[c-nsp] full duplex mismatch speed - dynamips

Mike Andrews mandrews at bit0.com
Thu Aug 19 13:54:10 EDT 2010

On 8/19/10 1:26 PM, Justin M. Streiner wrote:
> On Thu, 19 Aug 2010, Adam Armstrong wrote:
>> On 17/08/2010 23:50, Justin M. Streiner wrote:
>>> On Tue, 17 Aug 2010, Alessandro Braga wrote:
>>> > Verify duplex and speed configurations on interface, the rule is:
>>> > autoXauto, forcedXforced. If problem not solve, disable cdp.
>>> Also, while auto speed/duplex negotiation is fine for user
>>> workstation/PC ports in most cases, I recommend against using it on your
>>> network infrastructure if you can help it.
>> This is horribly terrible advice.
>> Autonegotiation should always be used as default, nailing should be
>> the fix for when things don't work, and where very old devices don't
>> do autoneg properly.
>> Note that for gigabit, autonegotiation is MANDATORY.
> For 1000baseT, yes, autoneg support is mandatory.
> I'll qualify my original statement. My FE experience is somewhat dated,
> but at that time, enabling autoneg would also often set the evil bit. It
> created more problems than it solved.
> It's been 5+ years since I had to worry about speed and duplex autoneg to
> any significant extent in my network infrastructure since the place I

And that's kind of the point the others are making: it's been well over 
5 years since autoneg breakage was the norm.  It USED to be good advice 
to hardcode speed/duplex.  I used to do it religiously myself -- in 
2002.  But it's 2010 now.  Times have changed, hardware has gotten 
better, then gigabit came along and made autoneg mandatory anyway.  Not 
many people are hooking broken Tulip-based cards (like the PA-FE-TX) to 
2924XL's anymore.  :)

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