auto-negotiation

Syntax

Hierarchy Level

Description

Auto-negotiation allows two connected devices to automatically agree on link speed and duplex settings. Use this configuration to enable to disable auto-negotiation for Gigabit Ethernet interfaces. Please see Platform-Specific auto-negotiation Behaviorfor more details.

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

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

Note:

1G mode is not supported on pic level port profile and port level port profile.

1G is supported in no-autonegotiation mode. This indicates link partner must disable autonegotiation.

Timing is not supported.

Table 1 shows the behaviour of auto-negotiation in different combinations.

Table 1: Behavior of auto-negotiation
Device (ACX5448/ACX710)	Peer device	Link status
auto-negotiation ON	auto-negotiation ON	UP
auto-negotiation ON	auto-negotiation OFF	Results in anomalous behaviour due to duplex mismatch
auto-negotiation OFF	auto-negotiation ON	Results in anomalous behaviour due to duplex mismatch
auto-negotiation OFF	auto-negotiation OFF	UP (If the speed and duplex mode matches on both the ends) DOWN (If the speed or duplex mode does not match on both the ends)

Default

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

Options

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.

Platform-Specific auto-negotiation Behavior

See Feature Explorer to know if your platform supports this feature.

Platform	Difference
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: Delete the `no-auto-negotiation` statement and commit the configuration. Set the link speed to 10 or 100 Mbps, set `no-auto-negotiation`, and commit the configuration. 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. PIC 0 does not support auto-negotiation on fiber optics ports.
EX4100 1GbE/10GbE uplink module (PIC 1/PIC 2) and EX4400 1GbE/10GbE interface QFX5120-48Y and QFX5120-48YM Switches	1GbE SFP optical transceivers do not support auto-negotiation. In such cases, we recommend to disable auto-negotiation on the remote end device for successful linkup.
ACX Series Routers	Auto-negotiation support enabled for SFP-LH and SFP-LX10 optics in ACX5448 and ACX710 platforms. And no-auto-negotiation support enabled for all the ports in ACX5448 and ACX710 platforms. 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 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. Auto-negotiation is not supported on ACX710 and ACX5448 devices at 10G speed. The auto-negotiation parameter `link partner speed` is displayed based on local speed even when auto-negotiation is disabled on ACX710 and ACX5448 devices.
MX10003 and MX204	Auto-negotiation is not supported
NFX350 devices	For Gigabit Ethernet interfaces on NFX350 devices, `auto-negotiation` is enabled by default. The `no-auto-negotiation` command is ignored for Gigabit Ethernet interfaces on NFX350 devices.
SRX Series Firewalls	When autonegotiatiation is disabled, you can set the `mdi-mode` to enable it in case of non-cross table.
PTX10001-36MR	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.

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