Header of IP is fixed part of
Header of IP is fixed part of 20 bytes.
An IP datagram consists of a header part and text part. The header has a 20 bytes fixed part and a variable length optional part. It is transmitted in big endian order.
The longest Internet Header (IP header) size can be 15*32 Bits = 480 Bits = 60 Bytes. This is why the header has a maximum size of 60 Bytes. The shortest header size is 20 bytes.
IP header:-
An IP header is header information at the beginning of an IP packet which contains information about IP version, source IP address, destination IP address, time-to-live, etc. Two different versions of IP are used in practice today: IPv4 and IPv6.