IP Header

An IP header is a prefix to an IP packet that having such information about the IP version, length, packet, source and destination IP addresses

Here is a sort of each field:

Version – IP protocol. IPv4 this field has a value of 4
Header Length – length of the header in 32 bit. Minumum value is 20 bytes
Priority and Type of Service – tells how the datagram should be take care. First 3 bits are the priority bits.
Total length – Entire packet that is header + data
Identification – Differentiate fragmented packets.
Flags – Used to control or identify fragments.
Fragmented offset – For fragmentation, if the packet is too large to put in a frame it self.
TTL – Limits a datagram lifetime
Protocol – Defines the protocol in data portion of IP datagram
Header checksum – For error-checking
Source IP address – IP address of the host
Destination IP address – IP address of the host that is accepting or receive the packet.

Version (4 bits)	Header Length (4 bits)	Priority and Type of Service (8 bits)	Total length (16 bits)
Identification (16 bits)		Flags (3 bits)	Fragmented offset
TTL – 8 bits	Protocol – 8 bits	Header checksum (16 bits)
	Source IP – 32 bits
	Destination IP – 32 bits
	Options upto 32 bits