HP Cisco Nexus 5000 Cisco Nexus 5000 Series Switch CLI Software Configuration - Page 103

Chapter 5 Configuring Ethernet Interfaces Information About Ethernet Interfaces Send feedback to [email protected] Figure 5-1 Unidirectional Link Device A TX RX TX RX Device B 187781 Default UDLD Configuration Table 5-1 shows the default UDLD configuration. Table 5-1 UDLD Default Configuration Feature UDLD global enable state UDLD aggressive mode UDLD per-port enable state for fiber-optic media UDLD per-port enable state for twisted-pair (copper) media Default Value Globally disabled Disabled Enabled on all Ethernet fiber-optic LAN ports Disabled on all Ethernet 10/100 and 1000BASE-TX LAN ports For information on configuring the UDLD for the device and its port, see the "Configuring the UDLD Mode" section on page 5-5. UDLD Aggressive and Nonaggressive Modes UDLD aggressive mode is disabled by default. You can configure UDLD aggressive mode only on point-to-point links between network devices that support UDLD aggressive mode. If UDLD aggressive mode is enabled, when a port on a bidirectional link that has a UDLD neighbor relationship established stops receiving UDLD frames, UDLD tries to reestablish the connection with the neighbor. After eight failed retries, the port is disabled. To prevent spanning tree loops, nonaggressive UDLD with the default interval of 15 seconds is fast enough to shut down a unidirectional link before a blocking port transitions to the forwarding state (with default spanning tree parameters). When you enable the UDLD aggressive mode, the following occurs: • One side of a link has a port stuck (both transmission and receive) • One side of a link remains up while the other side of the link is down In these cases, the UDLD aggressive mode disables one of the ports on the link, which prevents traffic from being discarded. OL-16597-01 Cisco Nexus 5000 Series Switch CLI Software Configuration Guide 5-3