100/full or auto

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Georg Pauwen Tue, 11/22/2005 - 12:15
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Hello,


as a rule of thumb, fixed settings (full/100 in your case) is usually the better choice. The only reason why you would leave an access port in auto-negotiation mode is when you do not know if the clients connecting to the port are capable of whatever you can configure (full/100 again, in your case). If you absolutely know that all your clients support full/100, set the ports to a fixed setting...


HTH,


GP

glen.grant Tue, 11/22/2005 - 14:09
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I'll throw 2 cents in here also on what we do . For any servers it's probably best to hardcode the ports. For all user clients we leave as auto unless they are having a specific problem because on a network of any size haveing to hardcode all user ports becomes unmanagable . Also if one person say moves and another user moves in and his is set as auto and you have the port hardcoded then you have duplex mismatches. Auto works pretty well nowadays and we have very few problems with it . Below is a blurb out of Cisco's best practices.


Recommendation


Whether to configure auto-negotiation on 10/100 links or to hard code speed and duplex ultimately depends on the type of link partner or end device you have connected to a Catalyst switch port. Auto-negotiation between end devices and Catalyst switches generally works well, and Catalyst switches are compliant with the IEEE 802.3u specification. Problems may result, however, when NIC or vendor switches do not conform exactly. Hardware incompatibility and other issues may also exist as a result of vendor-specific advanced features, such as auto-polarity or cabling integrity, that are not described in the IEEE 802.3u specification for 10/100 Mbps auto-negotiation. An example is given in the following field notice:


It is worth anticipating that there will be some situations that require host, port speed, and duplex to be set. In general, follow these basic troubleshooting steps:


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Make sure that either auto-negotiation is configured on both sides of the link or hard coding is configured on both sides.

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Check the CatOS release notes for common caveats.

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Verify the version of NIC driver or operating system you are running, as the latest driver or patch is often required.


As a rule, try using auto-negotiation first for any type of link partner. There are obvious benefits to configuring auto-negotiation for transient devices like laptops. Auto-negotiation should also work well with non-transient devices like servers and fixed workstations or from switch-to-switch and switch-to-router. For some of the reasons mentioned above, however, negotiation issues may arise. In these cases, follow the basic troubleshooting steps outlined in the TAC links provided.

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