Networking – Differences in ifconfig RX Packets Fields

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Can someone please elaborate on the difference between the various RX packets fields in ifconfig output?

For example, let's say I run ifconfig and see the following: 

eth0      Link encap:Ethernet  HWaddr AA:BB:CC:DD:EE:FF  
          inet addr:1.1.1.1  Bcast:1.1.1.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:202723544 errors:0 dropped:4959 overruns:0 frame:37
          TX packets:158354057 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:4261083782 (3.9 GiB)  TX bytes:1224803677 (1.1 GiB)
          Interrupt:83 Memory:f6bf0000-f6c00000

What is the difference between errors: dropped: overruns and frame:

My guess at this point (based on some vague googling) is that frame: specifically pertains to CRC failures when the nic analyzes incoming frames and that errors: is a broader generic category. Then again… if that were the case, I would expect both of those fields to show numbers.

Best Answer

That information is poorly documented. I will tell you what I understand from my experience.

  • frame 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.

  • Meanwhile errors counts CRC errors, too-short frames and too-long frames.

  • overruns 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.

  • At last, dropped counts things like unintended VLAN tags or receiving IPv6 frames when the interface is not configured for IPv6.

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