Ethernet autonegotiation

[mrtester2013]

I am just wondering what kind of procedures are running during the link  establishment in 100Base-T ethernet in case auto negotiation is disabled  (i.e. forced mode) at both ends of the ethernet connection (i.e. switch  and NIC)?. I just checked the 802.3-2008 standard but it only explaines auto-negotiation procedures with parallel detection. What I am wondering what kind of link establishment procedures are performed in case both end nodes are forced to configure for example 100B-T full duplex mode.

Thanks,

[paul driver]

Hello

Please review this post

https://supportforums.cisco.com/message/3845473#3845473

res

Paul

Please don't forget to rate this post if it has been helpful.

[mrtester2013]

Sorry but that did not help.

[Abzal]

Hi,

Both sides of a link should have auto-negotiation on, or both sides should have it off. Cisco recommends to leave auto-negotiation on for those devices compliant with 802.3u. Hard coding the speed on a port disables all auto-negotiation functionality on the port for speed and duplex.

In order to detect the speed, the link partner senses the type of electrical signal that arrives and sees if it is 10 Mb or 100 Mb. This is how switch B determines the port speed of the end.

It is not possible to detect the correct duplex mode in the same method that the correct speed can be detected. In this case, where the port of first switch is configured for auto-negotiation and the port of second switch is not, the port of second switch is forced to select the default duplex mode. On Catalyst Ethernet ports, the default mode is auto-negotiate. If auto-negotiation fails, the default mode is half-duplex.

http://www.cisco.com/en/US/tech/tk389/tk214/technologies_tech_note09186a0080094781.shtml

Hope it will help.

Best regards,
Abzal