As most administrators know, IPv6 is designed to increase the size of the IP address space, thus providing addresses for many more devices than IPv4. The 128-bit address size of IPv6 allows for 2128 possible addresses—which is over 54 million addresses for each square meter of the Earth’s surface.
In addition to providing more addresses, IPv6 will also reduce the size of the routing tables in the routers scattered around the Internet. This is because the size of the addresses provides for more than the two levels of subnetting currently possible with IPv4.
IPv6 addresses are different from IPv4 addresses in many ways other than length. Instead of the four 8-bit decimal numbers separated by periods that IPv4 uses, IPv6 addresses use a notation called colon-hexadecimal format, which consists of eight 16-bit hexadecimal numbers separated by colons, as follows:
Each X represents eight bits (or one byte), which in hexadecimal notation is represented by two characters, as in the following example:
CONTRACTING IPV6 ADDRESSES
When an IPv6 address has two or more consecutive 8-bit blocks of zeros, you can replace them with a double colon, as follows (but you can use only one double colon in any IPv6 address):
You can also remove the leading zeros in any block where they appear, as follows:
EXPRESSING IPV6 NETWORK ADDRESSES
There are no subnet masks in IPv6. Network addresses use the same slash notation as CIDR to identify the network bits. In this example, the network address is notated as follows:
This is the contracted form for the following network address:
IPv6 address types
There are no broadcast transmissions in IPv6, and therefore no broadcast addresses, as in IPv4. IPv6 supports three types of transmissions, as follows:
– Unicast Provides one-to-one transmission service to individual interfaces, including server farms sharing a single address
– Multicast Provides one-to-many transmission service to groups of interfaces identified by a single multicast address
– Anycast Provides one-to-one-of-many transmission service to groups of interfaces, only the nearest of which (measured by the number of intermediate routers) receives the transmission.
NOTE IPV6 SCOPES
In IPv6, the scope of an address refers to the size of its functional area. For example, the scope of a global unicast is unlimited; that is, the entire Internet. The scope of a link-local unicast is the immediate link; that is, the local network. The scope of a unique local unicast consists of all the subnets within an organization.
IPv6 also supports several address types, as described in the following sections.
GLOBAL UNICAST ADDRESSES
A global unicast address is the equivalent of a registered IPv4 address, routable worldwide and unique on the Internet.
LINK-LOCAL UNICAST ADDRESSES
In IPv6, systems that assign themselves an address automatically create a link-local unicast address, which is essentially the equivalent of an APIPA address in IPv4. All link-local addresses have the same network identifier: a 10-bit prefix of 1111111010 followed by 54 zeros, resulting in the following network address:
In its more compact form, the link-local network address is as follows:
Because all link-local addresses are on the same network, they are not routable, and systems possessing them can only communicate with other systems on the same link.
UNIQUE LOCAL UNICAST ADDRESSES
Unique local unicast addresses are the IPv6 equivalent of the 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 private network addresses in IPv4. Like the IPv4 private addresses, unique local addresses are routable within an organization. Administrators can also subnet them as needed to support an organization of any size.
NOTE: DEPRECATED IPV6 ADDRESSES
Many sources of IPv6 information continue to list site-local unicast addresses as a valid type of unicast, with a function similar to that of the private IPv4 network addresses. For various reasons, site-local unicast addresses have been deprecated, and although their use is not forbidden, their functionality has been replaced by unique local unicast addresses.
Multicast addresses always begin with a value of 11111111 in binary, or ff in hexadecimal.
The function of an anycast address is to identify the routers within a given address scope and send traffic to the nearest router, as determined by the local routing protocols. Organizations can use anycast addresses to identify a particular set of routers in the enterprise, such as those that provide access to the Internet. To use anycasts, the routers must be configured to recognize the anycast addresses as such.
Assigning IPv6 addresses
The processes by which administrators assign IPv6 addresses to network computers are similar to those in IPv4. As with IPv4, a Windows computer can obtain an IPv6 address by three possible methods:
– Manual allocation A user or administrator manually supplies an address and other information for each network interface.
– Self-allocation The computer creates its own address by using a process called stateless address autoconfiguration.
– Dynamic allocation The computer solicits and receives an address from a DHCPv6 server on the network.
MANUAL IPV6 ADDRESS ALLOCATION
For the enterprise administrator, manual allocation of addresses is even more impractical in IPv6 than in IPv4 because of the length of the addresses involved. However, it is possible, and the procedure for doing so in Windows Server 2012 R2 is the same as that for IPv4, except that you open the Internet Protocol Version 6 (TCP/IPv6) Properties sheet, as shown in Figure 4-3.
FIGURE 4-3 The Internet Protocol Version 6 (TCP/IPv6) Properties sheet
Because of the difficulties of working with IPv6 addresses manually, the following two options are far more prevalent.
STATELESS IPV6 ADDRESS AUTOCONFIGURATION
When a Windows computer starts, it initiates the stateless address autoconfiguration process, during which it assigns each interface a link-local unicast address. This assignment always occurs, even when the interface is to receive a global unicast address later. The link-local address enables the system to communicate with the router on the link, which provides additional instructions.
The steps of the stateless address autoconfiguration process are as follows.
1. Link-local address creation The IPv6 implementation on the system creates a linklocal address for each interface by using the fe80::/64 network address and generating an interface ID, either by using the interface’s media access control (MAC) address or a pseudorandom generator.
2. Duplicate address detection Using the IPv6 Neighbor Discovery (ND) protocol, the system transmits a Neighbor Solicitation message to determine if any other computer on the link is using the same address and listens for a Neighbor Advertisement message sent in reply. If there is no reply, the system considers the address to be unique on the link. If there is a reply, the system must generate a new address and repeat the
3. Link-local address assignment When the system determines that the link-local address is unique, it configures the interface to use that address. On a small network consisting of a single segment or link, this might be the interface’s permanent address assignment. On a network with multiple subnets, the primary function of the link-local address assignment is to enable the system to communicate with a router on the link.
4. Router advertisement solicitation The system uses the ND protocol to transmit Router Solicitation messages to the all routers multicast address. These messages compel routers to transmit the Router Advertisement messages more frequently.
5. Router advertisement The router on the link uses the ND protocol to transmit Router Advertisement messages to the system, which contain information on how the autoconfiguration process should proceed. The Router Advertisement messages typically supply a network prefix, which the system will use with its existing interface ID to create a global or unique local unicast address. The messages might also instruct the
system to initiate a stateful autoconfiguration process by contacting a specific DHCPv6 server. If there is no router on the link, as determined by the system’s failure to receive Router Advertisement messages, then the system must attempt to initiate a stateless autoconfiguration process.
6. Global or unique local address configuration Using the information it receives from the router, the system generates a suitable address that is routable, either globally or within the enterprise, and configures the interface to use it. If so instructed, the system might also initiate a stateful autoconfiguration process by contacting the DHCPv6 server specified by the router and obtaining a global or unique local address from that server, along with other configuration settings.
DYNAMIC HOST CONFIGURATION PROTOCOL V6
If you are an enterprise administrator with a multisegment network, it will be necessary to use unique local or global addresses for internetwork communication, so you will need either routers that advertise the appropriate network prefixes or DHCPv6 servers that can supply addresses with the correct prefixes.
The Remote Access role in Windows Server 2012 R2 supports IPv6 routing and advertising, and the DHCP Server role supports IPv6 address allocation.
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