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Ethical hacking simplified. IPv6 autoconfiguration (System fundamentals)

Autoconfiguration

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This ease the burden on network administrators. It allows the devices to assign network addresses to themselves automatically with a link-local unicast address. The autoconfiguration is the same with the IPv4 DCHP (dynamic host configuration protocol) they both configure devices/hosts automatically. By default an IPv6 host can configure a link-local address for each interface. Using router discovery, host can learn the address of routers, additional and other configuration settings. The router advertisement message (this is a multicast message the router always send out to help the IPv6 to configure itself) states whether the address is going to be stateful configuration.

NB: autoconfiguration can only be done on interfaces that support multicast addressing. This autoconfiguration is fully described in RFC 2462 IPv6 stateless address autoconfiguration.

Address states

  • Tentative: This is the process of being verified to be a unique address. As we already read in the definition of IP address. IP address can never be duplicated on the same network. If duplication of IP addressing occurs all the two addresses will report IP conflict. So this state make sure there is no IP conflict.
  • Proffered: This the next step after uniqueness verification, the address enters into the preferred step. This step means the address is unique. In this state a host can send and receive message/data. The amount of time a node/host stays in the tentative and preferred states is been defined in the router advertisement.
  • Deprecated: In this state the address is stil valid but its been discouraged to use for new communication. Meaning its preferred time is over. Host/node can still send and receive message/data with same address.
  • Valid: This is the state in which host can send and receive data with the unicast address. The valid states covers the preferred and deprecated state. The valid states time is defined in the router advertisement.
  • Invalid: This is the state after the valid time of an address has expired, a node cannot send or receive data with the IP address.

Types of autoconfiguration

  • Stateless: This configuration solely relies on the router advertisement message. It receives the prefix and require the host not to use stateful address.
  • Stateful: This configuration is based on the use of stateful configuration protocol. DHCPv6. To obtain address and other settings, the host uses stateful configuration when it receives the router advertisement that do not include the prefix, it then requires the host to use the stateful configuration protocol. Hosts uses stateful address when there is no router present.
  • Both: This is based on the router advertisement. The node receives messages which include stateless address prefix but requires the host the use stateful addressing protocols.
NB: link-local addressing is always configured for all systems using the above configuration system.

Autoconfiguration networking device process
  1. A tentative link-local address is derived, using the local link prefix which is FE80::/64 and the 64bit interface ID.
  2. A duplicate check is carried out to make sure the tentative address is unique.
  3. If the step two failed, the address must be configured manually.
  4. If step two is successful, the tentative address is seen as a unique and valid address. The address is then assigned to the interface and the corresponding multicast link-layer address is registered with network.
Autoconfiguration host process

  1. Host send a router request message.
  2. If the host didn't receive router advertisement message, the host uses the stateful configuration protocol (DHCPv6) to obtain address and other settings.
  3. If it receives the router advertisement, the host address will be included in the message.
  4. For each stateless configuration addressing, the prefix is always included.

NB: To make sure there are no duplicate addresses, when a duplicate address is identifies in the tentative state, the address will not be assigned to another device, but when duplicate is not sensed, its automatically assigned.

Reference: technet.microsoft.com
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