Thursday Study Session Flashcards
(15 cards)
Q: A PC can ping others in its VLAN but not devices in another VLAN. What’s the likely issue?
- Incorrect subnet mask
- Missing default gateway
- SVI not configured
- DNS failure
Correct Answer: SVI not configured
Explanation: Without a Switched Virtual Interface (SVI), VLANs cannot route between each other.
Practical Use: Ensure SVI exists for each VLAN involved in routing.
Why Others Are Incorrect:
- Subnet mask affects local comms but doesn’t block inter-VLAN.
- Gateway must be set, but it needs an active SVI.
- DNS only impacts name resolution, not pinging by IP.
Objective: Inter-VLAN routing diagnosis
Follow-up: What command shows active SVIs?
Q: What is the purpose of a default gateway on a host?
- Assign IP addresses
- Enable external communication beyond the local subnet
- Encrypt packets
- Resolve MAC addresses
Correct Answer: Enable external communication beyond the local subnet
Explanation: The default gateway forwards packets destined for outside the local subnet.
Practical Use: Required for inter-VLAN or Internet access.
Why Others Are Incorrect:
- IPs are assigned by DHCP.
- Encryption is done at other layers.
- ARP resolves MACs, not gateways.
Objective: Network access basics
Follow-up: What happens if the default gateway is on a different subnet than the host?
Q: A host has an IP of 192.168.20.10/24 and a default gateway of 192.168.10.1. What’s wrong?
- Gateway is unreachable due to subnet mismatch
- DNS is down
- SVI is misconfigured
- Trunk port is down
Correct Answer: Gateway is unreachable due to subnet mismatch
Explanation: The host and gateway are in different subnets, preventing communication.
Practical Use: IP and gateway must share the same subnet.
Why Others Are Incorrect:
- DNS wouldn’t prevent basic IP communication.
- SVI affects VLAN interfaces, not end-host config.
- Trunk ports affect VLAN transport, not IP configs.
Objective: Subnet troubleshooting
Follow-up: How can you verify a subnet mismatch from the CLI?
Q: What does show ip interface brief display?
- Active VLAN IDs
- Interface status and IP addresses
- MAC table
- Routing protocols in use
Correct Answer: Interface status and IP addresses
Explanation: It provides summary of IP-enabled interfaces and their states.
Practical Use: Check if SVI or routed interfaces are up and configured.
Why Others Are Incorrect:
- VLANs are in show vlan brief.
- MAC table uses show mac address-table.
- Routing protocols use show ip protocols.
Objective: Interface verification
Follow-up: What output column confirms if an SVI is active?
Q: What command shows all active VLANs on a switch?
- show ip interface brief
- show vlan brief
- show ip route
- show interfaces status
Correct Answer: show vlan brief
Explanation: Displays VLANs and their assigned ports.
Practical Use: Verifies VLAN creation and port assignment.
Why Others Are Incorrect:
- IP interfaces show SVI config.
- Routing table uses show ip route.
- Interface status doesn’t confirm VLANs.
Objective: VLAN review
Follow-up: What does it mean if a port shows as ‘inactive’ under a VLAN?
Q: Which command shows all static and dynamic routes known by a router?
- show vlan brief
- show ip interface brief
- show ip route
- show interfaces trunk
Correct Answer: show ip route
Explanation: Lists learned routes, next hops, and interface assignments.
Practical Use: Troubleshoot routing path availability.
Why Others Are Incorrect:
- VLAN and interface commands don’t show routes.
- Trunk status is unrelated.
Objective: Routing table review
Follow-up: What letter in show ip route output indicates a static route?
Q: A host cannot reach an external network. It has IP 10.0.0.10/8 and gateway 10.0.1.1. Which command confirms if the gateway exists?
- show interfaces trunk
- ping 10.0.1.1
- show vlan brief
- show mac address-table
Correct Answer: ping 10.0.1.1
Explanation: A direct ping test confirms if the default gateway is reachable.
Practical Use: First step in isolating local vs routing issue.
Why Others Are Incorrect:
- Trunk/VLAN commands are Layer 2.
- MAC table is not relevant yet.
Objective: Gateway diagnosis
Follow-up: What’s the next step if ping to gateway fails?
Q: What does a missing SVI IP address cause?
