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[EX] Auto-MDI/MDIX is also disabled when auto-negotiation is disabled on EX4300

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Article ID: KB30715 KB Last Updated: 27 Mar 2019Version: 3.0
Summary:

The auto MDI/MDIX feature detects if a port requires MDI or MDIX configuration on EX Series switches. On EX4300 Series switches, auto-MDI/MDIX is also disabled when auto-negotiation is disabled.

This article suggests a workaround and indicates the Junos OS release in which this behavior is changed.

 

Symptoms:

When you turn off the auto-negotiation feature to provide a fixed speed/duplex setting on EX Series switches, auto-MDI/MDIX stops working. If you are using a straight cable and auto-MDI/MDIX is required (for example, for an MDIX-to-MDIX connection), the link will fail to come up.

 

Cause:

On EX4300 Series switches, auto-MDI/MDIX requires that auto-negotiation must also be enabled.

 

Solution:

As per PR1212093, this behavior has been changed in Junos OS releases 14.1X53-D40 and later wherein auto-MDI/MDIX will work even though auto-negotiation is disabled.

Meanwhile, to work around this problem, use a crossover cable instead of a straight cable.

 

Modification History:

2019-03-27: Modified solution to include Junos OS release in which fix is available; made other minor non-technical changes

 

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