Juniper Networks Series Switches EX4100 and EX4400 per hardware limitation, do not support auto-negotiation on PIC 1 and PIC 2 for 1G/10G uplink module, only for 1G-T transceivers.

To resolve this configure no-auto-negotiation to match the EX4100 side on the peer device: 

{master:0}[edit]
user@switch# show interfaces ge-0/1/0  
speed 1g;
link-mode full-duplex;
ether-options {
    no-auto-negotiation;
}

Or in set commands:

set interfaces ge-0/1/0 ether-options no-auto-negotiation 
set interfaces ge-0/1/0 speed 1g         
set interfaces ge-0/1/0 link-mode full-duplex

Note: The commands above should be applied to peer devices. If the peer device is a Juniper Switch, some legacy Juniper devices may use the gigether-options configuration.

If the connection is established between two EX4100s or two devices on the same EX4K platform, the link will come up normally without needing a workaround, as both sides have no-auto-negotiation set on PIC1/PIC2 by default.

2023-09-25 : KB created
2025-10-14 : Minor changes to formatting, appearance and grammar.