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Definition of "ifconfig" error fields.

Subject:

Running the 'ifconfig' command will give you the statistics of the packets sent/received but also any errors that have been detected.

If any errors are listed there will need to be additional investigation to determine the cause.

 

Detail:

The output of the 'ifconfig command will look something like the output below:

Link encap:Ethernet HWaddr 0c:c4:7a:81:c7:e7
UP BROADCAST RUNNING SLAVE MULTICAST MTU:1500 Metric:1
RX packets:24079412175 errors:10086 dropped:6342 overruns:6342 frame:10086
TX packets:44713893216 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:13647921305814 (13.6 TB) TX bytes:62339538766816 (62.3 TB)

 

The error fields are not well documented so here is some additional information to help understand the output.

* Frame Errors
The "frame" field counts the number of received misaligned Ethernet frames.
Frame errors mean CRC failures on receipt of a frame.
The frame field counts only misaligned frames, it means frames with a length not divisible by 8. Because of that length is not a valid frame and it is simply discarded.
The root cause of this could be a bad cable, or a bad interface on either the machine or the switch.
Suggested trouble shooting would be replacing the cables, if the problem persists then move to another port on the switch.

* Errors
The "errors" field counts CRC errors, too-short frames and too-long frames.
This can result from faulty network cables, faulty hardware (e.g., NICs, switch ports), CRC errors, or a speed or duplex mismatch between computer and switch, which would also manifest itself in a high number of collisions.

* Dropped
The "dropped" field counts things like unintended VLAN tags or receiving IPv6 frames when the interface is not configured for IPv6.
Packet Dropped seen from ifconfig could be due to many reasons
Some possible things to check would be cable/hardware/duplex issues

Below are some general reasons for "dropped" packets:

- NIC ring buffers getting full and unable to cope-up with incoming bursts of traffic
- CPU receiving NIC interrupts is very busy and unable to process
- some cable/hardware/duplex issues
- some bug in NIC driver

* Overruns
The overruns field counts that times when there is fifo overruns, caused by the rate at which the buffer gets full and the kernel isn't able to empty it.

 

Additional Information:

If there are errors indicated in the 'ifconfig' output you may need to collect more information using the 'ethtool' command.

ethtool -S

Ethtool stats are from the time the driver was instantiated (eg. loaded and inited).

RX means receive. CRC is cyclic redundancy check, a mathematical calculation that is used to identify errors in a packet.

Typically errors of this type (errors that indicate bad data integrity) are the result of layer 1 problems.

This may indicate a hardware problem such as a cable problem, fault switch port, or other.
Typically errors of this type (errors that indicate bad data integrity) are the result of layer 1 problems. I'd investigate cabling and the physical layer interface first.

***

* Symptoms

Output of "ifconfig -a" shows excessive RX errors.

Output of "ethtool -S interface_name" command shows positive values in the following counters:

rx_errors
rx_length_errors
rx_crc_errors
rx_frame_errors
rx_no_buffer_count
rx_align_errors


* Cause
RX Error counters are incremented by frames received by the NIC that are corrupted in some way:

Possible duplex mismatch on both interfaces of the link.
Faulty NIC, cable, physical media issue.
CRC failures.
In addition, NIC speed / duplex mis-match with the connecting port on the switch/router might be the cause.

 

Quantastor network configuration link:

Network_Port_Configuration

 

 

 

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