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Hierarchy Level


For Gigabit Ethernet interfaces on M Series, MX Series, T Series, TX Matrix routers, and ACX Series routers explicitly enable autonegotiation and remote fault. For EX Series switches, explicitly enable autonegotiation only. You cannot disable autonegotiation on ACX5448 routers for Gigabit Ethernet interfaces by using the no-auto-negotiation command. The no-auto-negotiation command is not supported on ACX5448 routers.

  • auto-negotiation—Enables autonegotiation. This is the default.

  • no-auto-negotiation—Disable autonegotiation. When autonegotiation is disabled, you must explicitly configure the link mode and speed.

When you configure Tri-Rate Ethernet copper interfaces to operate at 1 Gbps, autonegotiation must be enabled.


On EX Series switches, an interface configuration that disables autonegotiation and manually sets the link speed to 1 Gbps is accepted when you commit the configuration; however, if the interface you are configuring is a Tri-Rate Ethernet copper interface, the configuration is ignored as invalid and autonegotiation is enabled by default.

To correct the invalid configuration and disable autonegotiation:

  1. Delete the no-auto-negotiation statement and commit the configuration.

  2. Set the link speed to 10 or 100 Mbps, set no-auto-negotiation, and commit the configuration.

On EX Series switches, if the link speed and duplex mode are also configured, the interfaces use the values configured as the desired values in the negotiation. If autonegotiation is disabled, the link speed and link mode must be configured.


On T4000 routers, the auto-negotiation command is ignored for interfaces other than Gigabit Ethernet.


On ACX Series routers, when you configure fiber interfaces (fiber media mode) to operate at 1 Gbps, autonegotiation is enabled by default to negotiate the speed and duplex settings. You can disable autonegotiation on ACX Series routers, except ACX5448 routers, in the fiber media mode, by using the (no-auto-negotiation) statement, and commit the configuration. In copper interfaces (copper media mode), autonegotiation is enabled by default. To disable autonegotiation, you need to explicitly configure the link speed to 10 or 100 Mbps, set no-auto-negotiation, and commit the configuration.

For SRX Series devices, when autonegotiatiation is disabled, you can set the mdi-mode to enable it in case of non-cross table.

From Junos OS Evolved Release 21.2R1, we support autonegotiation and link training using 400G DAC cable for PTX10001-36MR. This is not a default behavior. Use auto-negotiation under [edit interfaces interface-name ether-options] hierarchy level to enable autonegotiation and link training. Enabling autonegotiation automatically enables link training. This advertises configured speed on the interface hierarchy. It does not upgrade or downgrade speed based on peers advertised capability.

Autonegotiation and link training is supported only on one 400-Gigabit Ethernet interfaces (1x400G), two 200-Gigabit Ethernet interfaces (2x200G), and four 100-Gigabit Ethernet interfaces (4x100G) channelization.


Autonegotiation is automatically enabled. No explicit action is taken after the autonegotiation is complete or if the negotiation fails.


remote-fault (local-interface-online | local-interface-offline)—(Optional) For M Series, MX Series, T Series, TX Matrix routers, and ACX Series routers only, manually configure remote fault on an interface.

  • Default: local-interface-online

Required Privilege Level

interface—To view this statement in the configuration.

interface-control—To add this statement to the configuration.

Release Information

Statement introduced in Junos OS Release 7.6.