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Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 4.x
OL-20002-02
Chapter 3 Configuring IPv6
Information About IPv6
Site-Local Address
Because RFC 3879 deprecates the use of site-local addresses, you should follow the recommendations
of unique local addressing (ULA) in RFC 4193 when you configure private IPv6 addresses.
IPv6 Anycast Addresses
An anycast address is an address that is assigned to a set of interfaces that belong to different nodes. A
packet sent to an anycast address is delivered to the closest interface—as defined by the routing protocols
in use—identified by the anycast address. Anycast addresses are syntactically indistinguishable from
unicast addresses because anycast addresses are allocated from the unicast address space. Assigning a
unicast address to more than one interface turns a unicast address into an anycast address. You must
configure the nodes to which the anycast address to recognize that the address is an anycast address.
Note Anycast addresses can be used only by a router, not a host. Anycast addresses cannot be used as the
source address of an IPv6 packet.
Figure 3-5 shows the format of the subnet router anycast address; the address has a prefix concatenated
by a series of zeros (the interface ID). The subnet router anycast address can be used to reach a router
on the link that is identified by the prefix in the subnet router anycast address.
Figure 3-5 Subnet Router Anycast Address Format
IPv6 Multicast Addresses
An IPv6 multicast address is an IPv6 address that has a prefix of FF00::/8 (1111 1111). An IPv6
multicast address is an identifier for a set of interfaces that belong to different nodes. A packet sent to a
multicast address is delivered to all interfaces identified by the multicast address. The second octet
following the prefix defines the lifetime and scope of the multicast address. A permanent multicast
address has a lifetime parameter equal to 0; a temporary multicast address has a lifetime parameter equal
to 1. A multicast address that has the scope of a node, link, site, or organization, or a global scope, has
a scope parameter of 1, 2, 5, 8, or E, respectively. For example, a multicast address with the prefix
FF02::/16 is a permanent multicast address with a link scope. Figure 3-6 shows the format of the IPv6
multicast address.
52670
128 bits
0000000000000...000Prefix
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