Tuesday, 3 April 2018

Static and Dynamic IP Addressing


Well, you must have heard of static and dynamic IP addresses, but what these addresses are, when and why are they required, how are they assigned, I got to know the answers to these questions while teaching a core networking subject.
The simple meaning of static is fixed that does not change even if you move to a different network or when you reboot, and the dynamic address is the one that is assigned for a short duration and must be renewed after the lapse of that time or when you reboot your machine.
 Static are used when you wish that your system must be always reachable for other machines. Web applications like Web server or File server need to have static IP configured.  So if you plan to host a file server to your home machine, you have to assign it a static IP address so that client machine on your network can map this address to a name i.e. 192.168.1.0 mapped to a name as “file server”. Another reason is if you want to configure your machine/router for packet or port forwarding, it must have a static IP configured. Figure-1 shows dynamic and static situation, left side shows the routers and servers that would need static IP and on the right is a person in mobility, she leaves one AP and enters another AP, so may be assigned temporary IP by DHCP.

BOOTP is a static configuration protocol. When a client requests its IP address, the BOOTP server consults a table that matches the physical address of the client with its IP address. This implies that the binding between the physical address and the IP address of the client already exists. The binding is predetermined and another protocol DHCP is a dynamic configuration protocol.
DHCP on the other hand is a dynamic configuration protocol. It can be used for both static IP and dynamic IP assignment. For static assignment, DHCP is backward compatible with BOOTP. For dynamic assignment, it assigns temporary IP for a negotiable period of time. At the expiry of this time or on reboot, this IP must be renewed. Figure-2 shows screenshot of IP IPv4 address assignment. When you select Obtain an IP address automatically, you are assigned one by the DHCP protocol running on your machine.

Dr. Ravinder Nath Rajotiya
Department of ECE

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