about ccna exam

about ccna exam.L 10 1 14.4/32 is directly connected, GigabitEthernet0/00 IA 10 1 23.0/24 [110/66] via 10.1.14.1 ,11:04:43, GigabitEthernet0/0This example shows some new code that is particularly relevant to the OSPF protocol. As usual. a single character on the left identifies the source of the route. indicates OSPF. in addition, IOS also records any inter-area routes with IA codes. (This example does not list any intra-area OSPF routes, but these routes ignore IA codes.) Also note that in this example, there are routes on R4 that reach all seven subnets: two connection routes and five inter-area OSPF routes.OSPF Metric (Overhead)Previously, the section "Calculating the Best Route Using SPF" discussed how SPF calculates the metric value for each route and selects the route with the best metric value for each destination subnet. By modifying the OSPF interface overhead of any interface, OSPF routers can influence this selection.Cisco routers allow OSPF interface overhead to be changed in two different ways. One straightforward way is to set the overhead directly, using the interface subcommand:ip ospfcostx0 The other way is to let the IOS choose the default overhead based on a formula, but to modify the input to the formula. The second approach requires more thought and attention and will be highlighted in the next topic. Setting overhead based on interface bandwidthThe default OSPF overhead values can actually cause a bit of confusion for several reasons. So, to sort out some of the possible confusion, this section starts with some examples. First, IOS uses the following formula to select the OSPF overhead for an interface.IOS puts the interface's bandwidth in the denominator and the settable OSPF value (called the reference bandwidth) in the numerator. The higher the interface bandwidth in this formula, the better. The higher (faster) the interface bandwidth, the lower the calculated OSPF protocol overhead of the interface. The lower the interface overhead, the lower the metric of routes using that interface, and the more likely the SPF will choose to use that interface in its routes. Now, take some examples. Assume that the default reference bandwidth is set to 100 000 kbit/so Assume that the show interfaces command as182 Chapter 8 Implementing IPv4 OSPF Output shown, the default bandwidth values for the serial interface, the Ethernet interface, and the Fast Ethernet interface are 1544 kbit/s, 100008.3 Exam Prep 183 kbit/s (i.e., 10 Mbit/s) and 100 000 kbit/s (i.e., 100 Mbit/s) o Table 8-7 shows the results of IOS calculations of OSPF overhead for some example interfaces. Table 8-7 Example of OSPF Overhead Calculation Using Default Bandwidth SettingsConnect O Connect O Default Bandwidth (kbit/s) Formula (kbit/s) OSPF Overhead