This article is intended to provide solution for when the 1g SFP-SX interface with down state would not come up with auto-negotiation on Juniper EX4600 platforms.

The customer has installed 1g SFP-SX which is known to be working, but the same remains with "down" state at "> show interfaces terse".

EX4600 cannot support 1G auto negotiation due to hardware limitations, hence it operates in 1G forced mode only.

So, if any of these newer ELS platforms need to connect to another device via a 1G optic, we need to disable auto-negotiation on both ends via static configuration. At the same time, disabling auto-negotiation will require that we specify a speed to run at and the duplex setting as well.

Applying this configuration on both peering units will enable the link to come up and pass traffic correctly:

user@switch# set chassis fpc x pic x port x speed 1g
user@switch# set interfaces ge-x/x/x link-mode full-duplex
user@switch# set interfaces ge-x/x/x gigether-options no-auto-negotiation
user@switch# commit

Note that on EX4600 platforms the ports' speed should be configured in quads of 4 ports. It means that you should configure speed to port 0, and it will apply to ports 0 through 3.