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Difficulty: HardLayer 2 Discovery Protocols (CDP and LLDP)

A network administrator executes the following command on switch SW-1 to troubleshoot connectivity to an adjacent network device:

text
SW-1# show lldp neighbors detail
------------------------------------------------
Local Intf: Gi0/1
Chassis id: 0014.f25a.a100
Port id: GigabitEthernet1/0/24
Port Description: Trunk Link to SW-1
System Name: SW-2
System Description: Cisco IOS Software, C3750E Software (C3750E-UNIVERSALK9-M)
Time remaining: 98 seconds
System Capabilities: B, R
Enabled Capabilities: B
Management Addresses:
IP: 10.1.10.2
Auto Negotiation - supported, enabled
Physical media capabilities:
1000baseT(FD)
Media Attachment Unit type: 30
VLAN ID: 20

Based on the output provided, which conclusion accurately describes the neighbor relationship and port configuration?

  1. The adjacent switch SW-2 is connected via its interface GigabitEthernet1/0/24 to SW-1's local interface GigabitEthernet0/1, operating with a port VLAN ID of 20 and management address 10.1.10.2.Answer
  2. B
    SW-1 is physically connected using its local port GigabitEthernet1/0/24 to SW-2's remote port GigabitEthernet0/1.
  3. C
    A native VLAN mismatch is present because LLDP cannot report VLAN ID 20 on interface GigabitEthernet0/1 unless VLAN 1 is configured as the untagged native VLAN.
  4. D
    The neighbor device SW-2 is operating as a Layer 3 router because 'Enabled Capabilities: B' indicates routing functions are active on interface GigabitEthernet1/0/24.

Answer

The adjacent switch SW-2 is connected via its interface GigabitEthernet1/0/24 to SW-1's local interface GigabitEthernet0/1, operating with a port VLAN ID of 20 and management address 10.1.10.2.
The output of 'show lldp neighbors detail' shows that local interface Gi0/1 on SW-1 is connected to remote port GigabitEthernet1/0/24 on system SW-2. It also displays SW-2's management IP (10.1.10.2), system capabilities, and the advertised Port VLAN ID of 20.

Step-by-Step Solution

1
Identify local vs. remote interface designations in the LLDP CLI output.
'Local Intf: Gi0/1' is the local interface on SW-1. 'Port id: GigabitEthernet1/0/24' represents the interface on the remote neighbor (SW-2).
Layer 2 discovery outputs distinguish between local ports where traffic is received and remote port IDs advertised by neighbors.
2
Analyze System Name, System Capabilities, and Management Addresses.
System Name is SW-2, Management IP is 10.1.10.2, and Enabled Capabilities is 'B' (Bridge/Switch).
Capability code 'B' stands for Bridge/Switch, proving the active role of the device is Layer 2 switching.
3
Evaluate the IEEE 802.1 TLV Port VLAN ID information.
'VLAN ID: 20' reflects the advertised Port VLAN ID (PVID) associated with the link.
LLDP advertises PVID through Organizationally Specific TLVs, allowing operators to verify VLAN settings on connected links.

Key Concept

Interpretation of IEEE 802.1AB LLDP detailed neighbor table outputs and TLV fields.
Estimated Time:2m 0s
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Topics

Layer 2 Discovery Protocols (CDP and LLDP)

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