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BERT (Bit Error Rate Testing) - When to use?

Hi Cisco Support Community,

Can you please advise me when and where you would use Cisco BERT (Bit Error Rate Testing)? Is it only designed for WAN termination devices? Does it matter what type of circuit you are connected to?

Also, if this is going to be scalable (i.e. Enterprise wide), is there any software or other automation technique which can be used to both run the testing and collate / make sense of the output?

Are there any risks or other key factors to be aware of when using BERT?

Thank you!

Matt :-)

4 Replies 4

Charles Hill
Rising star
Rising star

Hey Matt,

Here is a Cisco BERT document that may be helpful.


Hope this helps.

Please rate helpful posts.


Hi Charles,

Thanks for sharing the link. Do you know if this is something you only do on a T1/E1 or T3/E3 line? (As no other circuit types are referred to in the document).





A BERT test is typically used on Serial interfaces which could be T1/E1 or T3/E3 depending on your  geographical location. It is intended to test circuit problems and I have not seen it used for ethernet links so far. Regardless Cisco is looking into ways of testing ethernet links as well, like being able to issue a software loopback test on the newer cards. Just keep in mind that for a BERT test you will need a way to loop part of the circuit in order for the test packets to return to you. Normally done with your ISP involved.

Hi Glennmar,

Thanks for your message explanation. So if I am right in understanding you, then in each router I would need a spare serial interface to logically loop the circuit to? 

Do you know if there is a scale which allows you to interpret if the amount of errors occurring are high, medium, low etc? Also, is there a best practice duration which the BERT should be run for?

Kind regards,


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