Practise routing and connectivity troubleshooting scenarios involving R1, R2, R3, static routes, OSPF, next hops and routing tables.
Start Scenario PracticeA small office wants to reduce the risk of malware arriving through email and malicious websites while keeping administration simple. Which two measures provide the strongest protection against these threats? (Choose two.)
Explanation: The strongest pairing couples host-level defense with network-level filtering. Endpoint antivirus catches payloads that reach the workstation, while a secure web gateway or DNS filtering service blocks the malicious domains that deliver those payloads. Together they cover both the email and web vectors named in the scenario without heavy administrative overhead, whereas disabling updates, permitting all outbound traffic, and sharing administrator accounts all increase exposure.
Users on VLAN 20 report that they can reach servers on VLAN 30 but cannot reach any hosts on VLAN 40. The administrator confirms that inter-VLAN routing is configured on a Layer 3 switch with switched virtual interfaces for all three VLANs. Which action should the administrator take first to isolate the problem?
Explanation: Because routing between VLAN 20 and VLAN 30 already works, the Layer 3 switch is functioning as a router. The fault is specific to VLAN 40, so the logical first check is whether its switched virtual interface is up and correctly addressed. An SVI stays down when the VLAN has no active member ports or when the VLAN itself has not been created.
Which feature is best suited to prevent VLAN hopping attacks where an attacker sends double-tagged 802.1Q frames to reach a restricted VLAN?
Explanation: VLAN hopping via double-tagging occurs when an attacker sends a frame with two tags to a switch, tricking it into bypassing port restrictions. By explicitly configuring ports as access ports and disabling DTP negotiation, administrators prevent the switch from automatically forming trunks with unauthorized devices. This is a critical hardening step because it removes the possibility of a device negotiating a trunk link, which is required for VLAN hopping to succeed.
A user is unable to reach 'cisco.com' in their web browser but can successfully ping the IP address '72.163.4.161'. Which network service is most likely failing or misconfigured?
Explanation: This scenario highlights the distinction between basic connectivity and name resolution. If a user can reach a destination by IP but not by name, the underlying network path is functional, but the translation service is broken. Diagnosing DNS issues is a daily task for technicians, as it is often the root cause of 'internet is down' complaints when the connection is actually active.
A user reports intermittent connectivity to the internal server. Which TWO commands are most useful to identify if the issue is caused by physical layer flapping or interface errors?
Explanation: Identifying physical layer issues requires inspecting interface statistics and state changes. 'show interfaces' reveals error counters like CRC, giants, and runts which signify physical layer degradation. 'show logging' provides a chronological history of interface state changes, allowing the technician to correlate connectivity drops with physical link flaps. Together, these tools provide a comprehensive view of the physical health of the connection between the host and the switch infrastructure.
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Practice all Router R1 Cannot Reach R3 Practice QuestionsPractise routing and connectivity troubleshooting scenarios involving R1, R2, R3, static routes, OSPF, next hops and routing tables. These appear throughout the 100-150 and require you to apply your knowledge, not just recall facts.
Cisco doesn't publish an exact breakdown, but scenario-based questions (especially exhibit and command-output formats) make up a significant portion of the 100-150. Practicing each scenario type ensures you're ready for any format.
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