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UDLD Questions

September 19th, 2017 in SWITCH 300-115 Go to comments

Question 1

Explanation

UDLD is a Layer 2 protocol that enables devices connected through fiber-optic or twisted-pair Ethernet cables to monitor the physical configuration of the cables and detect when a unidirectional link exists. All connected devices must support UDLD for the protocol to successfully identify and disable unidirectional links. When UDLD detects a unidirectional link, it administratively shuts down the affected port and alerts you. Unidirectional links can cause a variety of problems, including spanning-tree topology loops.

Reference: http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3550/software/release/12-1_19_ea1/configuration/guide/3550scg/swudld.html#wp1019932

Question 2

Explanation

A unidirectional link occurs whenever traffic sent by a local device is received by its neighbor but traffic from the neighbor is not received by the local device.

UDLD supports two modes of operation: normal (the default) and aggressive. In normal mode, UDLD can detect unidirectional links due to misconnected interfaces on fiber-optic connections. In aggressive mode, UDLD can also detect unidirectional links due to one-way traffic on fiber-optic and twisted-pair links and to misconnected interfaces on fiber-optic links.

Reference: http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3550/software/release/12-1_19_ea1/configuration/guide/3550scg/swudld.html

Question 3

Explanation

When unidirectional link occurs, UDLD can put that port into errdisable state (same as shutdown). The administrator must manually shut/no shut to bring that interface up. If we want the interface to automatically recover then configure the “errdisable autorecovery”. For example:

errdisable recovery cause udld
errdisable recovery interval 30

By doing so, the port will be place back in up state (no err-disabled state) after 30 seconds, if the port still has violation it will be placed again in “err-disabled” state, otherwise it will remain in up state.

Question 4

Explanation

UDLD aggressive mode is disabled by default. Configure UDLD aggressive mode only on point-to-point links between network devices that support UDLD aggressive mode. With UDLD aggressive mode enabled, when a port on a bidirectional link that has a UDLD neighbor relationship established stops receiving UDLD packets, UDLD tries to reestablish the connection with the neighbor. After eight failed retries, the port is disabled.

Reference: http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst6500/ios/15-0SY/configuration/guide/15_0_sy_swcg/udld.html#wp1027627

Question 5

Question 6

Question 7

Question 8

Question 9

Explanation

The Cisco-proprietary UDLD protocol monitors the physical configuration of the links between devices and ports that support UDLD. UDLD detects the existence of unidirectional links. When a unidirectional link is detected, UDLD puts the affected port into the errdisabled state and alerts the user. UDLD can operate in either normal or aggressive mode.

UDLD is a Layer 2 protocol that works with the Layer 1 protocols to determine the physical status of a link. At Layer 1, autonegotiation takes care of physical signaling and fault detection. UDLD performs tasks that autonegotiation cannot perform, such as detecting the identities of neighbors and shutting down misconnected LAN ports. When you enable both autonegotiation and UDLD, Layer 1 and Layer 2 detections work together to prevent physical and logical unidirectional connections and the malfunctioning of other protocols.

UDLD aggressive mode is disabled by default. Configure UDLD aggressive mode only on point-to-point links between network devices that support UDLD aggressive mode. With UDLD aggressive mode enabled, when a port on a bidirectional link that has a UDLD neighbor relationship established stops receiving UDLD packets, UDLD tries to reestablish the connection with the neighbor. After eight failed retries, the port is disabled -> C is correct.

Reference: http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst6500/ios/12-2SX/configuration/guide/book/udld.html

Comments
  1. yusuf cameroon
    April 26th, 2015

    i need to write exam 300-115 next week . are this questions enough to pass the exam ?

  2. CCAr Certified
    May 15th, 2015

    QUestion 5 should be E

  3. Bacho
    July 2nd, 2015

    CCAr Certified could you explain why q5 should be E?

