Input Errors and Overruns

[Adnan Razi Khan]

Hi, I have 2900 series router and I see increasing input errors and overruns but 0 CRC. is this physical cable issue or something else and how we can resolve this?

5 minute output rate 5914000 bits/sec, 988 packets/sec
49621095 packets input, 4017356338 bytes, 0 no buffer
Received 12256 broadcasts (0 IP multicasts)
0 runts, 0 giants, 1077 throttles
227 input errors, 0 CRC, 0 frame, 227 overrun, 0 ignored

[Elliot Dierksen]

Please post the full output of the 'show interface' command. Are you seeing collisions? It could be a duplex problem, but physical cable or interface is also a possibility. You did not say what kind of interface this is.

[Adnan Razi Khan]

Its Gig 0/0 interface

[Kasun Bandara]

most probably this can be issue of cable. try swapping new cable. also share full interface output

[Joseph W. Doherty]

Might be, if interface running at gig, router unable to keep up.  (2900 series, although they have gig interfaces, are not capable of [sustained] gig.)

Posting interface's complete stats would tell us more.

[Leo Laohoo]

"227" Input Errors, in the grand scheme of things, is insignificant.  

[Adnan Razi Khan]

I had cleared the counter but its increasing.

[Leo Laohoo]

Provide complete info. 

I do not like troubleshooting something with hands tied behind my back.

[Adnan Razi Khan]

Router#sh int gi 0/0
GigabitEthernet0/0 is up, line protocol is up
Hardware is CN Gigabit Ethernet, address (output omitted)
Internet address is (output omitted)
MTU 1500 bytes, BW 8192 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 197/255, rxload 255/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full Duplex, 1Gbps, media type is RJ45
output flow-control is unsupported, input flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:00, output 00:00:00, output hang never
Last clearing of "show interface" counters 1d18h
Input queue: 1/75/3257/2113 (size/max/drops/flushes); Total output drops: 2974
Queueing strategy: Class-based queueing
Output queue: 11/1000/415 (size/max total/drops)
5 minute input rate 8959000 bits/sec, 1470 packets/sec
5 minute output rate 6341000 bits/sec, 1138 packets/sec
94468385 packets input, 3642010020 bytes, 0 no buffer
Received 23719 broadcasts (0 IP multicasts)
0 runts, 0 giants, 1717 throttles
2523 input errors, 0 CRC, 0 frame, 2523 overrun, 0 ignored
0 watchdog, 21663 multicast, 0 pause input
97233194 packets output, 845623794 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
21663 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier, 0 pause output

[MHM Cisco World]

output flow-control is unsupported, input flow-control is unsupported <<- try run flow-control, this make Router send pause to SW/R to slow send traffic.  

[Joseph W. Doherty]

I believe (?) if interface shows flow-control unsupported, you cannot enable it for pausing traffic from another device to it and/or this device cannot respond to pause frames.

Also, if flow-control could be used, it might very well, indeed, keep a device from being overrun, it often has undesirable side effects.  The two major ones are:  it may just push a capacity issue off to another device (which may, or may not, better deal with the capacity issue - i.e. result might be, worst, no change, better) and real-time traffic, like VoIP, can be very adversely impacted by pausing traffic.  (The latter is addressed by DCB and similar technologies.)

[Leo Laohoo]

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@Adnan Razi Khan wrote:

txload 197/255, rxload 255/255​

---

Wow.  That is so not good.  

[Joseph W. Doherty]

Laugh, I first thought so too, but look at BW setting and/or actual bit rates vs. port speed.

[Leo Laohoo]

But look at the line errors.  The CRC are caused by Overruns.  And we all know what can cause it.

[Joseph W. Doherty]

Yup but consider:

Input queue: 1/75/3257/2113 (size/max/drops/flushes) vs. 2523 input errors, 0 CRC, 0 frame, 2523 overrun, 0 ignored

I.e. 5,370 vs. 2,523.  The former is over 2x the latter.

The former indicates a router unable to keep up with the input while the latter can indicate the same.

As also 1717 throttles can indicate that too.

BTW, I believe an overrun is when the NIC has received a frame, but the system doesn't pull it out of the NIC before another frame begins to arrive.