auto negotiate

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Oct 1st, 2008
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I was wondering why you can set your speed to a static entry and your duplex to auto or set your speed to auto and your duplex to static? This would be on IOS. I thought I recalled back on CatOS it would give you an error message if you tried to set one static and the other auto. So what type of configuration would you want this half static/half auto settings?


Thanks



-edit


I think if found my answer....


http://supportwiki.cisco.com/ViewWiki/index.php/Runts_and_CRC_errors_increment_in_the_show_interface_command_output_on_a_Cisco_IOS-based_switch,_or_FCS_errors_and_runts_increment_in_the_show_port_command_output_on_a_CatOS_based_switch_due_to_a_duplex_mismatch


"Never mix a hard set and an auto command on the same interface. For example, the speed auto and duplex full commands should never be issued on the same interface. "


Kind of odd it lets you put the commands in if you shouldn't be able to use them....

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Richard Burts Wed, 10/01/2008 - 07:27
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Kevin


It is one of the features of IOS that there are many (MANY) options that you can configure. A principle that I would stress when I was teaching Cisco classes is that just because you COULD do something does not necessarily mean that you SHOULD do something. Cisco provides many of these options to allow you to deal with unusual situations. It does not mean that you should use these options in common situations.


One of the things that you gain as you get more experience with configuring Cisco equipment is better understanding of which configuration options are commonly used and beneficial and which are less commonly used (and should be used with caution).


There might be a situtation where some device is connected to Cisco and the negotiation of duplex does not work as expected (I have seen that, especially on some older gear) and you might want to set the speed for auto negotiation and set the duplex manually. IOS allows you to do this. But I would only do this if I KNEW that I had need of it in a particular situation.


HTH


Rick


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