Packets in imput queue

Unanswered Question
Dec 16th, 2008

I have an interface (output of sh int below),but couldn't get to gateway I notice the queue having size far above 75. But when i restart the router,everything will be fine. Whats the cause of the large size. 2.whats the inplication. 3. how can i flush the packet through the queue.


sh int vlan1

Vlan1 is up, line protocol is up

Hardware is EtherSVI, address is 0017.5a40.ff40 (bia 0017.5a40.ff40)

Internet address is

MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,

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

Encapsulation ARPA, loopback not set

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

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

Last clearing of "show interface" counters 00:01:18

Input queue: 100/75/0/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: fifo

Output queue: 0/40 (size/max)

5 minute input rate 290000 bits/sec, 178 packets/sec

5 minute output rate 809000 bits/sec, 202 packets/sec

16831 packets input, 3760855 bytes, 0 no buffer

Received 788 broadcasts, 0 runts, 0 giants, 0 throttles

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

18450 packets output, 8249366 bytes, 0 underruns

0 output errors, 0 interface resets

0 output buffer failures, 0 output buffers swapped out

I have this problem too.
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Joseph W. Doherty Tue, 12/16/2008 - 06:15

Since your input queue notes its max size as 75 packets, it's interesting how there are 100 packets in that queue. Perhaps some kind of stats display bug or other bug? What's the device and how current is the IOS?


You might also be seeing a "wedged" interface.

crow930us Tue, 12/16/2008 - 11:21

When an interface is wedged, the router no longer forwards traffic that comes from the affected interface. Which sounds like your problem.

Use the 'show buffers old' and 'show buffers input-interface Vlan1' commands to locate the source of the buffer leak.

Troubleshooting Buffer Leaks:

Troubleshooting Input and Output Queue Drops:

Just Kennie Wed, 12/17/2008 - 22:22

this is my ios ver......Cisco IOS Software, 3800 Software (C3845-ADVIPSERVICESK9-M), Version 12.4(3g), R


Please explain what yuo mean by wegde interface,the cause and implication.

Since ints a vlan applied to a physical interface,I am thinking of making some changes.Is it the vlan interface that is affected or the physical.

Joseph W. Doherty Thu, 12/18/2008 - 04:00


"Wedged Interface Buffer Leaks

Wedged interface buffer leaks cause the input queue of an interface to fill up to the point where it can no longer accept packets. Under some specific traffic conditions, the input queue on an interface becomes wedged or, in other words, the input queue count is larger than the queue depth.

Here is an example of output from the show interfaces command, which shows that the interface is wedged:

Ethernet0/0 is up, line protocol is up

Output queue 0/40, 0 drops; input queue 76/75, 1250 drops The symptom of such buffer leak is a full input queue (76/75). Here, the values 76 and 75 represent the number of packets in the input queue, and the maximum size of the input queue, respectively. In this case, the number of packets in the input queue is larger than the queue depth. This is called a "wedged interface". When an interface is wedged, the router no longer forwards traffic that comes from the affected interface.

Reload the router to free the input queue and restore traffic until the queue is full again. This can take anywhere between a few seconds and a few weeks, based on the severity of the leak.




Tips to Troubleshoot

Buffer leaks are Cisco IOS software bugs. In order to fix known buffer leak bugs, upgrade to the latest version in your release train. For example, if you currently run Cisco IOS Software Release 11.2(14), upgrade to the latest 11.2(x) image. If this does not help, or if it is not possible to upgrade the router, contact the Cisco TAC, and provide the engineer with the output of the relevant show buffers commands, and the output of the show tech-support command.


If you have a support contract, try upgrading to a newer IOS in the 12.4 software train.


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