Can 3120/3130 Auto-Negotiate Duplex? (And if so, how do I tell it to?)

[Anonymous]

Just what it says on the tin. The AOS manual implies that setting speed to auto-negotiate will do this, but I've found no option to set Duplex to auto, nor to clear half/full duplex configuration to allow the speed auto-negotiation option to handle duplex.

[Anonymous · Accepted solution]

- Thanks for posting your question on the forum!

Setting the speed to auto negates any duplex setting on the interface and will allow the port to negotiate its speed AND duplex. The only time the duplex setting will be enforced is when the speed is hard-set to something other than auto.

If you have the speed set to auto and you are seeing the link negotiate to half-duplex, this usually indicates that the connected device is hard-set to a speed and duplex while the NetVanta is set to auto. You will want to make sure that both sides are either hard-set or are set to negotiate (auto). Otherwise, you may experience performance issues and start seeing errors on the interface. The following thread is an example where this was occuring:

Please do not hesitate to let us know if you have any questions.

Thanks,

Noor

[Anonymous]

Thanks Noor! You and your team really fill in the blanks in the manpages.

[Anonymous]

You know, something bothered me about this for months:

The Adtran is set to auto-negotiate speed and duplex.

If the other side is not set to auto-negotiate as well, then the Adtran cannot auto-negotiate? I really do not understand how that is automatically negotiating anything at all if I have to manually set both ends anyway. Why don't I just set both sides manually?

In what scenario would it make sense to:

1.) Be set to auto-negotiate,

2.) be able to detect the other side is at a certain speed/duplex setting, and yet

3.) not match those settings?

If I wanted to force a duplex/speed mismatch, I'd manually set both sides, after all. If I'm setting one side to auto-negotiate... it's pretty clear I'm expecting it to match the other side.

If this isn't a bug, is it part of some standard out there? Or am I just misunderstanding the point of setting auto-negotiate?

[Anonymous]

- The term "auto-negotiate" means that you do not have to hardset a speed/duplex for the ethernet link to come up, but it will need to negotiate with the connected device to see which speed/duplex to come up on. For example, say you had Adtran1 set to 100/full and Adtran2 set to auto-negotiate. Well, Adtran1 will bring its interface up at 100/full, but since it is not attempting to negotiate with Adtran2 as Adtran2 is expecting, Adtran2 will assume the worst case and come up at 100/half.

You will want to set the Adtran to auto-negotiate on a port so that it will attempt to negotiate the highest speed and duplex. However, the keyword is 'negotiate' so it will be expecting the peer device to give some notification about its speed/duplex as the link comes up. Unfortunately, the peer device will not do this unless it is also set to 'auto-negotiate'.

I hope this makes sense but please do not hesitate to let us know if you have any further questions.

Thanks,

Noor