AutoNegotiate Question

[dkblee]

Hi! If my switch's port that is connected to a host is set to full duplex 1000mbps, but the host is running on :

a)100mbps full duplex.

b)10mbps half duplex

c)10mbps full duplex

What will happen in the switch with each of these settings?

Thks!

[Bobby Thekkekandam]

Hi,

If your switchport is running 1000Mbps, and you connect a device that operates at any other speed, you will have no connectivity whatsoever, as the layer 1 bit encoding schemes for 10, 100, and 1000Mbps are all different.

HTH,

Bobby

*Please rate helpful posts.

[dkblee]

hi! if i understand you correctly, you meant if the switch port is running on 1000mbps full duplex(configured manually) and another end is configure to 10mbps,100mbps or 1000mbps(not autonegotiate), there won't be any connection?

If both end are configured as autonegotiate, then there will be able to communicate.

[dkblee]

hi! if i understand you correctly, you meant if the switch port is running on 1000mbps full duplex(configured manually) and another end is configure to 10mbps,100mbps or 1000mbps(not autonegotiate), there won't be any connection?

If both end are configured as autonegotiate, then there will be able to communicate.

[Bobby Thekkekandam]

Hi,

Your original question was how a link would behave if one side was coded for 1000, and the other was 10 full, 10 half, or 100 full. So with a speed mismatch, the link would not come up at all.

Now, with autonegotiation, if one side is coded to 1000 full, and the other side is coded to 1000, the link will be fine. If it is hardcoded to 10 or 100mbps, again, the link will not work.

Going further with that, if one side of the link is configured for autonegotiate, and the other end is hardcoded, it may or may not work, but is considered a misconfiguration. Both ends of the link should either be autonegotiate, or hardcoded to the same speed and duplex.

More on this here:

http://www.cisco.com/warp/public/473/46.html#auto_neg_valid

HTH,

Bobby

*Please rate helpful posts.

[dkblee]

Hi! Does this concept applies if both end are switches?

What is the default settings on a 10/100/1000mbps ports? is it auto negotiate or 1000mpbs? how about 10/100mbps port? is it default to autonegotiate or 100mbps?

Thks!

[Bobby Thekkekandam]

Yes, the same caveats apply for a switch to switch connection. However, it is generally recommended to always hardcode speed and duplex between static devices, such as switch to switch and switch to router connections.

HTH,

Bobby

[dkblee]

Hi! Thks!