UDLD : UDLD detects and disables unidirectional links.
UDLD monitors the physical configuration of fiber-optic and copper connections and detects when a one-way connection exists. When a unidirectional link is detected, the interface is shut down and the system alerted.
BPDU filtering : Restricts the switch from sending unnecessary BPDUsout access ports.
Recommended Practices for UDLD Configuration
UDLD enables devices to monitor the physical configuration of the cables and detect when a unidirectional link exists where bidirectional communication has not been established.
UDLD is typically deployed on fiber topologies where physical misconnections can occur that enable a link to appear to be up/up when there is a mismatched set of transmit/receive pairs. UDLD supports both fiber-optic and copper Ethernet cables connected to LAN ports.
Each switch port configured for UDLD will send UDLD protocol hello packets at Layer 2 containing the device and port identifications of the port, and the device and port identifications of the neighbor as seen by UDLD on that port. Neighboring ports should see their own device and port identifications in the packets received from the other side. If the port does not see its own device and port identifications in the incoming UDLD packets for a specific duration of time, the link is considered unidirectional and is shut down. The default 15-second hello timers are the same for normal and aggressive UDLD. In normal mode, UDLD will error-disable only the end where the UDLD is detected; aggressive mode will error-disable both ends of a connection after aging on a previously bidirectional link in eight seconds.
A recommended practice is to enable UDLD aggressive mode in all environments where fiber-optic interconnections are used. UDLD is enabled globally on all fiber-optic LAN ports with the Cisco IOS software udld {enable | aggressive} command. UDLD is enabled on individual LAN ports with the udld port [aggressive] interface command.
BPDU filter can be configured globally or under the interface level. When configured globally all portfast enabled ports stop sending and receiving BPDUs, but if a BPDU is received on the port it gets out of the portfast state and normally participate in the spanning tree calculations.
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