As stated earlier, there are three types of addresses in IPv6: anycast, unicast, and multicast. A description of each of these types of IPv6 addresses follows:
Note the absence of the broadcast type, which is included in IPv4. You can’t use broadcasts in IPv6; they’ve been replaced with multicasts.
Anycast Addresses Anycast addresses are not really new. The concept of anycast existed in IPv4 but was not widely used. An anycast address is an IPv6 address assigned to multiple devices (usually different devices). When an anycast packet is sent, it is delivered to one of the devices, usually the closest one.
Unicast Addresses A unicast packet uniquely identifies an interface of an IPv6 device.
The interface can be a virtual interface or pseudo- interface or a real (physical) interface.
Unicast addresses come in several types, as described in the following list:
Global Unicast Address As of this writing, the global unicast address space is defined as 2000:: /3. The 2001::/32 networks are the IPv6 addresses currently being issued to business entities. As mentioned, Microsoft has been allocated 2001:4898:: /32. A Microsoft DHCPv6 server would be set up with scopes (ranges of addresses to be assigned) within this address space. There are some special addresses and address formats that you will see in use as well. You’ll find most example addresses listed as 2001:DB8:: /32; this space has been reserved for documentation. Do you remember the loopback address in IPv4, 127.0.0.1? In IPv6 the loopback address is ::1 (or 0:0:0:0:0:0:0:0001). You may also see an address with dotted- decimal used. A dual-s tack Windows Server 2022 machine may also show you
FE80::5EFE:192.168.1.200. This address form is used in an integration/migration model of IPv6 (or if you just can’t leave the dotted- decimal era, I suppose).
Link- Local Address Link- local addresses are defined as FE80:: /10. If you refer to Figure 4.15 showing the ipconfig command, you will see the link-l ocal IPv6 address as fe80::a425:ab9d:7da4:ccba. The last 8 bytes (64 bits) are random to ensure a high probability of randomness for the link- local address. The link-l ocal 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 4.15, 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 2022 uses the random address by default instead of EUI- 64. The random value is called the AnonymousAddress in Microsoft Server 2022. 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 4.7 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.” |
TABLE 4.7 IPv6 address space known prefixes and addresses
Address prefix | Scope of use |
2000:: /3 | Global unicast space prefix |
FE80:: /10 | Link- local address prefix |
FC00:: /7 | Unique local unicast prefix |
FD00:: /8 | Unique local unicast prefix |
FF00:: /8 | Multicast prefix |
2001:DB8:: /32 | Global unicast prefix used for documentation |
::1 | Reserved local loopback address |
2001:0000: /32 | Teredo prefix (discussed later in this chapter) |
2002:: /16 | 6to4 prefix |