Enterprise Networking, Security & Automation -ENSA Practice Exam

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 5 minutes

• every 10 minutes

• every 30 minutes

• every 60 minutes

Answer 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 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?

• link-state update

• link-state request

• database description

• link-state acknowledgment

Answer 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.

Which step in the link-state routing process is described by a router building a link-state database based on received LSAs?

• building the topology table

• executing the SPF algorithm

• selecting the router ID

• declaring a neighbor to be inaccessible

Refer to the exhibit. A network administrator has configured OSPFv2 on the two Cisco routers as shown. The routers are unable to form a neighbor adjacency. What should be done to fix the problem?

• Remove the FastEthernet0/0 passive interface configuration on router R1.

• Add the command network 192.168.20.1 0.0.0.0 area 0 on router R1.

• Add the command network 192.168.30.0 0.0.0.255 area 0 on router R1.

• Change the IP address on S0/0 of router R2 to 192.168.20.2.

Answer explanation

In order to form OSPFv2 neighbor adjacencies, two connected router interfaces must share the same subnet. Router R2 is shown in the topology with an IP address of 192.168.20.5 and does not exist on the same subnet as the 192.168.20.1 /30 IP address of S0/0 on router R1.

Which command will a network engineer issue to verify the configured hello and dead timer intervals on a point-to-point WAN link between two routers that are running OSPFv2?

• show ip ospf neighbor

• show ip ospf interface serial 0/0/0

• show ipv6 ospf interface serial 0/0/0

• show ip ospf interface fastethernet 0/1

Answer explanation

The show ip ospf interface serial 0/0/0 command will display the configured hello and dead timer intervals on a point-to-point serial WAN link between two OSPFv2 routers. The show ipv6 ospf interface serial 0/0/0 command will display the configured hello and dead timer intervals on a point-to-point serial link between two OSPFv3 routers. The show ip ospf interface fastethernet 0/1 command will display the configured hello and dead timer intervals on a multiaccess link between two (or more) OSPFv2 routers. The show ip ospf neighbor command will display the dead interval elapsed time since the last hello message was received, but does not show the configured value of the timer.

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

• to facilitate the establishment of network convergence

• to uniquely identify the router within the OSPF domain

• to facilitate the transition of the OSPF neighbor state to Full

• to facilitate router participation in the election of the designated router

• to enable the SPF algorithm to determine the lowest cost path to remote networks

Answer 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.

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

• 782

• 74

• 128

• 65

Answer 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

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.

• Router R2 will become the DR and router R3 will become the BDR.

• Router R1 will become the DR and router R2 will become the BDR.

• Router R4 will become the DR and router R3 will become the BDR.

Answer 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 IDhighest 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.

What is the significant characteristic of worm malware?

• Worm malware disguises itself as legitimate software.

• A worm can execute independently of the host system.

• A worm must be triggered by an event on the host system.

• Once installed on a host system, a worm does not replicate itself.

Answer explanation

Worm malware can execute and copy itself without being triggered by a host program. It is a significant network and Internet security threat.

What is the best description of Trojan horse malware?

• It is the most easily detected form of malware.

• It is malware that can only be distributed over the Internet.

• It is software that causes annoying but not fatal computer problems.

• It appears as useful software but hides malicious code.

Answer explanation

The best description of Trojan horse malware, and what distinguishes it from viruses and worms, is that it appears as useful software but hides malicious code. Trojan horse malware may cause annoying computer problems, but can also cause fatal problems. Some Trojan horses may be distributed over the Internet, but they can also be distributed by USB memory sticks and other means. Specifically targeted Trojan horse malware can be some of the most difficult malware to detect.