ISR C1111 8P Lan port flapping

[mohamedgiumazwali]

Hi Group

I'm having a Cisco ISR C1111-8P   Dual GE WAN Ethernet Router in my organization today i am trying to make test speed to certain server the wan interface with the PE router is 1G also the Lan interface with my laptop is 1G directly connected with ISR  the problem is when i check interface  status of the Lan interface it set auto to 100M not to 1G i tried to force it to 1G but the port start flapping up-down , also i had the same scenario with customer but in the customer the port stable to 1G no flapping but the maximum speed test i got is 100M doesn't exceed while from the PE there is no restrictions on this port whish means it should reach 1G purely.

So i am asking !

1.Does ISR C1111 have kind of restrictions, Bug , license that set the speed of an interface to 100M and doesn't go further than that.

2. Flapping issue any suggestions btw i tried everything from changing duplex , speed , bandwidth still flapping.  

[Leo Laohoo · Accepted solution]

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@mohamedgiumazwali wrote:

Lan interface it set auto to 100M not to 1G i tried to force it to 1G but the port start flapping

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Faulty cable. 

If Pair "D" is not terminated properly, the link will flap if "forced" to 1 Gbps.

[mohamedgiumazwali]

I tried using the same cable to  another router 7604  the speed set to 1g auto not like ISR C1111 I think not cabling issue 

Any suggestion leo !

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[Leo Laohoo]

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@mohamedgiumazwali wrote:

I tried using the same cable to  another router 

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Show us the complete output to the command "sh interface <PORT>". 

Get a different cable and try again.

[mohamedgiumazwali]

You were right Leo it was cabling issue the funny is i tried about 3 different cable so i wasn't sure it is cabling issue yesterday i made new one all went good 1G speed

Also cable tester not accurate results all good from tester even for the bad cables.

So thanks buddy 

[Leo Laohoo]

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@mohamedgiumazwali wrote:

Also cable tester not accurate results all good from tester even for the bad cables.

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The only cable tester I will trust is from a Fluke DTX or DSX.