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This page has 15 Router R1 Cannot Reach R3 Practice Questions scenario questions for the 350-401 exam, each with detailed explanations and wrong-answer analysis.

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Read the full scenario before looking at the answer options. Identify the constraint or requirement in the scenario, then eliminate options that are generally true but wrong for this specific case. Scenario questions reward careful reading over pattern matching.

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Scenario-based practice

Router R1 Cannot Reach R3 Practice Questions

Practise identifying common networking hardware like routers, switches, access points, and their roles in a network.

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scenario questions

350-401

exam code

Cisco

vendor

Scenario guide

How to approach router r1 cannot reach r3 practice questions

Practise routing and connectivity troubleshooting scenarios involving R1, R2, R3, static routes, OSPF, next hops and routing tables.

Quick answer

Tests identification, purpose, and configuration of routers, switches, access points, and patch panels.

Identify routers, switches, and access points by function

Understand PoE and PoE+ power requirements

Differentiate managed vs unmanaged switches

Recognize cable types: Cat5e, Cat6, fiber

Practice scenarios

Question 1mediumdrag order

Review the full routing breakdown →

Drag and drop the steps to configure a static route on a Cisco IOS router into the correct order.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps

Order

1Step 1

2Step 2

3Step 3

4Step 4

5Step 5

Question 2hardmultiple choice

Review the full OSPF breakdown →

Refer to the exhibit. R1 has two equal-cost OSPF E2 routes to 10.1.1.0/24 via two different next hops. However, when tracing to 10.1.1.1, all traffic uses the path through 10.0.1.2. What is the most likely reason?

Exhibit

Refer to the exhibit.
R1# show ip route | include 10.1.1.0
O E2 10.1.1.0/24 [110/20] via 10.0.1.2, 00:00:34, GigabitEthernet0/0
O E2 10.1.1.0/24 [110/20] via 10.0.2.2, 00:00:34, GigabitEthernet0/1
R1# show ip ospf interface GigabitEthernet0/0 | include Cost
  Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 10
R1# show ip ospf interface GigabitEthernet0/1 | include Cost
  Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 100
R1# traceroute 10.1.1.1 source Loopback0
Type escape sequence to abort.
Tracing the route to 10.1.1.1
  1 10.0.1.2 4 msec 4 msec 4 msec
  2 10.0.3.2 8 msec 8 msec 8 msec

A
One route has a higher administrative distance.
Why wrong: Incorrect: Both routes have AD 110.
B
A default route is overriding the specific route.
Why wrong: Incorrect: No default route is shown.
C
The route via 10.0.2.2 is an E1 route.
Why wrong: Incorrect: Both are E2 as shown.
D
OSPF E2 routes do not factor interface cost; but the router uses the interface cost as a tie-breaker for equal-cost routes.
Correct: When E2 metrics are equal, some implementations prefer the path with lower interface cost.

Full breakdown with real-world context →

Question 3hardmultiple choice

Open the full VLAN trunking answer →

Your company has deployed a Cisco Catalyst 9300 switch stack as the distribution layer for a campus network. The network uses VLANs 10 (data), 20 (voice), and 30 (management). The switch stack is configured with DHCP snooping, Dynamic ARP Inspection (DAI), and IP Source Guard (IPSG) on access ports. Recently, users in VLAN 10 report intermittent connectivity issues. You notice that some users receive duplicate IP addresses from the DHCP server. The DHCP server is connected to a trunk port on the switch stack. After reviewing logs, you see that DHCPACK messages are being dropped on the trunk port. The DHCP snooping binding table shows entries for legitimate clients, but also some entries with MAC addresses from a different vendor. Which action should you take to resolve the issue?

