UniDirectional Link Detection (UDLD)

UDLD is a Cisco Layer 2 protocol to detect a uni-directional fiber link between two Ethernet switches in order to prevent a looped network. UDLD is often used in switched Ethernet networks where Spanning-Tree is required to block one or more ports to prevent a loop from forming.


UDLD was originally developed for the Cisco Catalyst 5000 series switches.

Protocol dependencies

Example traffic


UDLD support was added in Wireshark 0.99.4.

Preference Settings

There are no preference settings at the present time.

Example capture file

* SampleCaptures/udld.pcap

Display Filter

Show only UDLD packets:


A complete list of display filters can be found in the Display Filter Reference.

Capture Filter

You cannot directly filter UDLD protocols while capturing. However, if you use the Ethernet destination MAC address (see above), you can filter on that one:

  ether dst 01:00:0c:cc:cc:cc 

External links


The originally stated sample capture was void, so please add the udld.pcap capture to the SampleCaptures page.

Imported from https://wiki.wireshark.org/UDLD on 2020-08-11 23:26:59 UTC