Cisco 2821 MPLS Input Errors on Interface GigabitEthernet 0/0

ciscorouter

We have an MPLS with interface gi0/0 that is getting a lot of input errors and was wondering if there is a way to troubleshoot this issue to determine why this might be happening. I can provide more information if needed.
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Best Answer

From Cisco's document "Troubleshooting Ethernet":

input error

Includes runts, giants, no buffer, CRC, frame, overrun, and ignored counts. Other input-related errors can also cause the input error count to be increased, and some datagrams may have more than one error; therefore, this sum may not balance with the sum of enumerated input error counts.

In your case, the input errors seem to be mostly ignored packets, and a very small percentage of overruns.

overrun

Shows the number of times that the receiver hardware was incapable of handing received data to a hardware buffer because the input rate exceeded the receiver's capability to handle the data.

ignored

Shows the number of received packets ignored by the interface because the interface hardware ran low on internal buffers. These buffers are different from the system buffers mentioned previously in the buffer description. Broadcast storms and bursts of noise can cause the ignored count to be increased.

In conclusion, it seems that the router is heavily overloaded. However there are 2 things here that cause suspicion:

  1. the "no buffer" counter is very low
  2. the input errors are 4 times as high as the amount of error-free packets received.

So depending on your actual symptoms (do you experience actual packet loss or not, only at time of high load or all the time, etc.) there can be 2 other explanations:

  • If you just posted this question because you noticed the counters but are not experiencing any actual problem, then chances are that this is a cosmetic bug and that the counter is not accurately showing the real amount of errors.
  • If there is packet loss even at relatively low load, then chances are that the router interface is faulty and you need a hardware replacement:

This interface could be faulty if ignores are only increasing on one interface and are not followed by an increment of the no buffer counter. The interface could also be faulty if the interface is not heavily loaded.

(source: Ignored packets are on the router due to traffic overload or faulty interface)

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