VLAN & Trunking Questions
Note: If you are not sure about Virtual Local Area Network (VLAN), please read our Virtual Local Area Network VLAN Tutorial.
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Quick summary about VLAN: Be default all access ports belong to VLAN 1. If we want to assign a new VLAN, we have to use the command “switchport access vlan <vlan-id>” under interface mode. VLAN Benefits: – Logically group devices by department/function, not location so it provides more efficient use of bandwidth The following commands are used to a create a VLAN (for example VLAN 10) and assign it to an interface (for example fa0/1) on a switch: Switch(config)#vlan 10 //Create VLAN 10 first To verify a VLAN or check which ports belong to which VLAN, use the “show vlan” command (or “show vlan id <vlan-id>” for a specific VLAN) DTP Trunking modes
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Question 1
Explanation
From the output we see the native VLAN of Switch1 on Gi0/1 interface is VLAN 1 while that of Switch2 is VLAN 99 so there would be a native VLAN mismatch.
Question 2
Explanation
Maybe this question is missing the “SW2 is set to Dynamic Auto” part so we assume this part to find out the best answer. Dynamic Desirable + Dynamic Desirable/Dynamic Auto/Trunk will form a trunk link.
Question 3
Explanation
The trunk still forms with mismatched native VLANs and the traffic can actually flow between mismatched switches. But it is absolutely necessary that the native VLANs on both ends of a trunk link match; otherwise a native VLAN mismatch occurs, causing the two VLANs to effectively merge. For example with the above configuration, SW1 would send untagged frames for VLAN 999. SW2 receives them but would think they are for VLAN 99 so we can say these two VLANs are merged.
Question 4
Question 5
Explanation
For 802.1q encapsulation, the native VLAN must matched at both side; otherwise the link will not work. In this case the native VLAN of S1 is 1 while the native VLAN of S2 is 2. Therefore when a frame from VLAN 1 is sent from S1 to S2, it will be untagged before leaving S1. When S2 receives this untagged frame, it believes this frame was sent from the native VLAN. But the native VLAN on S2 is VLAN 2, not VLAN 1. Therefore only hosts on VLAN2 of S2 will receive this frame.
Question 6
Question 7
Explanation
From the configuration of SW1, we see it is using Port Aggregation Protocol (PAgP) with “auto” mode so the other end (SW2) must also runs PAgP with “desirable” mode to actively sending request to form an Etherchannel.
Question 8
Question 9
Question 10
Am new to Cisco and will to do an exam of ccna and need help
I have a question. In Question 1 we see the mismatched native VLANs not allowing traffic to pass but in question three we see that the mismatch VLANs will allow traffic to pass. Can somebody explain the difference?
How come the questions arent shown on most of these?
this is soo good, thanks 9tut i appreciate it!
Am new to Cisco and will to do an exam of ccna and need help
@Chris Jones: For me, on 1st question, PC can’t ping each other because ping is sent on tagged Vlan 99 from SW1, but on SW2 Vlan 99 is the native vlan so, it is waiting untagged frames on Vlan 99, that’s why it causes the problem. But I’m not sure :) .
I let other person correct or confirm my explanation if needed.
I have a question. I cant view the questions, all i can see are the explanation. Can someone help me?
@9tut I believe Q.1 should be “Based” not ” Baaed.”
@Da Hulk: Thanks for your detection, we have just fixed it!
In Q3, i think the correct aswer is C
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Can someone please clarify Q3.
I think the answer is C
I think Q7 should go to ‘EtherChannel questions’ section
In question 6:
SW1#show run int gig 0/1
interface GigabitEthernet0/1
switchport access vlan 11
switchport trunk allowed vlan 1-10
switchport trunk encapsulation dot1q
switchport trunk native vlan 5
switchport mode trunk
speed 1000
duplex full
How come the port is Trunk as well as Access? It just cannot be both…
may i ask a silly question regarding question 9,why a workstation connected to the phone sends and receives data in VLAN 1.?
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for question 6
is data using the default vlan as 1 and te voice traffic is using vlan 50? or when the data recieved by phone it sends voice and data traffic on vlan 50?
the reaosn im asking this is because normally vlan 1 isnt used for vlan traffic because its usually native vlan
On question 1, the answer is D
Native vlan mismatch is not an issue here, but vlan pruning is:
Pruning VLANs Enabled: 2-1001
@Amedeo: No, it is not the issue of this question. In fact, “Pruning VLANs Enabled” is just the “Pruning-Eligible List” and VTP pruning must be enabled for this procedure to take effect. It does not means all VLANs from 2 to 1001 were pruned.
@9tut in Question 6, how is it possible to configure an interface in both access & trunk modes??
@D: In Q6, that interface was configured in trunk mode only, not access mode.