Free CCNA practice questions

A duplex mismatch produces different symptoms on each end of the same link.

The half-duplex end transmits when it senses the line idle and treats incoming frames during its transmission as collisions, many detected after the first 64 bytes (late collisions). The full-duplex end ignores carrier sense, so it transmits over the half-duplex end's frames, and the frames the half-duplex end aborts arrive truncated as runts or with bad FCS (CRC errors). Here the outputs show 'Half-duplex' versus 'Full Duplex' at the same 100 Mb/s, which rules out a speed mismatch; a damaged cable or over-length run would not explain the asymmetric counters.

1. Compare the duplex and speed lines of both outputs.
2. Note that speeds match but duplex differs.
3. Match late collisions to the half-duplex end and CRC/runts to the full-duplex end.
4. Conclude duplex mismatch and set both ends to the same duplex (preferably autonegotiate both).

Exam tip: Late collisions on one end plus CRC errors on the other end of the same link means duplex mismatch.

DTP negotiation between two dynamic auto ports

The default administrative mode on these switch ports is dynamic auto. A dynamic auto port becomes a trunk only if the neighbour actively asks for one (trunk or dynamic desirable). With dynamic auto on both ends nobody asks, so both operate as access ports in VLAN 1 and VLAN 20 cannot cross. Encapsulation, allowed lists and native VLANs only matter once the link is trunking.

1. Read Operational Mode: static access means no trunk formed.
2. Note the Administrative Mode on both ends is dynamic auto.
3. Recall that dynamic auto responds to DTP but never initiates.
4. Set one or both ends to switchport mode trunk to form the trunk.

Exam tip: Dynamic auto on both ends never forms a trunk: someone has to ask.

An IPv4 default route is a static route to 0.0.0.0/0.

The default route is written as ip route 0.0.0.0 0.0.0.0 followed by a next hop or exit interface. A /0 prefix matches every destination, so the router uses it whenever no more specific route exists. Mask 255.255.255.255 turns the entry into a host route, and ip default-gateway only applies when the device is not routing.

1. Note that BR1 is routing, so the answer must be an ip route entry.
2. Recall that a default route has prefix 0.0.0.0 and mask 0.0.0.0.
3. Point it at the ISP router's address on the connected subnet.

Exam tip: Default route = ip route 0.0.0.0 0.0.0.0 <next hop>; ip default-gateway is only for non-routing devices.

Local accounts are created with the username command; secret hashes the credential and privilege sets the starting level.

username <name> privilege 15 secret <pw> creates a local account whose credential is stored as a one-way hash and whose session starts at level 15. The password keyword is the tempting near-twin: it stores clear text, and service password-encryption only turns it into reversible type 7. Privilege 1 would leave the user at the > prompt, needing the enable secret. Only the combination of secret and privilege 15 meets both rules.

1. Spot the two requirements: a one-way hash and level 15 at login.
2. Choose secret, not password, for the hash.
3. Check the privilege value on the same line.
4. Keep only the option that gets both parts right.

Exam tip: Local accounts: username NAME privilege 15 secret PW. Secret is a hash; password is clear or type 7.

Generative AI creates content from a prompt; agentic AI pursues a goal over several steps and uses tools to observe and act.

Tool 2 is triggered by what it observes, chooses which show commands to run, interprets the results and acts by opening a change request. Goal-driven, multi-step behaviour with tool use is what makes a system agentic. Tool 1 is generative AI: useful, but it waits for a prompt and only returns content.

1. Ask what starts each tool: a prompt, or an observed condition.
2. Ask whether the tool calls other systems (APIs, show commands) itself.
3. Several self-directed steps with tool calls point to an agent.

Exam tip: Generative AI answers; agentic AI observes, decides and acts toward a goal.