A
Manually shut down the access ports that have unknown MAC addresses in the binding table.
Why wrong: This does not address the DHCP server response being dropped.
B
Disable Dynamic ARP Inspection on VLAN 10.
Why wrong: DAI validates ARP packets, not DHCP messages.
C
Configure the trunk port connecting to the DHCP server as a trusted port for DHCP snooping.
DHCP snooping drops DHCP server responses on untrusted ports.
D
Disable IP Source Guard on all access ports in VLAN 10.
Why wrong: IPSG filters IP traffic based on binding table, not DHCP messages.

Full breakdown with real-world context →

Question 4hardmulti select

Review the full OSPF breakdown →

Which THREE conditions are required for OSPF routers to become fully adjacent? (Choose three.)

A
Same area ID
Routers must be in the same area.
B
Matching hello and dead intervals
Timers must match.
C
Matching authentication (if configured)
Authentication must match if used.
D
Different router IDs
Why wrong: Router IDs must be unique but not necessarily different? Actually they must be unique.
E
Same subnet mask
Why wrong: Subnet mask must match for broadcast links.

Full breakdown with real-world context →

Question 5mediummulti select

Open the full VLAN trunking answer →

Which TWO of the following are valid methods to mitigate VLAN hopping attacks?

A
Configure switchport mode dynamic auto on all ports.
Why wrong: Dynamic auto can negotiate trunk.
B
Disable Dynamic Trunking Protocol (DTP) on all access ports.
Prevents trunk negotiation.
C
Set the native VLAN to VLAN 1 on all trunk ports.
Why wrong: VLAN 1 is default and does not mitigate.
D
Set the native VLAN to an unused VLAN ID on all trunk ports.
Mitigates double-tagging VLAN hopping.
E
Use 802.1Q trunking instead of ISL.
Why wrong: Both are susceptible; switching encapsulation is not a mitigation.

Full breakdown with real-world context →

Question 6easymultiple choice

Review the full OSPF breakdown →

Refer to the exhibit. An administrator needs to ensure that traffic to 192.168.1.0/24 is forwarded via a different path than traffic to 192.168.2.0/24, even though both routes are learned via OSPF with the same metric. Which action should the administrator take?

Exhibit

Refer to the exhibit.

R1# show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override

Gateway of last resort is 10.0.0.2 to network 0.0.0.0

O E2     192.168.1.0/24 [110/20] via 10.0.0.2, 00:00:34, GigabitEthernet0/0
O E2     192.168.2.0/24 [110/20] via 10.0.0.2, 00:00:34, GigabitEthernet0/0
S*       0.0.0.0/0 [1/0] via 10.0.0.1

A
Configure policy-based routing to match 192.168.1.0/24 and set the next hop to 10.0.0.1.
Why wrong: This is more complex and not the simplest solution; a static route is easier.
B
Add a static route for 192.168.1.0/24 with a lower administrative distance than OSPF.
A static route with AD 1 would override the OSPF route (AD 110) for that prefix.
C
Use the 'distance ospf' command to change the OSPF administrative distance for all routes.
Why wrong: This would affect all OSPF routes, not just the specific prefix.
D
Adjust the OSPF cost on the interface to 10.0.0.2.
Why wrong: This would not differentiate between the two routes if they are both received via the same neighbor.

Full breakdown with real-world context →

Question 7hardmultiple choice

Open the full BGP breakdown →

An engineer is troubleshooting a BGP routing issue. The router is not receiving routes from an eBGP neighbor. The neighbor is reachable via ping. The BGP session is established and in the Established state. What is the most likely cause?

A
The AS number is incorrect.
Why wrong: If AS number is incorrect, session would not establish.
B
The BGP session is using an incorrect interface.
Why wrong: Session established means interface is fine.
C
The network is not advertised under BGP.
Why wrong: This would affect route advertisement, not receipt.
D
The next-hop IP address is not reachable.
eBGP routes require reachable next-hop to be installed.

Full breakdown with real-world context →

Question 8easymultiple choice

Study the full virtualization explanation →

A company is deploying a virtualized network function (VNF) for a Cisco CSR1000v router on a VMware vSphere hypervisor. The architect must choose the hypervisor type to ensure the best performance for the VNF. Which hypervisor type is VMware vSphere classified as, and why is it suitable for VNF deployment?

