Description

The Layer-1 issue typically occurs due to physical connectivity problems such as faulty cables, dirty or incompatible optics, or port-related hardware faults.

 Layer 1 troubleshooting helps isolate whether the fault lies in the cable, optics, or switch port.

 

Symptoms

This troubleshooting guide can be used to resolve the issue if following symptoms are reported on a Juniper device.

 

  1. Interface is down or frequently flapping.
  2. VC port down or flapping
  3. Link LED is OFF or intermittently turning OFF/ON.

Below logs observed on the switch :

 mib2d[11849]: %DAEMON-6-SNMP_TRAP_LINK_UP: ifIndex 1073, ifAdminStatus up(1), ifOperStatus up(1), ifName <interface name>

 mib2d[11849]: %DAEMON-4-SNMP_TRAP_LINK_DOWN: ifIndex 1020, ifAdminStatus up(1), ifOperStatus down(2), ifName <interface name>

 mib2d[11849]: %DAEMON-5-SNMP_TRAP_LINK_UP: ifIndex 1020, ifAdminStatus up(1), ifOperStatus up(1), ifName <interface name>

 mib2d[11849]: %DAEMON-6-SNMP_TRAP_LINK_UP: ifIndex 1073, ifAdminStatus up(1), ifOperStatus up(1), ifName <interface name>

mib2d[11849]: %DAEMON-4-SNMP_TRAP_LINK_DOWN: ifIndex 1020, ifAdminStatus up(1), ifOperStatus down(2), ifName <interface name>

Solution

Physical access to the switch is required to perform the following checks:
 

  1. Ensure the link LED for the affected interface is ON, indicating the cable is firmly seated.
  2. Confirm the correct type of SFPs and fiber cables are used. Compatibility can be checked here: https://apps.juniper.net/hct/category/?catKey=100001
  3. Verify auto-negotiation settings. If auto-negotiation is disabled, check If correct Speed/Duplex settings have been configured and it matches the peer port settings.
  4. Try unplugging and plugging (reseating) the optics. Clean the optics.
  5. Try rolling and cleaning the fibers.
  6. Perform a physical loopback test to see if the port comes UP  Performing Loopback Testing for Fast Ethernet and Gigabit Ethernet Interfaces .
    1. YES - Perform cable test to determine which part has gone bad.
    2. NO - The port is suspected to be bad. Contact Juniper Support.

 

Cable and Port Isolation Test:

  • Test the affected port with a known-good set of optics and cables.

    • If YES (link comes up): The original optics/cable may be faulty. Test individually to isolate the bad component.

    • If NO (link remains down): The port could be defective.

  • Test a different working port using the same optics and cables.

    • If YES: The original port is likely faulty.

    • If NO: The optics/cables may be defective

 

Modification History

version 1.0
version 2.0 - product added