All about Uni-Directional Link Detection (UDLD) Protocol
Today I am going to talk about another protocol named as UDLD (Uni-Directional Link Detection protocol) in details with the different modes used in UDLD.
What is the UDLD protocol and where we are using this protocol ?
UDLD is a Layer 2 protocol that works with the Layer 1 protocols to determine the physical status of a link. In Layer 1, auto negotiation takes care of physical signalling and fault detection. UDLD performs tasks that auto negotiation cannot perform, such as detecting the identities of neighbors and shutting down misconnected LAN ports.
Fig 1.1- UDLD protocol |
When you enable both auto negotiation and UDLD, the Layer 1 and Layer 2 detection work together to prevent physical and logical unidirectional connections and the malfunctioning of other protocols.
A unidirectional link occurs whenever the traffic transmitted by a local device over a link is received by a neighbor, but traffic transmitted from the neighbor is not received by the local device. If one of the fiber strands in a pair is disconnected, the link does not stay up as long as the auto negotiation is active. In such a scenario, the logical link is undetermined, and the UDLD does not take any action.
If both the fibers are working normally in Layer 1, the UDLD in Layer 2 determines whether those fibers are connected correctly and whether the traffic is flowing bidirectionally between the correct neighbors. This check cannot be performed by auto negotiation because auto negotiation operates in Layer 1
What are the different modes in UDLD ?
UDLD have two different modes. These modes are as below. We will discuss both these modes one by one in details.
- UDLD normal Mode
- UDLD Aggressive mode