overrun on 7206 and gigethernet

Unanswered Question
Jul 31st, 2007


my problem is, that i have overruns on one of the gigabitint on 7206 router.

the util of the gigabitint is in average "only" 10mb/s:

mplsrbgope01#sh int gig0/1

GigabitEthernet0/1 is up, line protocol is up

Hardware is BCM1250 Internal MAC, address is 000b.bfff.dc1b (bia 000b.bfff.dc1b)

Description: MPLSRBGOPE01: phy.Link to GRZC1 (Gi0/1-Trunk)

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

reliability 255/255, txload 1/255, rxload 2/255

Encapsulation 802.1Q Virtual LAN, Vlan ID 1., loopback not set

Keepalive set (10 sec)

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

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

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 00:16:28

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

Queueing strategy: fifo

Output queue: 0/40 (size/max)

30 second input rate 10127000 bits/sec, 2252 packets/sec

30 second output rate 3088000 bits/sec, 1811 packets/sec

2367581 packets input, 1383260933 bytes, 0 no buffer

Received 14438 broadcasts, 0 runts, 0 giants, 0 throttles

25 input errors, 0 CRC, 0 frame, 25 overrun, 0 ignored

0 watchdog, 9475 multicast, 0 pause input

0 input packets with dribble condition detected

1924875 packets output, 516916572 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

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


what to do with overruns?

i tried to increase the "hold-queu in" - but it does not help as i cant?t see input-drops

thanks for help

I have this problem too.
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Overall Rating: 4 (3 ratings)
Paolo Bevilacqua Tue, 07/31/2007 - 05:07

The overrun are too small in number to be possibly causing the problems.

With NPE is that? from which other interface the traffic is coming going? Is IP CEF enabled ?

rabeder Tue, 07/31/2007 - 05:12

hi, thanks for answer

it is a g1.

the router util is 30-50%

i did a clear counter a few minutes before - so the number is not very high.

fakt is, that we have sporadiclytroubles of missing pakets in the access-layer.

so the first thing is to troubleshoot the input errors (overrun).

Paolo Bevilacqua Tue, 07/31/2007 - 06:23

30-50% is very high for a million pps capable router. Is CEF enabled ? Are there ACLs or other special processing loading the router so much ?

hardiklodhia Tue, 07/31/2007 - 06:00


Overruns appear in the output of the show interface command when the receiver hardware is unable to hand received data to a hardware buffer because the input rate exceeds the receiver's ability to handle the data.

This occurs due to a limitation of the hardware. Overruns occur when the internal First In, First Out (FIFO) buffer of the chip is full, but is still tries to handle incoming traffic. The controller chip has limited internal FIFO.

there are 25 input errors. check physical connection as media type is cx , also check speed and duplex settings on both side.

hope this will help


Paolo Bevilacqua Tue, 07/31/2007 - 06:20

Why such a low rating for a perfectly clear and helpful answer? Moreover given by a qualified professional willing to share his precious time helping perfect strangers.

I've rated above post a '5' and invite everyone to fairness in rating.

rabeder Tue, 07/31/2007 - 06:30

.... because i tried everything as described

(duplex, cable, speed) - and the problem is still there, so it is an other problem.

so for me the answer isn?t extrem helpful -it is somewhat helpful -

it is not your job to tell me how helpful a answer is for me (i know i myself)

Paolo Bevilacqua Tue, 07/31/2007 - 07:55


The thing is that beside being only "somewhat helpful", 1 or 2 are low-ratings unnecessarily punishing the average rating of those providing answers in the best will.

So rather than rating low, if often better not to rate at all.

Regarding on how I should spend my time or not, one thing is sure, not anymore in this thread.

Good luck.

thomas.anthony Tue, 07/31/2007 - 06:03

As per your interface output 'overruns' have been reported because, the input rate exceeds the ability of the receiver to handle data. please check the utilization on this interface

rabeder Fri, 08/03/2007 - 06:24

found some interessting info:

If the capacity of the interface is exceeded, the frame that is currently being received is dropped and the overrun counter is incremented.

Each network interface on Cisco routers consists of a chipset for converting signals received in the media into bits of information, and a small packet buffer into which this information is stored before being copied into the I/O memory. On some interface types, this chipset and packet buffer cannot handle a long burst of frames. Such interfaces are meant to provide connectivity to a certain network type, and not to switch packets at line rate. The line rate of these interfaces is often higher than the switching capacity of the router. Therefore, building an interface that receives more traffic than the router can handle only increases the cost, without adding any real value to the router architecture.

Some examples of connectivity interfaces include PA-GE on c7200 routers, GEIP on c7500 routers, and FastEthernet interfaces on c3620 and c3640 routers.

Resolution In a small number of cases, the overrun counter may be incremented because of a software defect. However, in the majority of cases, it indicates that the receiving capability of the interface was exceeded. Nothing can be done on the router that reports overruns. If possible, the rate that frames are coming should be controlled at the remote end of the connection. Otherwise, if the number of overruns is high, the hardware should be upgraded.

Note: If the router drops packets because of performance problems of the main CPU (and not because of the capacity of the interface itself), the ignored counter is increased, and not the overruns counter.


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