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[M/MX/T series] Troubleshooting Checklist - Ethernet Physical Interfaces

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Article ID: KB26486 KB Last Updated: 19 Jun 2020Version: 2.0
Summary:

A basic troubleshooting checklist for troubleshooting Ethernet Physical Interfaces on M/MX/T Series devices.

To troubleshoot VLAN or IRB interfaces, refer to KB26487: Troubleshooting Checklist - VLAN & Bridging and KB26488: Troubleshooting Checklist - IRB Interface.
 
Symptoms:
  • Troubleshoot Ethernet Physical Interface
  • Ethernet interface is down
Solution:

Use the following checklist to troubleshoot Ethernet interfaces:

  1. Check if the correct cable is connected to the correct port (surprising, but common mistake).

    Note: Most routers need cross-over copper cables, but newer chassis's like MX have auto-MDI.

  2. Verify the physical link status of the interface with the 'show interface <interface-name> media' command:

    user@router> show interfaces ge-5/0/1 media 
    Physical interface: ge-5/0/1, Enabled, Physical link is Up
      Interface index: 317, SNMP ifIndex: 1602
      Link-level type: Ethernet, MTU: 1514, Speed: 1000mbps, BPDU Error: None, MAC-REWRITE Error: None, Loopback: Disabled,
      Source filtering: Disabled, Flow control: Enabled, Auto-negotiation: Enabled, Remote fault: Online, Speed-negotiation: Disabled,
      Auto-MDIX: Enabled
      Device flags   : Present Running
      Interface flags: SNMP-Traps Internal: 0x4000
      Link flags     : None
      CoS queues     : 8 supported, 8 maximum usable queues
      Current address: 2c:6b:f5:4c:26:73, Hardware address: 2c:6b:f5:4c:26:73
      Last flapped   : 2012-11-30 01:25:37 UTC (03:46:55 ago)
      Input rate     : 880 bps (1 pps)
      Output rate    : 312 bps (0 pps)
      Active alarms  : None
      Active defects : None
      MAC statistics:
        Input bytes: 901296, Input packets: 9799, Output bytes: 976587, Output packets: 10451
      Filter statistics:
        Filtered packets: 68, Padded packets: 0, Output packet errors: 0
      Autonegotiation information:
        Negotiation status: Complete
        Link partner:
            Link mode: Full-duplex, Flow control: Symmetric/Asymmetric, Remote fault: OK
        Local resolution:
            Flow control: Symmetric, Remote fault: Link OK
      Interface transmit statistics: Disabled
    

    If the Ethernet interface has a cable connected and is receiving a valid signal, the physical link shows an “up” status and there are no active alarms or defects. If the interface is not connected or is not receiving a valid signal, the output shows a physical link down status and an active LINK alarm and defect.

    For more information on the above command output refer to the technical documentation on show interfaces.

    If the physical link is down, confirm that the cable is connected properly on the local and remote ends. If you suspect that the Ethernet cable is bad, swap the cable for a known good one.

    If this is a fiber interface, make sure you have single-mode fiber cable for a single-mode interface and multimode fiber cable for a multimode interface. Make sure you use the correct SFP on both sides.

  3. Review the detailed interface statistics.

    If the Ethernet interface is up, but you are experiencing connectivity problems such as input errors and packet loss, use the 'show interface interface-name extensive' to display the detailed interface statistics.

    For a detailed explanation of the statistics, refer to the technical documentation on show interfaces.

