Ethernet Auto Negotiation
Acouple points of calrifcation Ethernet is the Data-Link layer 2 protocol that all of these standards (both Copper and Fiber) connections us.
At times seemly mainly from ISPs, but with certain products it is “recommened” staticly set speeds and duplex. This can espically for fiber not make sense to do, or go against standards and network vendor recommendations.
What is Auto Negotiation
- Ethernet Auto-Negotiation is a feature that allows two connected Ethernet devices to automatically determine the best common settings for communication. It helps optimize network performance by dynamically selecting the highest possible speed (like 10 Mbps, 100 Mbps, or 1 Gbps) and the appropriate duplex mode (full or half). By doing this, it ensures efficient data transmission without requiring manual configuration, reducing the risk of network misconfigurations and improving overall compatibility between different devices.
“Auto-Negotiation: The algorithm that allows two devices at either end of a link segment to negotiate common data service functions”
802.3ae 14.2.1.8 "
Auto Negotiation
| Eth Standard | Standard | AutoNeg |
|---|---|---|
| 802.3ae | 10GBASE-SR | M |
| 802.3ae | 10GBASE-LR | |
| 802.3ae | 10GBASE-ER | |
| 802.3ae | 10GBASE-LRM | |
| 802.3ae | 10GBASE-ER-LRM | |
| 802.3ba | 40GBASE-KR4 | M |
| 802.3ba | 40GBASE-CR4 | M |
| 802.3ba | 40GBASE-SR4 | |
| 802.3ba | 40GBASE-LR4 | |
| 802.3ba | 100GBASE-CR10 | M |
| 802.3ba | 100GBASE-SR10 | |
| 802.3ba | 100GBASE-LR4 | |
| 802.3ba | 100GBASE-ER4 |
M = Mandatory O = Optional R = Recommend
Ref 40/100GBASE (802.3ba-2010) Section 80.1.5
#Stratch
28.5 Protocol implementation conformance statement (PICS) proforma for Clause 28, Physical Layer link signaling for 10 Mb/s, 100 Mb/s, and 1000 Mb/s Auto-Negotiation on twisted pair[1]1 28.5.1 Introduction The supplier of a protocol implementation that is claimed to conform to Clause 28, Physical Layer link signaling for 10 Mb/s, 100 Mb/s, and 1000 Mb/s Auto-Negotiation on twisted pair, shall complete the following protocol implementation conformance statement (PICS) proforma. A detailed description of the symbols used in the PICS proforma, along with instructions for completing the PICS proforma, can be found in Clause 21.
In the IEEE 802.3 Ethernet standard, Auto-Negotiation is defined in Clause 28. Auto-Negotiation is a protocol that allows two Ethernet devices to exchange information and agree on the best common operational mode. It helps devices automatically choose the highest performance settings that both ends support, such as speed (e.g., 10, 100, 1000 Mbps) and duplex (half or full).
What Auto-Negotiation Does: Speed Detection: Auto-Negotiation helps detect and select the highest common speed supported by both devices. Duplex Mode: It also determines whether the devices should use full-duplex (simultaneous sending and receiving) or half-duplex (alternating between sending and receiving). Backward Compatibility: It ensures older devices can communicate with newer devices by allowing the negotiation of a common speed, even if one device is limited to a lower speed. Where Speeds are Defined in 802.3: Speeds and recommendations for Auto-Negotiation are detailed in various clauses:
Clause 28: Describes the basics of Auto-Negotiation for Ethernet, including 10/100 Mbps Ethernet. Clause 37: Extends Auto-Negotiation to 1000BASE-T Gigabit Ethernet. Clause 73: Extends Auto-Negotiation to 10 Gbps Ethernet and beyond. Auto-Negotiation ensures that the network runs at the best possible speed and configuration for both connected devices, minimizing manual intervention and avoiding misconfiguration.