Cisco Nexus 5000 Series Switch CLI Software Configuration Guide, NX-OS 4.0(1a)N1 (OL-16597-01, January 2009)

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5-3
Cisco Nexus 5000 Series Switch CLI Software Configuration Guide
OL-16597-01
Chapter 5 Configuring Ethernet Interfaces
Information About Ethernet Interfaces
Figure 5-1 Unidirectional Link
Default UDLD Configuration
Table 5-1 shows the default UDLD configuration.
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.
TX
TX
RX
RX
Device A
Device B
187781
Table 5-1 UDLD Default Configuration
Feature Default Value
UDLD global enable state Globally disabled
UDLD aggressive mode Disabled
UDLD per-port enable state for fiber-optic media
Enabled on all Ethernet fiber-optic LAN ports
UDLD per-port enable state for twisted-pair (copper)
media
Disabled on all Ethernet 10/100 and
1000BASE-TX LAN ports