CCNA 2 Routing and Switching Essentials v5 Chapter 5: Inter-VLAN Routing – Check Your Understanding Questions Answers
1. Classify each item as either physical interface or subinterface.
one physical interface for many VLANs
bandwidth contention
access mode switch port connection
complex cable configuration
trunk mode switch port connection
one physical interface per VLAN
| one physical interface for many VLANs | subinterface |
| bandwidth contention | subinterface |
| access mode switch port connection | physical interface |
| complex cable configuration | physical interface |
| trunk mode switch port connection | subinterface |
| one physical interface per VLAN | physical interface |
Explanation: Physical interface solutions involve more complex cabling, access port switch configurations, and one physical router interface per VLAN.
2. Classify each item as either router-on-a-stick, Layer 3 switch routing, or both.
____ all VLANs share a single cable
____ multiple SVIs
____ faster
____ trunk mode switch port connection
____ an IP address per VLAN
____ routed port
| router-on-a-stick | all VLANs share a single cable |
| router-on-a-stick | multiple SVIs |
| Layer 3 switch routing | faster |
| Layer 3 switch routing | trunk mode switch port connection |
| routeron-a-stick both | an IP address per VLAN |
| Layer 3 switch routing | routed port |
Explanation: A Layer 3 switch routed port is commonly used when Layer 3 switching is used to route between VLANs. The router-on-a-stick model involves setting up a trunk port on the switch and using subinterfaces on the router.
3. What are three advantages of having a single trunk link on a switch and subinterfaces on the router instead of individual VLAN links between a switch that has three VLANs and a router to route between the VLANs? (Choose three.)
- It would free two switch and router ports.
- It would reduce the complexity of the cabling runs.
- It would increase the amount of bandwidth available for inter-VLAN routing.
- It would allow for less complex troubleshooting of inter-VLAN routing issues.
- It would allow adding more VLANs without requiring more cabling or switch ports.
- It would allow for less-complex configuration of inter-VLAN routing.
Explanation: Keep in mind that the solution decreases available bandwidth and increases troubleshooting and configuration complexity.
4. What condition is required to enable Layer 3 switching?
- The Layer 3 switch must have IP routing enabled.
- All participating switches must have unique VLAN numbers.
- All routed subnets must be on the same VLAN.
- Inter-VLAN portions of Layer 3 switching must use router-on-a-stick.
Explanation: Some Layer 3 switches do not have an image loaded that supports Layer 3 switching; if it does, IP routing needs to be enabled by typing ip routing from global configuration mode. Layer 3 switches preclude the need for router-on-a-stick.
5. When implementing router-on-a-stick, what is necessary for establishing communication between VLANs?
- Multiple switch ports to connect to a single router interface
- Native VLAN IP address that is configured on the router physical interface
- All trunk ports configured in access mode
- Router subinterfaces
Explanation: Router-on-a-stick only requires a single trunk port with a native VLAN assigned to one subinterface.
6. How does the router-on-a-stick model for inter-VLAN routing differ from traditional routing?
- The router-on-a-stick model uses multiple physical interfaces on the router, each configured with a different Layer 3 address.
- The router-on-a-stick model uses a single physical interface on the router with only the no shutdown command issued.
- The router-on-a-stick model uses subinterfaces on the router with only the no shutdown command issued on the physical interface.
- The router-on-a-stick model uses subinterfaces on the switch with only the no shutdown command issued on the physical interface.
Explanation: Router-on-a-stick uses subinterfaces on the participating router.
7. Which command does the network administrator use to determine whether inter-VLAN communication is functioning?
- show vlan
- ping
- ipconfig
- show interfaces
Explanation: ping tests the connectivity between the source and destination devices.
8. Which three options are valid inter-VLAN routing methods? (Choose three.)
- Traditional routing
- Spanning-tree routing
- Router-on-a-stick
- 802.1Q routing
- Multilayer switch-based routing
Explanation: Traditional or legacy routing means one physical router interface per VLAN. There is no such thing as spanning-tree routing or 802.1Q routing.
9. A network technician is configuring a router to support inter-VLAN routing. After entering interface G0/0 configuration mode, the network administrator attempts to enter the command encapsulation dot1q 10. The router refuses to accept this command. What could account for this failure?
- Router port G0/0 is not physically connected to the switch.
- VLAN0001 has been renamed.
- R1 interface G0/0 was configured for subinterface operation.
- This command can be configured only on router subinterfaces.
- Interface G0/0 on the switch is shut down.
Explanation: G0/0 is a physical interface, and the command given is configured only on subinterfaces.
10. How many physical interfaces are required to perform inter-VLAN routing with each method indicated?
Legacy inter-VLAN routing: __________
Router-on-a-stick: _________
Multilayer switching: _________
| Legacy inter-VLAN routing | one physical port per VLAN |
| Router-on-a-stick | one physical interface (but multiple subinterfaces) |
| Multilayer switching | none |
Explanation: A company could implement routing between VLANs on just a multilayer switch. The switch would have devices connected to a physical interface, but these interfaces do not require any configuration to support inter- VLAN routing.
11. What command would be used to determine if all SVIs were “up and up” on a multilayer switch?
- show vlans
- show ip interface brief
- show running-config
- show interface switchport
Explanation: The show ip interface brief command is used on either a Layer 2 switch, multilayer switch, or a router to see if an interface (virtual or physical) is “up and up.”
12. A router-on-a-stick configuration will not allow PC1 on VLAN 10 to communicate with PC2 on VLAN 11. Which two of the following could be the problem? (Choose two.)
- The physical port on the router is shut down.
- The switch SVI is not “up and up.”
- The port between the switch and the router is not a routed port.
- The port between the switch and the router has been placed in access mode.
- One or both of the router subinterfaces have been configured with an IP address in a different network.
Explanation: Common problems in a router on-a-stick configuration include the physical port on the router being shut down, native VLAN mismatch between the router and the switch, and improper IP addressing to match the VLAN. Remember that each VLAN must have a different network number. On the switch side, ensure VLANs 10 and 11 are in the VLAN database, ensure the port connecting to the router is a trunk, and ensure the native VLAN matches the configured native VLAN on the router (or is the default of 1).