VLAN Trunking
Question 1
Explanation
These errors are generated because the native VLAN is not matched on the two switches (the native VLAN on SW-1 is not the default native VLAN 1 while the native VLAN on the other side is VLAN 1). The errors indicate that spanning tree has detected mismatched native VLANs and has shut down VLAN 1 on the trunk.
We should verify that the configurations of the native VLAN ID is consistent on the interfaces on each end of the IEEE 802.1Q trunk connection. When the configurations are consistent, spanning tree automatically unblocks the interfaces.
Question 2
Explanation
In 802.1Q, the trunking device inserts a 4-byte tag into the original frame and recomputes the frame check sequence (FCS) before the device sends the frame over the trunk link. At the receiving end, the tag is removed and the frame is forwarded to the assigned VLAN. 802.1Q does not tag frames on the native VLAN. It tags all other frames that are transmitted and received on the trunk.
Reference: http://www.cisco.com/c/en/us/support/docs/lan-switching/8021q/17056-741-4.html
Question 3
Explanation
802.1Q is a industry standards based implementation of carrying traffic for multiple VLANs on a single trunking interface between two Ethernet switches. 802.1Q is for Ethernet networks only.
Question 4
Explanation
We can use the “switchport trunk allowed vlan ” to specify which VLANs are allowed to go through. Other VLANs will be dropped.
Question 5
Explanation
Manually configure trunking with the “switchport mode trunk” command and manually configure access interfaces with the “switchport mode access” prevent auto trunking on that interface.
Disable DTP with the “switchport nonegotiate” so that DTP messages are not advertised out of the interface is also a good way to prevent auto trunking.
Question 6
Explanation
There are two protocols that can be used for trunking: Inter-Switch Link (ISL) and 802.1Q. We can choose which protocol to run by the “switchport trunk encapsulation “. After that we can configure trunking mode with the “switchport mode trunk” command.
In fact this question is not clear and may cause confusion because Dynamic Trunking Protocol (DTP) is the protocol that can automatically negotiate for trunking.
Note: The DTP options can be dynamic auto, dynamic desirable, and trunk.
Question 7
Explanation
By default all VLANs are allowed to go through a trunk but if we apply the “switchport trunk allowed vlan ” then only these VLANs are allowed to go through, other VLANs are dropped so be careful when limiting VLANs on the trunks with this command.
Question 8
Explanation
We can use the “switchport trunk allowed vlan ” to specify which VLANs are allowed to go through. Other VLANs will be dropped.
Question 9
Explanation
First we will explain these two commands:
| switchport access vlan 10 switchport mode trunk |
The first command is used for an access port whist the second is used for a trunk so why are they here at the same time? In fact this interface was set as a trunk. The “switchport access vlan 10” is still there but it does not affect the operational mode of the port -> Gi1/0/1 is a trunk port so it will not appear in the “show vlan” command.
The “switchport voice vlan 11” command here only tries to confuse you. But it does have an effect on the port: Cisco uses CDP to specify a Cisco IP Phone and will automatically place that traffic into the voice VLAN. For example if we configure like this:
| interface fa0/0 switchport trunk encapsulation dot1q switchport mode trunk switchport voice vlan 11 |
Then the voice traffic from a Cisco IP Phone will be placed into VLAN 11.
Note: In the above configuration, the data and voice use the same interface fa0/0 so it should be configured as a trunk link.
(Reference: http://www.cisco.com/en/US/products/hw/switches/ps4324/products_configuration_example09186a0080722cdb.shtml)
Question 10
Explanation
VLAN 1 is always used for CDP, VTP, PAgP traffic (except DTP uses native VLAN) even if VLAN 1 is not the native VLAN. If VLAN 1 is not the native VLAN then CDP, VTP, PAgP traffic will be tagged on the trunk.
In this question, after changing the default native VLAN to 999 while keeping the standard configuration on the other end, we cause a “native VLAN mismatched” error. Besides, CDP, VTP traffic is tagged on the local switch (as VLAN 1 is no longer the native VLAN) so the other end cannot understand them -> CDP, VTP traffic is dropped.
Question 11
What will be the behavior of an access port when a tagged packet is received, with a VLAN ID of an access port?
A. The tag is removed and packet is forwarded to a VLAN of access port
B. The tag is removed and packet is forwarded of the VLAN mentioned in the tag.
C. The tag is not removed and packet is forwarded of the VLAN mentioned in the tag.
D. Packet is dropped.
The Answer: A
Q10 the answers do not match the explanation. Answer should be native vlan mismatch or something along those line.
