N10-009 Router R1 Cannot Reach R3 Practice Questions

Common Traps on Router R1 Cannot Reach R3 Practice Questions

·Check both forward and return paths.
·A correct-looking route can still fail if the next hop is unreachable.
·Administrative distance and longest-prefix match can change which route is used.

Sample Questions

A network engineer is implementing OSPF on a router. All directly connected neighbors are listed with state FULL, but routes from another area are not appearing in the routing table. Which of the following is the most likely cause?

Explanation: When OSPF neighbors reach FULL state, the link-state database is synchronized. However, if routes from another area are missing, the issue is likely with the propagation of inter-area routes (Type 3 LSAs). An ACL configured to filter OSPF updates can block these LSAs. The router ID is required for OSPF operation but would prevent neighbor formation if missing. Virtual-links are only needed if an area is not directly connected to area 0. A corrupted link-state database is less likely than a simple ACL filter.

A network engineer has successfully established an IPsec site-to-site VPN tunnel between a branch office (10.0.1.0/24) and the main office (192.168.1.0/24). The tunnel status shows as active, and both sides can ping each other's tunnel interface IP addresses. However, users at the branch office cannot ping the main office server at 192.168.1.10, and the main office cannot ping the branch office server at 10.0.1.10. The firewall rules on both sides permit IPsec traffic and all internal traffic. What should the engineer check NEXT?

Explanation: Even if the IPsec tunnel is up and endpoints can ping the tunnel IPs, internal hosts may not be able to communicate if routing is not properly configured. The engineer must ensure that both routers have routes to the remote internal networks, either statically or dynamically, so that packets from internal hosts are sent through the tunnel. Additionally, Network Address Translation (NAT) policies should be checked to ensure they are not translating the internal traffic that should be encrypted.

A user reports intermittent inability to access websites. When the issue occurs, the user can ping external IP addresses (e.g., 8.8.8.8) but cannot ping domain names like google.com. The user's IP configuration shows a DNS server address of 8.8.8.8. What is the most likely cause?

Explanation: Since the user can ping external IPs but not domain names during the issue, DNS resolution is failing. Intermittent failure suggests that the DNS server is reachable (as ping to 8.8.8.8 works) but is not responding to DNS queries due to high load or timeout. A corrupted DNS cache would typically cause consistent failure for cached entries, not intermittent. A firewall blocking UDP port 53 would cause consistent failure. DNS server overload can cause timeouts and retransmissions, leading to intermittent resolution failures.

A network engineer has established an IPsec VPN tunnel between a branch office (10.0.0.0/24) and the main office (192.168.10.0/24). The tunnel shows as up and active, but users at the branch office cannot ping the main office server at 192.168.10.10. The main office can ping the branch office gateway successfully. What is the most likely cause of this issue?

Explanation: The VPN tunnel is established, indicating that IPsec parameters are correct. The issue is typically that the branch office router lacks a route to the main office LAN via the VPN tunnel. Without such a route, traffic destined for 192.168.10.0/24 is sent out the default WAN interface instead of through the tunnel.

A network administrator is configuring OSPF on routers in a multi-area network. The administrator wants to ensure that a router in area 1 does not learn external routes (Type 5 LSAs) injected by an ASBR in area 0, but it must still learn inter-area routes (Type 3 LSAs). The administrator wants to reduce the routing table size. Which OSPF area type should be configured for area 1?

Explanation: A totally stubby area blocks Type 3 LSAs (inter-area summary routes) and Type 5 LSAs (external routes), and uses a default route only. A stub area blocks Type 5 LSAs but allows Type 3 LSAs. A not-so-stubby-area (NSSA) allows Type 7 LSAs for external routes and can also block Type 5 LSAs. The question says the router must learn inter-area routes (Type 3 LSAs) but not Type 5 LSAs; this matches the stub area definition. A totally stubby area would block Type 3 LSAs as well, which is not what is required.

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Frequently asked questions

How do "Router R1 Cannot Reach R3 Practice Questions" appear on the real N10-009?

Practise routing and connectivity troubleshooting scenarios involving R1, R2, R3, static routes, OSPF, next hops and routing tables. These appear throughout the N10-009 and require you to apply your knowledge, not just recall facts.

How many scenario questions are on the N10-009 exam?

Cisco doesn't publish an exact breakdown, but scenario-based questions (especially exhibit and command-output formats) make up a significant portion of the N10-009. Practicing each scenario type ensures you're ready for any format.

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