stands for Internet Protocol and it is responsible for delivering packets from the source host to the destination host by looking at the IP addresses in the packet headers.
IP has 2 versions:
IPv4
IPv4 was the first version of IP. It was deployed for production in the ARPANET in 1983. Today it is the most widely used IP version. It is used to identify devices on a network using an addressing system.
The IPv4 uses a 32-bit address scheme allowing to store 2^32 addresses, which is more than 4 billion addresses. To date, it is considered the primary Internet Protocol and carries 94% of Internet traffic.
IPv6
It is the most recent version of the Internet Protocol. Internet Engineer Taskforce initiated it in early 1994. The design and development of that suite is now called IPv6.
This new IP address version is being deployed to fulfil the need for more Internet addresses. It was aimed to resolve issues which are associated with IPv4. With 128-bit address space, it allows 340 undecillion unique address space.
Types of IP addresses
There are mainly four types of IP addresses:
- Public
- Private
Public IP Addresses
A public IP address is an address where one primary address is associated with your whole network. In this type of IP address, each of the connected devices has the same IP address.
This type of public IP address is provided to your router by your ISP.
Types of Public IP Addresses:
Dynamic IP address:
Dynamic IP addresses always keep changing. It is temporary and are allocated to a device every time it connects to the web. Dynamic IPs can trace their origin to a collection of IP addresses that are shared across many computers.
Dynamic IP addresses are another important type of internet protocol addresses. It is active for a specific amount of time; after that, it will expire.
Static IP Addresses
A static IP address is an IP address that cannot be changed. In contrast, a dynamic IP address will be assigned by a Dynamic Host Configuration Protocol (DHCP) server, which is subject to change. Static IP address never changes, but it can be altered as part of routine network administration.
Static IP addresses are consistent, which is assigned once, that stays the same over the years. This type of IP also helps you procure a lot of information about a device.
Private IP Addresses
A private IP address is a unique IP number assigned to every device that connects to your home internet network, which includes devices like computers, tablets, smartphones, which is used in your household.
It also likely includes all types of Bluetooth devices you use, like printers or printers, smart devices like TV, etc. With a rising industry of internet of things (IoT) products, the number of private IP addresses you are likely to have in your own home is growing.
IP classes
There are 5 types of classes available in IPv4.
IP Packet header
Each IP packet contains both a header (20 or 24 bytes long) and data (variable length). The header includes the IP addresses of the source and destination, plus other fields that help to route the packet. The data is the actual content, such as a string of letters or part of a webpage.
- Version: the first field tells us which IP version we are using, only IPv4 uses this header so you will always find decimal value 4 here.
- Header Length: 4 bits field tells us the length of the IP header in 32 bits increments. The minimum length of an IP header is 20 bytes so with 32 bits increments, you would see value of 5 here. The maximum value we can create with 4 bits is 15 so with 32 bits increments, that would be a header length of 60 bytes. This field is also called the Internet Header Length (IHL).
- Type of Service: this is used for QoS (Quality of Service). There are 8 bits that we can use to mark the packet which we can use to give the packet a certain treatment. You can read more about this field in my IP precedence and DSCP lesson.
- Total Length: 16 bits field indicates the entire size of the IP packet (header and data) in bytes. The minimum size is 20 bytes (if you have no data) and the maximum size is 65.535 bytes, that’s the highest value you can create with 16 bits.
- Identification: If the IP packet is fragmented then each fragmented packet will use the same 16-bit identification number to identify to which IP packet they belong to.
- IP Flags: These 3 bits are used for fragmentation:
- The first bit is always set to 0.
- The second bit is called the DF (Don’t Fragment) bit and indicates that this packet should not be fragmented.
- The third bit is called the MF (More Fragments) bit and is set on all fragmented packets except the last one.
- Fragment Offset: 13 bits field specifies the position of the fragment in the original fragmented IP packet.
- Time to Live: Every time an IP packet passes through a router, the time to live field is decremented by 1. Once it hits 0 the router will drop the packet and sends an ICMP time exceeded message to the sender. The time to live field has 8 bits and is used to prevent packets from looping around forever (if you have a routing loop).
- Protocol: this 8-bits field tells us which protocol is encapsulated in the IP packet, for example TCP has value 6 and UDP has value 17.
- Header Checksum: this 16-bit field is used to store a checksum of the header. The receiver can use the checksum to check if there are any errors in the header.
- Source Address: here you will find the 32 bits source IP address.
- Destination Address: and here’s the 32 bits destination IP address.
- IP Option: this field is not used often, is optional and has a variable length based on the options that were used. When you use this field, the value in the header length field will increase. An example of a possible option is “source route” where the sender requests for a certain routing path.
Sanchit Gurukul 
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