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2.0 IPv6 Features
IPv4 headers and IPv6 headers are not interoperable and the IPv6 protocol is not backward compatible with the IPv4 protocol. A host or router must use an implementation of both IPv4 and IPv6 in order to recognize and process both header formats. The new IPv6 header is only twice as large as the IPv4 header, even though IPv6 addresses are four times as large as IPv4 addresses.
Can someone show examples of the old IPv6 header and compare it to the new IPv6 header?
In the late 1970s when the IPv4 address space was designed, it was unimaginable that it could be exhausted. However, due to changes in technology and an allocation practice that did not anticipate the recent explosion of hosts on the Internet, the IPv4 address space was consumed to the point that by 1992, it was clear a replacement would be necessary.
With IPv6, it is even harder to conceive that the IPv6 address space will be consumed. To help put this number in perspective, a 128-bit address space provides 655,570,793,348,866,943,898,599 (6.5 × 10^23) addresses for every square meter of the Earth's surface.
It is important to note that the decision to make the IPv6 address 128 bits in length was not so that every square meter of the Earth could have 6.5 x 10^23 addresses. Rather, the relatively large size of the IPv6 address is designed to be subdivided into hierarchical routing domains that reflect the topology of the modern-day Internet. The use of 128 bits provides multiple levels of hierarchy and flexibility in designing hierarchical addressing and routing that is currently lacking on the IPv4-based Internet.
•We divide it into 16 bit boundaries:
0010000111011010 000000011010011 0000000000000000 0010111100111011
0000001010101010 000000011111111 1111111000101000 1001110001011010
•Each of these 16 bit boundaries is converted to hexadecimal (base 16) and delimited with colons:
21DA : 00D3 : 0000 : 2F3B : 02AA : 00FF : FE28 : 9C5A
•Leading zeros are suppressed. However, there must be at least one single digit in each boundary:
Re. IPv6 Address Syntax (#10289) examples: The second and sixth binary boundaries (000000011010011 and 000000011111111, respectively) are each only 15 bits long.
I think you've missed two bits./PeterB