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cisco ccda dumps.19.3 Configuring OSPFThe configuration of OSPF is slightly different from RIP. To configure OSPF, use the following syntax.Router(config)# router ospf process_IDRouter(config-router)# network IP_address wi1dcard_mask area area_#processJDH is locally meaningful and is used to distinguish between different OSPF processes running on the same router and can be any number from 1.65535. The router may be a border router between two OSPF autonomous systems and to distinguish them on the router. a unique process ID needs to be assigned to them. note that the process IDs need not be the same for different routers and the process IDs have nothing to do with the autonomous system number. On routing devices connected to different OSPF networks, different process numbers need to be used: for each OSPF network, a locally unique process number needs to be used. Each OSPF process has its own OSPF database, identified by a process ID. How to configure two OSPF processes on the same router is beyond the scope of this book.When configuring an OSPF routing process, you must specify a process ID (identifier), which uniquely identifies an instance of the OSPF database on the router, but is only locally meaningful: the process ID does not have to be the same across the routers of the AS. The process ID can be any number from 1.65535. Use a different process number to identify the different OSPF networks to which the routing device is connected. The command network 0.0.0.0 255.255.255.255.255 area 0 adds all interfaces to area 0. each OSPF has its own OSPF database identified by the process ID.To add an interface to an OSPF area, use the command networko As you can see from the previous code listing, the syntax of this command is different than when configuring RIP. When configuring RIP, only the classified network number is specified in this command; when configuring OSPF, you can be very specific about which interfaces are to be added to the zone in this command: specify the IP address (or network number) and the wildcard mask. A wildcard mask differs from a subnet mask in that it tells the router which part of the address it should care about, i.e., which part must be the same. Wildcard masks are also used for access control lists, which are discussed in detail in Chapter 21.Chapter 19 OSPF Routing 505Wildcard masks are 32 bits long, where a bit of 0 must be the same and a bit of 1 indicates that it does not matter. In effect, a wildcard mask is an inverted subnet mask-turning a 0 into a 1 and a 1 into a 0. Use the wildcard mask to be very specific about which interfaces you want to add to the area. The last part of this command tells the router which zone to add the interface to.Unlike in RIP, in OSPF, you can specify the IP address and the wildcard mask-inverted subnet mask-in the command network, and you must also specify the area to which the interface belongs: network network_# wildcardjnask area areajo a way to convert the When converting a subnet mask to a wildcard mask, the trick is to subtract the subnet mask from 255.255.255.255 to get the corresponding wildcard mask. For more details and examples of how to do this conversion, see Chapter 21. You must be able to determine, based on the wildcard mask in the OSPF command network, which interfaces the command specifies QThe following are some examples to illustrate how wildcard masks work; these codes are for the router shown in Figure 19.4. Router(config)# router ospf 1 Router(config-router)# network 10.1.1.1 0.0.0.0 area 0 Router(config-router)# network 10.1.2.1 0.0.0.0 area 0 Router (config-router)# network 172.16.1.1 0.0.0.0 area Router(config-router)# network 172.16.2.1 0.0.0.0 area