BigIron RX Series Configuration Guide 27353-1001810-01Chapter10Configuring Uni-Directional Link Detection (UDLD)In this chapter• Configuration considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274• Configuring UDLD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274• Displaying UDLD information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275• Clearing UDLD statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278This chapter describes configuring Uni-Directional Link Detection.Uni-directional Link Detection(UDLD) monitors a link between two device and provides a fast detection of link failures. UDLDbrings the ports on both ends of the link down if the link goes down at any point between the twodevices. This feature is useful for links that are individual ports and for trunk links. Figure 20 showsan example.FIGURE 20 UDLD examplePorts enabled for UDLD exchange proprietary health-check packets once every 500 ms (thekeepalive interval). If a port does not receive a health-check packet from the port at the other endof the link within the keepalive interval, the port waits for two more intervals. If the port still doesnot receive a health-check packet after waiting for three intervals, UDLD will be kept in asuspended state until it receives the first keep-alive message from the other end. In thissuspended state, UDLD will continue to send the keep-alive message but will not bring the portdown after maximum number of retries is done and no keep-alive message is received from theother end. The UDLD will transition from this suspended state to active state after it receives thefirst keep-alive message from the other end. In the active state, UDLD peers will continue toexchange keep alive messages periodically and if there are keep-alive messages are missed forcertain number of times from the other end, UDLD will bring down the logical port. The UDLD willthen transition from active to suspended state.XWithout link keepalive, the ports remainenabled. Traffic continues to be load balanced to theports connected to the failed link.When link keepalive is enabled, the featurebrings down the ports connectedto the failed link.
