New CCNA Trunking Questions.

By | July 11, 2017

New CCNA Trunking Common Questions.

These are updated commonly asked CCNA exam questions on trunking. you might come across these but in a different context, so it’s beneficial if you understand Trunking.

Need a refresher; read Inter-VLAN routing


Question 1
Refer to the topology and router output shown in the exhibit:

A technician is troubleshooting host connectivity issues on the switches. The hosts in VLANs 10 and VLAN15 on Sw10 are unable to communicate with hosts in the same VLANs on Sw11. Hosts in the Admin VLAN are able to communicate. The port-to-VLAN assignments are identical on the two switches. What could be the problem?

A. The Fa0/1 port is not operational on one of the switches.
B. The Link connecting the switches has not been configured as a trunk.
C. At least one port needs to be configured in VLAN 1 for VLANs 10 and 15 to be able to communicate.
D. Port FastEthernet 0/1 needs to be configured as an access link on both switches.
E. A router is required for hosts on Sw10 in VLANs 10 and 15 to communicate with hosts in the same VLAN on Sw12.

Answer: B
Using the show vlan command only displays access ports,  trunk ports are not shown in this command.

Using the “show interface trunk” command would display trunked ports.

In the output above, you can see the ports Fa0/1 connecting between two switches in VLAN 20  which are access ports and only VLAN 20 can communicate.

To enable all VLANs to communicate (within the same VLAN at the other switch), the link between two switches must be set as a trunk.  that’s why B is chosen as the correct answer here.

Question 2
In a switched environment, what does the IEEE 802.1Q standard describe?
A. the operation of VTP
B. a method of VLAN trunking
C. an approach to wireless LAN communication
D. the process for root bridge selection
E. VLAN pruning

Answer: B

In Brief:

IEEE 802.1Q is the networking standard that supports virtual LANs (VLANs) on an Ethernet network. The standard defines a system of VLAN tagging for Ethernet frames and the accompanying procedures to be used by bridges and switches in handling such frames. The standard also contains provisions for a quality-of-service prioritization scheme commonly known as IEEE 802.1p

Question 3
As a network technician, do you know which are valid modes for a switch port used as a VLAN trunk? (Choose three)
A. transparent
B. auto
C. on
D. desirable
E. blocking
F. forwarding

Answer: B C D


Trunking Modes:

ON: Trunking is on for these links. They will also send DTP signals that attempt to initiate a trunk with the other side.

Desirable: These links would like to become trunk links and will send DTP signals that attempt to
initiate a trunk. They will only become trunk links if the other side responds to the DTP signal.

Auto: These links will only become trunk links if they receive a DTP signal from a link that is already trunking or desires to trunk. This will only form a trunk with other ports in the states on or desirable. This is the default mode for COS switches.


Question 4
Refer to the exhibit:

All switch ports are assigned to the correct VLANs, but none of the hosts connected to SwA can communicate with hosts in the same VLAN connected to SwB.

Based on the output shown, what is the most likely problem?

A. The access link needs to be configured in multiple VLANs.
B. The link between the switches is configured in the wrong VLAN
C. The link between the switches needs to be configured as a trunk.
D. VTP is not configured to carry VLAN information between the switches.
E. Switch IP addresses must be configured in order for traffic to be forwarded between the switches.

Answer: C


Trunks carry traffic from all VLANs to and from the switch by default but can be configured to carry only specified VLAN traffic. Trunk links must be configured to allow trunking on each end of the link.

Question 5
Which IEEE standard protocol is initiated as a result of successful DTP completion in a switchover FastEthernet?
A. 802.3ad
B. 802.1w
C. 802.1Q
D. 802.1d

Answer: C
Dynamic Trunking Protocol (DTP) is a Cisco proprietary protocol for negotiating trunking on a link between two devices and for negotiating the type of trunking encapsulation (802.1Q) to be used.

Question 6
Which three of these statements regarding 802.1Q trunking is correct? (Choose three)
A. 802.1Q native VLAN frames are untagged by default.
B. 802.1Q trunking ports can also be secure ports.
C. 802.1Q trunks can use 10 Mb/s Ethernet interfaces.
D. 802.1Q trunks require full-duplex, point-to-point connectivity.
E. 802.1Q trunks should have native VLANs that are the same at both ends.

Answer: A C E


Question 7
Refer to the exhibit:

D-router is to be used as a “router-on-a-stick” to route between the VLANs. All the interfaces have been properly configured and IP routing is operational. The hosts in the VLANs have been configured with the appropriate default gateway. What can be said about this configuration?

A. These commands need to be added to the configuration:
C-router(config)# router eigrp 123
C-router(config-router)# network

B. No further routing configuration is required.

C. These commands need to be added to the configuration:
C-router(config)# router ospf 1
C-router(config-router)# network area 0

D. These commands need to be added to the configuration:
C-router(config)# router rip
C-router(config-router)# network

Answer: B


Anytime you see an interface configure as Fa0/0.1 or more shows that is a subinterface configuration.

Read more on Router-on-a stick here or Subinterfaces.

Question 8
Refer to the exhibit:

What commands must be configured on the 2950 switch and the router to allow communication between host A and host B? (Choose two)
A. Router(config)#interface fastethernet 0/0
Router(config-if)#ip address
Router(config-if)#no shut down

B. Router(config)#interface fastethernet 0/0
Router(config-if)#no shutdown
Router(config)#interface fastethernet 0/0.1
Router(config-subif)#encapsulation dot1q 10
Router(config-subif)#ip address
Router(config-subif)#interface fastethernet 0/0.2
Router(config-subif)#encapsulation dot1q 20
Router(config-subif)#ip address

C. Router (config)#router eigrp 100

D. Switch1(config)# vlan database
Switch1(config-vlan)# vtp domain XYZ
Switch1(config-vlan)# vtp server

E. Switch1(config) # interface fastEthernet 0/1
Switch1(config-if)# switchport mode trunk

F. Switch1(config)# interface vlan 1
Switch1(config-if)# ip default-gateway

Answer: B E

In brief: Interfaces Fa0/0 and  Fa0/1 is configured here as sub-interfaces and trunked links with the 802.1Q protocol to enable inter-VLAN communication using a layer 3 network device or router.

Question 9
Which two of these are characteristics of the 802.1Q protocol? (Choose two)
A. It is a layer 2 messaging protocol which maintains vlan configurations across the network.
B. It includes an 8-bit field which specifies the priority of a frame.
C. It is used exclusively for tagging vlan frames and does not address network reconvergence following switched network topology changes.
D. It modifies the 802.3 frame header and thus requires that the FCS be recomputed.
E. It is a trunking protocol capable of earring untagged frames.

Answer: D E

IEEE 802.1Q is the networking standard that supports Virtual LANs (VLANs) on an Ethernet network. It is a protocol that allows VLANs to communicate with one another using a router. 802.1Q trunks support tagged and untagged frames.
If a switch receives untagged frames on a trunk port, it believes that frame is a part of the native VLAN. Also, frames from a native VLAN are not tagged when exiting the switch via a trunk port.

The 802.1q frame format is same as 802.3. The only change is the addition of 4 bytes fields. That additional header includes a field with which to identify the VLAN number. Because inserting this header changes the frame, 802.1Q encapsulation forces a recalculation of the original FCS field in the Ethernet trailer.

Note: Frame Check Sequence (FCS) is a four-octet field used to verify that the frame was received without loss or error. FCS is based on the contents of the entire frame.

Question 10
What are the possible trunking modes for a switch port? (Choose three)
A. transparent
B. auto
C. on
D. desirable
E. client
F. forwarding

Answer: B C D