Switching Basics
Here you will find answers to Switching Basics Questions
Question 1
What two features in Cisco switches help prevent Layer 2 loops? (Choose two)
A. UniDirectional Link Detection
B. Hot Standby Router Protocol
C. Virtual Router Redundancy Protocol
D. PortFast
E. root guard
F. loop guard
Answer: A F
Explanation
Both UniDirectional Link Detection (UDLD) and Loop Guard protect a switch trunk port from causing loops. Both features prevent switch ports from errantly moving from a blocking to a forwarding state when a unidirectional link exists in the network.
Unidirectional links are simply links for which one of the two transmission paths on the link has failed, but not both. This can happen as a result of miscabling, cutting one fiber cable, unplugging one fiber, GBIC problems, or other reasons
UDLD – Uses Layer 2 messaging to decide when a switch can no longer receive frames from a neighbor. The switch whose transmit interface did not fail is placed into an err-disabled state.
Loop Guard – When normal BPDUs are no longer received, the port does not go through normal STP convergence, but rather falls into an STP loop-inconsistent state.
(Reference: CCIE Routing and Switching Exam Certification Guide)
Question 2
Refer to the exhibit. Which switching feature is being tested?
aggregation-2 (enable) set spantree portfast 3/11 ena
Waning Spantree port fast start should only be enabled on ports connected to a single host.
Connecting hubs, concentrators, switches, bridges, etc. to a fast start port can cause temporary spannmg tree loops. Use with caution.
Spantree port 3/11 fast start enabled.
aggregation-2 (enable) set spantree portfast bpdu-filter ena
Spantree portfast bpdu-filter enabled on this switch.
2001 Feb 06 13:32:14 %SPANTREE-4-LOOPGUARDBLOCK: No BPDUs were received on port 3/21 m VLAN 99. Moved to loop inconsistent state
A. loop guard
B. PortFast
C. root guard
D. BDPU guard
Answer: A
Question 3
Which three of these statements about Dynamic Trunking Protocol are correct? (Choose three)
A. It supports autonegotiation for both ISL and IEEE 802.1 Q trunks.
B. It must be disabled on an interface if you do not want the interface to work as a trunk or start negotiation to become a trunk.
C. It is a point-to-multipoint protocol.
D. It is a point-to-point protocol.
E. It is not supported on private VLAN ports or tunneling ports.
Answer: A B D
Question 4
You are designing your network to be able to use trunks. As part of this process you are comparing the ISL and 802.1 Q encapsulation options. All of these statements about the two encapsulation options are correct except which one?
A. Both support normal and extended VLAN ranges.
B. ISL is a Cisco proprietary encapsulation method and 802.1 Q is an IEEE standard.
C. ISL encapsulates the original frame.
D. Both support native VLANs.
E. 802.1 Q does not encapsulate the original frame.
Answer: D
Question 5
Refer to the exhibit. From the MAC addresses shown in the command output, to which two ports is the multicast stream 225.230.57.199 being forwarded on this switch? (Choose two)
Switch#show mac-address-table multicast
| vlan | mac address | type | ports |
| —————–+ | ——————————+ | ———————+ | —————————————————————– |
| 2 2 2 3 3 |
0100.5ee6.39c7 0100.5e00.0123 0100.5e66.39c7 0100.5e00.017f 0100.5e50.4453 |
igmp igmp igmp igmp igmp |
Gi3/7,Fa6/28,Fa7/20 Fa5/7,Fa6/28,Fa7/20 Gi3/4,Gi3/7,Fa4/10,Fa4/14,Fa7/31,Fa7/40 Gi3/7,Fa6/21 Gi3/7,Fa4/2,Fa4/3,Fa4/14,Fa4/38,Fa5/3 |
A. Fa6/28
B. Fa7/20
C. Gi3/7
D. Fa4/2
E. Fa4/14
F. Fa4/38
G. Fa6/28
H. Fa5/7
Answer: C E
Question 6
You are about to migrate a customer network to use a VSS. Which of these statements is true about a VSS?
A. The VSS switch must be the root bridge for all VLANs and is automatically designated.
B. The VSS switch is defined in RFC 4318 as a managed object.
C. The PAgP+ or LACP protocols are used to maintain the operational state of the VSS devices.
D. A VSS interoperates with a virtual port channel.
E. The 802.1Q or ISL protocols are used to maintain the operational state of the VSS devices.
F. A VSS increases the size of the spanning-tree domain.
Answer: C
Explanation
Virtual switching system (VSS) is a network system virtualization technology that pools multiple Cisco Catalyst 6500 Series Switches into one virtual switch, increasing operational efficiency, boosting nonstop communications, and scaling system bandwidth capacity to 1.4 Tbps. At the initial phase, a VSS will allow two physical Cisco Catalyst 6500 Series Switches to operate as a single logical virtual switch called a virtual switching system 1440 (VSS1440)
Virtual Switching System 1440 Compared to Traditional Network Design
(Reference: http://www.cisco.com/en/US/products/ps9336/products_tech_note09186a0080a7c837.shtml)
C is the correct answer as in the recommendations of the above link, the author wrote:
Do not use on and off options with PAgP or LACP or Trunk protocol negotiation.
