3750 Port Flaps

Unanswered Question
Feb 21st, 2009

We have just deployed a LAN that has a pair of 6513 in the core with about 65 stacks of 3750 in the edge. The IOS version is 12.2(44)SE We have about 5000 end devices that attach to this network.

These devices are mainly building management systems such as CCTV, ANPR and building control systems.

All these systems are permanently powered on.

Cisco LMS is reporting about 400 of these ports across the network are flapping during any 24 hour period.

I'm not sure if these are the same ports each day or random ports each day. Not many of the end systems have reported any down time as looking as the time stamps the links flaps appear to be for a couple of seconds each time this happens.

The switch logs show the following errors.

Log Buffer (4096 bytes):

WN: Line protocol on Interface FastEthernet3/0/48, changed state to down

Feb 21 07:01:26: %LINK-3-UPDOWN: Interface FastEthernet3/0/48, changed state to down

Feb 21 07:01:28: %LINK-3-UPDOWN: Interface FastEthernet6/0/48, changed state to down

Feb 21 07:01:28: %LINK-3-UPDOWN: Interface GigabitEthernet2/0/48, changed state to up

Feb 21 07:01:29: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/48, changed state to up

Feb 21 07:01:30: %LINK-3-UPDOWN: Interface FastEthernet6/0/48, changed state to up

Feb 21 07:01:30: %LINK-3-UPDOWN: Interface FastEthernet3/0/48, changed state to up

Feb 21 07:01:31: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet6/0/48, changed state to up

Feb 21 07:01:31: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet3/0/48, changed state to up

Feb 21 07:01:50: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet3/0/48, changed state to down

Feb 21 07:01:51: %LINK-3-UPDOWN: Interface FastEthernet3/0/48, changed state to down

Has anybody seen this problem before, could this be an IOS bug? Or is this problem with the cabling system? Any help would be appreciated.

I have this problem too.
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johnlloyd_13 Sat, 02/21/2009 - 04:52

try to hard code speed and duplex settings on opposite devices attached on these flapping interfaces. if that fails, try to replace new cables.

glen.grant Sat, 02/21/2009 - 06:30

If it was mainly users I would say it is normal as that would just reflect users coming on and off the network but if it mainly control systems look for interface errors and as the previous poster speed/duplex mismatches.Each end must be configured the same . I'm not sure how you tell how all that equipment is setup whether the nics are hardcode to a speed or auto but you will have to determine that to solve the problem .

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