UDLD message timer vs. time out interval

Unanswered Question
Jun 8th, 2010

Hi,

i understand the meaning of the message timer, but what ist the use of the time out interval? On the cisco webpage i found: "When UDLD neighbors are established,           the configured message interval is sent and the timeout interval for  that peer           is calculated to be (3 * message_interval)."

But on my switch the output shows 2 kind of timers:

Interface Gi1/1
---
Port enable administrative configuration setting: Enabled / in aggressive mode
Port enable operational state: Enabled / in aggressive mode
Current bidirectional state: Bidirectional
Current operational state: Advertisement - Single neighbor detected
Message interval: 15
Time out interval: 5


    Entry 1
    ---
    Expiration time: 42
    Cache Device index: 1
    Current neighbor state: Bidirectional
  ...........->


So, what is the difference between Message Interval and Time out interval, can somebody explain?


Tia,

Stephan

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Giuseppe Larosa Tue, 06/08/2010 - 09:21

Hello Stephan,


as in other show like sh cdp neighbors the Expiration time tells you for how much time the neighbor will be considered valid


if we do multiple times the following:



sh udld te1/1 | inc Expiration time:

    Expiration time: 15

switch#sh udld te1/1 | inc Expiration time:

    Expiration time: 21



in my case I see



sh udld te1/1                     


Interface Te1/1

---

Port enable administrative configuration setting: Follows device default

Port enable operational state: Enabled

Current bidirectional state: Bidirectional

Current operational state: Advertisement - Single neighbor detected

Message interval: 15

Time out interval: 5


    Entry 1

    ---

    Expiration time: 14

    Cache Device index: 1

    Current neighbor state: Bidirectional

    Device ID: 0169C561C0

    Port ID: Te4/8

    Neighbor echo 1 device: FOX1027012K

    Neighbor echo 1 port: Te1/1




expiration time is varies between 15 and 21 seconds after receiving a message it looks like it can be message interval 15 + timeout interval is the effective expire timeout



Hope to help

Giuseppe

ssieger Wed, 06/09/2010 - 00:28

Hi Giuseppe,


so if i plan to use udld in a rstp environment, in a case of an unidirctional link i have to consider a maxage of 4-6 secplus listening and learning state 15 sec each (because there is no rstp communication and the system will fall back to 802.1D). That result in a total time from blocking to forwarding of approximately 34-36 sec. right?

UDLD have to recognize the link failure before a time of max. 36 sec, so if i use aggressive mode the following happens:

the timout of 5 sec expires

than 3 times of the transmit intervall expires

after that 8 additional packets are send in aggressive mode, one packet every second


So, 5 + 45 (3*15) + 8 = 58 sec , so i have to modify the transmit interval to 7 sec:


Than 5 + 21 (3*7) + 8 = 34 sec, and that is a value below the 36 sec for rstp.


Do you agree with that proposal?


Greetings,

Stephan

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