[MX/SRX] Meaning of the input and output errors in the 'show interface <interface name> extensive' command

Summary:

This article provides information on the various types of error fields which appear in the output of the show interface ge-0/0/0 extensive command.

Symptoms:

The following highlighted truncated output of the command indicates a few error fields; the meaning of which is unknown to many users.

user@srx>show interface extensive

Physical interface: ge-0/0/0, Enabled, Physical link is Up
  Interface index: 134, SNMP ifIndex: 505, Generation: 137
  Link-level type: Ethernet, MTU: 1514, Link-mode: Full-duplex, Speed: 1000mbps,
  BPDU Error: None, MAC-REWRITE Error: None, Loopback: Disabled,
  Source filtering: Disabled, Flow control: Enabled, Auto-negotiation: Enabled,
  Remote fault: Online
  Device flags   : Present Running
  Interface flags: SNMP-Traps Internal: 0x0
  Link flags     : None
  CoS queues     : 8 supported, 8 maximum usable queues
  Hold-times     : Up 0 ms, Down 0 ms
  Current address: 00:26:88:eb:62:c0, Hardware address: 00:26:88:eb:62:c0
  Last flapped   : 2012-06-04 14:39:14 UTC (00:35:10 ago)
  Statistics last cleared: Never
  Traffic statistics:
     Input  bytes  :                30972                    0 bps
     Output bytes  :                    0                    0 bps
     Input  packets:                  427                    0 pps
     Output packets:                    0                    0 pps
  Input errors:
     Errors: 0, Drops: 0, Framing errors: 0, Runts: 0, Policed discards: 0,
     L3 incompletes: 0, L2 channel errors: 0, L2 mismatch timeouts: 0,
     FIFO errors: 0, Resource errors: 0
  Output errors:
     Carrier transitions: 1, Errors: 0, Drops: 0, Collisions: 0, Aged packets: 0,
     FIFO errors: 0, HS link CRC errors: 0, MTU errors: 0, Resource errors: 0

Solution:

The errors can be classified as Input and Output. Input errors account for the erroneous counters, which occur at the input queue of SRX interface.

Errors: Sum of the incoming frame aborts and FCS errors.

Drops: Number of packets dropped by the input queue of the I/O Manager ASIC. If the interface is saturated, this number increments once, for every packet that is dropped by the ASIC's RED mechanism.

Framing errors: Number of packets received with an invalid frame checksum (FCS).

Runts: Number of received frames that are smaller than the runt threshold.

Policed discards: Number of frames that the incoming packet match code discarded, as they were not recognized or not of interest. Usually, this field reports protocols that the JUNOS software does not handle.

L3 incompletes: Number of incoming packets discarded, as they have failed Layer 3 sanity checks for the headers. For example, a frame with less than 20 bytes of available IP header is discarded.

L2 channel errors: Number of times the software did not find a valid logical interface for an incoming frame.

L2 mismatch timeouts: Number of malformed or short packets which caused the incoming packet handler to discard the frame as unreadable.

FIFO errors: Number of FIFO errors in the receive direction that are reported by the ASIC on the PIC. If this value is ever non-zero, the PIC is probably malfunctioning.

Resource errors: Sum of transmit drops.

Output errors can be broadly summarized as follows:

Carrier transitions: Number of times that the interface has gone from down to up. This number does not normally increment quickly; increasing only when the cable is unplugged, the far-end system is powered down and then up, or another issue occurs. If the number of carrier transitions increments quickly (perhaps once every 10 seconds), the cable, far-end system, PIC (Physical Interface Cards) or PIM (Physical Interface Module) is malfunctioning.
Errors: Sum of the outgoing frame aborts and FCS errors.
Drops: The number of packets which are dropped by the output queue of the I/O Manager ASIC. If the interface is saturated, this number increments once for every packet, which is dropped by the ASIC's RED mechanism.
Collisions: The number of Ethernet collisions. The Gigabit Ethernet PIC supports only full-duplex operation; so for Gigabit Ethernet PICs, this number should always remain 0. If it is non-zero, there is a software bug.
Aged packets: The number of packets which remained in the shared packet SDRAM for so long, that the system automatically purged them. The value in this field should never increment. If it does, it is most likely a software bug or possible malfunctioning hardware.
FIFO errors: The number of FIFO errors in the send direction, as reported by the ASIC on the PIC. If this value is ever non-zero, the PIC is probably malfunctioning.
HS link CRC errors: The number of errors on the high-speed links between the ASICs, which are responsible for handling the router interfaces.
MTU errors: The number of packets whose size exceeded the interface MTU.
Resource errors: Sum of transmit drops.

Modification History:

2020-06-03: Clarified PIM is Physical Interface Module and not Protocol-Independent Multicast.
2020-02-03: Article reviewed for accuracy. No changes made. Article is correct and complete.

Knowledge Base