This scenario involves an EX4300-48MP using PIC2, connected to a modem device that is operating with "Auto-Negotiation" and "Half-Duplex". Despite the interface showing as up, the EX4300-48MP does not transmit any outbound traffic.
Symptoms
In this case, the EX4300-48MP exhibits a behavior where, even though the interface is up, the configuration is correct, and the hardware components are in good condition, it fails to send traffic to its peer device. The affected interface is ge-0/2/0:
Physical interface: ge-0/2/0, Enabled, Physical link is Up
Interface index: 700, SNMP ifIndex: 618, Generation: 191
Description: Interface_ge-0/2/0
Link-level type: Ethernet, MTU: 9100, LAN-PHY mode, Speed: 1000mbps, BPDU Error: None, Loop Detect PDU Error: None, Ethernet-Switching Error: None, MAC-REWRITE Error: None, Loopback: Disabled, Source filtering: Disabled, Flow control: Enabled, Media type: Fiber
Traffic statistics:
Input bytes : 1491152 1104 bps
Output bytes : 0 0 bps
Input packets: 23239 1 pps
Output packets: 0 0 pps
Despite testing with different cables and optics, the interface still does not transmit traffic to its peer device. Upon checking the peer device, we confirmed that it is operating with "Auto-Negotiation" and "Half-Duplex" enabled. On the EX4300-48MP platform, however "Auto-Negotiation" and "Half-Duplex" are not supported on PIC2. For further details, please refer to the documentation section “Autonegotiation Support for EX4300-48MP Switches”:
https://www.juniper.net/documentation/us/en/software/junos/interfaces-ethernet-switches/topics/topic-map/switches-interface-gigabit.html#d64e37
We can still use PIC0 on any of the ge ports in the 0–23 range, as these ports support "Auto-Negotiation" and even though you cannot configure "Half-Duplex" on EX4300-48MP switches. If the link partner is "Half-Duplex" and capable of autonegotiating, then these ports can work a "Half-Duplex" modes. This ensures interoperability in scenarios where the peer device configuration cannot be modified.