Auto-Negotiation ON vs OFF - Welcome Back To Ethernet World

Auto negotiation is one of those thing which comes back to every network engineer at some point. There is always so much talk about idea  that - if we should keep auto-negotiation "ON" or should we turn it "OFF" and hard-cord the "Duplex" & "Speed" settings.

There are always two schools of thoughts about this and you may choose which one you like more. 

So idea boils down to which school you prefer. 

But...

Here are some of drawbacks or I should say list of things which you won't be able to figure out easily or will not work at all if you turn off auto-negotiation over interface:

1. Performance Issue
2. Link failures
3. Pause Frames or Flow Control
4. Bad Cable Problem
5. Link Partner Capabilities
6. Auto-MDIX will not work

For more:

http://en.wikipedia.org/wiki/Autonegotiation 

http://etherealmind.com/ethernet-autonegotiation-works-why-how-standard-should-be-set/

http://www.sun.com/blueprints/0704/817-7526.pdf

http://www.cisco.com/en/US/docs/internetworking/troubleshooting/guide/tr1923.html

http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a00800a7af0.shtml 

http://blog.ine.com/2008/07/08/802-3x-flow-control/ 
 
HTH...
Deepak  Arora