overruns in optical interface with low bandwidth utilization in Cisco 7206VXR

[f_baroumas]

Hello,

We have a Cisco 7206VXR and we're experiencing overrun input errors. In most of the documents i have read that these errors can be caused due to the fast rate of the packets that came in the interface. The problem is that the interface is gigabit ethernet with optical fibre and the utilization is approximately 15 Mbps/sec so i believe that oversubscription is difficult to happen.

ach7206PAR1#show interfaces gigabitEthernet 0/3

GigabitEthernet0/3 is up, line protocol is up

  Hardware is BCM1250 Internal MAC, address is 001d.7106.2c19 (bia 001d.7106.2c19)

  Internet address is 10.170.0.18/30

  MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,

     reliability 255/255, txload 1/255, rxload 3/255

  Encapsulation ARPA, loopback not set

  Keepalive set (10 sec)

  Full-duplex, 1000Mb/s, link type is autonegotiation, media type is LX

  output flow-control is XON, input flow-control is XON

  ARP type: ARPA, ARP Timeout 04:00:00

  Last input 00:00:50, output 00:00:00, output hang never

  Last clearing of "show interface" counters 16w6d

  Input queue: 0/75/0/182 (size/max/drops/flushes); Total output drops: 0

  Queueing strategy: fifo

  Output queue: 0/40 (size/max)

  5 minute input rate 13351000 bits/sec, 1871 packets/sec

  5 minute output rate 4152000 bits/sec, 1480 packets/sec

     13392736499 packets input, 11481619161979 bytes, 0 no buffer

     Received 2 broadcasts, 0 runts, 0 giants, 0 throttles

     7370 input errors, 0 CRC, 0 frame, 7370 overrun, 0 ignored

     0 watchdog, 0 multicast, 0 pause input

     0 input packets with dribble condition detected

     9652310207 packets output, 2505172836127 bytes, 0 underruns

     0 output errors, 0 collisions, 0 interface resets

     0 unknown protocol drops

     0 babbles, 0 late collision, 0 deferred

     0 lost carrier, 0 no carrier, 0 pause output

     0 output buffer failures, 0 output buffers swapped out

ach7206PAR1#show ver

Is there possible to have a Layer 1 issue?

[Joseph W. Doherty]

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Posting

Overruns would most likely be caused by a burst of (small) back-to-back packets - i.e. bandwidth utilization doesn't have to be high for this to be problem.

I also see your input queue has registered some flushes, another indication that the router occasionally cannot keep up with an incoming burst of packets.

What NPE are you using?

[paolo bevilacqua]

Which NPE are you using ?

[f_baroumas]

Cisco 7206VXR (NPE-G1). So what do you suggest to do in order to fix the issue?Increasing the input queue will reduce the errors?The specific circuit is operational for years but yesterday reported a lot of these errors which is strange.

Thanks for your answers.

[paolo bevilacqua]

The error to input ratio is minuscole. It can have been caused by a transient issue, and can be ignored.

[f_baroumas]

thanks