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Cisco 3750 stack - Interface flapping

Currently I have two Cisco 3750 switches stacked. They are both

Model : WS-C3750G-12S

IOS: Version 12.2(55)SE4

The stack is working as the distribution layer of my network and is currently servicing a number of buildings each with 3 fibre interlinked Cisco switches and links back to the 3750 stack via the 1st and 3rd switch for full redundancy.

On the 3750 stack - Show interface description.

Gi1/0/1                        up             up      

Gi1/0/2                        up             up       Link to Block_1

Gi1/0/3                        up             up       Link to Block_10

Gi1/0/4                        up             up       Link to Block_20

Gi1/0/5                        up             up       Link to Block_30

Gi1/0/6                        up             up       Link to Block_40

Gi1/0/7                        up             up       Link to Block_50

Gi1/0/8                        up             up       Link to Block_60

Gi1/0/9                        down           down     Link to Block_70

Gi1/0/10                       up             up       Link to Block_80

Gi1/0/11                       up             up     

Gi1/0/12                       down           down

Gi2/0/1                        admin down     down    

Gi2/0/2                        up             up       Link to Block_1

Gi2/0/3                        up             up       Link to Block_10

Gi2/0/4                        up             up       Link to Block_20

Gi2/0/5                        up             up       Link to Block_30

Gi2/0/6                        up             up       Link to Block_40

Gi2/0/7                        up             up       Link to Block_50

Gi2/0/8                        up             up       Link to Block_60

Gi2/0/9                        up             up       Link to Block_70

Gi2/0/10                       up             up       Link to Block_80

Gi2/0/11                       up             up       Link to Block_90

Gi2/0/12                       up             up       Link to Block_100

In the Logs I am seeing the following interfaces flap very regularly..

GigabitEthernet1/0/6   Block_40

GigabitEthernet1/0/5   Block_30

GigabitEthernet1/0/10  Block_80

GigabitEthernet2/0/5   Block_30

GigabitEthernet2/0/6   Block_40

GigabitEthernet2/0/9   Block_70        

At first I thought it was the IOS version so upgraded it to the most current version and the ports still flap.

Now I am thinking it may be the edge devices/ SFP incomparability or even spanning tree.

Everyone's tags (3)
3 REPLIES
Hall of Fame Super Gold

Cisco 3750 stack - Interface flapping

These are SFP links.  Define "flap"?  Can you please post the output to the "sh log"?

New Member

Re: Cisco 3750 stack - Interface flapping

Correct. There are 24 SFP links on the stack which are connected to each building via fibre which is presented at the other end as SC. The switches in each vary between Cisco 3550 24PWR and 3524tXL, therefore the switches in each building are connected to the patch panel using SC-SC MM fibre.

Here are the logs from the last two hours.

Jan 31 06:55:42 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/10, changed state to down

Jan 31 06:55:45 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/10, changed state to up

Jan 31 07:20:38 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/5, changed state to down

Jan 31 07:20:41 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/5, changed state to up

Jan 31 07:32:29 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/6, changed state to down

Jan 31 07:32:32 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/6, changed state to up

Jan 31 07:32:53 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/5, changed state to down

Jan 31 07:32:57 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/5, changed state to up

Jan 31 07:47:41 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/2, changed state to down

Jan 31 07:47:44 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/2, changed state to up

Jan 31 07:50:45 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/2, changed state to down

Jan 31 07:50:48 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/2, changed state to up

Jan 31 07:52:52 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/5, changed state to down

Jan 31 07:52:56 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/5, changed state to up

Jan 31 07:52:57 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/5, changed state to down

Jan 31 07:53:00 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/5, changed state to up

Jan 31 07:55:19 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/6, changed state to down

Jan 31 07:55:23 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/6, changed state to up

Jan 31 07:56:03 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/5, changed state to down

Jan 31 07:56:06 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/5, changed state to up

Jan 31 07:56:11 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/5, changed state to down

Jan 31 07:56:14 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/5, changed state to up

Jan 31 07:57:55 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/2, changed state to down

Jan 31 07:57:58 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/2, changed state to up

Jan 31 07:59:32 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/5, changed state to down

Jan 31 07:59:35 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/5, changed state to up

Jan 31 08:11:58 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/10, changed state to down

Jan 31 08:12:02 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/10, changed state to up

Jan 31 08:27:31 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/6, changed state to down

Jan 31 08:27:34 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/6, changed state to up

Jan 31 08:29:36 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/5, changed state to down

Jan 31 08:29:39 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/5, changed state to up

Jan 31 08:38:55 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/6, changed state to down

Jan 31 08:38:58 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/6, changed state to up

Jan 31 08:41:44 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/5, changed state to down

Jan 31 08:41:48 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/5, changed state to up

If you need anymore information, just ask. I will be more than happy to provide.

Thanks

Hall of Fame Super Gold

Cisco 3750 stack - Interface flapping

Freak me!  Now THAT is what I call "flapping"!

Here's how to fix this:

1.  Change the patch cable at both sides;

If it's still flapping;

2.  Change the SFP and GBIC at both sides;

If it's still flapping;

3.  Get an OTDR and check the integrity of your fibre optic;

If it's still flapping;

4.  Replace switch #2.

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