17 - Questions - Open Shortest Path First (OSPF)
A router has learned three possible routes that could be used to reach a destination network. These routes have been learned from three different routing protocols, OSPF, EIGRP and RIPv2. Which route will the router install in the routing table?
EIGRP route
Which two options are classified as link-state routing protocols? (Choose two.)
IS-IS OSFP
What is a concern of the default OSPF metric on Cisco routers?
Links with speeds greater than 100 Mbps have a cost of 1.
Which option regarding OSPF is true?
The correct answer is "A router creates a neighbor relationship by exchanging hello packets." OSPF does not exchange routing information periodically, like distance vector protocols do, but only when there are changes. Moreover, a router floods its own LSAs every 30 minutes by default as a periodic update for synchronization purposes with the other routers in the area. The messages are exchanged among the routers in the same area. Routers in one area build an LSDB based on exchanged messages and have the same LSDBs. One of the advantages of OSPF is that it can be used to build hierarchical routing domains, using multiple areas.
Which packet is used to ensure a reliable transport and a reliable exchange of information?
The correct answer is "LSAck packet." A DBD packet describes the network routes of each neighbor. An LSR packet is used to request the missing information. An LSU packet is used to send all missing information. An LSAck packet is used to ensure a reliable transport and a reliable exchange of information.
Related to OSPFv3, which of the following statements is correct?
The correct answer is "OSPFv3 was created specifically to support IPv6." OSPFv3 is still a link-state protocol, with the cost as the metric but with many internals, including LSA types, changed. As a result, OSPFv2 is not compatible with OSPFv3.
Which option is a key feature of link-state routing protocols?
The correct answer is "They are scalable." Link-state protocols use a hierarchical design and can scale to very large networks, if properly designed.
Which route is preferred by a router when the router is comparing them using default administrative distances?
The correct answer is "connected." A connected route has the lowest administrative distance.
Which command enables OSPF Area 0 on the interface that is configured with the IPv4 address 172.16.10.1 and the subnet mask 255.255.255.252?
The correct answer is "network 172.16.10.0 0.0.0.3 area 0." The network command identifies which IP networks on the router are part of the OSPF network. The network that is identified in the network command does not tell the router which network to advertise; instead, it indicates the interfaces on which OSPF will be enabled.
Which OSPF hello packet information must be different, for OSPF neighbor relationship to be formed between two routers?
The correct answer is "router ID." The OSPF router ID uniquely identifies the router. If two routers have the same identification, they will not form OSPF neighbor relationship.
Which command displays information about OSPF timers?
The correct answer is "show ip ospf interface interface-id." The show ip ospf neighbors command displays information about known neighbor OSPF routers. The show ip protocols command displays basic settings of all IPv4 outing protocols configured on a device. The show ip route command displays the routing table.
n Cisco devices, what is the OSPF cost metric calculation based on?
The correct answer is "the bandwidth of the link." The cost of an interface is inversely proportional to the bandwidth of this interface, so a higher bandwidth indicates a lower cost. There is more overhead, a higher cost, and more time delays that are involved in crossing a 10-Mbps Ethernet line than in crossing a 100-Mbps Ethernet line.
What is the same between routers running a link-state routing protocol in the same area?
The correct answer is "topology database." Routers running link-state protocol learn the complete topology of the network, by exchanging all LSAs. Each router will have the same topology database within an area.
What is a state of the OSPF neighbor relationship after a router becomes active on the link and receives an OSPF hello packet with its own OSPF router ID?
The correct answer is "two-way state." The two-way state is attained when the router receiving the hello packet sees its own Router ID within the received hello packet's neighbor field.
Which three dynamic routing protocols are considered classless? (Choose three.)
The correct answers are "IS-IS," "EIGRP," and "RIPv2." All three routing protocols transmit the subnet mask in route updates.
Refer to the figure. Which path will Router A, running OSPF, install in the routing table in order to reach 10.10.1.0/24?
The path A-D-C
How do link-state protocols limit the scope of route changes?
by segmenting the network into areas
What is the purpose of link-state advertisements?
constructing a topological database
Match the OSPF neighbor states on a LAN with their correct positions in the right order.
down 1 INIT 2 two-way 3 exstart 4 exchange 5 loading 6 full 7
Which three options represent information inside an OSPF hello packet that must be agreed upon before neighbor adjacency can be established? (Choose three.)
hello and dead interval area ID authentication data
The SPF algorithm uses a value that on a Cisco router is inversely proportional to the bandwidth. What is this value called?
link cost
Which two data structures do the link-state routing protocols use? (Choose two.)
neighbors database topology database
Which two options represent when the OSPF routing protocol sends LSAs?? (Choose two.)
periodically every 30 minutes on topology change
Match the OSPF packet type with the correct description.
sends specifically requested link-state records LSU acknowledges the other packet types LSAck checks for database synchronization DBD requests specific link-state records from another router LSR discovers neighbors hello