A
Type 2 hypervisor; it runs on top of an operating system, providing flexibility for VNF management.
Why wrong: Type 2 hypervisors (e.g., VirtualBox) run on a host OS and have higher overhead, which is not ideal for performance-sensitive VNFs.
B
Type 1 hypervisor; it runs directly on the hardware, offering near-native performance for VNFs.
Type 1 hypervisors like vSphere provide direct access to hardware resources, minimizing latency and maximizing throughput for VNFs.
C
Type 1 hypervisor; it requires a host OS for management, adding overhead.
Why wrong: Type 1 hypervisors do not require a host OS; they include a built-in management interface.
D
Type 2 hypervisor; it is embedded in the hardware firmware.
Why wrong: Type 2 hypervisors are not embedded in firmware; they are software installed on an OS.

Full breakdown with real-world context →

Question 9hardmultiple choice

Review the full OSPF breakdown →

A network administrator is troubleshooting an issue where OSPF routes are not being learned from a neighbor. The administrator checks the OSPF configuration and sees that both routers are in the same area. The neighbor state is stuck in EXSTART. What is the most likely cause?

A
The router ID is the same on both routers.
Why wrong: Duplicate router IDs cause a different issue.
B
The area ID is different.
Why wrong: Area ID mismatch causes INIT or DOWN.
C
The hello timer is set to 30 seconds on one router.
Why wrong: Hello timer mismatch causes INIT.
D
The interface MTU does not match.
MTU mismatch causes EXSTART state.

Full breakdown with real-world context →

Question 10mediumdrag order

Study the full QoS explanation →

Drag and drop the steps of the QoS shaping and policing configuration sequence into the correct order, from first to last.

Question 11mediummultiple choice

Review the full OSPF breakdown →

Examine the following configuration snippet:

interface GigabitEthernet0/1
 ip address 192.168.1.1 255.255.255.0
 ip ospf hello-interval 20
 ip ospf dead-interval 80

What is the effect of this configuration?

A
The OSPF hello interval is changed to 20 seconds, and the dead interval is changed to 80 seconds, maintaining the default 4:1 ratio.
Correct. The hello interval is set to 20, and dead interval to 80, which is 4 times the hello interval, as required by OSPF.
B
The OSPF hello interval is changed to 20 seconds, but the dead interval remains at the default of 40 seconds.
Why wrong: Incorrect. The dead interval is explicitly set to 80 seconds, overriding the default.
C
The OSPF hello interval is changed to 20 seconds, and the dead interval is automatically set to 60 seconds.
Why wrong: Incorrect. The dead interval is explicitly configured as 80 seconds, not automatically derived.
D
This configuration will cause OSPF adjacency failure because the dead interval must be exactly 4 times the hello interval.
Why wrong: Incorrect. The dead interval is exactly 4 times the hello interval (80 = 4 * 20), so adjacency will form normally.

Full breakdown with real-world context →

Question 12hardmultiple choice

Open the full VLAN trunking answer →

A network administrator is troubleshooting a DHCP snooping issue on a Cisco switch. The switch is configured with DHCP snooping globally and on VLAN 10. The trusted interface is GigabitEthernet0/1 connected to the DHCP server. However, clients on VLAN 10 are not receiving IP addresses from the DHCP server. What is the most likely cause?

A
The switch has IP Source Guard enabled, blocking valid DHCP traffic.
Why wrong: IP Source Guard uses DHCP snooping binding table, but it would not block initial DHCP exchanges.
B
The interface GigabitEthernet0/1 is not configured as a trusted port for DHCP snooping.
Correct: Untrusted ports drop DHCP server messages; the server port must be trusted.
C
The DHCP server is on a different subnet and the switch lacks an IP helper address.
Why wrong: If server is on same VLAN, no helper needed.
D
The DHCP server is sending offers too quickly, exceeding the rate-limit on the switch.
Why wrong: Rate-limit is on untrusted ports for client messages, not server responses.

