Web hosting colocation - 10 1.4 IPv6 Architecture from a Programmer s Point
10 1.4 IPv6 Architecture from a Programmer s Point of View into binary representation, such as struct in_addr (inet_pton(3)) and vice versa (inet_ntop(3)). 1.4 IPv6 Architecture from a Programmer s Point of View From a programer s point of view, IPv4 and IPv6 are almost exactly the same; we have an IP address (size differs: 32 bit and 128 bit) to identify nodes (actually network interfaces) and a TCP/UDP port number to identify services on the node. There are several points that programmers need to know: In both cases, users normally will use DNS names, rather than IP addresses, to identify the peer. For instance, users use http://www.example.com/ rather than http://10.2.3.4/. IPv4 addresses are presented as decimals separated by dots, such as 10.2.3.4. IPv6 addresses are presented as hexadecimals separated by colons, such as 3ffe:501:ffff:0:0:0:0:1. Two continuous colons can be used to mean continuous zeros for example, 3ffe:501:ffff:0:0:0:0:1 is equal to 3ffe:501:ffff::1. To avoid ambiguity with the separator for the port number, the numeric IPv6 address in a URL has to be wrapped with a square bracket: http:// [3ffe:501:ffff::1]:80/. Again, however, users won t, and shouldn t need to, use a numeric IPv6 address in URLs. DNS names should be used instead. In IPv4, we used variable-length subnet masks, such as /24 (netmask 0xffffff00), /28 (0xfffffff0), or /29 (0xfffffff8). Variable-length subnet mask was introduced to reduce IPv4 address space use; however, it has certain drawbacks: It limits how many devices you can connect to your subnet, and you will need to change subnet mask, or renumber the subnet, when the number of devices goes too high. In IPv6, we always use /64 as the subnet mask. Therefore, it is guaranteed that up to 264 devices can be connected to a given subnet. (See Figures 1.5 and 1.6.) In IPv4, a node normally has a single IPv4 address associated with it. In IPv6, it is normal to have multiple IP addresses onto a single node. More specifically, IPv6 addresses are assigned to interfaces, not to nodes. An interface can have multiple IPv6 addresses. In IPv4, there were three communication models: unicast, broadcast, and multicast. Unicast is for one-to-one communication, broadcast is for one-to-all communiation on a specific broadcast medium (e.g., an ethernet link), and multicast is for one-to-many communication with a specific set of nodes (within a multicast group). With IPv6, broadcast is deprecated and integrated
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