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[SRX/J-Series] Issues with interface speed/duplex settings - showing 100 Mbps / half-duplex

  [KB22388] Show Article Properties


This article discusses the speed and duplex settings of a Gigabit Ethernet link which are manually set at one end. In such a case, the user must also set [gigether-options no-auto-negotiation]. This article explains how to configure the system to operate in no-auto-negotiation mode on the local device.


By default, Gigabit Ethernet interfaces are configured for auto-negotiation speed and duplex settings. As per the IEEE standard, when the speed and mode are manually configured (100m or 10m) and are set to no-auto-negotiate, then the link-mode is not negotiated. So, the interfaces in a J or SRX series device will operate in half-duplex mode.

The output of the following command shows the configured and negotiated speed:

cli> show interfaces ge-0/0/0 extensive

Source filtering: Disabled, Flow control: Enabled, Auto-negotiation: Enabled   >>This says that auto negotiation is enabled on the interface.

Autonegotiation information:
Negotiation status: No-autonegotiation   >> No-autonegotiation has been set at the other end and tells the status of the negotiated value.

Link partner:
Link mode: Half-duplex, Flow control: None, Remote fault: OK   >>> Because of the above two reasons the interface goes into the half duplex mode.
Link partner Speed: 100 Mbps



If the remote end is configured for manual settings (no-auto-negotiation), then it is recommended to operate in no-auto-negotiation mode on the local device as well. Also, the manual settings that are set at the remote and local end should match, so as to avoid any quality and bandwidth issues.

Manual Ethernet Negotiation Settings - Configuration example:

set interfaces ge-0/0/1 speed 100m
set interfaces ge-0/0/1 link-mode full-duplex
set interfaces ge-0/0/1 gigether-options no-auto-negotiation
set interfaces ge-0/0/1 unit 0 family inet address x.x.x.x/y


  • The same concept also holds good for the Fast-Ether links. Here the no-auto-negotiation should be explicitly specified in [edit interfaces fastether-options].

  • These settings should match the settings at the remote end. Interface setting mismatch leads to poor quality and bandwidth issues across the link.

  • In case of SRX HA Cluster, configuring manual negotiation settings on Reth/Child interfaces is supported in newer Junos OS releases.  For more information, refer to KB16672 - [SRX/J] Do reth interfaces support hard-coding of member links?
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