    user@router> show interfaces ge-5/0/1 extensive        
    Physical interface: ge-5/0/1, Enabled, Physical link is Up
      Interface index: 317, SNMP ifIndex: 1602, Generation: 322
      Link-level type: Ethernet, MTU: 1514, Speed: 1000mbps, BPDU Error: None, MAC-REWRITE Error: None, Loopback: Disabled,
      Source filtering: Disabled, Flow control: Enabled, Auto-negotiation: Enabled, Remote fault: Online, Speed-negotiation: Disabled,
      Auto-MDIX: Enabled
      Device flags   : Present Running
      Interface flags: SNMP-Traps Internal: 0x4000
      Link flags     : None
      CoS queues     : 8 supported, 8 maximum usable queues
      Hold-times     : Up 0 ms, Down 0 ms
      Current address: 2c:6b:f5:4c:26:73, Hardware address: 2c:6b:f5:4c:26:73
      Last flapped   : 2012-11-30 01:25:37 UTC (04:38:32 ago)
      Statistics last cleared: Never
      Traffic statistics:
       Input  bytes  :               806283                    0 bps
       Output bytes  :              1153215                  424 bps
       Input  packets:                10818                    0 pps
       Output packets:                11536                    0 pps
       IPv6 transit statistics:
        Input  bytes  :                   0
        Output bytes  :                   0
        Input  packets:                   0
        Output packets:                   0
      Label-switched interface (LSI) traffic statistics:
       Input  bytes  :                    0                    0 bps
       Input  packets:                    0                    0 pps
      Dropped traffic statistics due to STP State:
       Input  bytes  :                    0
       Output bytes  :                    0
       Input  packets:                    0
       Output packets:                    0
      Input errors:
        Errors: 0, Drops: 0, Framing errors: 0, Runts: 0, Policed discards: 233060, L3 incompletes: 0, L2 channel errors: 0,
        L2 mismatch timeouts: 0, FIFO errors: 0, Resource errors: 0
      Output errors:
        Carrier transitions: 11, Errors: 0, Drops: 0, Collisions: 0, Aged packets: 0, FIFO errors: 0, HS link CRC errors: 0,
        MTU errors: 0, Resource errors: 0
      Egress queues: 8 supported, 4 in use
      Queue counters:       Queued packets  Transmitted packets      Dropped packets
        0 best-effort                 3216                 3216                    0
        1 expedited-fo                   0                    0                    0
        2 assured-forw                   0                    0                    0
        3 network-cont                8320                 8320                    0
      Queue number:         Mapped forwarding classes
        0                   best-effort
        1                   expedited-forwarding
        2                   assured-forwarding
        3                   network-control
      Active alarms  : None
      Active defects : None
      MAC statistics:                      Receive         Transmit
        Total octets                       1007655          1082219
        Total packets                        10886            11536
        Unicast packets                       4350             4184
        Broadcast packets                       32               77
        Multicast packets                     6504             7275
        CRC/Align errors                         0                0
        FIFO errors                              0                0
        MAC control frames                       0                0
        MAC pause frames                         0                0
        Oversized frames                         0
        Jabber frames                            0
        Fragment frames                          0
        VLAN tagged frames                       0
        Code violations                          0
      Filter statistics:
        Input packet count                   10886
        Input packet rejects                    68
        Input DA rejects                        68
        Input SA rejects                         0
        Output packet count                                   11536
        Output packet pad count                                   0
        Output packet error count                                 0
        CAM destination filters: 0, CAM source filters: 0
      Autonegotiation information:
        Negotiation status: Complete
        Link partner:
            Link mode: Full-duplex, Flow control: Symmetric/Asymmetric, Remote fault: OK
        Local resolution:
            Flow control: Symmetric, Remote fault: Link OK
      Packet Forwarding Engine configuration:
        Destination slot: 5
      CoS information:
        Direction : Output
        CoS transmit queue               Bandwidth               Buffer Priority   Limit
                                  %            bps     %           usec
        0 best-effort            95      950000000    95              0      low    none
        3 network-control         5       50000000     5              0      low    none
      Interface transmit statistics: Disabled

    The following statistics are worth mentioning:

    • Policed discards – Frames discarded that were not recognized or not of interest. For example, Cisco CDP packets.
    • L2 channel errors – Packets for which the router could not find a valid logical interface.  For example, when the packet is for a VLAN that is not configured on the interface.
    • Input DA rejects–Number of packets with a destination MAC address that is not on the accept list.  It is normal to see this number increment.
    • Input SA rejects–Number of packets with a source MAC address that is not on the accept list.  You should see this increment only when source MAC address filtering is configured.

    Usually, the error statistics do not pinpoint exactly the source of the connectivity problem.

    Important: Isolating the source of the problem typically requires you to verify the local Ethernet port (local loopback test), the cabling, and the remote Ethernet port.  These are explained in steps 4-6.

