What is an IP Address
The word “IP ” stands for “Internet Protocol.” An Internet Protocol address or IP Address is a unique logical numeric address assigned to every computer, printer, switch, router, or network device. It is the core component of the TCP/IP network. There is no possibility of a network without an IP address. IP addresses such as 192.168.1.1 uniquely identify every host in the network. There are two parts of the IP address.
The network part of IP Address
The network part specifies the unique number assigned to the network and identifies the class of the IP address. All hosts in a network are grouped in a single IP address range, called its net or subnet.
The host part of the IP Address
This is part of identifying the host uniquely in the network. Each host assigns a unique address from the network’s range. Each network has a different address range, and routers operating on layer 3 connect these networks.
Note: For each host on the network, the network part of the address will be the same, but the host part should be different.
How Do IP Addresses Work?
As network devices generate TCP or UDP segments, a header with source IP address and destination IP address, among other information, is added. This PDU (protocol data unit) is called a packet. When a router receives a packet, it looks at the destination address in the header and forwards it to the destination network. The packet may pass through multiple routers before it reaches the destination network. Each router it has to go through is called a hop.
IP address Fields
This field plays a very important role in sending data through different hops. Version 4 is the most used in today’s networking. The Figure below illustrates the header structure of the IPv4 address.
Version
This field shows the version of the IP address. For IPv4 address, this value is 4.
Header Length
Header length specifies the size of the header itself. The smallest size is 20 bytes. The figure does not show a variable length’s rarely used options field. Most IPv4 headers are 20 bytes in length.
DS Field
The Differentiated Services field marks packets for different quality-of-service (QoS) levels. For example, data belonging to voice and video protocols have no acceptance for delay. The DS field marks packets carrying data belonging to these protocols so that they get priority treatment through the network. On the other hand, peer-to-peer traffic is considered a major problem and can be marked down to give the best-effort treatment.
Total Length
The total length field specifies the size of the packet. The length contains the header size, including the data size.
Identification
When a device receives a segment from TCP or UDP, It may be required to break the segment into chunks called fragments before sending it out to the network. Identification fields find the fragments that make up the original segment. Each fragment of a segment will have the same identification number.
Flags
Used for fragmentation process.
Fragment Offset
The fragment offset field identifies the fragment number so that the segment can be reassembled in the correct order.
Time to Live (TTL)
The TTL value is set to the originating host. Each router that the packet passes through reduces the TTL by one. The packet is dropped if the TTL reaches 0 before reaching the destination. This is done to prevent the packet from moving around the network endlessly.
Protocol
The protocol field identifies the protocol to which the data belongs. For example, a value of 6 implies that the data has a TCP segment, while a value of 17 signifies a UDP segment. In addition to TCP and UDP, there are many protocols whose data can be carried in an IP packet.
Header Checksum
The header checksum field is used to check for errors in the header. For each router and at the destination, a cyclic redundancy check is performed on the header, and the result should match the value stored in this field. If the value does not match, the packet is discarded.
Source IP address
This field stores the IP address of the source of the packet.
Destination IP address
This field stores the IP address of the packet’s destination.
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