300-410 Layer 3 Technologies Practice Test 4 — 15 Questions

Question 1

A network engineer is configuring OSPF on a router. The router has two interfaces in the same OSPF area: GigabitEthernet0/0 (10.1.1.1/24) and GigabitEthernet0/1 (10.1.1.2/24). After configuration, the engineer notices that the router does not form an adjacency with a neighbor on GigabitEthernet0/1. Which of the following is the most likely cause?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

Duplicate IP subnet on two interfaces in the same area.. OSPF does not support two interfaces in the same area with overlapping IP subnets. When the same subnet is configured on multiple interfaces, OSPF only advertises one, and the other interface will not form adjacencies. This is a common misconfiguration that leads to adjacency problems. The other options are less likely given the specific scenario.

Answer

MTU mismatch on the interfaces.

Answer

Incorrect OSPF router ID.

Answer

OSPF network type mismatch on the interfaces.

Question 2

A network engineer is troubleshooting a DMVPN Phase 3 spoke-to-spoke communication issue. The hub router is configured with 'ip nhrp redirect' and the spokes with 'ip nhrp shortcut'. The spokes are in the same subnet and have established NBMA mappings to the hub. However, spoke-to-spoke traffic still goes through the hub. Which command should the engineer verify first on the spoke routers to ensure they can dynamically create shortcut paths?

Accepted Answer

show ip nhrp shortcut. In DMVPN Phase 3, spoke-to-spoke shortcuts are created when the hub sends an NHRP redirect and the spoke resolves the target NBMA address. The shortcut cache is the key indicator that this process has occurred. If the cache is empty, the spoke cannot build a direct tunnel, and traffic continues via the hub. Verifying the shortcut cache is the most direct troubleshooting step.

Answer

show ip nhrp nhs

Answer

show ip route nhrp

Answer

show dmvpn

Question 3

A network administrator is configuring OSPFv3 on a Cisco router. The router has been configured with the command 'ipv6 router ospf 1' and the interfaces have been enabled with 'ipv6 ospf 1 area 0'. However, the router is not forming any OSPFv3 adjacencies. Which of the following is the most likely cause?

Accepted Answer

The OSPFv3 router ID has not been configured.. OSPFv3 requires a router ID, which must be manually configured if no IPv4 address is present. Without it, the OSPFv3 process will not run, and adjacencies will not form. The other options are either not required or not the most likely cause.

Answer

The interfaces have not been configured with IPv6 addresses.

Answer

The OSPFv3 process has not been activated with the 'router-id' command.

Answer

The OSPFv3 process number is different from the area number.

Question 4

A network engineer is configuring VRF-Lite on a Cisco IOS router to separate traffic from two different customers. The engineer has created VRF CUST-A and VRF CUST-B. The engineer now needs to assign an interface to VRF CUST-A and configure an IP address. Which command sequence is correct?

Accepted Answer

interface GigabitEthernet0/1
 ip vrf forwarding CUST-A
 ip address 10.1.1.1 255.255.255.0. To assign an interface to a VRF, use the 'ip vrf forwarding' command in interface configuration mode. This must be done before configuring the IP address because assigning a VRF removes any existing IP address. The correct sequence ensures the interface is properly placed in the VRF and retains the IP address.

Answer

interface GigabitEthernet0/1
 ip vrf CUST-A
 ip address 10.1.1.1 255.255.255.0

Answer

interface GigabitEthernet0/1
 vrf forwarding CUST-A
 ip address 10.1.1.1 255.255.255.0

Answer

interface GigabitEthernet0/1
 ip address 10.1.1.1 255.255.255.0
 ip vrf forwarding CUST-A

Question 5

A network administrator is deploying MPLS Layer 3 VPNs and needs to ensure that customer routes are properly propagated across the service provider backbone. The administrator has configured MP-BGP with VPNv4 address family between PE routers. Which BGP attribute is used to uniquely identify customer routes and prevent routing loops between different VPNs?

Accepted Answer

Route Target (RT). The correct answer is the BGP extended community attribute that controls route import and export between VRFs. In MPLS L3VPN, the Route Target (RT) ensures that routes are only imported into VRFs that are configured to accept them, preventing routing loops and leaks. The Route Distinguisher (RD) only ensures uniqueness, while MED and Local Preference are used for path selection, not VPN membership.