  4. In order to test if the Ethernet port or PIC is faulty, perform a local loopback test (software and/or hardware).

    Software loopback test:

    Include the loopback statement at the [gigether-options] hierarchy level in order to configure an internal loopback on the interface and conduct a loopback test. This is used to verify the functionality of the local Ethernet port on the router.

    When an internal loopback is configured, the physical link should come up with no alarm. 

    [edit interfaces ge-5/0/1]
    root@router# set gigether-options loopback
    [edit interfaces ge-5/0/1]
    root@router# commit
    commit complete
    
    [edit interfaces ge-5/0/1]
    lab@Rack1-MX480> show interfaces ge-5/0/1 media 
    Physical interface: ge-5/0/1, Enabled, Physical link is Up
      Interface index: 317, SNMP ifIndex: 1602
      Link-level type: Ethernet, MTU: 1514, Speed: 1000mbps, BPDU Error: None, MAC-REWRITE Error: None, Loopback: Enabled,
      Source filtering: Disabled, Flow control: Enabled, Auto-negotiation: Enabled, Remote fault: Online, Speed-negotiation: Disabled,
      Auto-MDIX: Enabled
      Device flags   : Present Running
      Interface flags: SNMP-Traps Internal: 0x4000
      Link flags     : None
      CoS queues     : 8 supported, 8 maximum usable queues
      Current address: 2c:6b:f5:4c:26:73, Hardware address: 2c:6b:f5:4c:26:73
      Last flapped   : 2012-11-30 01:25:37 UTC (03:46:55 ago)
      Input rate     : 880 bps (1 pps)
      Output rate    : 312 bps (0 pps)
      Active alarms  : None
      Active defects : None
      MAC statistics:
        Input bytes: 901296, Input packets: 9799, Output bytes: 976587, Output packets: 10451
      Filter statistics:
        Filtered packets: 68, Padded packets: 0, Output packet errors: 0
      Autonegotiation information:
        Negotiation status: Complete
        Link partner:
            Link mode: Full-duplex, Flow control: Symmetric/Asymmetric, Remote fault: OK
        Local resolution:
            Flow control: Symmetric, Remote fault: Link OK
      Interface transmit statistics: Disabled
    

    Note:  Remember to delete the loopback statement after completing the test.

    Hardware loopback test:

    If the local Ethernet port is a fiber interface or an RJ-45 connector, you can do a physical loopback:

    • For an Ethernet PIC with a fiber optic interface, you can physically loop the TX and RX port and check the status of the physical link.

    • For an RJ-45 Ethernet interface, you can make a loopback plug by crossing pin 1 (TX +) to pin 3 (RX +) together and pin 2 (TX -) and pin 6 (RX -) together.

    For more information, refer to the technical documentation on Performing Loopback Testing for Fast Ethernet and Gigabit Ethernet Interfaces

  5. Verify the integrity of the cabling.

    To do this, you must use an external cable-testing tool.

    Important:  Before doing this, verify that you have the correct cables for the interface port. Make sure you have single-mode fiber cable for a single-mode interface and multi-mode fiber cable for a multi-mode interface.

    For a fiber optic connection, you can measure the received light level at the receiver end to make sure that it is within the receiver specification of your Ethernet interface.

    You can also measure the transmit light level on the TX port to verify that it is within specification.

  6. If this Ethernet interface is connected to the remote Ethernet device over multiple patch panels, check to see whether the connection can be looped back at the different patch panels so you can conduct a loopback test.

    For more information, refer to the technical documentation on Performing Loopback Testing for Fast Ethernet and Gigabit Ethernet InterfacesRefer.

  7. If there are no issues with the physical interface, check the following common reasons:

    • Check if physical interface and logical interfaces are not administratively disabled, using the command 'show interfaces <interface> terse':

      user@router> show interfaces ge-5/0/1 terse 

           Interface               Admin Link Proto    Local                 Remote
           ge-5/0/1                up    up
           ge-5/0/1.0              up    up   inet     20.1.1.2/24     
      
    • Verify that the speed and duplex and auto-negotiation settings are configured correctly for the interface.
      Tip: Specifically check if the hardware you're using like FPC/DPC/MPC, MIC/PIC or SFP/XFP supports auto-negotation and speed settings.

Modification History:
2020-06-12:​ ​Added EX and QFX product series. Article also reviewed for accuracy.
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