Type 8
Type 8 is a specialized LSA that is used in internetworking OSPF and Border Gateway Protocol (BGP).

Types 9, 10, and 11
The opaque LSAs, types 9, 10, and 11, are designated for future upgrades to OSPF for application-specific purposes. For example, Cisco Systems uses opaque LSAs for Multiprotocol Label Switching (MPLS) with OSPF. Opaque LSAs are distributed using standard LSDB flooding mechanisms. Each type has a different flooding scope. Interactive Media Activity Drag and Drop: OSPF LSA Types Upon completion of this activity, the student will be able to identify the different OSPF LSA types.

Content 3.6 Multiarea OSPF Operation 3.6.4 Interpreting the OSPF LSDB and Routing Table Figure displays a partial output of the show ip ospf database command used to get information about an OSPF LSDB. The router link-states are type 1 LSAs, the net link-states are type 2, and the summary net link-states are type 3. The database columns contain the following information:

Link ID: Identifies each LSA.
ADV Router: Advertising router; the source router of the LSA.
Age: The maximum age counter in seconds. The maximum age is 1 hour, or 3,600 seconds.
Seq#: Sequence number of the LSA. This number begins at 0x80000001 and increases with each update of the LSA.
Checksum: Checksum of the individual LSA to ensure reliable receipt of that LSA.
Link count: Total number of directly attached links, used only on router LSAs. The link count includes all point-to-point, transit, and stub links. Each point-to-point serial link counts as two; all other links count as one, including Ethernet links.

Figure displays the complete output of the show ip ospf database command.

Content 3.6 Multiarea OSPF Operation 3.6.5 Interpreting the Routing Table Figure defines each of the routing table descriptors for OSPF. Router and network LSAs describe the details within an area. The routing table reflects this link-state information with a designation of O, meaning that the route is intra-area. When an ABR receives summary LSAs, it adds them to its LSDB and regenerates them into the local area. When an ABR receives external LSAs, it adds them to its LSDB and floods them into the area. The internal routers then assimilate the information into their databases. Summary LSAs appear in the routing table as IA (interarea routes). External LSAs appear in the routing table marked as external type 1 (E1) or external type 2 (E2) routes. The SPF algorithm is then run against the LSDB to build the SPF tree. The SPF tree is used to determine the best paths. The order in which the best paths are calculated is as follows:

All routers calculate the best paths to destinations within their area (intra-area) and add these entries to the routing table. These are the type 1 and type 2 LSAs, which are noted in the routing table with a routing designator of O.
All routers calculate the best paths to the other areas within the internetwork. These best paths are the interarea route entries, or type 3 and type 4 LSAs, and are noted with a routing designator of O IA.
All routers (except those that are in a form of stub area) calculate the best paths to the external autonomous system (type 5) destinations. These are noted with either an O E1 or an O E2 route designator, depending on the configuration.

At this point, a router can communicate with any network within or outside the OSPF autonomous system.

Content 3.6 Multiarea OSPF Operation 3.6.6 Calculating Costs for E1 and E2 Routes The cost of an external route varies depending on the external type configured on the ASBR. The following external packet types can be configured, as shown in Figure :

E1: Type O E1 external routes calculate the cost by adding the external cost to the internal cost of each link that the packet crosses. Use this type when there are multiple ASBRs advertising an external route to the same autonomous system to avoid suboptimal routing.
E2 (default): The external cost of O E2 packet routes is just the external cost. Use this type if only one ASBR is advertising an external route to the AS.

The show ip route command example in Figure depicts both external type routes (O E2) and interarea (O IA) routes. The last entry (O E2) is an external route (from the ASBR, via the ABR). The two numbers in brackets, [110/50], are the administrative distance and the total cost of the route to a specific destination network. In this case, the administrative distance is set to a default of 110 for all OSPF routes, and the total cost of the route has been calculated as 50.

Content 3.6 Multiarea OSPF Operation 3.6.7 Configuring OSPF LSDB Overload Protection If other routers are misconfigured, a large number of LSAs might get generated. For example, a redistribution of a large number of prefixes can cause excessive LSAs to be generated, which can drain local CPU and memory resources on an OSPF router. You can configure OSPF LSDB overload protection with Cisco IOS Release 12.3(7)T and later (and some specific earlier releases) by using the max-lsa command. Figure lists the parameters of this command. When this feature is enabled, the router keeps count of the number of received (non-self-generated) LSAs that it keeps in its LSDB. An error message is logged when the configured threshold number is reached, and a notification is sent when the threshold number is exceeded. If the LSA count still exceeds the threshold after one minute, the OSPF process takes down all adjacencies and clears the OSPF database. This is called the ignore state. In the ignore state, interfaces that belong to that OSPF process do not send or received OSPF packets. The OSPF process remains in the ignore state for the time that is defined by the ignore-time parameter. The ignore-time parameter defines the maximum number of times that the OSPF process can consecutively enter the ignore state before remaining permanently down and requiring manual intervention. If the OSPF process remains normal for the time that is defined by the reset-time parameter, the ignore state counter is reset to 0.

Content 3.6 Multiarea OSPF Operation 3.6.8 Changing the Cost Metric By default, OSPF calculates the OSPF metric for an interface according to the inverse bandwidth of the interface. In general, the cost in Cisco routers is calculated using the formula (100 Mbps) / (bandwidth in Mbps). For example, a 64-kbps link gets a metric of 1562, a T1 link gets a metric of 64, and a Fast Ethernet link gets a metric of 1.The cost for interfaces with a bandwidth equal or larger than 108 bps is normalized to 1. If you have faster interfaces, you may want to recalibrate the cost of 1 to a higher bandwidth. Figure displays various mediums with their associated metric cost. When you are using the bandwidth of the interface to determine OSPF cost, always remember to use the bandwidth value interface command to accurately define the bandwidth of the interface (in kbps). If interfaces that are faster than 100 Mbps are being used, you should use the auto-cost reference-bandwidth ref-bw command on all routers in the network to ensure accurate route calculations. The ref-bw is a reference bandwidth in megabits per second, and ranges from 1 to 4,294,967. You must apply the same reference bandwidth to all OSPF routers in the domain to get the desired results. To override the default cost, manually define the cost using the ip ospf cost interface-cost command on a per-interface basis. The cost value is an integer from 1 to 65,535. The lower the number, the better the link and more strongly preferred.

Content 3.7 Stub, Totally Stubby, and Not-So-Stubby Areas 3.7.1 Configuring OSPF Area Types