On EX2200/EX3200/EX3300/EX4200/EX4500 platforms, when the link-mode is set as automatic or not set (default), the command "show interface ge-x/x/x extensive" indicates "Duplex: Half-duplex" in the output. This is a display issue and has no service impact.
username@hostname> show configuration interfaces ge-x/x/x
ether-options {
link-mode automatic;
username@hostname> show interfaces ge-x/x/x extensive
Physical interface: ge-x/x/x, Enabled, Physical link is Up
Interface index: 130, SNMP ifIndex: 502, Generation: 133
Link-level type: Ethernet, MTU: 1514, MRU: 0, Speed: Auto, Duplex: Half-duplex, BPDU Error: None, <<< Duplex indicates "Half-duplex" (Full-duplex or Auto is correct)
On EX2200, EX3200, EX3300, EX4200, and EX4500 devices, the "show interface ge-x/x/x extensive" command shows "Duplex: Half-duplex" in the output when link-mode is set to automatic or not set (default). This is a display issue and has no service impact.
Resolved-In: junos:14.1X53-D115 junos:14.1X53-D48 junos:15.1R7-S2 junos:15.1R8, and subsequent releases
This is already documented on PR1364659:
https://prsearch.juniper.net/problemreport/PR1364659