IPv6 Link Local Addressing
Link-local IPv6 addresses are significant only within the context of a single link. This means that packets with link-local addresses cannot be routed between interfaces, and link-local addresses may overlap as long as they exist on different interfaces. The address format is FE80::/10.Packets with link-local sources or destinations are mostly used by the router’s control plane protocols, such as IPv6 routing protocols. For broadcast segments, such as Ethernet, link-local reachability is implicit because of automatic resolution through ICMP Neighbor Discovery (ICMPv6).
IPv6 Unique Local Addressing
Unique Local IPv6 Unicast Addressing (ULA), defined in RFC 4193, deprecates the previously used Site-Local (FEC0::/10) addressing. ULA addresses in IPv6 are synonymous with the RFC 1918 private addresses and are not publicly routable prefixes on the Internet.Other than the addressing format, ULA addressing exhibits no other unique behavior when compared to normal publicly routable IPv6 addresses.
IPv6 Global Aggregatable Addressing
Global unicast addresses, are publicly allocated and routable on the Internet. Global unicast addresses start with the binary prefix 001 (2000::/3) and therefore encompass the range 2000:: – 3FFF::. Generally only prefix 2001::/16 is currently used for allocation.IPv6 EUI-64 Addressing
Extended Unique Identifiers (EUIs) are 64-bit values assigned to physical interfaces. EUIs are similar in many respects to IEEE MAC addresses, in that they identify a physical interface. IPv6 uses EUI-64 to construct a unique host address on a shared Ethernet segment automatically. When you use the eui-64 keyword, the IOS uses the 48-bit hardware address of the Ethernet interface as the foundation to construct the unique 64-bit interface identifier of the IPv6 address.IPv6 Auto-Configuration
IPv6 has a special feature called auto-configuration. It replaces many functions served by DHCP in IPv4 networks. With IPv6 auto-configuration, an IPv6 host may automatically learn the IPv6 prefixes assigned to the local segment, as well as determine the default routers on that segment. A special type of link-local IPv6 addressing and the ICMPv6 ND (Neighbor Discovery) protocol accomplish this.Router Advertisements can be sent at a specified interval, or the feature can be suppressed completely (“suppress-ra” is enabled by default on Ethernet interfaces; this default behavior can be changed with the no ipv6 nd suppress-ra).
