Cisco Systems 1000 Series Manual De Usuario

Configure the UDLD aggressive mode only on the point-to-point link between the network devices that 
support the UDLD aggressive mode. With UDLD aggressive mode enabled, a port on a bidirectional link 
that has a UDLD neighbor relationship established stops receiving the UDLD packets. The UDLD tries 
to re-establish the connection with the neighbor; the port is disabled after eight failed retries.

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 the UDLD aggressive mode is enabled, the UDLD will error disable the ports on the link to prevent 
the traffic from being discarded under the following scenarios:

One side of a link has a port (either Tx and Rx) stuck.

One side of a link remains up while the other side of the link has gone down.

 shows the default UDLD configuration.

These sections describe how to configure the UDLD protocol:

TX

TX

RX

RX

Switch A

Switch B

18720

UDLD global enable state

Globally disabled

UDLD aggressive mode

Disabled

UDLD per-port enable state for fiber-optic media Disabled

UDLD per-port enable state for twisted-pair 
(copper) media

Disabled on all Ethernet 10/100 and 
1000BASE-TX LAN ports