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Hierarchy Level

Release Information

Statement introduced before Junos OS Release 7.4.

Statement introduced in Junos OS Release 9.0 for EX Series switches.

Statement introduced in Junos OS Release 12.2 for ACX Series Universal Metro Routers.


Set the device’s link connection characteristic.


mode—Link characteristics:

  • automatic—Link mode is negotiated. This is the default for EX Series switches.

  • full-duplex—Connection is full duplex.

  • half-duplex—Connection is half duplex.

Default: Fast Ethernet interfaces can operate in either full-duplex or half-duplex mode. The router’s or switch’s management Ethernet interface, fxp0 or em0, and the built-in Fast Ethernet interfaces on the FIC (M7i router) autonegotiate whether to operate in full-duplex or half-duplex mode. Unless otherwise noted here, all other interfaces operate only in full-duplex mode.


On EX Series switches, if no-auto-negotiation is specified in [edit interfaces interface-name ether-options], you can select only full-duplex or half-duplex. If auto-negotiation is specified, you can select any mode.

  • Member links of an aggregated Ethernet bundle must not be explicitly configured with a link mode. You must remove any such link-mode configuration before committing the aggregated Ethernet configuration.

  • Starting with Junos OS release 17.4R1 and later, the link-mode configuration is not supported for 10-Gigabit Ethernet interfaces.

  • Starting in Junos OS release 18.4R1, half-duplex mode is supported on SRX340 and SRX345 devices.

Required Privilege Level

interface—To view this statement in the configuration.

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