TP-Link TL-SG3424P manual Global unicast address, Link-local address

For all IEEE 802 interface types (for example, Ethernet and FDDI interfaces), Interface IDs in the modified EUI-64 format are constructed in the following way:

The first three octets (24 bits) are taken from the Organizationally Unique Identifier (OUI) of the 48-bit link-layer address (the MAC address) of the interface, the fourth and fifth octets (16 bits) are a fixed hexadecimal value of FFFE, and the last three octets (24 bits) are taken from the last three octets of the MAC address. The construction of the interface ID is completed by setting the universal/local (U/L) bit--the seventh bit of the first octet--to a value of 0 or 1. A value of 0 indicates a locally administered identifier; a value of 1 indicates a globally unique IPv6 interface identifier.

Take MAC address 0012:0B0A:2D51 as an example. Insert FFFE to the middle of the address to get 0012:0BFF:FE0A:2D51. Then set the U/L bit to 1 to obtain an interface ID in EUI-64 format as 0212:0BFF:FE0A:2D51.

IPv6 unicast address can be classified into several types, as shown in Table 4-1.The two most common types are introduced below:

Global unicast address

A Global unicast address is an IPv6 unicast address that is globally unique and is routable on the global Internet.

Global unicast addresses are defined by a global routing prefix, a subnet ID, and an interface ID. The IPv6 global unicast address starts with binary value 001 (2000::/3). The global routing prefix is a value assigned to a site (a cluster of subnets/links) by IANA. The subnet ID is an identifier of a subnet within the site.

The figure below shows the structure of a global unicast address.

Figure 4-8 Global Unicast Address Format

Link-local address

A link-local address is an IPv6 unicast address that can be automatically configured on any interface using the link-local prefix FE80::/10 (1111 1110 10) and the interface identifier in the modified EUI-64 format. Link-local addresses are used in the neighbor discovery protocol and the stateless autoconfiguration process. Nodes on a local link can use link-local addresses to communicate. The figure below shows the structure of a link-local address.

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