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Beginner

UDLD confusing timer values and their function

Hi 

UDLD timers have always been mystery for me, is it possible for anyone to explain following attributes from show udld Fa0/16 

1. Message Interval 

2. Time Out Interval

3. Expiration time (in entry section)

How do above timers work on UDLD Hello, UDLD hold timer and how do they all add up to combat against STP's 50 second timer before port goes from blocking to listening and then all the way to designated port 

SW1------echo every 15 seconds---->SW2

SW1<--------response from SW2------SW2

What is Timeout interval and What is UDLD Hold Timer and What is Expiration time 

Please use above diagram to explain function and mechanics of UDLD if possible as I am stuck

Thanks 

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Enthusiast

Hi -

Hi -

UDLD uses a mechanism that amounts to data reflection.  The hello sent to the neighbor switch contains the ID of the local port and the ID of the remote port.  When UDLD receives a packet and sees it's own port ID, then it knows that communication is bidirectional.

When UDLD detects that the port is not bidirectional it puts the port in a down state which will cause STP to send a Topology Change Notification (TCN).  The TCN will cause an immediate reconvergence of the tree.  By shutting down the port UDLD prevents the switch from having to wait the entire timeout window for STP.

Understanding and Configuring UDLD

PSC

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Beginner

Thanks for response but I

Thanks for response but I still have no Idea of how above mentioned timers work
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