Multiple default routes and multiple prefix routes to a single prefix might be learned through router advertisements. If an adjacent router is on a link onto which z/OS® Communications Server TCP/IP has multiple IPv6 interfaces, multiple routes are learned for each route in the router advertisement from the adjacent router (one route through each interface onto the link). Default routes and indirect routes to a prefix might be learned from the router advertisements that are originated by multiple adjacent routers.
When multiple direct prefix routes to a single prefix are learned, all of the routes are installed in the stack main route table. The subset of the routes that are installed in a stack policy-based route table is controlled by the DynamicRoutingParms parameter on the RouteTable statement for that route table.
When multiple default routes or multiple indirect prefix routes to a single prefix are learned, the stack uses the following information to determine the subset of the routes that are installed in the stack route tables:
The routes with the highest preference value are installed in the route table; however, routes that are learned from routers that are reachable over active interfaces take priority, regardless of preference value.
When multiple default routes or multiple prefix routes to a single prefix are installed in the stack main route table, TCP/IP uses those routes according to the setting of the MULTIPATH parameter on the IPCONFIG6 statement. When multiple default routes or multiple prefix routes to a single prefix are installed in a stack policy-based route table, TCP/IP uses those routes according to the setting of the Multipath6 parameter on the RouteTable statement for that route table.