Foundation Summary

     

The "Foundation Summary" section of each chapter lists the most important facts from the chapter. Although this section does not list every fact from the chapter that will be on your exam, a well-prepared candidate should, at a minimum, know all the details in each "Foundation Summary" before going to take the exam.

Table 9-6 shows the codes used in the routing table.

Table 9-6. OSPF Routing Table Codes and Associated LSAs

LSA Type	Routing Table Entry	Description
1 Router Link	O	This is generated by the router, listing all the links to which it is connected, their status, and their cost. It is propagated within the area.
2 Network Link	O	This is generated by the designated router on a multiaccess network to the area.
3 or 4 Summary Link (between areas)	OIA	LSA Type 3 includes the networks or subnets within an area that may have been summarized and that are sent into the backbone and between ABRs. LSA Type 4 is information sent to the ASBR from the ABR. These routes are not sent into totally stubby areas.
5 Summary Link/External Link (between autonomous systems)	OE1 or OE2	The routes in this LSA are external to the autonomous system. They can be configured to have one of two values. E1 will include the internal cost to the ASBR added to the external cost reported by the ASBR. E2 does not compute the internal costit just reports the external cost to the remote destination.

Table 9-7 contains a list of the commands explained in this chapter. This list is not intended to teach the use of the commands, but to remind you of the options available.

Table 9-7. OSPF Command Summary

Command	Description
network network-number wildcard-mask area area-id	This command identifies the interfaces that are running OSPF and places them in the appropriate area.
summary-address address mask [ not-advertise ][ tag tag ]	This command consolidates routes into a summary route before injecting them into the external world. Remember that the mask is the subnet, not the wildcard mask. The option to not advertise will suppress routes that match the mask. The tag option is for use with redistribution. The summary-address command is also used to summarize external routes into OSPF, particularly during redistribution.
area area-id range address mask	This command is used to summarize the routes at the ABR before injecting them into another area.
no area area-id range address mask	This command disables the configured summarization at the ABR.
area area-id stub	This command turns the area into a stub area. This command must be configured on every router in the area.
area area-id stub no-summary	This command turns an area into a totally stubby area.
area area-id default-cost cost	This configures the cost for the default summary route used for a stub or totally stub area. The default is 1.
area area-id virtual-link router-id	This command creates a virtual link.
show ip ospf border-routers	This command lists the ABR and ASBR routers in the autonomous system.
show ip ospf virtual-links	This command shows the virtual links and the current parameters.
show ip ospf database	This command shows the OSPF database and the information taken from the LSAs that have been received.
debug ip ospf events	Displays information on OSPF- related events, such as adjacencies, flooding information, designated router selection, and SPF calculation. It verifies the value of the Hello timers on the interface.
debug ip ospf adjacencies	Displays information on the state of the adjacencies whenever there is a change of state.
log- adjacency -changes	Entered into the configuration file, beneath the routing process. This sends syslog messages in the event of a change in adjacencies. Fewer network resources are required in comparison to the debug commands.