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Input queue Drops and internet slow

syed kazim abbas

Hello experts,

i have router 2951 and its Lan side too many drops on input queue:

Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full Duplex, 1Gbps, media type is RJ45
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 21:39:36
Input queue: 0/75/20783/0 (size/max/drops/flushes); Total output drops: 877
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 3006000 bits/sec, 2040 packets/sec
5 minute output rate 15714000 bits/sec, 2078 packets/sec
92383982 packets input, 25104737639 bytes, 0 no buffer
Received 3 broadcasts (0 IP multicasts)
0 runts, 0 giants, 7804 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 0 multicast, 0 pause input
96737602 packets output, 85709878748 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
1 lost carrier, 0 no carrier, 0 pause output
0 output buffer failures, 0 output buffers swapped out

I have 20mbs link but mostly "5 minute output rate 15714000 bits/sec" cannot reach the 20mbs

please anybody help out to troubleshoot this problem


Kazim abbas

7 Replies 7

Georg Pauwen
VIP Master VIP Master
VIP Master

Hello Kazim,

the first thing you could try is to change the MTU size on your interface. Use the interface command 'ip tcp adjust-mss' and set it to 1452:

interface x

ip tcp adjust-mss 1452

or (depending on your IOS version):

interface x

ip mtu 1452


ip mtu 1480

and check if that makes a difference.

thanks Mr.gpauwen to quick response, may be its problem on UPlink (ISP)  may be no providing the good bandwidth.

Still i have problem, anybody have suggestion or solution.

What have you tried (to remediate)?

It is solved by ISP because problem on ISP end.

thanks to all


good to hear that it is solved !

Joseph W. Doherty
Hall of Fame Master Hall of Fame Master
Hall of Fame Master


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Input queue drops might be indicative that the router cannot keep up with a high speed burst of ingress traffic.

As your CIR is 20 Mbps, you might see if you can run the physical line at 100 Mbps rather than gig.

I recall (?) there's some Cisco documentation that increasing the input queue size, even to its maximum setting, might avoid input queue drops while often not being adverse to the traffic or the functioning of the router.

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