Difference Between Logical Design and Physical Design of a Network

Difference between Logical Design and Physical Design of a Network

When designing a network there are two key elements or attributes that should be taken into consideration, logical design and physical design. The logical and physical designs must consist of requirements which the both designs must incorporate of each other in order for the two designs to work. The logical portion of the network deals with the collection of devices on a network and how they communicate with each other. The physical portion of the network deals with the equipment required to formulate the logical portion of the network work. The question as to why can't we utilize one design or the other? Simply put, logical designs are how they appear to the user, whereas the physical designs are what are actually taking place. The mapping is provided by IP protocols between the logical address and the physical address. This is accomplished via the address resolution protocol (ARP), which is utilized to find the physical address when only the logical address is known.

How data is viewed throughout the network as well as the protocols implemented is all a part of what logical design deals with. When setting up the logical design the software is taken into consideration. Implementing configurations that will cause one router to talk to another is an example as well as various protocols can be utilized to make this possible. Utilizing the Open Shortest Path First (OSPF) protocol on the routers within the logical network design allows the routers to send data from one router to another. There are many other protocols, such as Border Gateway Protocol (BGP) or Routed Internet Protocol (RIP) which are both utilized by routers and switches that make up a network, which all work to determine the paths to be taken throughout the network. For all destinations using SPF (shortest path first) algorithm, the OSPF protocol utilized in the router will calculate a shortest path tree to all these destinations. Routing tables built that add and modify changes that occur via link-state advertisements, and the SPF algorithm is recalculated to find the shortest path the routers will utilize within the network.

The physical design of the network deals with the actual hardware utilized in the network. The hardware is identified as the routers, switches and the cables utilized to connect the network physically. Hardware does not have the ability to recognize other hardware or other hardware information without the assistance of the logical design input via the protocols and configurations setups within the hardware. If you were to connect two routers to each other, they would not be able to communicate with each other until they form some sort of adjacency or neighbor connection. Hardware though the physical connection is not a smart tool that can understand each other without actually being told to do so.

The physical design is required because without the hardware the logical design is just that, a design. In figure 1, the fastest way physically for Router D to get to Router A is going from Router D to Router C then to Router A. This is the optimal physical design for the network.

Figure 1

Figure 2.

These figures show how the data is sent logically through the network. The physical aspect of the network has not come into play until the type of transmission medium has been annotated. Utilizing the same physical network setup but this time there is a configuration issue that does