  4. Papi
    July 4th, 2015

    But we dont have E as an option

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    July 18th, 2015

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  6. Anony
    August 13th, 2015

    Where are the questions??
    I can’t see any of questions..
    only the explanatios are avaialabel

  7. Chia’tAtA
    August 24th, 2015

    Just from taking the switch exams. Scored 950 thanks to certprep.
    only one new question on VTP.

  8. $!L@
    October 8th, 2015

    Chia’tAtA congratz man…

  9. A
    October 21st, 2015

    @certprepare

    Your explanation to Q3 says ‘The administrator must manually shut/no shut to bring that interface up.’

    I’m not sure that’s entirely correct for UDLD. Should be ‘udld reset’. Refer to the cisco links in explanation of Q1 & Q2

  10. Sundar
    November 26th, 2015

    Hi,

    Where are questions?

  11. Ali
    February 15th, 2016

    Hi,

    I’m wondering about the questions as well. I only see answers. Can someone help me out! Thanks in advance!

  12. CLE
    March 10th, 2016

    Hi all,

    Can someone send me the latest switch dump to “dooeebear” at hotmail dot com.

  13. Jane
    March 22nd, 2016

    could somebody send me the dumps 191q please. It will be a big help. I do request. Thanks in advance. my email address

    jane_woken52 @ yahoo.com

  14. FustratedCCNPLoser
    March 26th, 2016

    My exam was taken on 3/25/2016 as I ended up with a humiliating 643/1000. All my study material was from the CiscoPress eBook (300-115), CBT Nuggets, VCE dumps (191q) and Certprep (SWITCH_JULY_2015). I put in 6-7 study hours a day for nearly a month to pass 300-115 with extreme confidence, but I was shot down when I was roasted by the exam. The latest dumps from this site only covered about 25% of the questions given, but all the Lab Sim simulation were correct as I had LACP with STP / HRSP / AAA. I was easily able to finish the lab sims on the exam with success but fell way short when it came the questions with educated guesses. I would like to know if anyone can help me out to receive the latest dumps soon. Thanks. c_brotha @ yahoo.com

  15. sd
    March 27th, 2016

    Hi all,
    can anyone plz confirm if dumps are still valid?
    i have 191q and SWITCH_Feb_2016

  16. master
    December 20th, 2016

    how many question for the simulation exams? and what are those?

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    March 22nd, 2017

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    April 1st, 2017

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  19. scaryg
    August 2nd, 2017

    does anyone have the questions to these answers? thanks

  20. vivian
    August 2nd, 2017
  21. Anonimo57
    August 23rd, 2017

    Please help,
    On question 6, if the port is configure as udld aggressive mode, what would happend of the port gets damage? Thanks

  22. 1209 D day
    September 10th, 2017

    Question 8
    about UDLD aggressive. (Choose two)

    A. UDLD messages are sent every 15 seconds
    B. UDLD tries to reestablish link once before declaring the link down
    C. When unidirectional fail is detected, port state is determined by spanning tree
    D. When unidirectional fail is detected, port is turned to errdisable
    E. UDLD sends messages four times the message interval by default
    F. UDLD automatically … message interval based on configured timers
    Answer: A D

    Certprepare please fix this answer.
    A is for normal mode, and question is about aggresive.

    Correct answers should be DF

  23. Anonymous
    September 11th, 2017

    @1209 D day
    A is for either normal or aggressive by default.

  24. Anonymoose
    September 20th, 2017

    Question 6 is too incomplete to be valuable. There’s nothing about the provided config to suggest that the other interface will recover, so I don’t believe the correct answer is available with the three options provided. B and C are definitely wrong though.

    A possible correct answer to this would be something along the lines of “it will retry the connection 8 times before shutting down the damaged link”

  25. Anonymous
    October 4th, 2017

    Q9 here shows C but the quiz states D – Assume it should be C as its Cisco Prop

  26. Mark10
    October 6th, 2017

    A switch which was connected with 2 fiber cable attached to another switch After initial boot (l think another switch), one of the link get error-disable or shutdown. What was the reason for that?

