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2-9
Cisco Nexus 7000 Series NX-OS Interfaces Configuration Guide, Release 5.x
OL-23435-03
Chapter 2 Configuring Basic Interface Parameters
Information About the Basic Interface Parameters
Default UDLD Configuration
Table 2-4 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 2-39.
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 frame, 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.
Note You enable the UDLD aggressive mode globally to enable that mode on all the fiber ports. You must
enable the UDLD aggressive mode on copper ports on specified interfaces.
Tip When a line card upgrade is being performed during an in-service software upgrade (ISSU) and some of
the ports on the line card are members of a Layer 2 port channel and are configured with UDLD
aggressive mode. If one of the remote ports is shutdown, UDLD puts the corresponding port on the local
device into error disabled state. This is correct behavior.
To restore service after the ISSU has completed, run a shutdown followed by a no shutdown command
on the local port.
Table 2-4 UDLD Default Configuration
Feature Default Value
UDLD global enable state Globally 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
UDLD aggressive mode Disabled
UDLD message interval
15 seconds
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