* PAgP — Run Desirable-Desirable with MEC links.
* LACP — Run Active-Active with MEC links.
* Trunk — Run Desirable-Desirable with MEC links.
Recommended link: http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps9336/prod_qas0900aecd806ed74b.html
Question 7
An 802.1 Q trunk is not coming up between two switches. The ports on both switches are configured as “switchport mode desirable.” Assuming that there is no physical issue, choose two possible causes. (Choose two.)
A. Incorrect VTP domain
B. Incorrect VTP password
C. Incorrect VTP mode
D. Incorrect VTP configuration revision
Answer: A B
Question 8
Refer to the exhibit. Look at the command output. Assume that there is no other path, and the configuration is correct. What would be the consequences of this situation?
Switch1#show cdp neighbor
Capability Codes: R – Router, T- Trans Bridge, B – Source Route Bridge S – Switch, H – Host, I – IGMP, r- Repeater, P – Phone
| Device ID | Local Intrfce | Holdtme | Capability | Platform | Port ID |
| Switch2 | Gig 1/0/3 | 160 | S I | WS-C2955C | Fas0/13 |
Switch2#show cdp neighbor
Capability Codes: R – Router, T- Trans Bridge, B – Source Route Bridge S – Switch, H – Host, I – IGMP, r- Repeater, P – Phone
| Device ID | Local Intrfce | Holdtme | Capability | Platform | Port ID |
| Switch1 | Fas0/13 | 173 | R S I | WS-C3750G | Gig1/0/4 |
A. Users in SW1 can ping SW2 but not vice versa.
B. Users in SW2 can ping SW1 but not vice versa.
C. Users in SW1 and SW2 can ping each other.
D. Users in SW1 and SW2 cannot ping each other.
Answer: D
Question 9
Refer to the exhibit. Look at the command output. What can you use to prevent this behavior?
Switch 1#show cdp neighbors
Capability Codes: R – Router, T – Trans Bridge, B – Source Route Bridge S – Switch, H – Host, I – IGMP, r – Repeater
| Device ID | Local Intrfce | Holdtme | Capability | Platform | Port ID |
| Switch2 | Gig 1/0/3 | 160 | S I | WS-C2955C | Fas0/13 |
Switch 1#
Switch2#show cdp neighbor
Capability Codes: R – Router, T- Trans Bridge, B – Source Route Bridge S – Switch, H – Host, I – IGMP, r- Repeater
| Device ID | Local Intrfce | Holdtme | Capability | Platform | Port ID |
| Switch1 | Fas0/13 | 173 | R S I | WS-C3750G | Gig1/0/4 |
A. UDLD
B. spanning-tree loopguard
C. VTP mode transparent
D. switchport mode desirable
Answer: A
Q5, IP 225.230.57.199 will become MAC 0100.5ee6.39c7, so the interfaces G3/7,F6/28 and F7/20 will receive the traffic. Does this question have 3 correct answers (A, B,C)? Why you answered E?
Mac address 0100.5e66.39c7 is accessible via Gi3/4,Gi3/7,Fa4/10,Fa4/14,Fa7/31,Fa7/40.
So options C and E i.e., Gi3/7 & Fa4/14 are the correct answers.
Can Someone please explain question no. 5 ??
Question 4. Answer D is incorrect. ISL is not support nativ Vlan. B is correct.
Bennet Eapen Why multicast IP address 225.230.57.199 will be Mac address 0100.5e66.39c7?
Ula – Q4 D is correct the question asked what is “not” true…
i.e. ISL does not support native VLAN thus answer D is correct
Ula Q5, this is a Layer 3 IP Multicast address to Layer 2 Multicast mapping question.
first thing is to convert the IP address to binary so : 225.230.57.199 in binary is
11100001 11100110 00111001 11000111
then put the first 6 hex charaters in front of the binary address and remove the first 4 bits (which are always 1110) this is the IEEE OUI for layer 2 multicast addressing
0100.5e | 0001 11100110 00111001 11000111
then we “always” change the next 5 bits to a binary 0 (which leaves us with 24 bits for the conversion to hex)
0100.5e | 01100110 00111001 11000111
this leaves you with 24 bits to convert into hex from binary
thus
01100110 00111001 11000111 = 66.39.c7
and the question asks which interfaces listed are forwarding this group..
All of the below are forwarding it,
Gi3/4,Gi3/7,Fa4/10,Fa4/14,Fa7/31,Fa7/40
but only 2 are listed in the multiple choice :
Gi3/7 & Fa4/14
Can someone please explain Question 8 and 9 ? Why port ID is different then the one of the peer ?
Thanks
8,9
Actually there is a question that asks that. This is a very fake thing that involves cabling the 2 fiber leads from a single port into 2 different ports on 2 different switches. It would be highly unlikely you would get lucky enough to get all the ports in a up status so they could even send/receive cdp neighbor.
I guess they wanted a example where you could use UDLD even though in reality it is a very rare to get both ports in a up state but have a broken connection between them.
