I have an interface (output of sh int below)192.168.100.2,but couldn't get to gateway 192.168.100.1. 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 192.168.100.2/24
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
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?
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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