Answer

Local Preference

Answer

Route Distinguisher (RD)

Answer

Multi-Exit Discriminator (MED)

Question 6

A network administrator is configuring OSPFv3 on a router and wants to enable authentication for a specific interface using IPsec AH. The administrator enters the command 'ipv6 ospf authentication ipsec ah sha1 key-string MyKey' under the interface. However, OSPFv3 adjacencies fail to form. Which action should the administrator take to resolve the issue?

Accepted Answer

Configure a key chain and reference it using the 'ipv6 ospf authentication ipsec ah sha1 key-chain <name>' command.. OSPFv3 IPsec authentication requires a key chain, which must be configured separately and then referenced under the interface. The key chain provides the key-string and optional lifetime parameters. Using 'key-string' directly is invalid and prevents adjacencies from forming because the authentication configuration is incomplete. The correct command references the key chain by name.

Answer

Change the authentication algorithm to MD5, as SHA1 is not supported for OSPFv3 IPsec AH.

Answer

Enable OSPFv3 authentication globally with 'ipv6 ospf authentication ipsec ah sha1 key-string MyKey' under router configuration mode.

Answer

Ensure that the same key-string is configured on all OSPFv3 routers in the area.

Question 7

A network engineer is configuring EIGRP on a router and notices that the EIGRP topology table shows a route with a reported distance of 1000 and a feasible distance of 1200. The route is not installed in the routing table. What is the most likely reason?

Accepted Answer

The route is a feasible successor, not a successor.. EIGRP installs only the successor route in the routing table. A feasible successor is a backup route that meets the feasibility condition: its reported distance must be less than the feasible distance of the successor. In this case, the reported distance (1000) is less than the feasible distance (1200), so the route is a feasible successor and not installed. It will be used only if the successor fails.

Answer

The route is stuck in active state due to a query boundary.

Answer

The route is not in the passive state.

Answer

The route has a higher administrative distance than another route.

Question 8

A Cisco IOS router is configured with OSPFv3 for IPv6 and OSPFv2 for IPv4 on the same GigabitEthernet0/0 interface. The network engineer notices that the IPv6 OSPF neighbor remains in EXSTART state, while the IPv4 neighbor is FULL. What is the most likely cause?

Accepted Answer

The interface MTU on the IPv6 side is lower than the MTU on the neighbor.. The EXSTART state in OSPFv3 indicates a failure during database descriptor exchange, often due to an MTU mismatch. Because OSPFv2 is FULL, the issue is specific to IPv6. An MTU mismatch on the IPv6 side would cause the master/slave negotiation to fail, leaving the neighbor in EXSTART. Therefore, the correct answer is the MTU mismatch.

Answer

IPv6 unicast routing is not enabled globally on the router.

Answer

OSPFv3 requires the use of a 64-bit process ID, which is not configured.

Answer

The OSPFv3 router ID is not unique within the area.

Question 9

A network engineer is troubleshooting a DMVPN Phase 3 network using OSPF. Spoke routers are not learning routes from other spokes despite being in the same OSPF area. The hub is configured with 'ip nhrp redirect' and spokes with 'ip nhrp shortcut'. Which OSPF network type should be configured on the tunnel interfaces to ensure proper route propagation and shortcut switching?

Accepted Answer

point-to-multipoint. The correct OSPF network type for DMVPN Phase 3 with redirect and shortcut is point-to-multipoint. It avoids DR/BDR election, supports dynamic neighbor discovery, and works with NHRP to enable spoke-to-spoke direct communication. Other network types either require manual configuration or do not support the necessary multicast and shortcut behavior.

Answer

point-to-point

Answer

non-broadcast

Answer

broadcast

Question 10

A network engineer is troubleshooting an OSPFv2 area where a new Cisco IOS-XE router (R3) was added. R3 is connected to R1 via a point-to-point GigabitEthernet link. R1's interface is configured with 'ip ospf network point-to-point'. R3's interface is left at default. The engineer notices that R1 forms a FULL adjacency with R3, but R3 does not install routes learned from R1 into its routing table. Which action resolves the issue?

Accepted Answer

Configure 'ip ospf network point-to-point' on R3's interface.. The issue is caused by mismatched OSPF network types on the link. While the adjacency can still form because Hello and Dead intervals match, the network type mismatch leads to inconsistent LSA generation and processing. R3, using broadcast network type, expects a DR/BDR and may not install routes properly. Configuring the same point-to-point network type on R3 ensures both routers agree on the link type, allowing correct route calculation and installation.

Answer

Configure 'ip ospf mtu-ignore' on R3's interface.

