IPv6 Addressing

Link-Local Unicast Address

Other Prefix Types. There are other designated global unicast prefixes such as those for the following address types:

■RFC 4380: “Teredo: Tunneling IPv6 over UDP”

■RFC 3056: “Connection of IPv6 Domains via IPv4 Clouds”

■RFC 4214: “Intra-Site Automatic Tunnel Addressing Protocol (ISATAP)”

For related information, refer also to:

■RFC 4291: “IP Version 6 Addressing Architecture”

Link-Local Unicast Address

A link-local unicast address is a non-routable address for use on a single VLAN interface, and provides basic connectivity to an IPv6 network. Because the scope of a link-local address is restricted to the VLAN on which the address is used, a link-local address must be unique only for the VLAN on which it is configured. (Traffic with a link-local source or destination address cannot be routed between VLANs.)

Autoconfiguring Link-Local Unicast Addresses

Enabling IPv6 on a given VLAN automatically generates a link-local address. This address is limited in scope to that VLAN, and is usable only for switched traffic. This address has a well- known, 64-bit prefix of fe80:0000:0000:0000 (hexadecimal), or fe80::, and a 64-bit device identifier derived from the VLAN's MAC address using the Extended Unique Identifier format (EUI-64, page 3­ 14). For example, if the MAC address of VLAN 10 is 021560-7aadc0, the automatically generated link-local address for VLAN 10 is:

fe80:0000:0000:0000:0215:60ff:fe7a:adc0

or, in standard IPv6 notation,

fe80::215:60ff:fe7a:adc0

Note that only one link-local address is allowed on an interface. Thus, on a given interface, statically configuring a link-local address type replaces the existing link-local address.

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