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New Member

6500 Input drops


I am have few drop on the input queue even after increasing the queue size.

The funny part is i dont see ant L2 or L3 switched packet on the interface .

When i did a etheral capture the only traffic is UDP for voice.

I have verified that CEF is working fine .

I have changed the ports and cable .

Any suggestions.

show interfaces gigabitEthernet 1/1

GigabitEthernet1/1 is up, line protocol is up

Hardware is C6k 1000Mb 802.3, address is 0005.7485.4014 (bia 0005.7485.4014)

Internet address is x.x.x.x/30

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

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

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Full-duplex, 1000Mb/s

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

Last clearing of "show interface" counters 00:51:34

Input queue: 0/1000/5596/5596 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: fifo

Output queue :0/40 (size/max)

30 second input rate 5322000 bits/sec, 715 packets/sec

30 second output rate 773000 bits/sec, 788 packets/sec

L2 Switched: ucast: 0 pkt, 0 bytes - mcast: 0 pkt, 0 bytes

L3 in Switched: ucast: 0 pkt, 0 bytes - mcast: 0 pkt, 0 bytes mcast

L3 out Switched: ucast: 0 pkt, 0 bytes

1616130 packets input, 1128926389 bytes, 0 no buffer

Received 17754 broadcasts, 0 runts, 0 giants, 0 throttles

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

0 input packets with dribble condition detected

2021443 packets output, 277679018 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 output buffer failures, 0 output buffers swapped out



Hall of Fame Super Gold

Re: 6500 Input drops

What is the egress interface ?

New Member

Re: 6500 Input drops

Hi P,

The switch is connected to a 3750.

If thats what u are asking,but i dont understand why there is no L2 or L3 packet even though there is traffic.



Hall of Fame Super Gold

Re: 6500 Input drops

Check what's going on on the output interface.

Display output may be irrelevant.

New Member

Re: 6500 Input drops

Hi P,

Interface gi1/1 is the output interface connected to 3750.



New Member

Re: 6500 Input drops

Hi P,

This is what i found:

1.From show interface status

Input queue: 0/2500/308438/308438 (size/max/drops/flushes)

2.From show interface switching for gi1/1

Throttle count 0

Drops RP 308293 SP 0

SPD Flushes Fast 308293 SSE 0

3.From debug ip traffic

Drop: 657562 encapsulation failed, 0 unresolved, 0 no adjacency

750915 no route, 0 unicast RPF, 0 forced drop

From the first 2 output we see that the Number of flushes and drops are same in input queue .

From the interface switching output the drops are also matching.

From the 3rd output we see that the total number of dropped packet for all the interface and Vlan is combination of Encapsulation and No route.

Encapsulation failed indicates that the router has no ARP request entry for a particular destination or is due to the fact that an interface is down.

No route errors occur when the router does not have a route in its routing table

So i guess i have check for virus and arp issue first then routing.



New Member

Re: 6500 Input drops

Your input queue drops are caused by spd flushes. Search for "Selective Packet Discard" - I think the command you want is

ip spd queue max

My experience has been that the 6500s have the charming property of NOT automatically changing the SPD threshold. So no matter what your input q size is it still acts like it's set to the default 75.. the only difference is you get input q flushes instead of drops.

For whatever it's worth, everything I've read indicates that packets are put on the input queue only when the MSFC has to process them - so you need to be looking for pkts punted to the MSFC, broadcasts & pkts addressed to the router. An excessive number of ARP requests could do it. Unless you're doing something horrid like pointing a static route at an ethernet interface I kind of doubt a virus would be giving your router heartburn..



Hall of Fame Super Gold

Re: 6500 Input drops

Lee, nice analysis here. Seems to me you take networking the right way.

New Member

Re: 6500 Input drops

Hi Lee,

Thanks a lot for clearing the doubt.

I knew that SPD is happening but had no idea on what you have explained ,i am going to use this command and wait for the magic.



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