Cisco ASA 5505 - Manual (Page 1889)

B-7
Cisco ASA 5500 Series Configuration Guide using the CLI
Appendix B Addresses, Protocols, and Ports
IPv6 Addresses
Global Address
The general format of an IPv6 global unicast address is a global routing prefix followed by a subnet ID
followed by an interface ID. The global routing prefix can be any prefix not reserved by another IPv6
address type (see the
“IPv6 Address Prefixes” section on page B-10 , for information about the IPv6
address type prefixes).
All global unicast addresses, other than those that start with binary 000, have a 64-bit interface ID in the
Modified EUI-64 format. See the
“Interface Identifiers” section on page B-8 , for more information about
the Modified EUI-64 format for interface identifiers.
Global unicast address that start with the binary 000 do not have any constraints on the size or structure
of the interface ID portion of the address. One example of this type of address is an IPv6 address with
an embedded IPv4 address (see the
“IPv4-Compatible IPv6 Addresses” section on page B-7 ).
Site-Local Address
Site-local addresses are used for addressing within a site. They can be used to address an entire site
without using a globally unique prefix. Site-local addresses have the prefix FEC0::/10, followed by a
54-bit subnet ID, and end with a 64-bit interface ID in the modified EUI-64 format.
Site-local routers do not forward any packets that have a site-local address for a source or destination
outside of the site. Therefore, site-local addresses can be considered private addresses.
Link-Local Address
All interfaces are required to have at least one link-local address. You can configure multiple IPv6
addresses per interfaces, but only one link-local address.
A link-local address is an IPv6 unicast address that can be automatically configured on any interface
using the link-local prefix FE80::/10 and the interface identifier in modified EUI-64 format. Link-local
addresses are used in the neighbor discovery protocol and the stateless autoconfiguration process. Nodes
with a link-local address can communicate; they do not need a site-local or globally unique address to
communicate.
Routers do not forward any packets that have a link-local address for a source or destination. Therefore,
link-local addresses can be considered private addresses.
IPv4-Compatible IPv6 Addresses
There are two types of IPv6 addresses that can contain IPv4 addresses.
The first type is the IPv4-compatibly IPv6 address. The IPv6 transition mechanisms include a technique
for hosts and routers to dynamically tunnel IPv6 packets over IPv4 routing infrastructure. IPv6 nodes
that use this technique are assigned special IPv6 unicast addresses that carry a global IPv4 address in the
low-order 32 bits. This type of address is termed an IPv4-compatible IPv6 address and has the format
::y.y.y.y, where y.y.y.y is an IPv4 unicast address.
Note The IPv4 address used in the IPv4-compatible IPv6 address must be a globally unique IPv4 unicast
address.
The second type of IPv6 address, which holds an embedded IPv4 address, is called the IPv4-mapped
IPv6 address. This address type is used to represent the addresses of IPv4 nodes as IPv6 addresses. This
type of address has the format ::FFFF:y.y.y.y, where y.y.y.y is an IPv4 unicast address.