    A. Due to STP.

    B. Due to UDLD aggressive mode, the other switch didn’t get the BPDU message.

    C. Due to UDLD normal mode, the other switch didn’t get the BPDU message.

    D. Due to port security configuration

    Answer: A

    Is A the correct answer or B?

  27. Mark10
    October 6th, 2017

    How to recover err-disable after an IJDLD failure?

    A. I-IDLD reset

    B. Err-disable auto recovery

    C. Shut and no shutdown (restart)

    D. Reboot the switch

    E I-IDLD recovery

    Correct Answer: AB

    Shouldn’t this be A and E

  28. Mark10
    October 6th, 2017

    Typo not IJDLD or I-IDLD = but UDLD. I am using copy text from pic feature

  29. Anonymous
    October 9th, 2017

    what is the correct answer for question 7 In the quiz its B

  30. Anonymous
    October 9th, 2017

    what is the correct answer for question 9 In the quiz its B? Please ignore the above question. Thanks

  31. Anonymous
    October 10th, 2017

    Errdisable Port State Recovery on the Cisco IOS Platforms

    https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/69980-errdisable-recovery.html?dtid=osscdc000283

    Causes of Errdisable
    ———————
    There are various reasons for the interface to go into errdisable. The reason can be:

    Duplex mismatch

    Port channel misconfiguration

    BPDU guard violation

    UniDirectional Link Detection (UDLD) condition

    Late-collision detection

    Link-flap detection

    Security violation

    Port Aggregation Protocol (PAgP) flap

    Layer 2 Tunneling Protocol (L2TP) guard

    DHCP snooping rate-limit

    Incorrect GBIC / Small Form-Factor Pluggable (SFP) module or cable

    Address Resolution Protocol (ARP) inspection

    Inline power

    Note: Error-disable detection is enabled for all of these reasons by default. In order to disable error-disable detection, use the no errdisable detect cause command. The show errdisable detect command displays the error-disable detection status.

    Here is an example of the same port in the error disabled state:
    ——————————————————————

    cat6knative#show interfaces gigabitethernet 4/1 status

    !— Refer to show interfaces status for more information on the command.

    Port Name Status Vlan Duplex Speed Type
    Gi4/1 err-disabled 100 full 1000 1000BaseSX

    Note: When a port is error disabled, the LED on the front panel that is associated with the port is set to the color orange.

    Determine the Reason for the Errdisabled State (Console Messages, Syslog, and the show errdisable recovery Command)
    ———————————————————————————————–

    When the switch puts a port in the error-disabled state, the switch sends a message to the console that describes why it disabled the port. The example in this section provides two sample messages that show the reason for port disablement:

    One disablement is because of the PortFast BPDU guard feature.

    The other disablement is because of an EtherChannel configuration problem.

    Note: You can also see these messages in the syslog if you issue the show log command.

    Here are the sample messages:

    %SPANTREE-SP-2-BLOCK_BPDUGUARD:
    Received BPDU on port GigabitEthernet4/1 with BPDU Guard enabled. Disabling port.

    %PM-SP-4-ERR_DISABLE:
    bpduguard error detected on Gi4/1, putting Gi4/1 in err-disable state

    %SPANTREE-2-CHNMISCFG: STP loop – channel 11/1-2 is disabled in vlan 1

  32. Anonymous
    October 10th, 2017

    If you have enabled errdisable recovery, you can determine the reason for the errdisable status if you issue the show errdisable recovery command. Here is an example:
    ——————————————————————————————————–
    cat6knative#show errdisable recovery
    ErrDisable Reason Timer Status
    —————– ————–
    udld Enabled
    bpduguard Enabled
    security-violatio Enabled
    channel-misconfig Enabled
    pagp-flap Enabled
    dtp-flap Enabled
    link-flap Enabled
    l2ptguard Enabled
    psecure-violation Enabled
    gbic-invalid Enabled
    dhcp-rate-limit Enabled
    mac-limit Enabled
    unicast-flood Enabled
    arp-inspection Enabled

