Core Issue
Packets are ignored if there are no free buffers to accept the new packet.
Resolution
If ignores are present on all interfaces, the router is probably overloaded with traffic, or does not have sufficient free buffers in the pool that match the Maximum Transmission Unit (MTU) on the interfaces, as shown:
router#show interfaces ethernet 0
Ethernet0/0 is up, line protocol is up
...
21 input errors, 0 CRC, 0 frame, 0 overrun, 21 ignored
In this case, an increment of the ignored counter is followed by an increment of the no buffer counter, as shown in this sample output:
router#show interfaces serial 0
...
1567 packets input, 0 bytes, 22 no buffer
22 input errors, 0 CRC, 0 frame, 0 overrun, 22 ignored, 0 abort
You may also see an increase in the buffer failures counter in the pool that matches the MTU size, as shown in this sample output:
router#show buffers
...
Big buffers, 1524 bytes (total 50, permanent 50):
50 in free list (5 min, 150 max allowed)
3066 hits, 189 misses, 0 trims, 24 created
12 failures (0 no memory)
The number of preconfigured permanent, free and maximum allowed buffers may not be completely compatible for every environment.
For more information, refer to Buffer Tuning.
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.
If this is the case, capture the output of the show technical-support command. To open a TAC Service Request for a hardware replacement, refer to the Cisco Technical Assistance Center (TAC) TAC Service Request Tool.
The load on the interface can be viewed in the output of the show interfaces command, as shown in this command output:
router#show interfaces serial 0
...
reliability 255/255, txload 100/255, rxload 122/255
For more information on ignored packets, refer to the Router Is Dropping Packets section of Hardware Troubleshooting for Cisco 1700 Series Routers.
