TABLE 29 IPv6 address types (continued)
Address type Description Address structure
interface assigned an anycast address must be
congured to recognize the address as an
anycast address.
An anycast address can be assigned to a switch
only.
An anycast address must not be used as the
source address of an IPv6 packet.
A switch automatically congures a link-local unicast address for an interface by using the prex of FE80::/10 (1111 1110 10) and a
64-bit interface ID. The 128-bit IPv6 address is then subjected to duplicate address detection to ensure that the address is unique on
the link. If desired, you can override this automatically congured address by explicitly conguring an address.
NOTE
Brocade FastIron devices support RFC 2526, which requires that within each subnet, the highest 128 interface identier values
reserved for assignment as subnet anycast addresses. Thus, if you assign individual IPv6 addresses within a subnet, the second
highest IPv6 address in the subnet does not work.
IPv6 stateless auto-conguration
Brocade routers use the IPv6 stateless autoconguration feature to enable a host on a local link to automatically congure its interfaces
with new and globally unique IPv6 addresses associated with its location. The automatic conguration of a host interface is performed
without the use of a server, such as a Dynamic Host Conguration Protocol (DHCP) server, or manual conguration.
The automatic conguration of a host interface works in the following way: a switch on a local link periodically sends switch
advertisement messages containing network-type information, such as the 64-bit prex of the local link and the default route, to all
nodes on the link. When a host on the link receives the message, it takes the local link prex from the message and appends a 64-bit
interface ID, thereby automatically conguring its interface. (The 64-bit interface ID is derived from the MAC address of the host’s NIC.)
The 128-bit IPv6 address is then subjected to duplicate address detection to ensure that the address is unique on the link.
The duplicate address detection feature veries that a unicast IPv6 address is unique before it is assigned to a host interface by the
stateless auto conguration feature. Duplicate address detection uses neighbor solicitation messages to verify that a unicast IPv6
address is unique.
NOTE
For the stateless auto conguration feature to work properly, the advertised prex length in switch advertisement messages
must always be 64 bits.
The IPv6 stateless autoconguration feature can also automatically recongure a host’s interfaces if you change the ISP for the host’s
network. (The host’s interfaces must be renumbered with the IPv6 prex of the new ISP.)
The renumbering occurs in the following way: a switch on a local link periodically sends advertisements updated with the prex of the
new ISP to all nodes on the link. (The advertisements still contain the prex of the old ISP.) A host can use the addresses created from the
new prex and the existing addresses created from the old prex on the link. When you are ready for the host to use the new addresses
only, you can congure the lifetime parameters appropriately using the ipv6 nd prex-advertisement command. During this transition,
the old prex is removed from the switch advertisements. At this point, only addresses that contain the new prex are used on the link.
IPv6 addressing overview
FastIron Ethernet Switch Layer 3 Routing
154 53-1003627-04
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