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Layer 2 Practice Questions

15 original questions covering ENCOR 3.1.a to 3.1.c. Answer every one before opening any explanation. Target: 12 of 15 (80%).

1. Blueprint 3.1.a

Refer to the exhibit.

SW1# show running-config interface GigabitEthernet0/1
interface GigabitEthernet0/1
 switchport trunk encapsulation dot1q
 switchport mode trunk
 switchport nonegotiate

SW2# show running-config interface GigabitEthernet0/1
interface GigabitEthernet0/1
 switchport mode dynamic desirable

What is the operational mode of each port?

  • A. Both ports are trunks, because desirable forms a trunk with trunk
  • B. Both ports are access ports
  • C. SW1 is a trunk and SW2 is an access port
  • D. Both ports are err-disabled
Answer: C

switchport nonegotiate stops SW1 from sending DTP frames. SW1 is hard-coded as a trunk, so it trunks regardless. SW2 is dynamic desirable and asks to trunk, but never hears a reply, so it falls back to access. A would be true without nonegotiate. DTP never err-disables a port (D). Fix it by hard-coding SW2 as a trunk too.

2. Blueprint 3.1.a

Refer to the exhibit.

DIST1# show interfaces trunk

Port        Mode             Encapsulation  Status        Native vlan
Gi0/3       on               802.1q         trunking      999

Port        Vlans allowed on trunk
Gi0/3       10,20,40,999

Port        Vlans allowed and active in management domain
Gi0/3       10,20,999

Port        Vlans in spanning tree forwarding state and not pruned
Gi0/3       10,20,999

Hosts in VLAN 40 cannot communicate across this trunk. What is the fix on DIST1?

  • A. switchport trunk allowed vlan add 40 on Gi0/3
  • B. spanning-tree vlan 40 priority 4096
  • C. switchport trunk native vlan 40 on Gi0/3
  • D. Create VLAN 40 in the VLAN database
Answer: D

VLAN 40 is allowed on the trunk but does not appear in the "allowed and active" section, which means the VLAN does not exist (or is suspended) on DIST1. Creating it fixes the problem. It is already in the allowed list (A). Spanning tree is not the issue because the VLAN never reached the STP section (B). Changing the native VLAN (C) would create a native VLAN mismatch.

3. Blueprint 3.1.a

A trunk between ACC3 and DIST1 carries VLANs 10, 20 and 99 (management). An engineer connected by SSH to ACC3's VLAN 99 address needs to add VLAN 30 to the uplink and enters:

ACC3(config)# interface GigabitEthernet0/1
ACC3(config-if)# switchport trunk allowed vlan 30

What happens?

  • A. VLAN 30 is added and the other VLANs are unaffected
  • B. The allowed list becomes only VLAN 30, and the SSH session drops
  • C. VLAN 30 becomes the native VLAN
  • D. The command is rejected because add is required
Answer: B

Without add, the command replaces the whole allowed list. VLANs 10, 20 and 99 stop crossing the trunk, so the management session over VLAN 99 is cut. The correct command is switchport trunk allowed vlan add 30. The command is valid syntax, so it is not rejected (D).

4. Blueprint 3.1.a

Refer to the exhibit.

SW2# show interfaces GigabitEthernet0/2 switchport | include Mode
Administrative Mode: dynamic auto
Operational Mode: static access

SW1# show interfaces GigabitEthernet0/2 switchport | include Mode
Administrative Mode: dynamic desirable
Operational Mode: static access

%DTP-5-DOMAINMISMATCH: Unable to perform trunk negotiation on port Gi0/2 because of VTP domain mismatch.

Which two changes would make the link a trunk? (Choose two.)

  • A. Configure the same VTP domain name on both switches
  • B. Change SW2 to switchport mode dynamic desirable
  • C. Configure both ports with switchport mode trunk
  • D. Configure the same native VLAN on both ports
  • E. Enable VTP pruning
Answer: A, C

DTP carries the VTP domain name, and negotiation fails when the two non-empty names differ. Matching the domain name lets desirable and auto negotiate (A). Static trunks do not depend on DTP negotiation, so hard-coding both ends also works (C). Desirable on both ends (B) still negotiates through DTP and still fails on the domain mismatch. Native VLAN (D) and pruning (E) do not affect whether a trunk forms.

5. Blueprint 3.1.a

A switch in VTP client mode, domain CAMPUS, configuration revision 52, is taken from a lab and connected by a trunk to the production network. The production server for domain CAMPUS is at revision 17. All switches run VTP version 2 with no password. What is the most likely result?

  • A. The lab switch learns the production VLANs because servers always win over clients
  • B. The trunk is err-disabled because of a revision mismatch
  • C. Nothing happens because a client cannot send advertisements
  • D. The production switches replace their VLAN databases with the lab switch's database
Answer: D

VTP compares configuration revision numbers, not modes. A client forwards and originates its database in advertisements, and switches in the same domain accept a higher revision. The production switches overwrite their VLAN databases, which can delete VLANs in use. VTP version 3 prevents this with the primary server concept. Reset the revision (change the domain name or go transparent and back) before connecting any switch.

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