Answer

Configure 'ip ospf hello-interval 30' on R3's interface.

Answer

Configure 'ip ospf priority 0' on R3's interface.

Question 11

A network engineer at a branch office is configuring OSPFv2 on a router that connects to two different areas: Area 0 and Area 10. The router must advertise a default route into Area 10 without flooding it into Area 0. Which OSPF command should be used on the Area Border Router (ABR)?

Accepted Answer

area 10 default-information originate. The area-specific default-information originate command allows an ABR to inject a default route into a single OSPF area without affecting other areas. This is useful when you want to provide a default path for internal routers in a stub or normal area while keeping the backbone area free of unnecessary default routes. The command does not require an existing default route in the routing table, unlike the standard default-information originate command.

Answer

default-information originate

Answer

redistribute static subnets

Answer

default-information originate always

Question 12

A network engineer configured a static route on a Cisco IOS XE router: ip route 10.10.10.0 255.255.255.0 192.168.1.2. The router also runs EIGRP AS 100 and has learned the same prefix via EIGRP with a metric of 33280. The engineer wants the static route to be preferred over the EIGRP route but also wants EIGRP to advertise the static route to neighbors. Which configuration should be used?

Accepted Answer

ip route 10.10.10.0 255.255.255.0 192.168.1.2. The default static route has an administrative distance of 1, which is lower than EIGRP's internal AD of 90, so it is installed in the routing table. Because it uses the default AD, it is also eligible for redistribution into EIGRP when the redistribute static command is configured, allowing EIGRP to advertise the prefix. Using a non-default AD would require additional configuration to achieve the same result.

Answer

ip route 10.10.10.0 255.255.255.0 192.168.1.2 90

Answer

ip route 10.10.10.0 255.255.255.0 192.168.1.2 200

Answer

ip route 10.10.10.0 255.255.255.0 192.168.1.2 1

Question 13

A network administrator is troubleshooting an OSPFv3 network. The router R1 is configured with the command 'ipv6 router ospf 1' and 'router-id 1.1.1.1'. The interface GigabitEthernet0/0 is enabled for OSPFv3 using 'ipv6 ospf 1 area 0'. However, R1 does not form an adjacency with its neighbor R2. The output of 'show ipv6 ospf interface GigabitEthernet0/0' shows that the interface is in the DR state and the neighbor list is empty. What is the most likely cause?

Accepted Answer

The interface is configured as passive.. The most likely cause is that the interface is configured as passive under the OSPFv3 process. A passive interface does not send or receive OSPFv3 hellos, so no neighbors are discovered. The interface can still be in DR state if it was previously elected, but without hellos, adjacencies cannot form. Checking the running configuration for 'passive-interface' is essential.

Answer

The OSPFv3 router ID is not unique in the area.

Answer

The OSPFv3 process is not enabled on the interface.

Answer

The interface's MTU is lower than the neighbor's MTU.

Question 14

A network engineer is configuring a GRE tunnel between two Cisco routers to transport multicast traffic. The engineer wants to ensure that the tunnel interface supports multicast and that the physical interface is not a bottleneck. Which command must be configured on the tunnel interface to enable multicast support?

Accepted Answer

ip pim sparse-mode. The correct answer is the command that enables PIM on the tunnel interface. GRE tunnels can carry multicast traffic, but PIM must be enabled on the tunnel interface to route multicast packets. Global multicast routing is necessary but not sufficient. The other options either configure multipoint GRE, which is for DMVPN, or are used for receiving multicast, not routing it.

Answer

ip multicast-routing

Answer

ip igmp join-group

Answer

tunnel mode gre multipoint

Question 15

A network engineer is configuring a GRE tunnel between two routers to transport IPv6 traffic over an IPv4-only core. The engineer wants to ensure that the tunnel interface supports multicast and that OSPFv3 can form an adjacency over the tunnel. Which configuration is required on the tunnel interface?

Accepted Answer

ipv6 address 2001:db8::1/64 and ipv6 ospf 1 area 0. A GRE tunnel for IPv6 over IPv4 requires the tunnel mode to be 'gre ip' and the tunnel interface to have IPv6 enabled. To run OSPFv3, the interface must have an IPv6 address and be included in an OSPFv3 process. Multicast is supported by default on GRE tunnels once IPv6 is enabled. The correct configuration includes both an IPv6 address and OSPFv3 activation.

Answer

ipv6 enable

Answer

tunnel mode gre ipv6

Answer

ipv6 address fe80::1 link-local