Windows 7 / Networking

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Assigning IPv6 addresses

The processes by which administrators assign IPv6 addresses to network computers are basically 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 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 IPv6 addresses is even more impractical 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 is the same as that for IPv4, except that you open 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 link-local address for each interface by using the fe80::/64 network address and generating an interface ID, either 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 procedure.
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

For the enterprise administrator with a multisegment network, it will be necessary to use unique local or global addresses for internetwork communication, so you will either need 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 supports IPv6 routing and advertising, and the DHCP Server role supports IPv6 address allocation.