaks the loop and can take down the entire network

. To implement a ring network, one typically uses FDDI, SONET, or Token Ring technology. Ring topologies are found in some office buildings or school campuses.

Why Use Firewalls ?

Firewalls run much less code, and hence have few bugs(and holes).
            Firewalls can be professionally (and hence better) administerted.
Firewalls run less software, with more logging and monitoring