|
|
# 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.
|
|
|
|
|
|
## History
|
|
|
|
|
|
UDLD was originally developed for the Cisco Catalyst 5000 series switches.
|
|
|
|
|
|
## Protocol dependencies
|
|
|
|
|
|
- [Ethernet](/Ethernet): UDLD uses [Ethernet](/Ethernet) as its transport protocol using destination mac address 0100.0CCC.CCCC.
|
|
|
|
|
|
## Example traffic
|
|
|
|
|
|
## Wireshark
|
|
|
|
|
|
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](uploads/__moin_import__/attachments/SampleCaptures/udld.pcap)
|
|
|
|
|
|
## Display Filter
|
|
|
|
|
|
Show only UDLD packets:
|
|
|
|
|
|
```
|
|
|
udld
|
|
|
```
|
|
|
|
|
|
A complete list of display filters can be found in the [Display Filter Reference](http://www.wireshark.org/docs/dfref/u/udld.html).
|
|
|
|
|
|
## Capture Filter
|
|
|
|
|
|
You cannot directly filter UDLD protocols while capturing. However, if you use the [Ethernet](/Ethernet) destination MAC address (see above), you can filter on that one:
|
|
|
|
|
|
```
|
|
|
ether dst 01:00:0c:cc:cc:cc
|
|
|
```
|
|
|
|
|
|
## External links
|
|
|
|
|
|
- [RFC 5171](http://www.tools.ietf.org/rfc/rfc5171.txt) Informational UniDirectional Link Detection (UDLD) Protocol RFC
|
|
|
|
|
|
## Discussion
|
|
|
|
|
|
The originally stated sample capture was void, so please add the udld.pcap capture to the [SampleCaptures](/SampleCaptures) page.
|
|
|
|
|
|
---
|
|
|
|
|
|
Imported from https://wiki.wireshark.org/UDLD on 2020-08-11 23:26:59 UTC |