Module 1-2 Exam

Match the description to the term. (Not all options are used.)

*adjacency database- This is where the details of the neighboring routers can be found. *Shortest Path First- This is the algorithm used by OSPF *single-area OSPF- All the routers are in the backbone area *link-state database- this is where you can find the topology table. ****Explanation: DUAL is the algorithm used by EIGRP. In multiarea OSPF, OSPF is implemented using multiple areas, and all of them must be connected to the backbone area.

An administrator is configuring single-area OSPF on a router. One of the networks that must be advertised is 192.168.223.0 255.255.254.0. What wildcard mask would the administrator use in the OSPF network statement?

-0.0.1.255

By default, what is the OSPF cost for any link with a bandwidth of 100 Mb/s or greater?

-1 ***Explanation: OSPF uses the formula: Cost = 100,000,000 / bandwidth. Because OSPF will only use integers as cost, any bandwidth of 100 Mb/s or greater will all equal a cost of 1.

What is the default router priority value for all Cisco OSPF routers?

-1 ***Explanation: The router priority value is used in a DR/BDR election. The default priority for all OSPF routers is 1 but it can be manually altered to any value 0 to 255.

Refer to the exhibit. If no router ID was manually configured, what would router Branch1 use as its OSPF router ID?

-192.168.1.100 -image needed

Refer to the exhibit. What is the OSPF cost to reach the router A LAN 172.16.1.0/24 from B?

-65 ***Explanation: The formula used to calculate the OSPF cost is as follows: Cost = reference bandwidth / interface bandwidth The default reference bandwidth is 10^8 (100,000,000); therefore, the formula is Cost = 100,000,000 bps / interface bandwidth in bps Thus the cost to reach the A LAN 172.16.1.0/24 from B is as follows: Serial link (1544 Kbps) from B to A cost => 100,000,000 / 1,544,000 = 64 Gigabit Ethernet link on A cost => 100,000,000 / 1,000,000,000 = 1 Total cost to reach 172.16.1.0/24 = 64 + 1 = 65

Open the PT Activity. Perform the tasks in the activity instructions and then answer the question. -Examine the router configuration and state of OSPF on the network. Which task has to be performed on Router1 for it to establish an OSPF adjacency with Router2? Which task has to be performed on Router 1 for it to establish an OSPF adjacency with Router 2?

-Change the subnet mask of interface FastEthernet 0/0 to 255.255.255.0. ***Explanation: Each interface on the link connecting the OSPF routers must be in the same subnet for an adjacency to be established. The IP address subnet mask on FastEthernet interface 0/0 must be changed to 255.255.255.0. The FastEthernet interface 0/0 is not passive. The 10.0.1.0/24 network is only connected to Router2 so should not be advertised by Router1. The clear ip ospf process command will start the OPSF process on Router1 but will not cause an adjacency to be established if the subnet mask mismatch on the connecting interfaces still exists.

What is the recommended Cisco best practice for configuring an OSPF-enabled router so that each router can be easily identified when troubleshooting routing issues?

-Configure a value using the router-id command. ***Explanation: A Cisco router is assigned a router ID to uniquely identify it. It can be automatically assigned and take the value of the highest configured IP address on any interface, the value of a specifically-configured loopback address, or the value assigned (which is in the exact form of an IP address) using the router-id command. Cisco recommends using the router-id command.

After modifying the router ID on an OSPF router, what is the preferred method to make the new router ID effective?

-HQ# clear ip ospf process ***Explanation: To modify a router-id on an OSPF-enabled router, it is necessary to reset the OSPF routing process by entering either the clear ip ospf process command or the reloadcommand.

Which three OSPF states are involved when two routers are forming an adjacency? (Choose three.)

-Init -Two-way -Down ***Explanation: OSPF operation progresses through 7 states for establishing neighboring router adjacency, exchanging routing information, calculating the best routes, and reaching convergence. The Down, Init, and Two-way states are involved in the phase of neighboring router adjacency establishment.

Refer to the exhibit. A network administrator has configured OSPFv2 on the two Cisco routers but PC1 is unable to connect to PC2. What is the most likely problem?

-Interface Fa0/0 has not been activated for OSPFv2 on router R2. ***Explanation: If a LAN network is not advertised using OSPFv2, a remote network will not be reachable. The output displays a successful neighbor adjacency between router R1 and R2 on the interface S0/0 of both routers.

Which three statements describe features of the OSPF topology table? (Choose three.)

-It is a link-state database that represents the network topology. -When converged, all routers in an area have identical topology tables. -The table can be viewed via the show ip ospf database command. ***Explanation: The topology table on an OSPF router is a link-state database (LSDB) that lists information about all other routers in the network, and represents the network topology. All routers within an area have identical link-state databases, and the table can be viewed using the show ip ospf database command. The EIGRP topology table contains feasible successor routes. This concept is not used by OSPF. The SPF algorithm uses the LSDB to produce the unique routing table for each router which contains the lowest cost route entries for known networks.

In an OSPFv2 configuration, what is the effect of entering the command network 192.168.1.1 0.0.0.0 area 0 ?

