Internet Protocol (IP) Address Assignment

You have learnt about identifying network & Host ID’s of an IP address, public and private IP addresses in the previous article. IP addresses are assigned by administrators either manually or automated through DHCP servers. In this article, you will learn about IP address assignment. You will learn about DHCP servers later on.

IP Address Assignment

Internet Protocol addresses is assigned to a host either on booting (when on the OS starts), or permanently by a fixed configuration of its hardware or software. Administrators can allocate and assign unique non-changing IP addresses to hosts or computers. Such addresses are called Static IP address. On large networks, administrators automate the IP address assignment using a special service called the DHCP that assigns IP addresses automatically; such dynamically assigned addresses are called Dynamic IP address.

Static IP provided by Administrator for each computer or host (left) and a DHCP Server configured to assign a dynamic IP address through a pre-defined range. If you want to host a website or provide email services to employees or users, generally you should use static IP addresses. If you want to provide Internet access to users, you can use dynamic IP address. Dynamic IP addresses are assigned by a network device such as SOHO Router or Servers that have DHCP capability.

PING

PING is a command line utility used for testing network connectivity. PING operates using ICMP echo request packets for its response from another computer and measures the time taken by the packet from transmission to reception (referred to as Round-Trip). PING is widely used by administrators to understand and troubleshoot network related issues particularly at the network layer of the OSI model.

ARP

Address Resolution Protocol is used for resolving IP addresses to MAC address. When two computers communicate using IP address (Layer 3) on the same subnet, IP address will be resolved to MAC address (Layer 2) and they start communicating using MAC Address through Network Switch. Thus ARP, a layer 3 protocol serves as an intermediate between Layer 3 and Layer 2 establishing connectivity between network layer and the Ethernet.

Once resolved, mapping of IP Address to MAC addresses are stored in cache for som time for future use. Entries resolved automatically are referred as dynamic entries and is used most of the time.

Loopback IP Address

Loopback IP address is a special IP address reserved for testing local machine’s NIC or device drivers or TCP/IP stack within the local computer. It cannot be assigned to any computer and is implemented at the software level. IP address in the range of 127.0.0.1 to 127.255.255.254 is reserved for loopback address. However, 127.0.0.1 is most commonly used for testing and management purposes by administrators.

CIDR

Assigning numbers based on Classful network was easier during early stages of networking networks were smaller. As time evolved, due to explosive growth of the Internet, IP addresses were getting exhausted. An addressing scheme, CIDR (Classless Inter-domain Routing), was introduced for efficient use of IP addresses.

If you have noticed, a Class A IP address can accommodate 16 million hosts. However, in most organization’s the number of computers will be probably in thousands and not millions. Assuming if an organization has around 2000 computers, imagine the wastage of number of IP addresses if Class A was used.

Similarly, a Class C IP address can accommodate only 254 host; and in the same situation, the IP address range is insufficient and multiple ranges from Class C wi be needed. CIDR helps resolve these issues.

Special IPv4 Addresses

Given below is a list of special IP addresses that cannot be assigned to computer as they are reserved for specific functions.

IP Addresses	Description
0.0.0.0	Refers to unspecified IP address indicating the absence of an IP address.
255.255.255.255	Refers to the broadcast address, used for broadcasting in a network. IP. 127.0.0.1 broadcasts are used by DHCP & BOOTP clients.
127.0.0.1	Referred to as loopback address, it is assigned to the internal network adapter.
169.254.x.x	Reserved for Auto IP.