Directly Attached Static Routes In directly attached static routes, only the output interface is specified. The...

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Directly Attached Static Routes In directly attached static routes, only the output interface is specified. The destination is assumed to be directly attached to this interface, so the packet destination is used as the next- hop address. This example shows such a definition: ipv6 route 2001: DB8::/32 gigabitethernet 1/0/0 The example specifies that all destinations with address prefix 2001:DB8::/32 are directly reachable through interface GigabitEthernet1/0/0. Directly attached static routes are candidates for insertion in the IPv6 routing table only if they refer to a valid IPv6 interface; that is, an interface that is both up and has IPv6 enabled on it. Recursive Static Routes In a recursive static route, only the next hop is specified. The output interface is derived from the next hop. This example shows such a definition: ipv6 route 2001: DB8::/32 2001: DB8:3000:1 This example specifies that all destinations with address prefix 2001:DB8::/32 are reachable via the host with address 2001:DB8:3000:1. A recursive static route is valid (that is, it is a candidate for insertion in the IPv6 routing table) only when the specified next hop resolves, either directly or indirectly, to a valid IPv6 output interface, provided the route does not self-recurse, and the recursion depth does not exceed the maximum IPv6 forwarding recursion depth. A route self-recurses if it is itself used to resolve its own next hop. For example, suppose we have the following routes in the IPv6 routing table: IPv6 Routing Table 9 entries Codes: C- Connected, L - Local, S - Static, R - RIP, B - BGP Per-user Static route U I1 ISIS L1, I2 - ISIS L2, IA - ISIS interarea 0. OSPF intra, OI - OSPF inter, OE1 - OSPF ext 1, OE2 - 0 2001: DB8::/32 [130/0] via, Serial2/0 B 2001: DB8:3000:0/16 [200/45] Via 2001: DB8: : 0104 R The following examples defines a recursive IPv6 static route: ipv6 route 2001: DB8/32 2001:0BD8:3000:1 This static route will not be inserted into the IPv6 routing table because it is self-recursive. The next hop of the static route, 2001:DB8:3000:1, resolves via the BGP route 2001:DB8:3000:0/16, which is itself a recursive route (that is, it only specifies a next hop). The next hop of the BGP route, 2001:DB8::0104, resolves via the static route. Therefore, the static route would be used to resolve its own next hop. It is not normally useful to manually configure a self-recursive static route, although it is not prohibited. However, a recursive static route that has been inserted in the IPv6 routing table may become self-recursive as a result of some transient change in the network learned through a dynamic routing protocol. If this occurs, the fact that the static route has become self- recursive will be detected and it will be removed from the IPv6 routing table, although not from the configuration. A subsequent network change may cause the static route to no longer be self-recursive, in which case it will be reinserted in the IPv6 routing table. Directly Attached Static Routes In directly attached static routes, only the output interface is specified. The destination is assumed to be directly attached to this interface, so the packet destination is used as the next- hop address. This example shows such a definition: ipv6 route 2001: DB8::/32 gigabitethernet 1/0/0 The example specifies that all destinations with address prefix 2001:DB8::/32 are directly reachable through interface GigabitEthernet1/0/0. Directly attached static routes are candidates for insertion in the IPv6 routing table only if they refer to a valid IPv6 interface; that is, an interface that is both up and has IPv6 enabled on it. Recursive Static Routes In a recursive static route, only the next hop is specified. The output interface is derived from the next hop. This example shows such a definition: ipv6 route 2001: DB8::/32 2001: DB8:3000:1 This example specifies that all destinations with address prefix 2001:DB8::/32 are reachable via the host with address 2001:DB8:3000:1. A recursive static route is valid (that is, it is a candidate for insertion in the IPv6 routing table) only when the specified next hop resolves, either directly or indirectly, to a valid IPv6 output interface, provided the route does not self-recurse, and the recursion depth does not exceed the maximum IPv6 forwarding recursion depth. A route self-recurses if it is itself used to resolve its own next hop. For example, suppose we have the following routes in the IPv6 routing table: IPv6 Routing Table 9 entries Codes: C- Connected, L - Local, S - Static, R - RIP, B - BGP Per-user Static route U I1 ISIS L1, I2 - ISIS L2, IA - ISIS interarea 0. OSPF intra, OI - OSPF inter, OE1 - OSPF ext 1, OE2 - 0 2001: DB8::/32 [130/0] via, Serial2/0 B 2001: DB8:3000:0/16 [200/45] Via 2001: DB8: : 0104 R The following examples defines a recursive IPv6 static route: ipv6 route 2001: DB8/32 2001:0BD8:3000:1 This static route will not be inserted into the IPv6 routing table because it is self-recursive. The next hop of the static route, 2001:DB8:3000:1, resolves via the BGP route 2001:DB8:3000:0/16, which is itself a recursive route (that is, it only specifies a next hop). The next hop of the BGP route, 2001:DB8::0104, resolves via the static route. Therefore, the static route would be used to resolve its own next hop. It is not normally useful to manually configure a self-recursive static route, although it is not prohibited. However, a recursive static route that has been inserted in the IPv6 routing table may become self-recursive as a result of some transient change in the network learned through a dynamic routing protocol. If this occurs, the fact that the static route has become self- recursive will be detected and it will be removed from the IPv6 routing table, although not from the configuration. A subsequent network change may cause the static route to no longer be self-recursive, in which case it will be reinserted in the IPv6 routing table.