When a 100G transceiver is a fiber cable, then the port won't come up and when a 100G transceiver is a DAC (Direct Attach Copper) cable, then the port will come up as 40G instead of 100G. The CLI command "show interfaces vcp-<> extensive" will show the speed as 40G.

This issue might be seen if the following conditions are met:

• On Junos QFX5110 and QFX5120 platforms
• 100G transceiver (DAC/Fiber) as VC port or network port

Physical interface: vcp-<>, Enabled, Physical link is Down
  Interface index: 128, SNMP ifIndex: 0, Generation: 131
  Type: 105, Link-level type: Virtual-Chassis-Interface, MTU: 1514, Clocking: Unspecified, Speed: 40000mbps  <<<  Speed will be set as 40G.