@YMD I completely agree. It doesn’t matter that the native VLAN isn’t present on the trunk as the VTP and CDP traffic is still being sent but dropped at the other end because of the mismatch.
Hi
Could you please send me latest dump for ccnp switching??
my mail : ali_luay_92 at yahoo dot com
Q9 .I have got the following output :
s1(config-if)#sw acc vlan 10
s1(config-if)#sw tr enc dot1q
s1(config-if)#sw mode tr
s1(config-if)#sw voice vlan 11
% Voice VLAN does not exist. Creating vlan 11
s1(config-if)#
s1(config-if)#span
s1(config-if)#spanning-tree prt
s1(config-if)#spanning-tree port
s1(config-if)#spanning-tree portfast
s1(config-if)#end
s1#sh vlan
VLAN Name Status Ports
—- ——————————– ——— ——————————-
1 default active Fa0/1, Fa0/2, Fa0/3, Fa0/4, Fa0/5, Fa0/6
Fa0/7, Fa0/8, Fa0/9, Fa0/10, Fa0/11
Fa0/12, Fa0/13, Fa0/14, Fa0/15, Fa0/16
Fa0/17, Fa0/18, Fa0/19, Fa0/20, Fa0/21
Fa0/22
10 VLAN0010 active Fa0/23, Gi0/2
11 VLAN0011 active Gi0/2
20 VLAN0020 active Fa0/24
1002 fddi-default act/unsup
1003 trcrf-default act/unsup
1004 fddinet-default act/unsup
1005 trbrf-default act/unsup
This is from a real c3560 switch
Q9 & Q10 answers are very strange because:
Q9: GNS3 can show anythink but on real SW (es. Cisco 4500) the correct answer is B. Also if it’s configured and work like a trunk, the show vlan command show the access port and the voice port on configured vlan.
Q10: Correct answer is E; normally with mode trunk enabled the native vlan 1 is already on trunk. In this case, changing the default native vlan to 999, the control traffic must be manually enabled on the new native vlan 999 with “switchport trunk native vlan 999” command on both peers oh the connection. On the answer there is not “on both peers….”.
Why are all questions deleted? Do I need premium access or is this some kind of legal problem?
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On Question 9:
It will show the G1/0/1 interface in both the 10 and 11 vlan
10 VLAN0101 active Fa1/0/39
11 VLAN0102 active Fa1/0/39
question 3 for me is ISL, because question is asking about a trunking protocol developed by CIsco. what do you think?
thenks
@Kjuta
The key point here is the wording “multivendor environment”. ISL won’t work on any other switches other than Cisco. So, the answer “dot1q” is correct.
@lalaversa
Depending on Cisco exam wording of the question could be “D” or “E”. Because technically native vlan should not need to be allowed on trunk interface as you can see below extract is taken directly from the official cert guide book for the SWITCH exam by David Hucaby. (P460, Chapter 20 – Securing vlans)
“Although maintenance protocols such as Cisco Discovery Protocol (CDP), Port Aggregation Protocol (PAgP), and Dynamic Trunking Protocol (DTP) normally are carried over the native VLAN of a trunk, they will not be affected if the native VLAN is removed or manually pruned from the trunk. They still will be sent and received on the native VLAN as a special case even if the native VLAN ID is not in the list of allowed VLANs.”
So, definitely “switchport trunk native vlan 999” command is missing on trunk interface configuration and that cause the issue. But, is this mean by Cisco “enabling the control traffic manually on the new Native Vlan?”. I never heard a term enabling control traffic manually, but it could be a trick question by Cisco. In any case, the native vlan 999 should not need to be allowed on trunk link. It will work without allowing it. It is very confusing wording in the question.
Im not quite sure about this answer,.
A network engineer must implement Ethernet links that are capable of transporting frames and IP traffic for different broadcast domains that are mutually isolated. Consider that this is a multivendor environment. Which Cisco IOS switching feature can be used to achieve the task?
A. PPP encapsulation with a virtual template
B. Link Aggregation Protocol at the access layer
C. dot1q VLAN trunking
D. Inter-Switch Link
Answer: C
Since ISL (Inter-Swich Link) is also used to make trunks and is Cisco Propietary.
SOmeone could help me?
Nevermind, I found it. the word ” multivendor environment”
Its clear now
Q.10 Anser D is not correct.
Although maintenance protocols such as Cisco Discovery Protocol (CDP), Port
Aggregation Protocol (PAgP), and Dynamic Trunking Protocol (DTP) normally are carried
over the native VLAN of a trunk, they will not be affected if the native VLAN is removed
or manually pruned from the trunk. They still will be sent and received on the native
VLAN as a special case even if the native VLAN ID is not in the list of allowed VLANs.
