dicates that the router should not be used as a default router) [41]. Reachable Time: The time other nodes can be assumed to stay reachable after positive reachable confirmation. A value of zero means unspecified by the router sending the Router Advertisement [41]. Retransmit Timer: The retransmit time between consecutive Neighbor Solicitation messages. A value of zero means unspecified, by the router sending the Router Advertisement [41]. Additionally, a number of options have also been standardized for Router Advertisements. Some of these are used only in specific circumstances, such as those defined for use with Mobile IPv6 (see Section 3.7.2) or Secure Neighbor Discovery (see Section 3.4.9). Source Link-Layer address: The link-layer address of the router that sent the Router Advertisement [41]. Link MTU: The MTU of the attached link (see Section 3.2.3) [41]. Prefix information: List of prefixes that nodes may possibly use for on-link determination (if 'L'-flag is set), possibly for SLAAC (if 'A'-flag is set) [41], and in the case of Mobile IPv6, may additionally communicate the complete IPv6 address of the sending router [35]. DNS configuration: List of recursive DNS server addresses and DNS search lists that a node can utilize for DNS queries [69]. Route Information option: Information about more specific routes and their preferences on the router listed within the option [68]. This information is used for address and router selection purposes. IPv6 Router Advertisement flags option: This option extends the number of flag bits that can be carried in Router Advertisement [70]. Advertisement interval: Mobile IPv6 uses this option to communicate to nodes the send interval of unsolicited Router Advertisements [35]. This information can be used for movement detection. Home Agent information: Mobile IPv6 uses this option to communicate preferences between Home Agents and the time that a Home Agent may be used. CGA: SEND uses the CGA option to make it possible for a node to verify a router's cryptographically gener