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[SRX] SRX300 series interface down after disabling auto-negotiation

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Sometimes, a SRX300 Series interface goes to down after disabling auto-negotiation. This article explains this behavior and provides a workaround.


In the SRX300 series, when auto-negotiation is disabled, auto-MDI/MDI-X will be also disabled and port will be a MDI port. If auto-MDI/MDI-X is also disabled at the peer device side, the link will not go up by straight cable connection.


In Junos OS 15.1x49-D80 and later releases, one new command has been added to enable auto-MDI/MDI-x forcibly when auto-negotiation is disabled. This will cause the link to go up

#set interfaces ge-0/0/0 ether-options mdi-mode force

Note: Please also configure the link-mode and speed parameters when disabling auto-negotiation under the interface. Otherwise, the link will not up even if mdi-mode force is added. 

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