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40G DAC connection between EX4300 and any other Juniper switches may not come up.



Article ID: KB31457 KB Last Updated: 22 Feb 2017Version: 1.0

This article describes a known issue when EX4300 tries to connect to other Juniper switches with 40G DAC cable. A workaround is provided below.


When a 40G DAC connection is attemped between EX4300 and any other Juniper switches (Broadcom based switches, QFX3500, QFX3600, QFX5100, QFX4600, etc.), the link may not come up. However, 40G QSFP connection works fine and does not have this issue.


This issue occurs because EX4300 has auto-negotiation enabled on the 40G DAC interface by default. Any other Juniper switches have auto-negotiation disabled by default.


As a workaround, disabling auto-negotiation on the EX4300 side will recover the connection.


Disable auto-negotiation on the interface et-0/1/0:

root@EX4300> configure
Entering configuration mode

root@EX4300# set interfaces et-0/1/0 ether-options no-auto-negotiation

root@EX4300# commit

Note: When 40G interface works as a virtual chassis port (VCP) in VC/VCF scenario, it does not have this issue; disable auto-negotiation is not required.

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