2.3 Layer 2 Discovery Protocols

Question 1

What is Cisco Discovery Protocol?

(CDP)

Answer 1

A Layer 2 protocol for discovering connected Cisco devices.

CDP shares device information such as IP address, platform, and port, helping with network troubleshooting.

Question 2

Define:

Link Layer Discovery Protocol

(LLDP)

Answer 2

An open standard Layer 2 protocol for discovering connected devices.

LLDP is IEEE 802.1ab compliant and works across multi-vendor devices, unlike CDP, which is Cisco-specific.

Question 3

Why is Cisco Discovery Protocol (CDP) used in Cisco networks?

Answer 3

To gather device information like IP address and model.

CDP helps network admins troubleshoot and maintain network topology in Cisco-based environments.

Question 4

Why is LLDP considered a vendor-neutral alternative to CDP?

Answer 4

It works across devices from different vendors.

LLDP is based on IEEE 802.1ab and ensures interoperability in multi-vendor networks, unlike CDP, which is proprietary to Cisco.

Question 5

What are the advantages of using LLDP over CDP in a network?

Answer 5

• Vendor neutrality
• Interoperability
• IEEE compliance

Vendor neutrality: LLDP works across devices from different vendors, while CDP is Cisco-specific.

Interoperability: LLDP enables communication between devices from various manufacturers.

IEEE compliance: LLDP follows the IEEE 802.1AB standard, ensuring broader support and acceptance.

Question 6

What type of information can CDP provide about a connected device?

Answer 6

• Device name
• IP
• Platform
• Port

CDP provides detailed information that aids in troubleshooting, including the IOS version and hardware model of the device.

Question 7

Define:

CDP neighbor

Answer 7

A device that shares information with another via CDP.

A CDP neighbor is a directly connected device that exchanges information like device name, platform, and port.

Question 8

How do you verify CDP neighbors on a Cisco device?

Answer 8

show cdp neighbors

This command displays all Cisco devices that are directly connected and sharing CDP information.

Question 9

Which command shows detailed information about a specific CDP neighbor on a Cisco device?

Answer 9

show cdp neighbors detail

This command provides in-depth details, such as IP address and platform, about a specific device discovered via CDP.

Question 10

What is the default hold time for CDP information on a Cisco device?

Answer 10

180 seconds

After 180 seconds, CDP data is discarded unless updated, helping keep neighbor information current.

Question 11

How does LLDP function in network discovery?

Answer 11

It shares device identity, capabilities, and port information with neighbors.

LLDP helps create a network map by exchanging device details like ID, port, and capabilities with directly connected devices.

Question 12

True or False:

LLDP is only supported by Cisco devices.

Answer 12

False

LLDP is an open standard supported by devices from various vendors, making it suitable for mixed-vendor environments.

Question 13

What command is used to enable CDP on a Cisco interface?

Answer 13

cdp run

This command activates CDP on an interface, enabling it to send and receive CDP packets.

Question 14

What does the acronym LLDP-MED stand for?

Answer 14

Link Layer Discovery Protocol - Media Endpoint Discovery

LLDP-MED is used for devices like IP phones, enabling features like PoE and network policy identification.

Question 15

How does CDP be used for troubleshooting network connectivity issues?

Answer 15

It helps identify device connections and configurations.

By providing device details, CDP assists in verifying network connections and resolving issues in Cisco-only environments.

Question 16

Why would you disable CDP on certain interfaces?

Answer 16

To enhance security by preventing device information exposure.

Disabling CDP can protect sensitive device data from unauthorized access or potential attacks.

Question 17

What are common use cases for LLDP?

Answer 17

• Device discovery
• VoIP device integration
• Network monitoring

Device discovery: Identifies devices on the network for management.

VoIP device integration: Helps in configuring and managing VoIP devices.

Network monitoring: Provides network topology and status information for monitoring.

Question 18

How does CDP contribute to network security?

Answer 18

It helps detect unauthorized devices but can expose critical information.

While useful for discovery, CDP’s exposure of device details can be a security risk if not managed properly.

Question 19

Fill in the blank:

The command to display the LLDP neighbors on a Cisco device is ______ _______ _______.

Answer 19

show lldp neighbors

This command lists the devices discovered via LLDP and provides details such as port IDs and device capabilities.

