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How Do I generate a large number of input errors or crc errors on a cisco router ethernet interface ios 12.4

I'm evaluating software that calculates interface error %
I'd like to prove that it's working correctly by generating a large number of input errors on the ethernet interface.

I have tried using nmap scans with the --bad crc flag but the cisco router doesn't consider these packets to be input errors.

i have also tried building packets by hand with bad checksums and I have send giant packets but it appear that giant is not considered an input error

the router interface is directly connected to a windows pc by crossover cable.
I have changed the link speed and duplex settings between the pc and router interface, this causes occasional input errors but not enough. I'm trying to drive input errors up near 100%

I run the command
show interface fastethernet 0/0 and get
199239 packets input, 54063855 bytes
Received 2744 broadcasts, 0 runts, 83 giants, 0 throttles
4555 input errors, 0 CRC, 0 frame, 0 overrun, 4555 ignored

I'd like to push the number of input errors close to the number of total packets
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danielswanson
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danielswanson
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1 Solution
 
Todd GerbertIT ConsultantCommented:
I wrote a program some time ago for a friend who had a similar idea in mind.  It's in .Net and uses WinPCap to send packets, and has the option to send a packet with valid to/from addresses, and the rest just random bytes.  Might be able to dig up a copy if you're interested?
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danielswansonAuthor Commented:
I'd be happy to try it out if you can find it.
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Todd GerbertIT ConsultantCommented:
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danielswansonAuthor Commented:
I did give this a try. I watched the wire and saw several packets that should have triggered input errors, lots of bad frames etc..  but for some reason the cisco doesn't increase the input error count.
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danielswansonAuthor Commented:
I did solve this by breaking the ethernet cable. I cut the cable apart and spliced it back together incorrectly. Now I'm receiving roughly 1000 crc errors for every 10 incoming packets.
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Todd GerbertIT ConsultantCommented:
Good solution, simpler is usually better!

I'm not surprised the software didn't do it for you now that I think about it, since the lower-level data link/physical layers (i.e. the NIC itself) are responsible for calculating CRC's.
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danielswansonAuthor Commented:
The tool didn't work however tgerbert did point out why I did indeed to case an actual hardware failure as opposed to a software generated error
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