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Webcast-Catalyst9k
New Member

collisions threshold

Hi, recently I encountered a port disabled by err-disable due to collision. Anyone know what is the threshold of the collisions (excessive or late collision) that may result in err-disable. How cisco switches know when to disable the port when it detected the collision on a port?

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Accepted Solutions
Cisco Employee

Re: collisions threshold

16 collisions in a row implies an "excessive collision"

By definition, the single collision counter increments when frames have been successfully transmitted after one collision. Multiple collisions occur when more than one collision occurs before a frame is transmitted.

So, when a single or multiple collision occurs, a frame is eventually transmitted, so the threshold counter is effectively zeroed out again.

An excessive collision, by definition, occurs if an interface fails to allocate a slot in which it can transmit its frame without another collision 16 times. This is when the interface is errdisabled.

HTH,

Bobby

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3 REPLIES
Cisco Employee

Re: collisions threshold

Hi,

on the desktop switch platforms, the threshold is 16 collisions in a row within a 2 second interval. Prior to the changes in CSCed92917, this threshold was 2 collisions in a row within a 2 second interval.

You can disable this check altogether with "no errdisable cause loopback"

HTH,

Bobby

*please rate helpful posts

New Member

Re: collisions threshold

Thanks for the info.

BTW, what is means by "16 collisions in a row"? Does these collisions include single collision, multiple collision, late collision and excessive collison?

Cisco Employee

Re: collisions threshold

16 collisions in a row implies an "excessive collision"

By definition, the single collision counter increments when frames have been successfully transmitted after one collision. Multiple collisions occur when more than one collision occurs before a frame is transmitted.

So, when a single or multiple collision occurs, a frame is eventually transmitted, so the threshold counter is effectively zeroed out again.

An excessive collision, by definition, occurs if an interface fails to allocate a slot in which it can transmit its frame without another collision 16 times. This is when the interface is errdisabled.

HTH,

Bobby

*Please rate helpful posts

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