nx.os.and.cisco.nexus.switching.2nd.edition.1587143046

Click here to view code image
Congo(config)# vpc domain 1
Congo(config-vpc-domain)# ip arp synchronize
Unidirectional Link Detection
Full-duplex communication creates a situation in which a node can receive traffic but cannot
transmit or vice versa; this condition is known as a unidirectional link and can be
problematic for protocols that require a bidirectional exchange of information. This
condition is most-often attributed to fiber-optic cabling as the physical medium.
Unidirectional link conditions can exist in other mediums such as twisted-pair copper
cabling. Although upper-layer protocols can overcome this scenario easily, this scenario
can produce unexpected results at Layer 2. For these Layer 2 protocols, Cisco provides a
mechanism for detecting and disabling links where bidirectional traffic flow is not possible.
Cisco developed Unidirectional Link Detection to eliminate any negative behavior
associated with the failure of bidirectional communication. UDLD enables each device to
send packets to the directly connected device at periodic intervals (15 seconds by default);
the sending and receiving of these packets ensure that traffic flow is bidirectional. The
Cisco UDLD implementation defines two modes that devices can operate:
• Aggressive mode: Typically used for copper-based mediums such as twisted-pair
copper
• Nonaggressive mode: Typically used for fiber-based networks
Example 2-72 shows the configuration and verification of UDLD.
Example 2-72. UDLD Configuration
Click here to view code image
! Enabling UDLD
Congo(config)# feature udld
Congo(config)#
! Verifying UDLD global status
Congo# show udld global
UDLD global configuration mode: enabled
UDLD global message interval: 15
Congo# show udld
Interface Ethernet1/1
--------------------------------
Port enable administrative configuration setting: devicedefault
Port enable operational state: enabled
Current bidirectional state: bidirectional