Interface between EX4300-48T and QFX5100 does not come online when a 40G DAC is connected. 

root@LAB> show chassis hardware detail no-forwarding

Hardware inventory:
Item             Version  Part number  Serial number     Description
Chassis                                PE3713480072      EX4300-48T
Routing Engine 0 REV 08   650-044933   PE3713480072      EX4300-48T
FPC 0            REV 08   650-044933   PE3713480072      EX4300-48T
  CPU                     BUILTIN      BUILTIN           FPC CPU
  PIC 0          REV 08   BUILTIN      BUILTIN           48x 10/100/1000 Base-T
  PIC 1          REV 08   BUILTIN      BUILTIN           4x 40GE QSFP+
    Xcvr 0       REV 01   740-052306   C1506010437       QSFP+-40G-ACU5M
    Xcvr 3       REV 01   740-052306   C1506010402       QSFP+-40G-ACU5M
Power Supply 0   REV 01   740-046873   1EDE3340254       JPSU-350-AC-AFO-A
Power Supply 1   REV 01   740-046873   1EDE3340265       JPSU-350-AC-AFO-A
Fan Tray 0                                               Fan Module, Airflow Out (AFO)
Fan Tray 1                                               Fan Module, Airflow Out (AFO)
 

Once we configure no-auto-negotiation on the interface on EX4300-48T the interface comes online.


    et-0/1/0 {
        description et-0/1/0
        ether-options {
            no-auto-negotiation;
            802.3ad ae1;
        }
    }
    et-0/1/3 {
        description et-0/1/3
        ether-options {
            no-auto-negotiation;
            802.3ad ae2;
        }
    }


Physical interface: et-0/1/0, Enabled, Physical link is Up
  Interface index: 694, SNMP ifIndex: 602, Generation: 185
  Description: et-0/1/0
  Link-level type: Ethernet, MTU: 9192, LAN-PHY mode, Speed: 40Gbps, Duplex: Full-Duplex, BPDU Error: None, Loop Detect PDU Error: None, Ethernet-Switching Error: None, MAC-REWRITE Error: None, Loopback: Disabled, Source filtering: Disabled, Flow control: Disabled, Auto-negotiation: Disabled, Remote fault: Online, Media type: Fiber
  Device flags   : Present Running
  Interface flags: SNMP-Traps Internal: 0x0
  Link flags     : None
  CoS queues     : 12 supported, 12 maximum usable queues
  Hold-times     : Up 500 ms, Down 0 ms



Physical interface: et-0/1/3, Enabled, Physical link is Up
  Interface index: 695, SNMP ifIndex: 603, Generation: 186
  Description: et-0/1/3
  Link-level type: Ethernet, MTU: 9192, LAN-PHY mode, Speed: 40Gbps, Duplex: Full-Duplex, BPDU Error: None, Loop Detect PDU Error: None, Ethernet-Switching Error: None, MAC-REWRITE Error: None, Loopback: Disabled, Source filtering: Disabled, Flow control: Disabled, Auto-negotiation: Disabled, Remote fault: Online, Media type: Fiber
  Device flags   : Present Running
  Interface flags: SNMP-Traps Internal: 0x0
  Link flags     : None
  CoS queues     : 12 supported, 12 maximum usable queues