The DTP Trunking question answers are wrong. DTP is not supported on Private VLANs or tunnel ports which is verbatim from the Design Guides:
http://www.cisco.com/en/US/docs/switches/lan/catalyst3750e_3560e/software/release/12.2_58_se/configuration/guide/swvlan.html#wp1200245
Q3 is therefore, A D E and not B.
B is wrong because you don’t need to disable DTP to stop trunking or the port attempting to negotiate. Auto won’t start the negotiation, nonegotitate doesn’t negotiatet and some combinations of DTP settings won’t from a trunk link.
“DTP is not supported on private-VLAN ports or tunnel ports.”
Great find mate.Thanks.
Is the wording of Q4 right?
If its is,D is not the correct answer..802.1Q does not actually encapsulate the original frame. Instead, for Ethernet II frames, it adds a 32-bit field between the source MAC address and the EtherType/Length fields of the original frame.
Q6
I think that the right answer is D. A VSS interoperates with a virtual port channel.
You can find the anwers in this link:
http://www.cisco.com/en/US/prod/collateral/switches/ps9441/ps9670/C07-572831-00_Dsgn_Nexus_vPC_DG.pdf
vPC and VSS
Mixed data centers consisting of both Cisco Catalyst and Cisco Nexus products can interoperate by using both vPC and VSS technologies.
The PAgP+ or LACP protocols are not required in order to the VSL to function. The recomendation to use PAgP or LACP is to conect others equipments to the VSS Cluster by Multi Chassis Etherchannel MCE.
Question 6: The correct answer is C (Matches with Rstut)
Just deployed nexus 7000 series in the LAB. HSRP interoperates with virtual port channels (vPCs). Here is the link. Under the link, review the section vPC and HSRP
http://www.cisco.com/en/US/docs/switches/datacenter/sw/5_x/nx-os/unicast/configuration/guide/l3_hsrp.html#wp1509498
Q6 answer is C (agree with rstut). believe me guys you’ll get your point.
Q5 answer from rstut is also confirmed. its better to have knowledge about L3 multicast address mapping to L2 multicast address. But if you re-checked the question for a valid two choice, you will only ports from 0100.5e66.39c7 mac. other mac would give you less than two or more than two ports.
Q6: You can connect VSS with Nexus over vPC. So for me Answer D is correct.
Cisco Catalyst 6500 VSS and Cisco Nexus 7000 vPC Interoperability and Best Practices:
http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps708/white_paper_c11_589890.html
For the VSS link it does not use LACP or PAgP, see here: http://www.cisco.com/en/US/docs/solutions/Enterprise/Campus/VSS30dg/VSS-dg_ch2.html#wp1056015
Anyone have insight for 7?
FTP affects DTP?
Sorry typo above should read:
VTP affects DTP?
Q6 After reading carefully the linkl Sirathan mentioned, I must agree with answer D.
wow.. Q6 is indeed D. i’m lucky not having this question in my test.
Question 3
B is definitly wrong. If you do not want the interface to work as a trunk, put it in access mode.
E. “It is not supported on private VLAN ports or tunneling ports” –> from cisco documents, so definitly correct.
rstut, why don’t you correct this answer? It’s quite obvious…
Answer: A D E
Q3 for me answer is ADE
Q6 Answer C is correct.
From Cisco documentation: “Virtual Switch Link (VSL)—A special port channel required to bundle two physical switches into one virtual switch.”
http://www.cisco.com/en/US/products/ps9336/products_tech_note09186a0080a7c837.shtml
Q6 answer is C
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Q6:
I think that the right answer is D.see the link below
http://www.cisco.com/en/US/docs/solutions/Enterprise/Campus/VSS30dg/VSS-dg_ch2.html#wp1056015
“Since VSL EtherChannel uses LMP per member link, the link-aggregation protocols, such as PAgP and LACP, are not required”
Can anyone please explain for Q8?
Can anyone please explain for Q8?
Q8 is obvious as it is a uni-direction communication between 3 switches.
A ping needs to be work in bidirectional.
Q6 is a question about how we understand the English?
I hate this kind of question.
Q3 RSTUT answer is correct. And its obvious answers. Ppl just confused with arguments. Cisco answers are the final. Look at the questions and answers before saying
Q6 is of course D. How can be LACP or PAgP+ used to maintain the operational state of the VSS devices??? 🙂 And vPC interoperates with VSS, so this answer is correct.
Q3, E is right as well, it’s stated clearly here: http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750/software/release/12-2_55_se/configuration/guide/scg3750/swvlan.html
“Note: DTP is not supported on private-VLAN ports or tunnel ports.”
So 4 right answers here, choose 3.
Cisco, you screwed up again!!!!
Q7: I agree that VTP domain name mismatch prevents trunking,but what is the reference that vtp password mismatch also prevents trunking to form?
Q8: From what we can definitely say that users can not ping each other?
Q9: Question says:”What can you use to prevent this behavior?” ,prevent what? CDP is working,what should be prevented??? :/
Q8&9,a got them.Miscabling (it seems,fiber media is in use)
But,Q7 still is unclear.Nowhere it says that mismatching password prevents trunking
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which three statements about dtp are true?