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[SRX] Auto-MDI/MDI-X is disabled when auto-negotiation is disabled



Article ID: KB32053 KB Last Updated: 26 Mar 2020Version: 2.0

When SRX300 Series, SRX550HM, SRX1500, and a PC are directly connected with a straight cable and auto-negotiation is off, the link will not go up.

This article explains the issue and offers two solutions.



When SRX300 Series, SRX550HM, and SRX1500 Series devices and a PC are connected directly with a straight cable and auto-negotiation is off, the link does not go up.



For SRX300 Series, SRX1500 Series and SRX550HM devices, when auto-negotiation is disabled, auto-MDI/MDI-X will also be disabled and port will be the MDI port. If the device (for example, a PC), which is connected to the SRX port, is also in MDI mode, the link will not go up by straight cable.



We have two options to solve this issue.

  1. Use a crossover cable instead of a straight cable.


  1. On Junos OS 15.1X49-D80 and later releases, a new command was added to forcibly enable the auto-MDI/MDI-X function. But this is valid only in the case of SRX300 Series and SRX550HM and not for SRX1500 Series devices.

#set interfaces ge-0/0/0 ether-options mdi-mode force
root# set interfaces ge-0/0/0 ether-options mdi-mode ?
Possible completions:
    auto                 Automatic mdi/mdi-x mode
    force                Enable auto-MDIX always

When the  force option is configured, auto-MDI/MDI-X will be enabled even if auto-negotiation is disabled.


Note: For SRX1500, the only solution would be to use a crossover cable instead of a straight cable.


Modification History:

2020-03-26: This issue is also seen for SRX1500 Series along with SRX300 series and SRX550MH. But the workaround introduced in Junos OS 15.1X49-D80 and later releases is not applicable for SRX1500 series.


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