Unidirectional Link Detection: Difference between revisions

Revision as of 15:40, 23 March 2017

Revision as of 04:27, 19 April 2017

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:* In order for UDLD to work, both switch devices on the link must support UDLD and have it enabled on respective ports.

==[[Allied Telesis|Description]]==

If two devices, A and B, are connected via a pair of [[optical fiber]]s, one used for sending from A to B and other for sending from B to A, the link is bidirectional (two-way). If one of these fibres is broken, the link has become one-way or unidirectional. The goal of the UDLD protocol is to detect a broken bidirectional link (e.g. transmitted [[packet (information technology)|packets]] do not arrive at the receiver, or the fibres are connected to different [[computer port (hardware)|ports]]).

For each device and for each port, a UDLD packet is sent to the port it links to. The packet contains sender identity information (device and port), and expected receiver identity information (device and port). Each port checks that the UDLD packets it receives contain the identifiers of his own device and port.

UDLD is a Cisco-proprietary protocol. [[Allied Telesis]] also uses this protocol (UDLD) on their X-Series switches whilebut HP, [[Extreme Networks]], and [[Avaya|AVAYA]] all have a similar feature calling it by a different name. HP calls theirs Device Link Detection Protocol (DLDP). Extreme Networks call it Extreme Link Status Monitoring (ELSM) and AVAYA calls theirs, Link-state Tracking.

Similar functionality in a standardized form is provided as part of the [[Ethernet]] [[OA&M|OAM]] protocol that is defined as part of the [[Ethernet in the First Mile]] changes to [[802.3]] (previously [[802.3ah]]). [[D-Link]] has their DULD feature built on top of [[Ethernet]] [[OA&M|OAM]] function. [[Brocade Communications Systems|Brocade]] devices running Ironware support a proprietary form of UDLD.