Question 20

True or False:

LLDP requires more configuration than CDP on Cisco devices.

Answer 20

False

Both CDP and LLDP are typically easy to configure, but LLDP may need additional settings for vendor-specific features like PoE.

Question 21

Define:

CDP hold time

Answer 21

The duration CDP information remains valid.

The default hold time is 180 seconds, after which the data is cleared unless refreshed.

Question 22

What are the components of a CDP message?

Answer 22

• Device ID
• Address
• Port ID
• Capabilities
• Platform

These elements form the complete message shared between CDP neighbors, helping administrators identify and manage devices.

Question 23

Define:

LLDP TLV

Answer 23

Type-Length-Value, a format used in LLDP to carry device information.

TLVs provide a flexible and extensible method for encoding data such as device capabilities and port identifiers in LLDP messages.

Question 24

What is the default LLDP hold time on most devices?

Answer 24

120 seconds

This is the period for which LLDP information is stored before being discarded unless updated.

Question 25

Describe the **relationship** between LLDP and LLDP-MED.

Answer 25

LLDP-MED **extends** LLDP for multimedia devices like VoIP phones. ## Footnote *LLDP-MED* **supports** features such as PoE and power management specific to media devices, enabling better integration of multimedia systems.

Question 26

# True or False: CDP can be used on **non-Cisco devices**.

Answer 26

False ## Footnote **CDP** is *Cisco proprietary* and cannot be used with devices from other vendors unless they support the protocol.

Question 27

Which **Layer of the OSI model** do CDP and LLDP operate on?

Answer 27

Layer 2 | (Data Link Layer) ## Footnote Both protocols work at Layer 2, enabling them to *discover directly connected devices* within the same network segment.

Question 28

How do you **disable CDP** on a Cisco interface?

Answer 28

By using the command **no cdp enable** ## Footnote This **command** disables CDP on an interface, preventing it from sending or receiving CDP information.

Question 29

What are the commands to **verify LLDP operation** on a Cisco device?

Answer 29

1. show lldp neighbors 1. show lldp ## Footnote These commands *verify LLDP neighbors and display LLDP settings*, ensuring correct operation of the protocol.

Question 30

# Define: LLDP neighbor

Answer 30

A device that **shares its information** with other devices using LLDP. ## Footnote *LLDP neighbors* **communicate** details about device identity and port capabilities, helping to build a network map.

Question 31

# True or False: LLDP is **only used** for device discovery.

Answer 31

False ## Footnote **LLDP** can also be used for *network management* and provides features like VLAN and PoE information.

Question 32

Which command will **disable LLDP** on a Cisco interface?

Answer 32

**no lldp transmit** or **no lldp receive** ## Footnote These commands *stop LLDP packets from being sent or received* on a specific interface.

Question 33

Describe how LLDP **improves** network management.

Answer 33

It helps **map** network topology and **monitor** connected devices. ## Footnote **LLDP** *allows for better network visibility* and *easier troubleshooting* in environments with multiple vendors.

Question 34

What **type of information** does LLDP transmit about a device?

Answer 34

* Device ID * Port ID * VLAN ID * Power status * Capabilities ## Footnote **LLDP** *shares vital device details*, including port and capabilities, to help build a comprehensive network map.

Question 35

# True or False: CDP and LLDP **operate simultaneously** on the same network.

Answer 35

True ## Footnote Both protocols can **coexist**, allowing devices to discover neighbors using either protocol.

Question 36

What is the **default advertisement interval** for LLDP on most devices?

Answer 36

30 seconds ## Footnote The default interval at which LLDP advertisements are sent is typically 30 seconds. This period ensures *timely updates of device information*.

Question 37

What **security considerations** should be taken into account when using CDP?

Answer 37

**Exposure** of device details. ## Footnote **CDP** broadcasts *detailed information about network devices*, such as device names, IP addresses, and operating system versions. If intercepted, this data could be exploited by unauthorized entities.

Question 38

How does LLDP **support** Voice over IP (VoIP) deployments?

Answer 38

Through LLDP-MED ## Footnote LLDP-MED (Media Endpoint Discovery) is an **extension** of LLDP designed to *enhance VoIP deployments*.