![]() ![]() To calculate global ID, the current time reported by an NTP server in 64-bit format is concatenated with a EUI-64 interface ID of an interface on the host performing this algorithm. If global ID is locally defined, it must be calculated using a pseudorandom algorithm, not sequentially. The next 40 bits represent a globally unique prefix or a global ID. If the value in this field is set to 0, it means that global ID is assigned by Internet Registries. If the value of this field is set to 1, it means the global ID is locally assigned. The 8 th bit defines how a unique local address is assigned. In hexadecimal, these bits are represented FC00::/7. In unique local addresses the first seven bits, are always remain 1111 110. The following image shows how unique local addresses are structured. Unique local addresses work the same as the site-local address but use a different format and structure. To avoid such a situation, Site-local addresses have been deprecated in RFC 3879 and a new type of address known as the unique local addresses defined in RFC 4193. If two sites using the same site-local addressing scheme merge, they may end up with too many ambiguous addresses. In the real world, the merging and separating of sites are very common. Since site-local addresses are not used outside the site, the subnetting scheme adopted by administrators usually does not create any problem. There are no pre-defined rules for organizing subnet bits. In site-local addresses, subnet bits are configured by network administrators. Site-local addresses must not be reachable from outside the site. Routers of the site must not forward site-local traffic outside the site. The scope of site-local addresses is the site. The following image shows the structure of site-local addresses. The Interface ID field identifies a specific interface on a subnet. After 54 subnet bits, the last 64-bits are available for the Interface ID. They can use a flat topology or can create a hierarchical topology by subnetting the subnet bits. Administrators can use subnet bits to create subnets within the organization. After the first 10 bits, the next 54-bits are available for local subnets. In hexadecimal notation, these addresses start with FEC0::/10. In site-local addresses, the first 10 bits are always set to 1111 1110 11. In IPv4 these addresses are known as APIPA (Automatic Private IP addressing) addresses and use the 169.254.0.0/16 prefix. IPv6 enabled devices automatically configure these addresses if other Unicast addresses are absent. Routers never forward traffic sent to link-local addresses. These addresses are used to communicate between hosts on the same link. ![]() The following image shows the structure of these addresses. The scope of the link-local addresses is the local link. ![]() The prefix for link-local addresses is always FE80::/64. In hexadecimal notation, these addresses always begin with FE80. In link-local addresses, the first 10 bits are always set to 1111 1110 10, and the next 54 bits are set to 0. Routers never forward packets sent on the loopback address. In IPv4, the loopback address is 127.0.0.1. ![]() It allows the host device to send packets to itself. It is commonly used for testing and debugging purposes. A loopback interface is a virtual interface. Loopback addressĪ loopback address is assigned to a loopback interface. Interfaces usually use the unspecified address to learn their own unique addresses. Routers never forward an IPv6 packet with a source address of unspecified. The unspecified address is never assigned to an interface or used as a destination address. An interface uses the unspecified address as a source address only if a valid address is not assigned to the interface. The unspecified address indicates the absence of an address. The unspecified address in IPv4 is 0.0.0.0 while the unspecified address in IPv6 is 0.0.0.0.0.0.0.0. In other words, if an interface that is not configured with a valid IP address wants to send a data packet, it can use the unspecified address in the source address field of the packet. Unspecified addressĪn unspecified address represents an interface that does not have an address. These types are unspecified, loopback, link-local, site-local or unique local, and global. There are five main types of unicast addresses in IPv6. Packets sent to a unicast address are delivered to a single interface. A unicast address identifies a single interface in the network. ![]()
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