Page 103 - M. Abrahim Thesis

Computer Network 2021

4.4.2 Static Assignment of an IP Address

When IP addresses are assigned statically, each device must be configured with an IP address.
Each operating system has its own way of configuring TCP/IP. This method requires records of the
address assignments to be kept, because problems can occur in a network if duplicate IP addresses
are used. Some operating systems, such as Windows 95 and Windows NT, send an ARP request to
check for a duplicate IP address when they attempt to initialize TCP/IP. If a duplicate is discovered,
the operating system does not initialize TCP/IP and generates an error message. Not all operating
systems identify duplicate IP addresses.
This again emphasizes the need for good record-keeping. The main reason that a device
would be assigned a static IP address is if the device needs to be referenced by other devices. A good
example is a web server. If a web server got a new IP address each time it started up, it would be
difficult to find the web server.
As an example of this address changing, if a city were to constantly change street names and
building addresses, maps would no longer help you locate a particular building. If an address changes,
it is no longer easy to return to the location. If a building is difficult to get to, people will stop trying
to locate it. Certain types of devices need to maintain a static IP address. Web servers, network
printers, application servers, and routers are good examples of devices that require permanent IP
addresses. https://www.youtube.com/watch?v=OqsXzkXfwRw

4.5 Address Resolution Protocol
For devices to communicate, the sending device needs the destination device’s IP address
and MAC address. When a device tries to communicate with a device whose IP addresses it knows,
it must determine the MAC addresses.

The TCP/IP suite has a protocol called Address Resolution Protocol (ARP) that can
automatically obtain the MAC address. ARP lets a computer find the MAC address of the computer
that is associated with an IP address, as shown in Figure 4-25. Some devices keep ARP tables, which
contain the MAC addresses and IP addresses of other devices that are connected to the same LAN.

ARP tables map IP addresses to the corresponding MAC addresses. ARP tables are sections of
RAM memory that are maintained automatically on each device, as shown in Table 4-6 and Table 4-
7.

It is rare that you must manually make an ARP table entry. Each computer on a network
maintains its own ARP table.

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