Cisco Sg3008 Manual

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Cisco Small Business 200, 300 and 500 Series Managed Switch Administration Guide (Internal Version)  146
 
Port Management: Unidirectional Link 
Detection
This section describes how the Unidirectional Link Detection (UDLD) feature.
It covers the following topics:
•UDLD Overview
•UDLD Operation
•Usage Guidelines
•Dependencies On Other Features
•Default Settings and Configuration
•Before You Start
•Common UDLD Tasks
•Configuring UDLD
UDLD Overview
UDLD is a Layer 2-protocol that enables devices...

Port Management: Unidirectional Link Detection
UDLD Operation
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All connected devices must support UDLD for the protocol to successfully detect 
unidirectional links. If only the local device supports UDLD, it is not possible for the 
device to detect the status of the link. In this case, the status of the link is set to 
undetermined. The user can configure whether ports in the undetermined state...

Port Management: Unidirectional Link Detection
UDLD Operation
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UDLD is enabled on a port when one of the following occurs:
•The port is a fiber port and UDLD is enabled globally.
•The port is a copper port and you specifically enable UDLD on it. 
How UDLD Works
When UDLD is enabled on a port, the following actions are performed:
•UDLD initiates the detection state on the port. 
In this state, UDLD...

Port Management: Unidirectional Link Detection
UDLD Operation
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If an interface is down and UDLD is enabled, the device removes all neighbor 
information and sends at least one ULDL message to the neighbors informing them 
that the port is down. When the port is brought up, the UDLD state is changed to 
detection.
UDLD Not Supported or is Disabled on a Neighbor
If UDLD is not supported or disabled...

Port Management: Unidirectional Link Detection
Usage Guidelines
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UDLD again begins running on the port. If the link is still unidirectional, UDLD 
shuts it down again after the UDLD expiration time expires, for instance.
•Manually—You can reactivate a port in the Port Management > Error 
Recovery Settings page
Usage Guidelines
Cisco does not recommend enabling UDLD on ports that are connected to...

Port Management: Unidirectional Link Detection
Default Settings and Configuration
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•UDLD and Layer 2 Protocols
UDLD runs on a port independently from other Layer 2 protocols running on 
the same port, such as STP or LACP. For example, UDLD assigns the port a 
status regardless of the STP status of the port or regardless of whether the 
port belongs to a LAG or not.
Default Settings and...

Port Management: Unidirectional Link Detection
Configuring UDLD
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STEP  2Click Apply
Workflow2: To change the UDLD configuration of a fiber por t or to enable 
UDLD on a copper por t, perform the following steps:
STEP 1Open the Port Management > UDLD Global Settings page. 
a. Select a port.
b. Select either Default, Disabled, Normal or Aggressive as the port’s UDLD 
status. If you select Default, the...

Port Management: Unidirectional Link Detection
Configuring UDLD
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•Fiber Port UDLD Default State—This field is only relevant for fiber ports. 
The UDLD state of copper ports must be set individually in the UDLD 
Interface Settings page. The possible states are:
-Disabled—UDLD is disabled on all ports of the device.
-Normal—Device shuts down an interface if the link is unidirectional. If 
the link...

Port Management: Unidirectional Link Detection
Configuring UDLD
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determination (if there was one), or since UDLD began running on the 
port, so that the state is not yet determined.
-Bidirectional—Traffic sent by the local device is received by its 
neighbor, and traffic from the neighbor is received by the local device.
-Undetermined—The state of the link between the port and its 
connected port...

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Configuring UDLD
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•State—State of the link between the local and neighboring device on the 
local port. The following values are possible: 
-Detection—The latest UDLD state of the port is in the process of being 
determined. Expiration time has not yet expired since the last 
determination (if there was one), or since UDLD began running on the 
port,...