Link-local addresses are automatically created when an IPv6 global unicast address is assigned to the interface. Global unicast addresses are not required on an interface; however, IPv6 link-local addresses are.
Unless configured manually, Cisco routers create the link-local address using FE80::/10 prefix and the EUI-64 process, as shown in Figure 1. EUI-64 involves using the 48-bit Ethernet MAC address, inserting FFFE in the middle and flipping the seventh bit. For serial interfaces, Cisco uses the MAC address of an Ethernet interface. A router with several serial interfaces can assign the same link-local address to each IPv6 interface, because link-local addresses only need to be local on the link.
Link-local addresses created using the EUI-64 format, or in some cases random interface IDs, make it difficult to recognize and remember those addresses. Because IPv6 routing protocols use IPv6 link-local addresses for unicast addressing and next hop address information in the routing table, it is common practice to make it an easily recognizable address. Configuring the link-local address manually provides the ability to create an address that is recognizable and easier to remember.
Link-local addresses can be configured manually using the same interface configuration mode command used to create IPv6 global unicast addresses, but with different parameters:
Router(config-if)# ipv6 address link-local-address link-local
A link-local address has a prefix within the range FE80 to FEBF. When an address begins with this hextet (16-bit segment), the link-local keyword must follow the address.
Figure 2 shows the configuration of a link-local address using the ipv6 address interface configuration mode command. The link-local address FE80::1 is used to make it easily recognizable as belonging to router R1. The same IPv6 link-local address is configured on all of R1’s interfaces. FE80::1 can be configured on each link because it only has to be unique on that link.
Similar to R1, in Figure 3, router R2 is configured with FE80::2 as the IPv6 link-local address on all of its interfaces.
Use the Syntax Checker in Figure 4 to configure FE80::3 as the link-local address on all of R3’s interfaces.
As shown in Figure 5, the show ipv6 interface brief command is used to verify the IPv6 link-local and global unicast addresses on all interfaces.