Full breakdown with real-world context →

Question 13mediummultiple choice

Read the full MPLS explanation →

A network engineer is configuring MPLS L3VPN on a Cisco IOS-XE router. The VRF CUSTOMER_C has route-target import 300:1 and export 300:1. The PE receives VPNv4 routes from the route reflector, but the CE router connected to the PE cannot ping any remote site IP addresses. The PE can ping the remote site IP addresses from the VRF. What is the most likely cause?

A
The CE router does not have a default route pointing to the PE's VRF interface.
Correct because if the CE does not have a route to remote sites, it cannot send traffic. The PE can ping because it has the routes in the VRF.
B
The VRF is missing the route-target export command.
Why wrong: Incorrect because the PE can reach remote sites, meaning VPNv4 routes are imported correctly, so export is working.
C
The PE router is not running a routing protocol with the CE router.
Why wrong: Incorrect because even without a routing protocol, static routes can be used; the issue is the CE's lack of a route.
D
The MPLS LDP is not enabled on the PE-CE link.
Why wrong: Incorrect because MPLS is not required on the PE-CE link for L3VPN.

Full breakdown with real-world context →

Question 14mediummultiple choice

Review the full OSPF breakdown →

Router R3 has the following OSPF configuration:

router ospf 1

router-id 3.3.3.3

network 10.0.0.0 0.255.255.255 area 0

default-information originate always metric 20 metric-type 2

What is the effect of the 'default-information originate always' command?

A
It redistributes all connected routes into OSPF.
Why wrong: Redistribution of connected routes requires 'redistribute connected' command.
B
It injects a default route into OSPF only if a default route is present in the routing table.
Why wrong: The 'always' keyword forces injection even without a default route in the routing table.
C
It injects a default route into OSPF unconditionally, with metric 20 and type E2.
The 'always' keyword makes the default route always injected, with specified metric and type.
D
It sets the OSPF router ID to 3.3.3.3 and enables default route filtering.
Why wrong: The router-id is set separately; 'default-information originate' does not filter routes.

Full breakdown with real-world context →

Question 15mediumdrag order

Review the full OSPF breakdown →

Drag and drop the steps of OSPF virtual link configuration into the correct order, from first to last.

These 350-401 practice questions are part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style 350-401 questions with detailed explanations, topic-based practice, mock exams, readiness tracking, and study analytics.

Router R1 Cannot Reach R3 Practice Questions

How to approach router r1 cannot reach r3 practice questions

Quick answer

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Practice scenarios

Drag and drop the steps to configure a static route on a Cisco IOS router into the correct order.

Refer to the exhibit. R1 has two equal-cost OSPF E2 routes to 10.1.1.0/24 via two different next hops. However, when tracing to 10.1.1.1, all traffic uses the path through 10.0.1.2. What is the most likely reason?

Exhibit

Which THREE conditions are required for OSPF routers to become fully adjacent? (Choose three.)

Which TWO of the following are valid methods to mitigate VLAN hopping attacks?

Refer to the exhibit. An administrator needs to ensure that traffic to 192.168.1.0/24 is forwarded via a different path than traffic to 192.168.2.0/24, even though both routes are learned via OSPF with the same metric. Which action should the administrator take?

Exhibit

An engineer is troubleshooting a BGP routing issue. The router is not receiving routes from an eBGP neighbor. The neighbor is reachable via ping. The BGP session is established and in the Established state. What is the most likely cause?

A network administrator is troubleshooting an issue where OSPF routes are not being learned from a neighbor. The administrator checks the OSPF configuration and sees that both routers are in the same area. The neighbor state is stuck in EXSTART. What is the most likely cause?

Drag and drop the steps of the QoS shaping and policing configuration sequence into the correct order, from first to last.

Drag and drop the steps of OSPF virtual link configuration into the correct order, from first to last.