A router advertisement can contain route information options. Each route information option contains an IPv6 prefix and information that indicates whether the prefix can be reached by way of the router that originated the router advertisement.

If the option contains a nonzero Route Lifetime value, which indicates that the prefix can be reached by way of the router, the following actions occur:

• If the dynamic prefix route that is to be added as the result of the received router advertisement has already been added by a previous advertisement, the length of time that that route remains valid is reset using the Route Lifetime value from the route information option.
• If no route for the prefix exists, or if a route exists that has equal or lower precedence than the route that is to be added, then a dynamic prefix route is added as the result of the received router advertisement. If a route with lower precedence exists, it is removed but is reinstated later if the dynamic prefix route that is added is removed. The following types of routes have equal or lower precedence:
  • A router advertisement route that has a reachable gateway, an active interface, and the same preference value as the preference value that was received in the route information option; this type of route has equal precedence.
  • A router advertisement route that has an unreachable gateway, an inactive interface, or a lower preference value than the preference value that was received in the route information option; this type of route has lower precedence
  • A replaceable static route; this type of route has lower precedence

  The dynamic prefix route that is added has the following characteristics:

  • The next-hop address is the source address of the advertisement.
  • The interface is the interface on which the advertisement was received
  • The metric is set according to the preference value that was received in the Route Information option. The setting 1 indicates high preference, 2 indicates medium preference, and 3 indicates low preference.
  • The length of time that the route remains valid is equal to the Route Lifetime value set on the option.
• If a route for the prefix exists that has a higher precedence than the route that is to be added, a dynamic prefix route is not added as the result of the received router advertisement. A dynamic prefix route is added later if the route with the higher precedence is removed. The following types of routes have higher precedence:
  • A router advertisement route that has a reachable gateway, an active interface, and a higher preference value than the preference value that was received in the route information option
  • A non-replaceable static route
  • An IPv6 OSPF route
  • An IPv6 RIP route

If the option contains the value 0 for the Route Lifetime value, which indicates that the prefix can no longer be reached by way of the router, the following action occurs:

• If an IPv6 dynamic prefix route exists that has the source of the advertisement as its next hop and the receiving interface as its interface, and that route was added as the result of a received router advertisement (but not, for example, as the result of IPv6 OSPF or IPv6 RIP), that route is deleted.