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Difficulty: MediumLayer 2 Discovery Protocols (CDP and LLDP)

A network engineer is configuring Layer 2 neighbor discovery on a Cisco Catalyst switch connected to both Cisco switches and third-party network endpoints. Which two statements correctly describe the operational characteristics and default behaviors of Cisco Discovery Protocol (CDP) and Link Layer Discovery Protocol (LLDP)? (Choose two.)

  1. CDP is a Cisco proprietary protocol enabled by default with a 60-second update timer, whereas LLDP is an IEEE 802.1AB standard that uses a 30-second update timer by default.Answer
  2. Both CDP and LLDP use Type-Length-Value (TLV) structures within Layer 2 frames to convey neighbor information such as device capabilities, port identifiers, and management addresses.Answer
  3. C
    LLDP relies strictly on fixed IPv4 header fields rather than TLVs to communicate native VLAN IDs and system capabilities across multi-vendor trunk links.
  4. D
    Enabling LLDP globally automatically prevents untagged native VLAN frames from traversing trunk links if a native VLAN mismatch occurs.

Answer

CDP is a Cisco proprietary protocol enabled by default with a 60-second update timer, whereas LLDP is an IEEE 802.1AB standard that uses a 30-second update timer by default; both CDP and LLDP use Type-Length-Value (TLV) structures within Layer 2 frames to convey neighbor information.
CDP is a Cisco proprietary protocol operating with a 60-second update timer and 180-second holdtime, whereas LLDP is an open standard defined by IEEE 802.1AB that operates with a 30-second update timer and 120-second holdtime. Both protocols organize neighbor information using Type-Length-Value (TLV) structures within Layer 2 frames.

Step-by-Step Solution

1
Identify default protocol parameters and standards for CDP and LLDP.
CDP is Cisco proprietary (default 60-second update, 180-second holdtime), while LLDP is defined by IEEE 802.1AB (default 30-second update, 120-second holdtime).
Distinguishing between proprietary and open standards along with their default timer values is essential for multi-vendor network administration.
2
Analyze frame structure and data encoding methods.
Both protocols encapsulate neighbor metadata into modular Type-Length-Value (TLV) elements transmitted inside Data Link layer frames.
TLVs allow flexible exchange of system attributes, management IP addresses, and port descriptions across Layer 2 neighbors.
3
Evaluate protocol reaction to native VLAN configuration errors.
Layer 2 discovery protocols report mismatches using log messages but do not alter port forwarding states or block traffic.
Traffic suppression due to misconfiguration is handled by Spanning Tree Protocol (STP) mechanisms, not CDP or LLDP.

Key Concept

Layer 2 Discovery Protocols (CDP and LLDP) standards, default timers, and TLV structure
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Topics

Layer 2 Discovery Protocols (CDP and LLDP)

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