IPV6 Addressing | IPv6 Addresses | IPV6 general categories | IPv6 main types | Understand IPv6 Addresses
IPv6 addressing, however, includes several other types of unicast IPv6 addresses beside the global unicast address. Additionally, IPv6 defines other general categories of ad- dresses, as summarized in this list.
■ Unicast: Like IPv4, hosts and routers assign these IP addresses to a single interface for the purpose of allowing that one host or interface to send and receive IP packets.
■ Multicast: Like IPv4, these addresses represent a dynamic group of hosts, allowing a host to send one packet that is then delivered to every host in the multicast group. IPv6 defines some special-purpose multicast addresses for overhead functions (such as NDP). IPv6 also defines ranges of multicast addresses for application use.
■ Anycast: This address type allows the implementation of a nearest server among du- plicate servers concept. This design choice allows servers that support the exact same function to use the exact same unicast IP address. The routers then forward a packet destined for such an address to the nearest server that is using the address.
Unicast IPv6 Addresses
IPv6 supports three main types of unicast addresses: link local, global unicast, and unique local. This section takes a brief look at link local and unique local addresses.Unique local unicast IPv6 addresses have the same function as IPv4 RFC 1918 private ad-dresses. RFC 4193 states that these addresses should be used inside a private organiza-tion, and should not be advertised into the Internet. Unique local unicast addresses begin with hex FD (FD00::/8) .
Link Local Unicast Addresses
IPv6 uses link local addresses for sending and receiving IPv6 packets on a single subnet. Many such uses exist; here’s just a small sample:
■ Used as the source address for RS and RA messages for router discovery (as previ-ously shown in Figure 16-7)
■ Used by Neighbor discovery (the equivalent of ARP for IPv6)
■ As the next-hop IPv6 address for IP routes By definition, routers use a link local scope for packets sent to a link local IPv6 address. The term link local scope means exactly that–the packet should not leave the local link, or local subnet if you will. When a router receives a packet destined for such a destination address, the router does not forward the packet.
The link local IPv6 addresses also help solve some chicken-and-egg problems because each host, router interface, or other device can calculate its own link local IPv6 address without needing to communicate with any other device. So, before sending the first pack- ets, the host can calculate its own link local address, so the host has an IPv6 address to use when doing its first overhead messages. For example, before a host sends an NDP RS (router solicitation) message, the host will have already calculated its link local address, which can be used as the source IPv6 address on the RS message.
Link local addresses come from the FE80::/10 range, meaning the first 10 bits must be 1111 1110 10. An easier range to remember is that all hex link local addresses begin FE8,FE9, FEA, or FEB. However, practically speaking, for link local addresses formed auto-matically by a host (rather than through static configuration), the address always starts FE80, because the automatic process sets bits 11-64 to binary 0s. Figure 16-10 shows theformat of the link local address format under the assumption that the host or router is de-riving its own link local address, therefore using 54 binary 0s after the FE80::/10 prefix.
IPV6 Addressing | IPv6 Addresses | IPV6 general categories | IPv6 main types | Understand IPv6 Addresses
The Following Table Shows Common Link-Local Multicast Addresses :
| Type of Address | Purpose | Prefix | Easily Seen Hex Prefix(es) |
| Global unicast | Unicast packets sent through the public In- ternet | 2000::/3 | 2 or 3 |
| Unique local | Unicast packets inside one organization | FD00::/8 | FD |
| Link local | Packets sent in the local subnet | FE80::/10 | FE8 |
| Site local | Deprecated; originally meant to be used like private IPv4 addresses | FECO::/10 | FEC, FED, FEE, FEF |
| Unspecified | An address used when a host has no usable IPv6 address | ::/128 | N/A |
| Loopback | Used for software testing, like IPv4’s 127.0.0.1 | ::1/128 | N/A |
Multicast and Other Special IPv6 Addresses
IPv6 supports multicasts on behalf of applications and multicasts to support the inner workings of IPv6. To aid this process, IPv6 defines ranges of IPv6 addresses and an associ-ated scope, with the scope defining how far away from the source of the packet that the network should forward a multicast.
All IPv6 multicast addresses begin with FF::/8 – in other words, with FF as the first two digits. Multicasts with a link local scope, begin with FF02::/16; the 2 in the fourth hex digit identifies the scope as link local. A fourth digit of hex 5 identifies the broadcast as site local scope, with those multicasts beginning with FF05::/16.
For reference, The Following Table lists some of the more commonly seen IPv6 multicast addresses. Of particular interest are the addresses chosen for use by RIP, OSPF, and EIGRP, which somewhat mirror the multicast addresses each protocol uses for IPv4. Note also that all but the last two entries have link local scope .
| Purpose | IPv6 Address | IPv4 Equivalent |
| All IPv6 nodes on the link | FF02::1 | subnet broadcast address |
| All IPv6 routers on the link | FF02::2 | N/A |
| OSPF messages | FF02::5, FF02::6 | 224.0.0.5, 224.0.0.6 |
| RIP-2 messages | FF02::9 | 224.0.0.9 |
| EIGRP messages | FF02::A | 224.0.0.10 |
| DHCP relay agents (routers that forward to the DHCP server) | FF02:1:2 | N/A |
| DHCP servers (site scope) | FF05::1:3 | N/A |
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