| 9.1 |  | Examining the Routing Table |
| 9.1.2 |  | Determining the gateway of last resort |

| It is not feasible, or even desirable, for a router to maintain routes to every possible destination. Instead, routers keep a default route, or a gateway of last resort. Default routes are used when the router is unable to match a destination network with a more specific entry in the routing table. The router uses this default route to reach the gateway of last resort in an effort to forward the packet. A key scalability feature is that default routes keep routing tables as lean as possible. They make it possible for routers to forward packets destined to any Internet host without having to maintain a table entry for every Internet network. Default routes can be statically entered by an administrator or dynamically learned using a routing protocol. Default routing begins with the administrator. Before routers can dynamically exchange information, an administrator must configure at least one router with a default route. Depending on the desired results, an administrator can use either of the following commands to statically configure a default route: ip default-network or ip route 0.0.0.0 0.0.0.0 The ip default-network command establishes a default route in networks using dynamic routing protocols. The global command ip default-network 192.168.17.0 defines the Class C network 192.168.17.0 as the destination path for packets that have no routing table entries. For every network configured with ip default-network, if a router has a route to the network, that route is flagged as a candidate for the default route. Creating an ip route to 0.0.0.0/0 is another way to configure a default route. Router(config)#ip route 0.0.0.0 0.0.0.0 [next-hop-ip-address | exit-interface] After configuring a default route or default network, the command show ip route will show the following: Gateway of last resort is 172.16.1.2 to network 0.0.0.0
| Lab Activity Lab Exercise: Gateway of Last Resort In this lab, students will configure RIP routing and default routes (gateways) on the routers.
| Web Links ip default-network Command http://www.cisco.com/en/US/products/sw/ iosswrel/ps1835/ products_command_reference_ chapter09186a008007ff84.html#1050101