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TOPIC: 2950G x2 - Crossover cable resulting in down ports

2950G x2 - Crossover cable resulting in down ports 7 years 4 months ago #31228

Hi all,

Hopefully a nice easy one for someone : )

Recently acquired two 2950g's but when I crossover cable the two together the ports flap and end up shutdown and I'm not sure why!?!

Facts:
The switches are both running the default config nothing has been altered.
I've updated both to 12.1.22EA13.
Looking at the buffered log apart from the up-downs entries I have a few CDP-Duplex-mismatch and a Ethchan-Loopback-Fail.

Things I've Tried:
Upgrading the ios.
Globally turning off CDP
Fixing the Speed and Duplex on the two ports (Full & 100)
Testing the Crossover cable port to port on the same switch which works fine and from both 2950s to a aging 1924 switch I have which again works fine.
And finally "no errdisable detect cause loopback" which results in the ports forever flapping : (

I'm guessing its some ether-channel setting but I've never covered this in my CCNA anyway any advice or suggested areas I should look into would be greatly appreciated.

Thanks

Chris
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Re: 2950G x2 - Crossover cable resulting in down ports 7 years 4 months ago #31239

  • TheBishop
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If there was an etherchannel set up you would see it in the config. Could you post the config for us to have a look at?
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Re: 2950G x2 - Crossover cable resulting in down ports 7 years 4 months ago #31242

Hi Bishop thanks for the reply I'm currently away from the switches but I'll post the configs later this evening.
Reason I mentioned the ether-channel is because I misread one of the errors I was getting in my syslog which was:

Ethcntr-3-Loop_back_detected: Keepalvie Packet Loop-back detected

I read this as ether-channel, but more likely ethernet controller.


After a little more googling these links describe similar problems:

www.cisco.com/en/US/products/hw/switches...01b42bf.shtml#prob1b -- thou on a 6000/6500
&
news.clnz.net/2007/10/19

Problem: The problem occurs because the keepalive packet is looped back to the port that sent the keepalive

switching of the keepalives seems to be a good starting point which I'll try later and post if this solves the problem.

Cheers,

Chris
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Re: 2950G x2 - Crossover cable resulting in down ports 7 years 4 months ago #31329

Problem resolved. I simply changed the crossover cable javascript:emoticon(':oops:').

Not a hundred percent as to why my other cable didn't work,
as I stated above this cable was tested between the troubled 2950s and a old 1924 I have.
I can only guess that as my 1924 ports are only 10MB the 2950 negotiated to 10MB using the original RX & TX wires in the cable but when trying to negotiate the 100MB between the two 2950s one of the additional wires wasn't terminated correctly.

One to remember when testing anyway

Thanks again,

Chris
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Re: 2950G x2 - Crossover cable resulting in down ports 7 years 4 months ago #31330

  • TheBishop
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Chop it and bin it!
Glad you fixed the problem
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