Dell N3200-ON EMC Networking N-Series Switches CLI Reference Guide version 6.7 - Page 862

recognize only the sending failures on unidirectional links. If all devices in the network support UDLD, this functionality is enough to detect all unidirectional links. Processing UDLD Traffic from Neighbors Every UDLD-capable device collects information about all other UDLDcapable devices. Each device populates UDLD echo packets with collected neighbor information to help neighbors identify unidirectional links. Every frame basically contains the device ID of the sender and the collection of device IDs of its discovered neighbors. UDLD in Normal-mode In normal mode, a port's state is classified as undetermined if an anomaly exists. These include the absence of its own information in received UDLD messages or the failure to receive UDLD messages. The state of undetermined has no effect on the operation of the port. The port is not disabled and continues operating as it previously did. When in normal mode, a port is diagnostically disabled for the following cases: a UDLD PDU is received from partner that does not have the port's own details (echo). b When there is a loopback, information sent out on a port is received back as is. UDLD in Aggressive-mode Aggressive mode differs from normal UDLD mode - it can diagnostically disable a port if the port does not receive any UDLD echo packets after a bidirectional connection was established. It expands the cases when port can be disabled. There can be several causes for a port not to receive UDLD echoes. These include: • A link is up on one side and down on the other. This can occur on fiber ports if the transmit port is unplugged on one side. • Loss of connectivity, i.e. the port is neither transmitting nor receiving, but the port also reports it is up. Layer 2 Switching Commands 862