    Timer interval: 300 seconds

    Interfaces that will be enabled at the next timeout:

    Interface Errdisable reason Time left(sec)
    ——— ——————— ————–
    Fa2/4 bpduguard 273

  33. Anonymous
    October 10th, 2017
  34. Anonymous
    October 10th, 2017

    Resetting Disabled LAN Interfaces
    =====================

    To reset all LAN ports that have been shut down by UDLD, perform this task:

    Command:

    Router# udld reset

    Purpose: Resets all LAN ports that have been shut down by UDLD.

  35. Anonymous
    October 11th, 2017

    In order to turn on errdisable recovery and choose the errdisable conditions, issue this command:
    ===========================================================
    cat6knative#errdisable recovery cause ?
    all Enable timer to recover from all causes
    arp-inspection Enable timer to recover from arp inspection error disable
    state
    bpduguard Enable timer to recover from BPDU Guard error disable
    state
    channel-misconfig Enable timer to recover from channel misconfig disable
    state
    dhcp-rate-limit Enable timer to recover from dhcp-rate-limit error
    disable state
    dtp-flap Enable timer to recover from dtp-flap error disable state
    gbic-invalid Enable timer to recover from invalid GBIC error disable
    state
    l2ptguard Enable timer to recover from l2protocol-tunnel error
    disable state
    link-flap Enable timer to recover from link-flap error disable
    state
    mac-limit Enable timer to recover from mac limit disable state
    pagp-flap Enable timer to recover from pagp-flap error disable
    state
    psecure-violation Enable timer to recover from psecure violation disable
    state
    security-violation Enable timer to recover from 802.1x violation disable
    state
    udld Enable timer to recover from udld error disable state
    unicast-flood Enable timer to recover from unicast flood disable state

    This example shows how to enable the BPDU guard errdisable recovery condition:

    cat6knative(Config)#errdisable recovery cause bpduguard

    A nice feature of this command is that, if you enable errdisable recovery, the command lists general reasons that the ports have been put into the error-disable state. In this example, notice that the BPDU guard feature was the reason for the shutdown of port 2/4:

    cat6knative#show errdisable recovery
    ErrDisable Reason Timer Status
    —————– ————–
    udld Disabled
    bpduguard Enabled
    security-violatio Disabled
    channel-misconfig Disabled
    pagp-flap Disabled
    dtp-flap Disabled
    link-flap Disabled
    l2ptguard Disabled
    psecure-violation Disabled
    gbic-invalid Disabled
    dhcp-rate-limit Disabled
    mac-limit Disabled
    unicast-flood Disabled
    arp-inspection Disabled

    Timer interval: 300 seconds

    Interfaces that will be enabled at the next timeout:

    Interface Errdisable reason Time left(sec)
    ——— ——————— ————–
    Fa2/4 bpduguard 290

    If any one of the errdisable recovery conditions is enabled, the ports with this condition are reenabled after 300 seconds. You can also change this default of 300 seconds if you issue this command:

    cat6knative(Config)#errdisable recovery interval

    timer_interval_in_seconds

    This example changes the errdisable recovery interval from 300 to 400 seconds:

    cat6knative(Config)#errdisable recovery interval 400

    Verify

    show version—Displays the version of the software that is used on the switch.

    show interfaces interface interface_number status—Shows the current status of the switch port.

    show errdisable detect—Displays the current settings of the errdisable timeout feature and, if any of the ports are currently error disabled, the reason that they are error disabled.

    Troubleshoot

    show interfaces status err-disabled—Shows which local ports are involved in the errdisabled state.

    show etherchannel summary—Shows the current status of the EtherChannel.

    show errdisable recovery—Shows the time period after which the interfaces are enabled for errdisable conditions.

    show errdisable detect—Shows the reason for the errdisable status.

