Default routes are learned from both methods if adjacent routers are advertising themselves as default routers using both IPv6 OSPF or IPv6 RIP and router discovery. When this situation occurs, the default routes learned from IPv6 OSPF or IPv6 RIP take precedence and generate the default routes in the TCPIP stack's IPv6 route table. Any default routes learned from router discovery are ignored as long as the default routes learned from IPv6 OSPF or IPv6 RIP exist.

Prefix routes are learned from both router discovery and OMPROUTE under each of the following conditions:

• A router is advertising by way of router discovery that the prefix is on-link and the prefix is also manually configured to OMPROUTE using the Prefix keyword on an IPv6_Interface, IPv6_OSPF_Interface, or IPv6_RIP_Interface configuration statement.
  Guideline: Use the Prefix keyword only when the prefix is not learned dynamically (using router discovery or a dynamic routing protocol).

  For example, if there is a need to supplement the list of prefixes being advertised as on-link by the routers. If the same prefix is configured using the Prefix keyword and learned from router discovery, the route in the TCPIP stack's route table is the route added by OMPROUTE as a result of the Prefix keyword. Any route for the same prefix that is learned from router discovery is ignored as long as the OMPROUTE route exists.

  Restriction: Prefixes learned from only OMPROUTE are not used for address autoconfiguration. If a prefix is learned from both OMPROUTE and router discovery, it can still be used for autoconfiguration even though the route learned from OMPROUTE is the one in the TCPIP stack route table.
• A router is advertising by way of router discovery that either the prefix is on-link or the prefix can be reached by way of an adjacent router, and a router is also advertising by way of IPv6 OSPF that the prefix is on-link.

  In this case, the route in the TCPIP stack route table is the route added by OMPROUTE as a result of the information received by way of IPv6 OSPF. Any route for the same prefix that is learned from router discovery is ignored as long as the OMPROUTE route exists. As in the previous condition, an on-link prefix that is learned from router discovery can still be used for address autoconfiguration.

• A router is advertising by way of router discovery that the prefix is on-link and it is also learned, by way of IPv6 OSPF or IPv6 RIP, that the prefix can be reached by way of an adjacent router.

  In this case, the route in the TCPIP stack route table is the route added as the result of router discovery. This occurs because the router discovery information indicates that the prefix resides on a directly attached link, while the IPv6 OSPF or IPv6 RIP information indicates that the prefix can be reached indirectly, by way of the router from which the IPv6 OSPF or IPv6 RIP information was received. Any route for the prefix that is learned from IPv6 OSPF or IPv6 RIP is ignored as long as the router discovery route exists.

• Router discovery advertisements are received that indicate that the prefix can be reached by way of an adjacent router. In addition, IPv6 OSPF or IPv6 RIP advertisements are received that indicate that the prefix can be reached by way of an adjacent router.

  In this case, the route in the TCPIP stack route table is the route that was added by OMPROUTE as a result of the information that was received by way of IPv6 OSPF or IPv6 RIP. Any route for the same prefix that is learned from router discovery is ignored as long as the OMPROUTE route exists.