Displaying UDLD Information

UDLD information is displayed using several show commands.
  1. To display UDLD information for all ports, use the show link-keepalive command with no options. 
    device# show link-keepalive

Total link-keepalive enabled ports: 4
Keepalive Retries: 3    Keepalive Interval: 1 Sec.
Port    Physical Link   Logical Link    State           Link-vlan
1/1/1   up              up              FORWARDING      3
1/1/2   up              up              FORWARDING
1/1/3   down            down            DISABLED
1/1/4   up              down            DISABLED
  2. If a port is disabled by UDLD, the change also is indicated in the output of the show interfaces brief command.
    device# show interfaces brief

Port    Link State      Dupl Speed Trunk Tag Priori MAC            Name
1/1/1   Up   LK-DISABLE None None  None  No  level0 0000.00a9.bb00
1/1/2   Down None       None None  None  No  level0 0000.00a9.bb01
1/1/3   Down None       None None  None  No  level0 0000.00a9.bb02
1/1/4   Down None       None None  None  No  level0 0000.00a9.bb03
    If the port was already down before you enabled UDLD for the port, the port state is listed as None.
  3. To display detailed UDLD information for a specific port, use the show link-keepalive command with a port number. 
    device# show link-keepalive ethernet 4/1/1

Current State   : up            Remote MAC Addr  : 0000.00d2.5100
Local Port      : 4/1/1         Remote Port      : 2/1/1
Local System ID : e0927400      Remote System ID : e0d25100
Packets sent    : 254           Packets received : 255
Transitions     : 1             Link-vlan        : 100
  4. The show interface ethernet command also displays the UDLD state for an individual port. In addition, the line protocol state listed in the first line will say "down" if UDLD has brought the port down. 
    device# show interface ethernet 1/1/1

FastEthernet1/1/1 is down, line protocol is up, link keepalive is enabled
  Hardware is FastEthernet, address is 0000.00a9.bbca (bia 0000.00a9.bbca)
  Configured speed auto, actual unknown, configured duplex fdx, actual unknown
  Member of L2 VLAN ID 1, port is untagged, port state is DISABLED
  STP configured to ON, priority is level0, flow control enabled
  mirror disabled, monitor disabled
  Not member of any active trunks
  Not member of any configured trunks
  No port name
  300 second input rate: 0 bits/sec, 0 packets/sec, 0.00% utilization
  300 second output rate: 0 bits/sec, 0 packets/sec, 0.00% utilization
  0 packets input, 0 bytes, 0 no buffer
  Received 0 broadcasts, 0 multicasts, 0 unicasts
  0 input errors, 0 CRC, 0 frame, 0 ignored
  0 runts, 0 giants, DMA received 0 packets
  19 packets output, 1216 bytes, 0 underruns
  Transmitted 0 broadcasts, 19 multicasts, 0 unicasts
  0 output errors, 0 collisions, DMA transmitted 19 packets
    In this example, the port has been brought down by UDLD. Notice that in addition to the information in the first line, the port state on the fourth line of the display is listed as DISABLED.
Parent topic: UDLD