Term
| How ofter does OSPF send out routing updates to all its neighbors? |
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Definition
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OSPF (and other link-state routing protocols) generate routing updates only when a change occurs in the network topology.
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Term
| What are 3 different tables that are maintained by OSPF? |
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Definition
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- OSPF neighbor table (or adjacency database) - OSPF topology table ( or topology database) - Routing table ( or forwarding database)
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Term
| What are the 2 different types of areas used in an OSPF heirarchy? |
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Definition
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- Transit area - An area whose primary function is to connect other areas to each other. Generally, end used are not found on a transit area. Area 0 is by definition a transit area - Regular area - An area that connects end users and resources. Regular areas normally do not allow traffic from other areas to use its links to reach other areas.
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Term
| For OSPF, what is the befault behavior for calculating the cost of an interface? |
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Definition
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The default behavior is that the interface cost is calculated based on its configured bandwidth; the higher the bandwidth, the lower the cost.
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Term
| How is the default cost for an OSPF interface calculated? |
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Definition
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100Mbps/(bandwidth in Mbps)
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Term
| What is the default aging timer for each LSA entry? |
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Definition
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The default value for OSPF is 30 minutes.
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Term
| What does an OSPF router do when an LSA timer has expired for a specific neighbor? |
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Definition
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The router that originated the entry sends the LSA, with a higher sequence number, in a link-state update (LSU), to verify that the link is still active.
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Term
| What are the different types of OSPF packets? |
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Definition
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- Type 1 = Hello - Type 2 = Database description (DBD) - Type 3 = Link-state request (LSR) - Type 4 = Link-state update (LSU) - Type 5 = LSAck
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Term
| Describe a type 1 OSPF packet. |
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Definition
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A type 1 OSPF packet is a hello packet. They are used to discover neighbors and build adjancencies between them.
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Term
| Describe a type 2 OSPF packet. |
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Definition
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A type 2 OSPF packet is a database description packet. They are used to check database synchronization between routers.
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Term
| Describe a type 3 OSPF packet. |
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Definition
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A type 3 OSPF packet is a link-state request (LSR) packet. They are used to request specific link-state records from another router.
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Term
| Describe a type 4 OSPF packet. |
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Definition
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A type 4 OSPF packet is a link-state update. They are used to send specifically requested link-state records.
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Term
| Describe type 5 OSPF packets. |
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Definition
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A type 5 OSPF packet is an LSAck. They are used to acknownledge the other packet types.
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Term
| How does a router know that it has formed a neighbor adjacency with another router? |
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Definition
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Bidirectional communication occurs when a router sees itself listed in the hello packet received from the neighbor.
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Term
| What are the default hello and dead intervals on an OSPF router? |
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Definition
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The hello interval is 15 seconds on a multiaccess network. The dead interval is 4 times the hello interval by default.
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Term
| What are the 2 multicast addresses used by OSPF? |
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Definition
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- 224.0.0.5 goes to all OSPF routers - 224.0.0.6 goes to the DR and BDR
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Term
| How often are summaries of individual link-state entries sent to ensure LSDB synchronization? |
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Definition
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Term
| What is the maximum age of each link-state entry in the LSDB? |
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Definition
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Term
| What command specifies the network or interface that will be involved inthe OSPF process? |
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Definition
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network ip-address wildcard-mask area area-id
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Term
| What command directly enabled OSPF on a particular interface? |
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Definition
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ip ospf process-id area area-id [secondary none]
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Term
| What command will display the OSPF routes known on a router? |
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Definition
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Term
| What command displays a detailed list of OSPF neighbors? |
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Definition
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show ip ospf neighbors [type-number] [neighbor-id] [detail]
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Term
| What command displays OSPF-related events, such as adjancencies, flooding information, DR selection, and SPF calculations? |
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Definition
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Term
| What command tracks adjancencies as they go up and down? |
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Definition
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Term
| What does the drother entry mean in the output of a show ip ospf neighbor command? |
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Definition
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The drother entry means that a router other than this neighboring router is the designated router.
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Term
| On what types of interfaces are DR and BDR used? |
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Definition
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DR and BDR are used only on multiaccess interfaces. They are not used on point-to-point interfaces.
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Term
| How is the router ID chosen on an router using OSPF? |
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Definition
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The highest IP address of any active physical interface when OSPF starts is chosen as the router ID. The interface does not have to be part of the OSPF process, but it has to be up.
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Term
| What happens when OSPF is enabled on a router without an "up" interface? |
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Definition
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The router will generate an error indicating that the OSPF process could not start.
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Term
| How do loopback interfaces play a role in choosing a router ID for a router? |
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Definition
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If a loopback interface exist, its IP address will always be preferred as the router ID instead of a physical interface, because a loopback interface never goes down.
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Term
| What command can be used to manually configure the router ID on a router running OSPF? |
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Definition
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