Cisco IOS – Enabling LLDP

KB ID 0001289 Dtd 08/03/17

Problem

If you're running Cisco IOS on all you devices then you can use CDP  to see what's directly connected, (unless you are on a Cisco firewall, but I did say IOS devices). 

Petes-Switch#show cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
                  S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone,
                  D - Remote, C - CVTA, M - Two-port Mac Relay

Device ID        Local Intrfce     Holdtme    Capability  Platform  Port ID
Petes-CPE.petenetlive.com
                 Gig 1/0/19        148             R S I  CISCO2901 Gig 0/0
Petes-Switch#

But just about every other vendor uses LLDP (Link Layer Discovery Protocol,) to do the same job. So how do you discover what ports you are plugged into on them, or what they are?

Cisco Switches enable LLDP

 

Solution

Well in most cases, (depending on your code) your devices also support LLDP, it's just disabled by default. You simply turn it on with an 'lldp run' command.

Petes-Switch(config)#lldp run
Petes-Switch(config)#exit
Petes-Switch#show lldp ?
  entry      Information for specific neighbor entry
  errors     LLDP computational errors and overflows
  interface  LLDP interface status and configuration
  neighbors  LLDP neighbor entries
  traffic    LLDP statistics
  |          Output modifiers
  

Now I see my neighbours, (yes that is how it's spelt I'm English!) In my example below the neighbour is a Dell Switch.

Petes-Switch#show lldp neighbors
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
90b1.1cf4.39e1      Gi1/0/11       120                        ManagementEthernet 0/0
90b1.1cf4.39e1      Gi1/0/14       120                        TenGigabitEthernet 1/45
90b1.1cf4.39e1      Gi2/0/13       120                        TenGigabitEthernet 0/44
90b1.1cf4.39e1      Gi1/0/13       120                        TenGigabitEthernet 1/44
90b1.1cf4.39e1      Gi2/0/14       120                        TenGigabitEthernet 0/45
90b1.1cf4.39e1      Gi1/0/16       120                        TenGigabitEthernet 1/47
90b1.1cf4.39e1      Gi2/0/16       120                        TenGigabitEthernet 0/46
90b1.1cf4.39e1      Gi1/0/15       120                        TenGigabitEthernet 1/46
90b1.1cf4.39e1      Gi2/0/15       120                        TenGigabitEthernet 0/47

Total entries displayed: 9

 

Related Articles, References, Credits, or External Links

HP Networking – Tracing Networks and Locating IP addresses

Author: PeteLong

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