  36. Anonymous
    October 11th, 2017

    The interface goes to errdisabled state.
    ==========================
    You can manually reenable the port (by issuing a “shutdown, no shutdown” command sequence) or if errdisable recovery is enabled, the operation is retried after a specified time interval.

    The interface can be recovered from errdisable state by reenabling the port using the command “errdisable recovery cause udld”

  37. Anonymous
    October 11th, 2017

    How to recover err-disable after an UDLD failure?

    A. UDLD reset

    B. Err-disable auto recovery

    C. Shut and no shutdown (restart)

    D. Reboot the switch

    E UDLD recovery

    Correct Answer: A & C

  38. Anonymous
    October 11th, 2017

    How to recover err-disable after an UDLD failure?

    A. UDLD reset <—- Valid Command

    B. Err-disable auto recovery <—— This is not a Valid Command.

    C. Shut and no shutdown (restart) <—– Valid Command

    D. Reboot the switch

    E UDLD recovery <—— This is not a Valid Command

    Correct Answer: A & C

    Correct auto recovery Commands are : In Global mode
    cat6knative(Config)#errdisable recovery cause udld
    cat6knative(Config)#errdisable recovery interval 30
    In this case recovery interval set to 30 Sec. But can be set to different values. even 400

  39. Anonymous
    October 13th, 2017

    How to recover err-disable after an UDLD failure?
    A. UDLD reset
    B. Err-disable auto recovery
    C. Shut and no shutdown (restart)in
    D. Reboot the switch
    E UDLD recovery

    Checking on a cisco 3550 the option UDLD Reset is not present , neither in the interface. The questions is HOW TO RECOVER, NOT WHICH COMMAND YOU USE. For experience
    i know that the shut and no shut works, and the auto recovery is just a wait to call it.

    show errdisable recovery—Shows the time period after which the interfaces are enabled for errdisable conditions.

    https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/69980-errdisable-recovery.html

    (config)#udld ?
    aggressive Enable UDLD protocol in aggressive mode on fiber ports except where locally configured
    enable Enable UDLD protocol on fiber ports except where locally configured
    message Set UDLD message parameters

  40. Anonopolis
    October 20th, 2017

    https://www.youtube.com/watch?v=ivXCDghnjTM go to 7:15 where he talks about udld reset

    You don’t issue the udld reset command from global config mode, rather from privileged EXEC mode.

    So example would be:
    switch#udld reset

  41. Paturuzú
    October 26th, 2017

    Hi team,

    Flash-based questions which represents UDLD Q9, is set to the wrong answer. Kindly correct this.

  42. Anonymous
    November 2nd, 2017

    Hi team, I recognised the same issue as mentioned above.
    Flash-based questions which represents UDLD Q9, is set to the wrong answer.
    Thanks.

  43. Gigi2
    November 12th, 2017

    Is ¨LUDLD aggressively disables the port after eight failed retries to connect to neighbor¨ the correct answer for Q9? The answer in the Quiz is:UDLD is an IEEE standard that can be configured on non-Cisco devices

    Thank you!

  44. Finjool
    November 16th, 2017

    UDLD is not an IEEE standard. Although UDLD is a proprietary protocol, its operation and packet format are defined in RFC 5171.

  45. RA
    December 4th, 2017

    Aggressive mode : When a unidirectional link condition is detected, the switch takes
    action to reestablish the link. UDLD messages are sent out once a second for 8 seconds.
    If none of those messages is echoed back, the port is placed in the errdisable
    state so that it cannot be used
    Question 8 possible answers:
    A. UDLD messages are sent every 15 seconds
    B. UDLD tries to reestablish link once before declaring the link down
    D. When unidirectional fail is detected, port is turned to errdisable
    F. UDLD automatically … message interval based on configured timers

    what do you think?

  46. RA
    December 4th, 2017

    Disregard option b. UDLD tried to reestablish link by sending out UDLD messages 8 times (8 secs). Option B says “ONCE”.
    Option F is not complete, so not sure if that is correct or not.
    I would stay with A and D as the answers.

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