-It tells the router which interface to turn on for the OSPF routing process. ***Explanation: Entering the command network 192.168.1.1 0.0.0.0 area 0 will turn on only the interface with that IP address for OSPF routing. It does not change the router ID. Instead, OSPF will use the network that is configured on that interface.

Which OPSF packet contains the different types of link-state advertisements?

-LSU

Refer to the exhibit. On which router or routers would a default route be statically configured in a corporate environment that uses single area OSPF as the routing protocol?

-R0-A ***Explanation: The default route is applied to the router that connects to the Internet, or R0-A. R0-A then distributes that default route using the OSPF routing protocol.

Refer to the exhibit. Which command did an administrator issue to produce this output? Serial0/0/1 is up, line protocol is up Internet address 172.16.30.1/30, Area 0, Attached via Network Statement Process ID 10, Router ID 2.2.2.2, Network type POINT_TO_POINT, Cost: 64 Topology-MTID Cost Disabled Shutdown Topology Name 0 64 no no Base Transmit Delay 1 sec, state POINT_TO_POINT Time intervals configured, Hello 5, Dead 20, Wait 20, Retransmit 5 oob-resync timeout 40 Hello due in 00:00:02 Supports Link-local Signaling (LLS) Cisco NSF helper support enabled IETF NSF helper support enabled Index 2/2, flood queue length 0 Next 0x0(0)/ 0x0(0) Last flood scan length is 1, maximum 1 Last flood scan time is 0 msec, maximum is 0 msec Neighbor Count is 1, Adjacent neighbor is count is 1 Adjacent with neighbor 1.1.1.1 Suppress hello 0 for neighbor(s) Message digest authentication enabled Youngest key id is 1 R1#

-R1# show ip ospf interface serial0/0/1

Refer to the exhibit. Which three statements describe the results of the OSPF election process of the topology that is shown in the exhibit? (Choose three.)

-R3 will be elected BDR. -The R4 router ID is 172.16.1.1. -R2 will be elected DR. *image needed ***Explanation: R2 will be elected DR because it has the highest priority of 255, all of the others have a priority of 1. R3 will be elected BDR because it has the numerically highest router-ID of 192.168.1.4. The R4 router-ID is 172.16.1.1 because it is the IPv4 address attached to the loopback 0 interface.

21. Refer to the exhibit. If the switch reboots and all routers have to re-establish OSPF adjacencies, which routers will become the new DR and BDR?

-Router R4 will become the DR and router R1 will become the BDR. *image needed ***Explanation: OSPF elections of a DR are based on the following in order of precedence: -highest pritority from 1 -255 (0 = never a DR) -highest router ID -highest IP address of a loopback or active interface in the absence of a manually configured router ID. Loopback IP addresses take higher precedence than other interfaces. In this case routers R4 and R1 have the highest router priority. Between the two, R3 has the higher router ID. Therefore, R4 will become the DR and R1 will become the BDR.

Refer to the exhibit. A network administrator has configured the OSPF timers to the values that are shown in the graphic. What is the result of having those manually configured timers?

-The R1 dead timer expires between hello packets from R2. ***Explanation: The dead timer (20 seconds) on R1 expires before the next hello packet from R2 (25 seconds).

A network engineer has manually configured the hello interval to 15 seconds on an interface of a router that is running OSPFv2. By default, how will the dead interval on the interface be affected?

-The dead interval will now be 60 seconds. ***Explanation: Cisco IOS automatically modifies the dead interval to four times the hello interval.

What is a benefit of multiarea OSPF routing?

-Topology changes in one area do not cause SPF recalculations in other areas. ***Explanation: With multiarea OSPF, only routers within an area share the same link-state database. Changes to the network topology in one area do not impact other areas, which reduces the number of SPF algorithm calculations and the of link-state databases.

What is the format of the router ID on an OSPF-enabled router?

-a 32-bit number formatted like an IPv4 address ***Explanation: A router ID is a 32-bit number formatted like an IPv4 address and assigned in order to uniquely identify a router among OSPF peers.

What will an OSPF router prefer to use first as a router ID?

-any IP address that is configured using the router-id command ***Explanation: The first preference for an OSPF router ID is an explicitly configured 32-bit address. This address is not included in the routing table and is not defined by the networkcommand. If a router ID that is configured through the router-id command is not available, OSPF routers next use the highest IP address available on a loopback interface, as loopbacks used as router IDs are also not routable addresses. Lacking either of these alternatives, an OSPF router will use the highest IP address from its active physical interfaces.

Which type of OSPFv2 packet contains an abbreviated list of the LSDB of a sending router and is used by receiving routers to check against the local LSDB?

-database description ***Explanation: The database description (DBD) packet contains an abbreviated list of the LSDB sent by a neighboring router and is used by receiving routers to check against the local LSDB.

To establish a neighbor adjacency two OSPF routers will exchange hello packets. Which two values in the hello packets must match on both routers? (Choose two.)

-dead interval -hello interval ***Explanation: The hello and dead interval timers contained in a hello packet must be the same on neighboring routers in order to form an adjacency.

When an OSPF network is converged and no network topology change has been detected by a router, how often will LSU packets be sent to neighboring routers?

