There are many differences between IPv4 header and IPv6 header. Following images are IPv4 header and IPv6 header respectivly.
IPv4 Datagram Header
IPv6 Datagram Header
Following are the main differences and comparison between IPv4 header and IPv6 header.
• IPv6 header is much simpler than IPv4 header.
• The size of IPv6 header is much bigger than that of IPv4 header, because of IPv6 address size. IPv4 addresses are 32bit binary numbers and IPv6 addresses are 128 bit binary numbers.
• In IPv4 header, the source and destination IPv4 addresses are 32 bit binary numbers. In IPv6 header, source and destination IPv6 addresses are 128 bit binary numbers.
• IPv4 header includes space for IPv4 options. In IPv6 header, we have a similar feature known as extension header. IPv4 datagram headers are normally 20-byte in length. But we can include IPv4 option values also along with an IPv4 header. In IPv6 header we do not have options, but have extension headers.
• The fields in the IPv4 header such as IHL (Internet Header Length), identification, flags are not present in IPv6 header.
• Time-to-Live (TTL), a field in IPv4 header, typically used for preventing routing loops, is renamed to it's exact meaning, "Hop Limit".