Large number of input drops on vlan

Answered Question
Sep 25th, 2008

Hi All,

i have router that shows

sh int vlan90

Vlan90 is up, line protocol is up

Hardware is Cat6k RP Virtual Ethernet, address is 000b.bfcd.40fc (bia 000b.bfcd.40fc)

Description: server back-up network

Internet address is 10.20.90.251/24

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

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

Encapsulation ARPA, loopback not set

ARP type: ARPA, ARP Timeout 00:04:30

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

Last clearing of "show interface" counters 2d19h

Input queue: 1/75/16831372/16557170 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: fifo

Output queue: 0/40 (size/max)

5 minute input rate 13498000 bits/sec, 2705 packets/sec

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

254887886 packets input, 152447435528 bytes, 0 no buffer

Received 271539036 broadcasts (0 IP multicast)

0 runts, 0 giants, 0 throttles

can someone explain me what are input drops,why we have large number of input drops,what are output drops ?

why output drops are 0?

many thanks

mahesh

I have this problem too.
0 votes
Correct Answer by Prashanth Krishnappa about 8 years 2 months ago

Correct.. You might also want to set the "load-interval 30" under interface vlan 90 so that you get a more accurate snap shot rather than 5 minute average

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Prashanth Krishnappa Thu, 09/25/2008 - 09:21

Your switch is seeing too much traffic coming into VLAN 90 which is not being hardware switched which is filling up input queue and hence seeing drops. You might want to see whats going on in VLAN 90.

Here is a document written for routers and does not directly apply to switches(which forward traffic in hardware asics) but should give you an idea

http://www.cisco.com/en/US/products/hw/routers/ps133/products_tech_note09186a0080094791.shtml

mahesh18 Thu, 09/25/2008 - 10:05

Hi,

thanks for reply.

how do you figure this out that traffic is not hardware switched?

So when input queue is filled we see input

drops?in this case output drops are zero

right.

Prashanth Krishnappa Thu, 09/25/2008 - 11:40

When input queue is filled and not cleared, we would see input

drops. If traffic is hardware switched, you should not see any input rate(but for control traffic) but you are seeing about 15 Mbps. Yes there are no output drops in your interface.

mahesh18 Thu, 09/25/2008 - 11:49

Hi,

thanks for eply again.

with input rare u eman this ??????

5 minute input rate 20476000 bits/sec, 3983 packets/sec

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

Many thanks again

Correct Answer
Prashanth Krishnappa Thu, 09/25/2008 - 15:30

Correct.. You might also want to set the "load-interval 30" under interface vlan 90 so that you get a more accurate snap shot rather than 5 minute average

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