New EX2300C connected to various EX4400 switches running various JUNOS versions has only one way traffic via monitoring the ports on the upstream EX4400 but no connectivity on the EX2300C on both ports GE-0/1/0 and GE-0/1/1. If same EX2300C is connected with same fiber transceivers (either single mode or multimode) to an upstream EX2300C running the same JUNOS version, successfully duplex fiber connectivity is achieved.

Notification that the SFP transceivers may not be on the hardware compatibility matrix.

lab> show chassis hardware detail | no-more   
Hardware inventory:
Item           Version  Part number  Serial number Description
FPC 1                   BUILTIN      BUILTIN       MPC BUILTIN
  MIC 0        REV 26   750-028392   ########      3D 20x 1GE(LAN) SFP
    PIC 1               BUILTIN      BUILTIN       10x 1GE(LAN) SFP
      Xcvr 0   T        NON-JNPR     ########      SFP-SX <<<----- NON-JNPR SFP detected by Junos
      Xcvr 1   REV 01   740-031851   ########      SFP-SX <<<----- Juniper supported SFP are identified with part-number

Check the link to confirm the SFP compability according to the platform.

https://apps.juniper.net/home/ex2300-c/hardware-compatibility