trunk is up up but unable to send data

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Apr 30th, 2008
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c3750 core and c3560 access, trunk port is up and up but unable to send data or ping, intermittent fault rectified by rebooting the c3560 switch,sfp modules and fibre cables checked all okay no errors on port and connection between switches never goes down but we have intermittent fault where no data will pass.

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VictorAKur Wed, 04/30/2008 - 13:22
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Could you post a log please.

A thing springs in mind (providing that harware is fine) - possible stp loop?

A simillar problem may hapen when UDLD is disabled and Rx fiber on one of the ends is broken, so the port does not receive BPDUs anymore and goes into forwarding state (providing there are two uplinks there), cuasing a loop.

Would be nice to have a look at the loggs though.


andrewerowley Wed, 04/30/2008 - 22:47
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thanks for your reply, no loop as only one uplink, I will double check UDLD but it should be enabled also fibers have been checked,communication can be okay for between two and seven days before problem reoccurs.Sorry unable to post any logs because of security.

glen.grant Wed, 04/30/2008 - 17:16
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My guess is maybe you have trunk config incorrect and that you forced on the trunk so it isn't working correctly. This is the problem if you force the trunks on as long as you have a layer 1 link it will show the port as trunking even if its not configured correcly which is why I let them negotiate the trunks , its either up or its not when you set it up this way . you would have to post the configs in order to look at though .

andrewerowley Wed, 04/30/2008 - 22:49
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Sorry unable to post configs due to security. Trunks are configured correctly as they are configured identical to all our trunks and also the switch can work fine for anything between two and seven days before a reboot is needed. Thanks


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