udld aggressive...

set up udld globally...

dls2#config t
Enter configuration commands, one per line.  End with CNTL/Z.
dls2(config)#udld aggressive
dls2(config)#

verify...

dls2(config)#do sh udld g0/1

Interface Gi0/1
---
Port enable administrative configuration setting: Follows device default
Port enable operational state: Enabled / in aggressive mode
Current bidirectional state: Bidirectional
Current operational state: Advertisement - Single neighbor detected
Message interval: 15
Time out interval: 5

    Entry 1
    ---
    Expiration time: 40
    Cache Device index: 1
    Current neighbor state: Bidirectional
    Device ID: CAT0812N33C 
    Port ID: Gi0/1 
    Neighbor echo 1 device: CHK0648W1BG
    Neighbor echo 1 port: Gi0/1

    Message interval: 15
 --More--

yank out one of the fibers...

dls2#sh udld g0/1

Interface Gi0/1
---
Port enable administrative configuration setting: Follows device default
Port enable operational state: Enabled / in aggressive mode
Current bidirectional state: Unknown
Current operational state: Link down


replace  and verify...

dls2#sh udld g0/1

Interface Gi0/1
---
Port enable administrative configuration setting: Follows device default
Port enable operational state: Enabled / in aggressive mode
Current bidirectional state: Bidirectional
Current operational state: Advertisement - Single neighbor detected
Message interval: 15
Time out interval: 5

    Entry 1
    ---
    Expiration time: 45
    Cache Device index: 1
    Current neighbor state: Bidirectional
    Device ID: CAT0812N33C 
    Port ID: Gi0/1 
    Neighbor echo 1 device: CHK0648W1BG
    Neighbor echo 1 port: Gi0/1


that's aggressive...