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Configure switch optical ports with auto-negotiation

Fiber and communications infrastructure knowledge brief Published 14 Mar 2022

Use this reference to prepare product questions for CJC FIBRE. Check interfaces, capacity, protection and installation requirements against the current product documentation.

Auto-negotiation allows optical switch ports to automatically determine the optimal speed and duplex settings with connected devices. Understanding Auto-NegotiationAuto-negotiation is a protocol defined in IEEE 802. 3u that enables two connected devices to exchange information about their capabilities and automatically select the highest compatible speed and duplex mode.

This ensures optimal link performance and reduces duplex mismatches, which can cause packet loss or collisions. Auto-negotiation only works if both ends of the link support it; otherwise, manual configuration of speed and duplex is required.

General Configuration Principles

Enable Auto-

Negotiation: Most modern switches have auto-negotiation enabled by default on optical ports. For example, on Huawei GE optical interfaces, auto-negotiation is enabled by default, but rate auto-negotiation may be disabled. Check Port Capabilities: Some SFP modules, such as 1GbE SFPs, require auto-negotiation to operate correctly, while certain 10G or higher ports may not support auto-negotiation.

Medium Selection: On switches with combination ports (copper/fiber), specify the medium when configuring auto-negotiation to ensure the correct settings are applied. Example Commands by PlatformCisco IOS (Catalyst Switches): CodeCopyinterface GigabitEthernet1/0/1speed autoduplex auto This enables auto-negotiation for both speed and duplex on 10/100/1000 Mbps ports. ExtremeXOS: CodeCopyconfigure ports 1 auto on For SFPs that support multiple speeds, you can specify the speed along with auto-negotiation: CodeCopyconfigure ports 1 auto on speed 1000 Huawei Switches: CodeCopyinterface GigabitEthernet0/0/1undo shutdownnegotiation auto Use display interface to verify the negotiation status.

Juniper Junos: CodeCopyset interfaces ge-0/0/1 ether-options auto-negotiationcommit Auto-negotiation is required for Tri-Rate Ethernet copper interfaces at 1 Gbps, while some SFP optical transceivers may not support it.

Verification

After enabling auto-negotiation, verify the link status and negotiated parameters: Cisco: show interfaces GigabitEthernet1/0/1 statusHuawei: display interface GigabitEthernet0/0/1 (check the Negotiation field)Juniper: show interfaces ge-0/0/1 mediaTroubleshooting TipsEnsure both ends of the link support auto-negotiation. If one device does not, manually configure speed and duplex on both ends.

For SF

Ps with multiple supported speeds, explicitly configure auto-negotiation with the correct speed to avoid link failures. If the interface shows Up but the remote interface is Down, perform a shutdown and undo shutdown on the remote interface to re-establish the link. By following these steps, optical switch ports can reliably negotiate the optimal speed and duplex settings, ensuring stable and efficient network connectivity.

Configure switch optical ports with auto-negotiation - CJC FIBRE CONSULTANTS [PDF]

Configure switch optical ports with auto-negotiation

Configuring Switch Port Speed and Duplex Setting

Auto-negotiation determines the port speed and duplex setting for each port (except 10 and 40 Gbps ports). You can manually configure the duplex setting and the speed of 10/100/1000 Mbps ports.

Configuring and Troubleshooting Auto-Negotiation

By default, auto-negotiation is enabled on GE optical interfaces and rate auto-negotiation is disabled. You can run the speed auto-negotiation command to enable rate auto-negotiation.

Configuring Auto-Negotiation

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Configuring Port Speed

A port set in auto-negotiate mode is negotiating full duplex and use of pause frames (802.3X) with the attached switch. The port will come up if there is a mismatch in the negotiated parameters.

Switch Engine Command Reference Guide

Switch Engine™ Command Reference Guide Version 32.3 > Commands > configure ports auto on Published December 2022 Print this pageEmail this pageView PDFPreviousNext

SG :: Ethernet auto-sensing and auto-negotiation

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Auto-Negotiation About Auto-Negotiation Auto-negotiation is an optional function of the IEEE 802.3u Fast Ethernet standard that enables devices to automatically exchange information

Related Video Reference

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Technical note

This reference is intended for preliminary fiber and communications infrastructure research. Optical interface, fiber type, port or core capacity, electrical input and output, enclosure protection, cooling, installation limits and applicable standards must be verified for the specific project.

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