Q9 explanation:
Real device
SW1_POP_Chapala#sh inv
NAME: “SW1_POP_Chapala”, DESCR: “Cisco Catalyst 3550 24 10/100 baseT ports + 2 Gig uplinks fixed configuration Layer 2/3 Ethernet Switch”
PID: WS-C3550-24
Same config as in the question.
interface FastEthernet0/5
switchport access vlan 10
switchport trunk encapsulation dot1q
switchport mode trunk
switchport voice vlan 11
spanning-tree portfast
IP phone connected
W1_POP_Chapala#sh cdp ne
Device ID Local Intrfce Holdtme Capability Platform Port ID
SEP001647BC350A Fas 0/5 166 H IP Phone 7Port 1
W1_POP_Chapala#sh interface fa 0/5 switchport
Name: Fa0/5
Switchport: Enabled
Administrative Mode: trunk <<<<<<<
Operational Mode: trunk <<<<<<< this is the key DTP negotiated Trunk a trunk with the IP-phone
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: dot1q
Negotiation of Trunking: On <<<<<<<< Trunk negotiation == "DTP"
Access Mode VLAN: 10 (INTERNET)
Trunking Native Mode VLAN: 1 (default)
Administrative Native VLAN tagging: enabled
Voice VLAN: 11 (VOICE)
W1_POP_Chapala#sh vlan br
VLAN Name Status Ports
—- ——————————– ——— ——————————-
1 default active Fa0/1, Fa0/3, Fa0/4, Fa0/6
Fa0/7, Fa0/8, Fa0/10, Fa0/13
Fa0/14, Fa0/15, Fa0/16, Fa0/17
Fa0/18, Fa0/19, Fa0/20, Fa0/22
Fa0/24, Gi0/1, Gi0/2
2 VLAN0002 active Fa0/9
5 NATIVE active
8 VLAN0008 active Fa0/21
10 INTERNET active <<<<<<<<<<
11 VOICE active <<<<<<<<<<
*** if the port is connected an ip phone it will negotiate the trunk, it will result in Operational Mode trunk ***
What will be the behavior of an access port when a tagged packet is received, with a VLAN ID of an access port?
A. The tag is removed and packet is forwarded to a VLAN of access port
B. The tag is removed and packet is forwarded of the VLAN mentioned in the tag.
C. The tag is not removed and packet is forwarded of the VLAN mentioned in the tag.
D. Packet is dropped.
Refer to https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus5000/sw/configuration/guide/cli/CLIConfigurationGuide/AccessTrunk.pdf says
“If an access port receives a packet with an 802.1Q tag in the header other than the access VLAN value, that port drops the packet without learning its MAC source address.”
if the tag matches access port vlan, why would switch access port remove a tag from a packet and add it back?
I would go for D.
is this site is sufficient to clear CCNP exam?
Q10
I bet this question is not even an actual exam question, as ALL answers are wrong. It probably comes from some Boson crap or something.
A. The interface is administratively down.
WRONG, there is no “shutdown” command in the exhibit.
B. The encapsulation type is incorrect.
WRONG, the encapsulation type is correct.
C. The switchport mode trunk command should be first in the output.
WRONG, that command could be anywhere in the interface commands list and a proper trunk would still be established.
D. The native VLAN is not present on the trunk.
WRONG, from CCNP Routing and Switching SWITCH 300-115 Official Cert Guide:
“Although maintenance protocols such as Cisco Discovery Protocol (CDP), Port Aggregation Protocol (PAgP),
and Dynamic Trunking Protocol (DTP) normally are carried over the native VLAN of a trunk,
they will not be affected if the native VLAN is removed or manually pruned from the trunk.
They still will be sent and received on the native VLAN as a special case even if the native VLAN ID is not in the list of allowed VLANs.”
Try it with real hardware and you will that’s indeed the case, control traffic isn’t affected, you can’t remove it from a trunk.
E. The control traffic must be manually enabled on the new native VLAN.
WRONG, it keeps working even if there’s a native VLAN mismatch between the switches, it will still be carried on the native VLAN 1 no matter what, even if you change it as the native VLAN across the trunk.
Q10,
Tested on real gears,
Different encapsulation ISL/Dot1q causes the issue – not propagating vtp & cdp info
ANSWER IS BBBBBBBBBBB
Saji that is correct, different encapsulation definitely will cause the issue,
But as my understanding it is implied that it was working, then a network engineer JUST change Native vlan, then stop working.
So that my be tricky.