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Question

Difficulty: MediumLayer 2 Discovery Protocols (CDP and LLDP)

A network technician displays the active Layer 2 discovery parameters on a switch port using the `show cdp interface gigabitethernet 0/1` command and observes the following output:

text
GigabitEthernet0/1 is up, line protocol is up
Encapsulation ARPA
Sending CDP packets every 60 seconds
Holdtime is 180 seconds

If the technician disables CDP on this interface and enables Link Layer Discovery Protocol (LLDP) globally and locally, which default update timer and holdtime timer values will LLDP use?

  1. Update timer of 30 seconds and holdtime timer of 120 secondsAnswer
  2. B
    Update timer of 60 seconds and holdtime timer of 180 seconds
  3. C
    Update timer of 15 seconds and holdtime timer of 60 seconds
  4. D
    Update timer of 30 seconds and holdtime timer of 180 seconds

Answer

Update timer of 30 seconds and holdtime timer of 120 seconds
The correct answer specifies an update timer of 30 seconds and a holdtime timer of 120 seconds. In Cisco IOS, LLDP transmits discovery advertisements every 30 seconds by default and retains neighbor information for 120 seconds (using a holdtime multiplier of 4).

Step-by-Step Solution

1
Identify the default timer parameters for Cisco Discovery Protocol (CDP)
CDP defaults to transmitting advertisement frames every 60 seconds with a holdtime value of 180 seconds.
This establishes the baseline shown in the CLI command output.
2
Recall default timer parameters for IEEE 802.1AB Link Layer Discovery Protocol (LLDP)
LLDP defaults to an update message interval of 30 seconds and a holdtime multiplier of 4 (30×4=12030 \times 4 = 120 seconds).
Standard IEEE LLDP specifications mandate shorter advertisement intervals and holdtimes than proprietary CDP.
3
Compare the option choices to select the accurate LLDP default timer values
The option specifying an update timer of 30 seconds and a holdtime timer of 120 seconds is correct.
It accurately reflects standard Cisco IOS default behavior when LLDP is enabled.

Key Concept

CDP vs LLDP Default Timers
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Topics

Layer 2 Discovery Protocols (CDP and LLDP)

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