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CDP and LLDP configuration 1

Topology

Tasks:

A company has a small network with three switches (SW1, SW2, and SW3) interconnected to form a network core. The network administrators want to ensure that all switches can discover each other’s device information. They need to use Cisco Discovery Protocol (CDP) within the Cisco network and configure Link Layer Discovery Protocol (LLDP) to discover any non-Cisco devices that may be connected in the future.

  1. Enable CDP and Verify Neighbor Information
    • Enable CDP globally on each switch.
    • Verify that each switch can discover its neighboring switches using CDP.
  2. Enable LLDP and Verify Neighbor Information
    • Enable LLDP globally on each switch.
    • Verify that each switch can discover its neighboring switches using LLDP.
  3. Disable CDP and LLDP on Specific Interfaces
    • Disable CDP on FastEthernet0/1 on SW1 and FastEthernet0/3 on SW3.
    • Disable LLDP on FastEthernet0/2 on SW2.

Solution:

Task 1: Enable CDP and Verify Neighbor Information

  • Enable CDP globally on each switch.
  • Verify that each switch can discover its neighboring switches using CDP.

On SW1:

SW1#configure terminal
SW1(config)#cdp run
SW1(config)#exit

On SW2:

SW2#configure terminal
SW2(config)#cdp run
SW2(config)#exit

On SW3:

SW3#configure terminal
SW3(config)#cdp run
SW3(config)#exit

The cdp run command enables CDP globally on each switch. This allows the switches to discover and share information about directly connected Cisco devices.

After enabling CDP on each switch, we will verify that each switch can detect its neighbors.

On SW1:

SW1#show cdp neighbors

Output:

Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge

                  S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone

Device ID Local Intrfce Holdtme Capability Platform Port ID

SW3       Fas 0/3        145               3560     Fas 0/3

SW2       Fas 0/1        145               3560     Fas 0/1

On SW2:

SW2#show cdp neighbors

Output:

Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge

                  S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone

Device ID Local Intrfce Holdtme Capability Platform Port ID

SW1       Fas 0/1        145               3560     Fas 0/1

SW3       Fas 0/2        145               3560     Fas 0/2

On SW3:

SW2#show cdp neighbors

Output:

Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge

                  S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone

Device ID Local Intrfce Holdtme Capability Platform Port ID

SW1       Fas 0/3        145               3560     Fas 0/3

SW2       Fas 0/2        145               3560     Fas 0/2

The show cdp neighbors command provides information on directly connected Cisco devices, including device ID, local interface, hold time, capability, platform, and port ID. This confirms that CDP is functioning correctly.

 

Task 2: Enable LLDP and Verify Neighbor Information

  • Enable LLDP globally on each switch.
  • Verify that each switch can discover its neighboring switches using LLDP.

First we enable LLDP on all switches.

On SW1:

SW1(config)#lldp run
SW1(config)#exit

On SW2:

SW2(config)#lldp run
SW2(config)#exit

On SW3:

SW3(config)#lldp run
SW3(config)#exit

The lldp run command enables LLDP globally on each switch. LLDP is a vendor-neutral protocol used to discover information about directly connected devices, even if they are non-Cisco devices.

After enabling LLDP, verify that each switch can detect its neighbors.

On SW1:

SW1#show lldp neighbors

Output:

Capability codes:

   (R) Router, (B) Bridge, (T) Telephone, (C) DOCSIS Cable Device

   (W) WLAN Access Point, (P) Repeater, (S) Station, (O) Other

Device ID   Local Intf   Hold-time   Capability   Port ID

SW2         Fa0/1        120         R            Fa0/1

SW3         Fa0/3        120         R            Fa0/3

On SW2:

SW2#show lldp neighbors

Output:

Capability codes:

   (R) Router, (B) Bridge, (T) Telephone, (C) DOCSIS Cable Device

   (W) WLAN Access Point, (P) Repeater, (S) Station, (O) Other

Device ID   Local Intf   Hold-time   Capability   Port ID

SW1         Fa0/1        120         R            Fa0/1

SW3         Fa0/2        120         R            Fa0/2

On SW3:

SW2#show lldp neighbors

Output:

Capability codes:

   (R) Router, (B) Bridge, (T) Telephone, (C) DOCSIS Cable Device

   (W) WLAN Access Point, (P) Repeater, (S) Station, (O) Other

Device ID   Local Intf   Hold-time   Capability   Port ID

SW2         Fa0/2        120         R            Fa0/2

SW1         Fa0/3        120         R            Fa0/3

The show lldp neighbors command provides information on directly connected devices using LLDP. This confirms that LLDP is functioning correctly.

 

Task 3: Disable CDP and LLDP on Specific Interfaces

  • Disable CDP on FastEthernet0/1 on SW1 and FastEthernet0/3 on SW3.
  • Disable LLDP on FastEthernet0/2 on SW2.

First we will disable CDP on required interfaces.

On SW1:

SW1#configure terminal
SW1(config)#interface f0/1
SW1(config-if)#no cdp enable

On SW3:

SW3#configure terminal
SW3(config)#interface f0/3
SW3(config-if)#no cdp enable

The no cdp enable command disables CDP on the specified interface. This means CDP will not advertise or receive neighbor information on that particular port.

Next we will disable LLDP on the FastEthernet0/2 interface of SW2.

On SW2:

SW2#configure terminal
SW2(config)#interface f0/2
SW2(config-if)#no lldp transmit
SW2(config-if)#no lldp receive

The no lldp transmit command disables LLDP transmission on the interface, and no lldp receive disables LLDP reception on the interface. Together, these commands effectively disable LLDP on Ethernet0/2 of SW2.

Now exit the configuration mode and save the configuration.

SW1(config-if)#end
SW1#write memory

SW2(config-if)#end
SW2#write memory

SW3(config-if)#end
SW3#write memory

 

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