VLANs Practice Questions

Answers and explanations appear when you work through the set above.

1. On a freshly reset Catalyst switch, which VLANs already exist in the VLAN database before any configuration is entered?

   • Only VLAN 1
   • VLAN 1 and the reserved VLANs 1002 to 1005 for legacy media types
   • VLANs 1 through 10
   • No VLANs exist until vlan database is initialized

2. Which two commands, entered in the correct order under interface configuration mode, place a switchport into VLAN 20 as an access port?

   • switchport mode trunk, then switchport trunk allowed vlan 20
   • switchport mode access, then switchport access vlan 20
   • switchport access vlan 20, then no switchport trunk
   • vlan 20, then switchport mode access

3. Both ends of a connected switch link are set to dynamic auto, with DTP enabled. Why does the link remain in access mode?

   • The link is already trunking normally
   • Neither side is actively initiating trunk negotiation, so the link stays in access mode
   • The link has a VLAN mismatch that must be fixed with switchport trunk allowed vlan
   • The port is administratively shut down

4. Which command explicitly forces a switch interface into trunking mode regardless of what the neighboring device negotiates?

   • switchport mode dynamic desirable
   • switchport nonegotiate
   • switchport mode trunk
   • switchport trunk encapsulation dot1q

5. On a switch that supports multiple trunk encapsulation types, which command must sometimes run before switchport mode trunk will succeed?

   • switchport trunk native vlan 1
   • switchport trunk encapsulation dot1q
   • switchport voice vlan
   • spanning-tree portfast trunk

6. Why would an administrator change a trunk's native VLAN away from VLAN 1 to an unused VLAN such as 199?

   • To increase the trunk's available bandwidth
   • To reduce the risk of VLAN hopping and keep untagged management traffic off the default VLAN
   • Because VLAN 1 cannot carry tagged frames
   • To allow more than one native VLAN per trunk

7. With native-VLAN tagging disabled, what risk does a native-VLAN mismatch introduce on an 802.1Q trunk?

   • The trunk automatically negotiates a shared native VLAN
   • The link refuses to come up at all
   • Untagged frames can be classified into different VLANs at the two ends
   • Only the lower numbered native VLAN is used by both sides

8. Which command restricts a trunk so that only VLANs 10, 20, and 199 are permitted to cross it?

   • switchport trunk allowed vlan 10,20,199
   • switchport access vlan 10,20,199
   • vlan filter 10,20,199
   • switchport trunk native vlan 10,20,199

9. In the router-on-a-stick model, what must be configured on a router subinterface so it can process 802.1Q tagged frames for a specific VLAN?

   • switchport trunk encapsulation dot1q
   • encapsulation dot1q <vlan-id>
   • ip address <vlan-id> secondary
   • channel-group <vlan-id> mode active

10. A router-on-a-stick design uses one physical interface with two subinterfaces, f0/0.10 and f0/0.20. What must the connected switchport be configured as?

    • An access port in VLAN 10
    • An access port in VLAN 20
    • A trunk port carrying both VLAN 10 and VLAN 20
    • An EtherChannel member port

11. Which inter-VLAN routing design avoids using any router hardware entirely, instead routing directly on the switch?

    • Router-on-a-stick using subinterfaces
    • Separate physical router interfaces per VLAN
    • A Layer 3 switch with ip routing enabled and per-VLAN SVIs
    • A single access port shared by all VLANs

12. A multilayer switch has correctly addressed SVIs that are administratively shut down, and global IPv4 routing is disabled. Which commands address these two configuration faults?

    • ip routing globally, and no shutdown on each interface vlan
    • switchport mode trunk on the SVIs
    • vtp mode transparent, and ip default-gateway
    • spanning-tree mode rapid-pvst and ip routing

13. Both PCs can reach their correctly configured SVI gateways, but not each other across VLANs. ACLs permit the traffic and the switch configuration shows no ip routing. Which change addresses the demonstrated forwarding fault?

    • The VLANs need matching names
    • ip routing has not been enabled globally on the switch
    • The PCs need static ARP entries
    • The switch needs a loopback interface

14. What does the command interface range fastethernet0/1 - 3 let an administrator do?

    • Bundle three interfaces into a single EtherChannel automatically
    • Apply the same configuration commands to interfaces 1 through 3 in one step
    • Create a VLAN spanning three switches
    • Assign three IP addresses to one interface

15. Which VLAN feature carries phone traffic on the same physical access port as data traffic, but keeps it in a separate VLAN from the PC?

    • Private VLAN
    • Voice VLAN
    • Native VLAN
    • Management VLAN

16. An engineer deletes VLAN 20 from a switch while several ports are still assigned to it in access mode. What happens to those ports?

    • They automatically move back to VLAN 1
    • They retain VLAN 20 membership but cannot forward access traffic until that VLAN is restored or they are reassigned
    • They are automatically shut down permanently
    • They become trunk ports

17. What command shows the operational trunking encapsulation and administrative/operational mode for a single interface in detail?

    • show interfaces trunk
    • show interface <name> switchport
    • show vlan id 1
    • show spanning-tree interface

18. Two switches are connected with a trunk, but show interfaces trunk on one of them lists no VLANs under 'Vlans allowed and active in management domain'. What is the most likely cause?

    • The trunk is down at Layer 1
    • No VLANs exist in the VLAN database on that switch, or all VLANs have been pruned from the allowed list
    • The switch has no IP address
    • STP is blocking the trunk

19. Why might a network designer choose separate physical router interfaces per VLAN instead of router-on-a-stick, despite it using more hardware?

    • It supports more VLANs than subinterfaces can
    • It avoids relying on trunking and 802.1Q tagging, which some environments still restrict for troubleshooting simplicity
    • It is required whenever more than two VLANs exist
    • Subinterfaces cannot carry an IP address