- VLAN not to exist
- Devices unable to communicate across VLANs
- STP failure
- Trunk port shutdown
Correct Answer: Devices unable to communicate across VLANs
Explanation: The SVI must have an IP for routing between VLANs to function.
Practical Use: Always assign IP to each SVI for inter-VLAN routing.
Why Others Are Incorrect:
- VLAN can still exist.
- STP handles loops.
- Trunk port is unaffected.
Objective: SVI setup troubleshooting
Follow-up: What command assigns an IP address to an SVI?
Q: Which protocol is used to dynamically share routing information between routers?
- DNS
- STP
- EIGRP
- DHCP
Correct Answer: EIGRP
Explanation: Enhanced Interior Gateway Routing Protocol dynamically shares routes.
Practical Use: Automates routing table updates.
Why Others Are Incorrect:
- DNS resolves names.
- STP prevents loops.
- DHCP assigns IPs.
Objective: Dynamic routing fundamentals
Follow-up: What command shows EIGRP neighbors?
Q: What is ‘Router-on-a-Stick’?
- A switch using static routing
- A router with one trunk port handling multiple VLANs
- A DHCP server setup
- A Layer 3 switch interface
Correct Answer: A router with one trunk port handling multiple VLANs
Explanation: It routes traffic between VLANs using a single interface with subinterfaces.
Practical Use: Common on smaller networks with one router.
Why Others Are Incorrect:
- Static routing doesn’t define Router-on-a-Stick.
- Not tied to DHCP or Layer 3 switching.
Objective: Inter-VLAN routing setups
Follow-up: What command creates a subinterface on a router?
Q: A switch trunk port is missing VLAN 30. What issue will this cause for inter-VLAN routing?
- VLAN 30 cannot be pinged across switches
- SVI fails
- IP addresses reset
- MAC addresses duplicate
Correct Answer: VLAN 30 cannot be pinged across switches
Explanation: If a trunk doesn’t carry a VLAN, routing traffic for that VLAN fails.
Practical Use: Always check trunk port VLAN allowance.
Why Others Are Incorrect:
- SVI may be fine locally.
- IPs and MACs are unaffected directly.
Objective: VLAN transport validation
Follow-up: What command shows allowed VLANs on a trunk?
Q: What is the purpose of a static route?
- Block unknown VLANs
- Assign hostnames
- Manually define a next hop for a destination network
- Enable DHCP
Correct Answer: Manually define a next hop for a destination network
Explanation: Static routes provide fixed paths to specific networks.
Practical Use: Used in small networks or for security control.
Why Others Are Incorrect:
- VLAN blocking uses VTP or trunk settings.
- Hostnames and DHCP unrelated.
Objective: Static routing use
Follow-up: What command configures a static route in Cisco IOS?
Q: What does ‘Administrative Distance’ refer to?
- VLAN ID priority
- Trustworthiness of a route source
- DNS preference
- MAC aging time
Correct Answer: Trustworthiness of a route source
Explanation: Lower administrative distance values are preferred.
Practical Use: Helps routers choose between static, EIGRP, OSPF, etc.
Why Others Are Incorrect:
- VLAN ID and MAC aging aren’t related.
- DNS doesn’t involve this metric.
Objective: Routing decision hierarchy
Follow-up: What is the AD for a directly connected route?
Q: What command shows IPs and interfaces used to reach different networks?
- show interfaces trunk
- show ip protocols
- show ip route
- show vlan brief
Correct Answer: show ip route
Explanation: Displays routing table entries including next hop and exit interface.
Practical Use: Verifies connectivity paths and routing logic.
Why Others Are Incorrect:
- Other commands relate to VLANs, trunks, or protocols.
Objective: Route analysis
Follow-up: What does a route with ‘C’ in the output mean?
Q: A host can access its VLAN but not others. The switch has SVIs, and the trunk is correct. What’s missing?
- Subnet mask
- MAC address
- Default gateway
- IP helper address
Correct Answer: Default gateway
Explanation: Without a default gateway, the host can’t send traffic to other subnets.
Practical Use: Set host gateway to the SVI of its VLAN.
Why Others Are Incorrect:
- Mask may still allow local traffic.
- MAC isn’t related here.
- IP helper is for DHCP relay.
Objective: Host config validation
Follow-up: What command shows a host’s gateway setting in Windows?
