We have recently migrated a service to a Juniper ACX series router in our public network. Following the migration, we observed intermittent Ethernet errors (input errors/CRC) on the remote end of the optical link, specifically on a microwave equipment.

Environment:

• Connectivity: Optical fiber link (approx. 5km)

• SFP Module: Original Juniper optical transceiver

Observed Behavior:

• The errors typically appear within 1-2 days after the initial connection.

• The issue results in intermittent packet loss and Ethernet interface errors on the far-end device.

Troubleshooting and Lab Results: We have successfully reproduced the issue in a controlled laboratory environment with the following findings:

1. Distance Dependency: The errors only occur when there is a significant length of optical fiber (5km) between the ACX and the microwave equipment.

2. Direct Connection: When the ACX and the peer device are connected via a short patch cable, no errors are observed.

3. Transceiver Swap Test:

• Using the original Juniper SFP in the ACX: Errors persist over the 5km span.

• Using the previously used Old SFP (from the old platform) in the ACX: The issue is resolved, and the link is stable without errors.

Question/Request: The Old transceiver seems to handle the signal characteristics or link budget better over this specific distance than the Juniper-branded module.

• What configuration changes or tuning (e.g., power levels, autonegotiation settings, or framing adjustments) are recommended to make the ACX work reliably with the original Juniper transceiver?

• Is there a known compatibility or signal integrity issue between ACX Juniper SFPs and microwave Ethernet ports over mid-range distances?

Please advise on the next steps to ensure stability using our Juniper hardware inventory.

On Junos OS Evolved ACX platforms with 1G fibre Optics, when the Inter-Packet Gap (IPG) setting intermittently falls below the IEEE minimum requirement of 8 bytes, and traffic passes through the PHY, certain receiving devices are sensitive to this reduced IPG, which leads to CRC (Cyclic Redundancy Check) errors and packet loss on the peer device connected to 1G fibre optics connection.

RCA:

CRC errors and packet loss are observed on the peer device when using 1G fibre optic connections. This happens because the Inter-Packet Gap setting is left at its default value.

When 1G traffic passes through the PHY, the gap between packets can occasionally become shorter than the minimum required 8 bytes defined by IEEE standards.

Some receiving devices are sensitive to this shorter gap. When the IPG drops below the required value, the receiving device will see CRC errors, which result in packet loss.

The issue can be observed in multiple scenarios, such as device boot / reboot / upgrade having 1G fibre optic.

This is fixed via below PR.

https://prsearch.juniper.net/problemreport/PR1931077