Windows Server 2008 and Windows Vista include a DHCPv6-capable DHCP client that will perform stateful address autoconfiguration with a DHCPv6 server. Windows Server 2008 includes a DHCPv6-capable DHCP server.
A host (DHCP Client) can configure itself with an IPv6 address to be used on the network. Address
configuration can be performed in a stateful or a stateless mode. A host can use both stateless and stateful address configuration completely independent of each other. The router advertisement messages with the appropriate flags set would indicate the precise method to be used. However the host (DHCP Client) can also be configured by manual means. The latter is seldom an occurrence in a well managed network.
The stateless mechanism allows a host to generate its own addresses using a combination of locally available information and information advertised by routers. The stateless approach is used when a site is not particularly concerned with the exact addresses hosts use, so long as they are unique and properly routable.
Stateless Address Autoconfiguration is used to configure both link-local addresses and additional non-link-local addresses by exchanging Router Solicitation and Router Advertisement messages with neighboring routers.
Following are the two approaches with which IPv6 node can configure its address in a stateless fashion:
· Using automatic address configuration with prefix discovery: This is based on RFC2462. If the ‘autonomous’ flag of a Prefix Information Option contained in a router advertisement is set, the IPv6 host may automatically generate its global IPv6 address by appending its 64-bit interface identifier to the prefix contained in the router advertisement.
· Stateless DHCPv6: This is not mentioned as an option given in router advertisements [RFC2461].
In the stateful address auto-configuration model, hosts obtain interface addresses and/or configuration information and parameters from a server. The stateful approach is used when a site requires tighter control over exact address assignments.
Stateful Address Autoconfiguration is used to configure non-link-local addresses through the use of a configuration protocol such as DHCP.
As far as the IPv6 host is concerned, using stateful DHCPv6 is little different to using stateless
DHCPv6 as the observed request/response times should be the same in most cases. However, it is possible that the extra overhead of reading and writing state to memory inside the DHCPv6 server may lead to a small increase in latency when compared to its stateless equivalent. This may be important for the configuration time of mobile nodes, which must perform address configuration when moving into a new network.
Delegating a prefix to an entire site is commonly a stateful operation, as the service provider routing scheme must always know where a site topologically resides, a packet targeted to a site must be routed back to the site. DHCPv6 server typically stores the DHCPv6 delegated prefix.
An IPv6 host performs stateless address autoconfiguration automatically and uses a configuration protocol such as DHCPv6 based on the following flags in the Router Advertisement message sent by a neighboring router:
Managed Address Configuration Flag, which is also known as the M flag. When set to 1, this flag instructs the host to use a configuration protocol to obtain stateful addresses.
Other Stateful Configuration Flag , which is also known as the O flag. When set to 1, this flag instructs the host to use a configuration protocol to obtain other configuration settings.
Combining the values of the M and O flags can yield the following:
Both M and O Flags are Set to 0. This combination corresponds to a network without a DHCPv6 infrastructure. Hosts use router advertisements for non-link-local addresses and other methods (such as manual configuration) to configure other settings.
Both M and O Flags are Set to 1. DHCPv6 is used for both addresses and other configuration settings. This combination is known as DHCPv6 stateful, in which DHCPv6 is assigning stateful addresses to IPv6 hosts.
The M Flag is Set to 0 and the O Flag is Set to 1. DHCPv6 is not used to assign addresses, only to assign other configuration settings. Neighboring routers are configured to advertise non-link-local address prefixes from which IPv6 hosts derive stateless addresses. This combination is known as
DHCPv6 stateless: DHCPv6 is not assigning stateful addresses to IPv6 hosts, but stateless configuration settings.
The M Flag is Set to 1 and the O Flag is Set to 0. In this combination, DHCPv6 is used for address configuration but not for other settings. Because IPv6 hosts typically need to be configured with other settings, such as the IPv6 addresses of Domain Name System (DNS) servers, this is an unlikely combination.
Like DHCP for IPv4, the components of a DHCPv6 infrastructure consist of DHCPv6 clients that request configuration, DHCPv6 servers that provide configuration, and DHCPv6 relay agents that convey messages between clients and servers when clients are on subnets that do not have a DHCPv6 server.
In the installation of DHCP Server using the role installation in the Server Manager, following is specific details with regard to IPv6 configuration during the role installation:
In case, “Enable DHCPv6 stateless mode for this server” option was selected during role installation
It would have asked for Parent Domain and IPv6 DNS Server (primary – mandatory and secondary – optional) information.
Therefore, in the post installation phase following Server Options under IPv6 node in the DHCP MMC will be with the configured values:
- 00023 DNS Recursive Name Server IPv6 Address List
- 00024 Domain Search List
In case, “Disable DHCPv6 stateless mode for this server” option was selected during role installation
It would NOT have asked for Parent Domain and IPv6 DNS Server (primary – mandatory and secondary – optional) information at all as that page in wizard will be hidden.
Therefore, in the post installation phase if you do not see Server Options under IPv6 node in the DHCP MMC.
In this case, this means the DHCPv6 Stateless mode is NOT configured on the DHCP Server.
However, in this stage if Admin wants to configure DHCP Server as stateless mode, he needs to configure the above mentioned Server Options explicitly.
Following are the options that can be configured at the IPv6 Scope Level and/or the IPv6 Server Level
00021 SIP Server Domain Name List
This option specifies a list of the domain names of the SIP outbound proxy servers for the client to use.
00022 SIP Servers IPv6 Address List
This option specifies a list of IPv6 addresses indicating SIP outbound proxy servers available to the client. Servers MUST be listed in order of preference.
00023 DNS Recursive Name Server IPv6 Address
The DNS Recursive Name Server option carries a list of IPv6 addresses of RDNSSes to which the host may send DNS queries. The DNS servers are listed in the order of preference for use by the DNS resolver on the host.
00024 Domain Search List
The Domain Search List option specifies the domain search list the client is to use when resolving hostnames with DNS. This option does not apply to other name resolution mechanisms.
00027 NIS IPv6 Address List
This option specifies a list of IPv6 addresses indicating Network Information Services (NIS) Servers available to the client. Clients MUST treat the list of NIS servers as an ordered list. The server MAY list the NIS servers in the order of preference.
00028 NIS + IPv6 Address List
This option specifies a list of IPv6 addresses indicating Network Information Services v2 (NIS +) Servers available to the client. Clients MUST treat the list of NIS+ servers as an ordered list. The server MAY list the NIS+ servers in the order of preference.
00029 NIS Domain List
The Network Information Service (NIS) Domain Name List is used by the server to convey client's list of NIS Domain Name info to the client.
00030 NIS + Domain Name List
The Network Information Service v2 (NIS+) Domain Name List is used by the server to convey client's list of NIS+ Domain Name info to the client.
00031 SNTP Servers IPv6 Address List
Simple Network Time Protocol (SNTP) servers option provides a list of one or more IPv6 addresses of SNTP  servers available to the client for synchronization.