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IPv6 addresses are assigned to organizations in much larger blocks as compared to IPv4 address assignments—the recommended allocation is a / 48 block which contains 2 80 addresses, being 2 48 or about 2.8 × 10 14 times larger than the entire IPv4 address space of 2 32 addresses and about 7.2 × 10 16 times larger than the / 8 blocks of IPv4 ...
This is a list of the IP protocol numbers found in the field Protocol of the IPv4 header and the Next Header field of the IPv6 header. It is an identifier for the encapsulated protocol and determines the layout of the data that immediately follows the header. Both fields are eight bits wide.
A previous format, called "IPv4-compatible IPv6 address", was ::192.0.2.128; however, this method is deprecated. [36] Because of the significant internal differences between IPv4 and IPv6 protocol stacks, some of the lower-level functionality available to programmers in the IPv6 stack does not work the same when used with IPv4-mapped addresses.
Packets that hold Internet Protocol data carry a 4-bit IP version number as the first field of its header. [1] [2] Currently, only IPv4 and IPv6 packets are seen on the Internet, having IP version numbers 4 and 6, respectively.
Extension headers form a chain, using the Next Header fields. The Next Header field in the fixed header indicates the type of the first extension header; the Next Header field of the last extension header indicates the type of the upper-layer protocol header in the payload of the packet. All extension headers are a multiple of 8 octets in size ...
Internet Header Length (IHL): 4 bits The IPv4 header is variable in size due to the optional 14th field (Options). The IHL field contains the size of the IPv4 header; it has 4 bits that specify the number of 32-bit words in the header. The minimum value for this field is 5, [33] which indicates a length of 5 × 32 bits = 160 bits = 20 bytes. As ...
IPv4 is the fourth version in the development of the Internet Protocol, and routes most traffic on the Internet. [1] [non-primary source needed] The IPv4 header includes thirteen mandatory fields and is as small as 20 bytes. A fourteenth optional and infrequently used options field can increase the header size.
Though the header formats are different for IPv4 and IPv6, analogous fields are used for fragmentation, so the same algorithm can be reused for IPv4 and IPv6 fragmentation and reassembly. In IPv4, hosts must make a best-effort attempt to reassemble fragmented IP packets with a total reassembled size of up to 576 bytes.