Information Technology Reference
In-Depth Information
probability of randomness for the link-local address. The link-local address is to be used
on a single link (network segment) and should never be routed.
There is another form of the local-link IPv6 address called the
Extended User Interface
64-bit (EUI-64)
format. This is derived by using the MAC address of the physical
interface and inserting an FFFE between the third and fourth bytes of the MAC. The
first byte is also made 02 (this sets the universal/local or U/L bit to 1 as defined in IEEE
802 frame specification). Again looking at Figure 8.15, the EUI-64 address would take
the physical (MAC) address 00-03-FF-11-02-CD and make the link-local IPv6 address
FE80::0203:FFFF:FE11:02CD. (I've left the preceding zeros in the link-local IPv6
address to make it easier for you to pick out the MAC address with the FFFE inserted.)
AnonymousAddress
Microsoft Server 2012 R2 uses the random address by default
instead of EUI-64. The random value is called the
AnonymousAddress
in Microsoft
Server 2012 R2. It can be modified to allow the use of EUI-64.
Unique Local Address
The
unique local address
can be Fc00 or FD00, and it is used
like the private address space of IPv4. RFC 4193 describes unique local addresses. They
are not expected to be routable on the global Internet. They are used for private routing
within an organization.
Multicast Address
Multicast addresses
are one-to-many communication packets.
Multicast packets are identifiable by their first byte (most significant byte, leftmost byte,
leftmost 2 nibbles, leftmost 8 bits, and so on). A multicast address is defined as FF00::/8.
In the second byte shown (the 00 of FF00), the second 0 is what's called the
scope
.
Interface-local is 01, and link-local is 02. FF01:: is an interface-local multicast.
There are several well-known (already defined) multicast addresses. For example, if you
want to send a packet to all nodes in the link-local scope, you send the packet to FF02::1
(also shown as FF02:0:0:0:0:0:0:1). The all-routers multicast address is FF02::2.
You can also use multicasting to get the logical link layer address (MAC address) of a
device with which you are trying to communicate. Instead of using the ARP mechanism of
IPv4, IPv6 uses the ICMPv6 neighbor solicitation (NS) and neighbor advertisement (NA)
messages. The NS and NA ICMPv6 messages are all part of the new
Neighbor Discovery
Protocol (NDP)
. This new ICMPv6 functionality also includes router solicitation and router
advertisements as well as redirect messages (similar to the IPv4 redirect functionality).
Table 8.7 outlines the IPv6 address space known prefixes and some well-known addresses.
unicast vs. anycast
Unicast and anycast addresses look the same and may be indistinguishable from each
other; it just depends on how many devices have the same address. If only one device
has a globally unique IPv6 address, it's a unicast address. If more than one device has the
same address, it's an anycast address. Both unicast and anycast are considered one-to-
one communication, although you could say that anycast is one-to-“one of many.”
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