I am finding conflicting info among cisco documentation for the acceptable threshold of collisions on a ethernet segment. A CCDA question was that the Cisco standard for collisions was .1% of total throughput. Divide collisions by packet output to arrive at this number. Assuming that there is no collisions on full duplex, this must therfore apply to 1/2 duplex operation.
The former seems like the most logical, but I have interfaces in the network I support clocking 12% collisions per the equation above, and there is not users complaining of latency on these segments. I have seen interfaces communicating with a duplexing mismatch go above 30% collisions and it is my belief that the 12% segments are set correctly. I should also add that these segments are connected to a baystack switch, so i think this could be the cause.
the CCDA is the theory, the CCO is more a best practice.
A good guide, in theory, to use is collisions should not total more than 1% of the frames transmitted. The following table gives a guide as to recommendations of collision levels with respect to bandwidth utilisation of a segment:
%age Utilisation/Maximum %age Collisions
less than 20% / 1%
20-49% / 5%
over 50% / 15%
Remember that, in practice, collision do not constitute "always" a problem. When I have collisions, as CRC or late collisions or errors in general, normally I check my topology, essentially L1 and L2.
Hi everyone, I would like to thank you in advance for any help you can provide a newcomer like myself!
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