interfaces output drop packets

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May 14th, 2008
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could the interfaces drop packets because the workstations connected to them are not processing the data fast enough?

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bvsnarayana03 Wed, 05/14/2008 - 12:07
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There are number of factors:

- slow processing by receiver

- a congested link

- hardware queue or buffer size of interface may be full

- tcp flow control due to window size etc.

Tshi M Wed, 05/14/2008 - 12:10
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thanks for the quick reply. Switchports are configured to 100 full so are the workstations. Where would a congestion occurs? How do i increase the buffer size on a 6509?

Tshi M Wed, 05/14/2008 - 12:14
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The drops seem to on the transmit part according to this output:


Interface FastEthernet1/24 queueing strategy: Weighted Round-Robin


QoS is disabled globally

Trust state: trust DSCP

Extend trust state: not trusted [COS = 0]

Default COS is 0

Queueing Mode In Tx direction: mode-cos

Transmit queues [type = 2q2t]:

Queue Id Scheduling Num of thresholds

-----------------------------------------

1 WRR low 2

2 WRR high 2


WRR bandwidth ratios: 1[queue 1] 255[queue 2]

queue-limit ratios: 0[queue 1] 100[queue 2]


queue tail-drop-thresholds

--------------------------

1 100[1] 100[2]

2 100[1] 100[2]


queue thresh cos-map

---------------------------------------

1 1

1 2

2 1 0 1 2 3 4 5 6 7

2 2


Queueing Mode In Rx direction: mode-cos

Receive queues [type = 1q4t]:

Queue Id Scheduling Num of thresholds

-----------------------------------------

1 Standard 4



queue tail-drop-thresholds

--------------------------

1 100[1] 100[2] 100[3] 100[4]


queue thresh cos-map

---------------------------------------

1 1

1 2

1 3 0 1 2 3 4 5 6 7

1 4



Packets dropped on Transmit:

BPDU packets: 0


queue thresh dropped [cos-map]

---------------------------------------------------

2 1 29299 [0 1 2 3 4 5 6 7 ]


Packets dropped on Receive:

BPDU packets: 0


queue thresh dropped [cos-map]

---------------------------------------------------

1 3 0 [0 1 2 3 4 5 6 7 ]

bvsnarayana03 Wed, 05/14/2008 - 12:24
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It is good to understand the rate at which drops are occuring. Unless theres CRC on the link, drops are too less in rate.What is the output of sh int fa0/21. Buffer size can be increased with hold-queue command on the interface.

Tshi M Wed, 05/14/2008 - 12:27
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No CRCs on the link, please see the output below:


FastEthernet1/24 is up, line protocol is up (connected)

Hardware is C6k 100Mb 802.3, address is 000d.bd3c.e53b (bia 000d.bd3c.e53b)

Description: <<< 16B >>>

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

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

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Full-duplex, 100Mb/s

input flow-control is off, output flow-control is unsupported

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

Last input never, output never, output hang never

Last clearing of "show interface" counters 05:50:38

Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 29299

Queueing strategy: fifo

Output queue: 0/40 (size/max)

5 minute input rate 0 bits/sec, 0 packets/sec

5 minute output rate 1247000 bits/sec, 501 packets/sec

301113 packets input, 240285033 bytes, 0 no buffer

Received 207606 broadcasts (207500 multicasts)

0 runts, 0 giants, 0 throttles

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

0 watchdog, 0 multicast, 0 pause input

0 input packets with dribble condition detected

89211777 packets output, 26794965996 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

bvsnarayana03 Wed, 05/14/2008 - 12:54
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Hello, output drops in your case as compared to the interface output is less than .1%. I dnt think this should be bothering, at such a low rate. Is there any impact on access to applications. are they observing any slowness or latency. Otherwise this is ok.

Tshi M Wed, 05/14/2008 - 13:16
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No, no one has yet to complain. I was just curious since other interfaces are not showing it. I'd rather have everything clean :-)


Thanks.

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