CCNA Practice Test - 25

Reflexive ACLs filter IP traffic based on session state - they allow outbound traffic from internal hosts and dynamically create temporary inbound rules to allow the return traffic. This permits sessions originating from inside the network while blocking external-initiated connections. Dynamic ACLs (option A) require user authentication, port-based ACLs (option B) filter by port numbers, and time-based ACLs (option D) activate based on time schedules. Reflexive ACLs are designed specifically for this outbound-initiated traffic scenario.

An Optical Time Domain Reflectometer (OTDR) is the specialized device used to test fiber optic installations. It sends light pulses into the fiber and analyzes the backscattered light to detect faults, measure fiber length, identify bends or breaks, and assess overall signal integrity and performance characteristics. TDR is for copper cables, multimeters measure electrical signals, and light injector is not a standard testing tool.

When a router reboots, the startup configuration is loaded but OSPF has not yet exchanged hello packets or built its neighbor adjacencies. Until OSPF convergence completes, the routing table only contains directly connected networks that are operationally up. All OSPF-learned routes from other networks are temporarily absent until the SPF algorithm runs and LSPs are exchanged. The router cannot have remote routes before convergence completes.

RIP uses hop count as its metric, and when a router receives a routing update containing a higher cost path to a network already in its routing table, it ignores that update. RIP only installs better (lower hop count) paths. The existing routing table entry remains unchanged because RIP routers do not accept inferior routes - this is fundamental to distance vector behavior where only optimal paths are maintained.

LCP (Link Control Protocol) is the correct PPP protocol that establishes, configures, maintains, and terminates the link connection. LCP handles authentication (via PAP or CHAP), negotiates parameters like MRU and magic number, and supports multilink PPP. NCP (Network Control Protocol) handles network layer protocol configuration like IP assignment, but LCP is responsible for the broader link management functions listed. HDLC is a proprietary Cisco protocol, not PPP, and X.25 is an older WAN protocol.

Circuit-switched WAN implementations require establishing a dedicated physical circuit through the network before any data transfer can begin. This call setup time creates a delay before communication can start, which is inefficient for bursty data traffic compared to packet-switched networks. The circuit must be fully established end-to-end first, then data flows, then the circuit is torn down - this setup/teardown overhead is the key drawback. Voice traffic is actually well-suited to circuit switching.

The show ip route command displays the routing table where you can see multiple equal-cost paths to the same destination, which indicates load balancing is active. When load balancing is implemented, the routing table shows multiple next-hop addresses for the same network prefix. Show ip protocols shows routing protocol parameters, and show ip interface commands display interface status but not load balancing state.

When the no version 2 command is used in RIP configuration, the router stops sending RIPv2 updates but still receives both RIPv1 and RIPv2 updates. This allows compatibility with mixed-version networks during migration. The router doesn't add subnet masks (RIPv1 doesn't support them), doesn't use multicast (RIPv1 uses broadcast 255.255.255.255), and doesn't remove RIP entirely - it just changes the transmission behavior to version 1 while remaining backward-compatible for receiving.

RARP (Reverse Address Resolution Protocol) is used to obtain an IP address when the MAC address is known. This is the reverse of ARP, which resolves MAC addresses from known IP addresses. RARP was historically used by diskless workstations to obtain their IP configuration at boot. TCP handles transport, IP handles routing, and ARP resolves MAC from IP - none of these look up IP from Ethernet addresses like RARP does.

A PDU (Protocol Data Unit) is the technical term for a layer-specific encapsulation unit as data moves down the OSI or TCP/IP stack. At each layer, data is encapsulated with that layer's header (and trailer) creating a PDU - bits at Physical, frames at Data Link, packets at Network, segments at Transport, and data at Application layers. The other options describe transmission problems or processes, not what a PDU fundamentally is.

A Denial of Service (DoS) attack overwhelms a server with fake requests, consuming resources and preventing legitimate users from accessing the service. The key symptom is a server operating slowly under a high volume of malicious requests. Reconnaissance (A) is information gathering, access attacks (B) involve unauthorized entry, while worms (D) and viruses (E) are self-replicating malware.

ACLs applied inbound on an interface filter traffic entering that interface. Since hosts on 172.11.10.0/24 can still telnet to 10.10.0.0/16, the traffic isn't passing through the serial0/0/0 interface where the ACL is applied inbound. Applying the ACL outbound (on serial0/0/0) would filter traffic leaving R1 toward the 172.11.10.0 network. Applying it on FastEthernet0/0 (B) would be incorrect since that's a different interface.

RIP (Routing Information Protocol) is a Distance Vector routing protocol that uses hop count as its metric. OSPF (Open Shortest Path First) is a Link-State protocol that uses Dijkstra's algorithm. Option A correctly pairs RIP with Distance Vector. Option B is wrong because RIP is not Link-State. Option C is wrong because OSPF is not Distance Vector. Option D has the correct protocol-type pairing but A is the answer that's marked correct.

If Computer A can communicate with Computer B (likely on the same switch) but not with C or D (on the other switch), the trunk link between switches isn't carrying VLAN 50 traffic. By default, trunks carry all VLANs unless explicitly restricted. If VLAN 50 was previously removed from the allowed list or the trunk wasn't properly configured, inter-switch communication for that VLAN fails. Native VLAN mismatch (A) would cause different errors. A non-trunked link (B) wouldn't allow any VLAN traffic to pass.

Split horizon is a mechanism that prevents a router from advertising a route back out the same interface through which it was learned. When the 10.4.0.0 network fails, R2 would receive information about it from R1. Without split horizon, R2 might advertise this route back to R1, causing routing loops or confusion. Split horizon prevents this by not advertising the route back toward its source. Hold-down timers (B) suppress route updates for a period, route poisoning (C) marks routes as unreachable, and triggered updates (D) send immediate notifications.

The default subnet mask associated with a Class B IP address is 255.255.0.0