-every 30 minutes ***Explanation: After all LSRs have been satisfied for a given router, the adjacent routers are considered synchronized and in a full state. Updates (LSUs) are sent to neighbors only under the following conditions: -when a network topology change is detected (incremental updates) -every 30 minutes

Which step does an OSPF-enabled router take immediately after establishing an adjacency with another router?

-exchanges link-state advertisements ***Explanation: The OSPF operation steps are as follows: 1.Establish neighbor adjacencies 2.Exchange link-state advertisements 3.Build the topology table 4.Execute the SPF algorithm 5.Choose the best route

Which step in the link-state routing process is described by a router running an algorithm to determine the best path to each destination?

-executing the SPF algorithm

Match the OSPF state with the order in which it occurs. (Not all options are used.)

-first state= Down state -second state= Init state -third state= Two-way state -fourth state= Exstart state -fifth state= Exchange state -sixth state= Loading state -seventh state= Full state

What indicates to a link-state router that a neighbor is unreachable?

-if the router no longer receives hello packets ***Explanation: OSPF routers send hello packets to monitor the state of a neighbor. When a router stops receiving hello packets from a neighbor, that neighbor is considered unreachable and the adjacency is broken.

Which OSPF data structure is identical on all OSPF routers that share the same area?

-link-state database ***Explanation: Regardless of which OSPF area a router resides in, the adjacency database, routing table, and forwarding database are unique for each router. The link-state database lists information about all other routers within an area and is identical across all OSPF routers participating in that area.

An OSPF router has three directly connected networks; 172.16.0.0/16, 172.16.1.0/16, and 172.16.2.0/16. Which OSPF network command would advertise only the 172.16.1.0 network to neighbors?

-router(config-router)# network 172.16.1.0 255.255.255.0 area 0 ***Explanation: To advertise only the 172.16.1.0/16 network the wildcard mask used in the network command must match the first 16-bits exactly. To match bits exactly, a wildcard mask uses a binary zero. This means that the first 16-bits of the wildcard mask must be zero. The low order 16-bits can all be set to 1.

What does an OSPF area contain?

-routers that have the same link-state information in their LSDBs ***Explanation: An OSPF area contains one set of link-state information, although each router within the area will process that information individually to form its own SPF tree. OSPF process IDs are locally significant and are created by the administrator. Router IDs uniquely identify each router.

What command would be used to determine if a routing protocol-initiated relationship had been made with an adjacent router?

-show ip ospf neighbor ***Explanation: While the show ip interface brief and ping commands can be used to determine if Layer 1, 2, and 3 connectivity exists, neither command can be used to determine if a particular OSPF or EIGRP-initiated relationship has been made. The show ip protocols command is useful in determining the routing parameters such as timers, router ID, and metric information associated with a specific routing protocol. The show ip ospf neighbor command shows if two adjacent routers have exchanged OSPF messages in order to form a neighbor relationship.

Which command is used to verify that OSPF is enabled and also provides a list of the networks that are being advertised by the network?​

-show ip protocols ***Explanation: The command show ip ospf interface verifies the active OSPF interfaces. The command show ip interface brief is used to check that the interfaces are operational. The command show ip route ospf displays the entries that are learned via OSPF in the routing table. The command show ip protocols checks that OSPF is enabled and lists the networks that are advertised.

A network technician issues the following commands when configuring a router: R1(config)# router ospf 11 R1(config-router)# network 10.10.10.0 0.0.0.255 area 0 What does the number 11 represent?

-the OSPF process ID on R1 ***Explanation: There is no autonomous system number to configure on OSPF. The area number is located at the end of the network statement. The cost of a link can be modified in the interface configuration mode. The process ID is local to the router.

What is used to facilitate hierarchical routing in OSPF?

-the use of multiple areas ***Explanation: OSPF supports the concept of areas to prevent larger routing tables, excessive SPF calculations, and large LSDBs. Only routers within an area share link-state information. This allows OSPF to scale in a hierarchical fashion with all areas that connect to a backbone area.

What is a function of OSPF hello packets?

-to discover neighbors and build adjacencies between them

What is the reason for a network engineer to alter the default reference bandwidth parameter when configuring OSPF?

-to more accurately reflect the cost of links greater than 100 Mb/s ***Explanation: By default, Fast Ethernet, Gigabit, and 10 Gigabit Ethernet interfaces all have a cost of 1. Altering the default reference bandwidth alters the cost calculation, allowing each speed to be more accurately reflected in the cost.

What are the two purposes of an OSPF router ID? (Choose two.)

-to uniquely identify the router within the OSPF domain -to facilitate router participation in the election of the designated router ***Explanation: OSPF router ID does not contribute to SPF algorithm calculations, nor does it facilitate the transition of the OSPF neighbor state to Full. Although the router ID is contained within OSPF messages when router adjacencies are being established, it has no bearing on the actual convergence process.

In an OSPF network when are DR and BDR elections required?

-when the routers are interconnected over a common Ethernet network ***Explanation: When the routers are interconnected over a common Ethernet network, then a designated router (DR) and a backup DR (BDR) must be elected.