Solved: Re: Traffic shaping - excessive drops?

sketterman · ‎02-20-2012

I am shaping my outbound router (2921) link to 50Mbs. I have my QOS policy nested inside my shaping policy and I have noticed (what I think) is a high amount of packet drops in one of my queues.

Below is the output of 2 show policy-map interface g0/0 run back to back. As you can see I lost around 21 packets in just a few seconds, yet my link is only using around 7Mbs. My counters were cleared around 3 hours before I took this sample. I have my 2 QOS policies listed after the output. Any ideas why I am seeing all these packet drops? My QoS understanding isn't exactly expert level yet, but it seems like something isn't working correctly. Any tips would be appreciated. Thanks in advance.

SAMPLE 1

GigabitEthernet0/0

Service-policy output: SHAPE

Class-map: class-default (match-any)

31573394 packets, 23655469220 bytes

30 second offered rate 7131000 bps, drop rate 13000 bps

Match: any

Queueing

queue limit 256 packets

(queue depth/total drops/no-buffer drops) 0/55237/0

(pkts output/bytes output) 31518160/23588134456

shape (average) cir 50000000, bc 200000, be 200000

target shape rate 50000000

Service-policy : WAN_QOS

queue stats for all priority classes:

queue limit 64 packets

(queue depth/total drops/no-buffer drops) 0/0/0

(pkts output/bytes output) 120258/23706082

Class-map: EF (match-all)

120258 packets, 23706082 bytes

30 second offered rate 0 bps, drop rate 0 bps

Match: dscp ef (46)

Priority: 25% (12500 kbps), burst bytes 312500, b/w exceed drops: 0

Class-map: AF41 (match-any)

20181 packets, 2770959 bytes

30 second offered rate 2000 bps, drop rate 0 bps

Match: dscp af41 (34)

20181 packets, 2770959 bytes

30 second rate 2000 bps

Match: access-group 120

0 packets, 0 bytes

30 second rate 0 bps

Queueing

queue limit 64 packets

(queue depth/total drops/no-buffer drops) 0/0/0

(pkts output/bytes output) 20181/2770959

bandwidth 40% (20000 kbps)

QoS Set

dscp af41

Packets marked 20181

Class-map: AF21 (match-all)

28562372 packets, 22381305435 bytes

30 second offered rate 4721000 bps, drop rate 13000 bps

Match: dscp af21 (18)

Queueing

queue limit 64 packets

(queue depth/total drops/no-buffer drops) 0/55091/0

(pkts output/bytes output) 28507286/22314221299

bandwidth 34% (17000 kbps)

Class-map: class-default (match-any)

2870584 packets, 1247686802 bytes

30 second offered rate 2410000 bps, drop rate 0 bps

Match: any

queue limit 256 packets

(queue depth/total drops/no-buffer drops) 0/146/0

(pkts output/bytes output) 2870438/1247436290

QoS Set

dscp default

Packets marked 2869359

Exp-weight-constant: 9 (1/512)

Mean queue depth: 0 packets

class Transmitted Random drop Tail drop Minimum Maximum Mark

pkts/bytes pkts/bytes pkts/bytes thresh thresh prob

0 2870438/1247436290 134/64490 12/984 20 40 1/10

1 0/0 0/0 0/0 22 40 1/10

2 0/0 0/0 0/0 24 40 1/10

3 0/0 0/0 0/0 26 40 1/10

4 0/0 0/0 0/0 28 40 1/10

5 0/0 0/0 0/0 30 40 1/10

6 0/0 0/0 0/0 32 40 1/10

7 0/0 0/0 0/0 34 40 1/10

SAMPLE 2

GigabitEthernet0/0

Service-policy output: SHAPE

Class-map: class-default (match-any)

31589736 packets, 23665225208 bytes

30 second offered rate 7131000 bps, drop rate 13000 bps

Match: any

Queueing

queue limit 256 packets

(queue depth/total drops/no-buffer drops) 0/55258/0

(pkts output/bytes output) 31534478/23597868640

shape (average) cir 50000000, bc 200000, be 200000

target shape rate 50000000

Service-policy : WAN_QOS

queue stats for all priority classes:

queue limit 64 packets

(queue depth/total drops/no-buffer drops) 0/0/0

(pkts output/bytes output) 120258/23706082

Class-map: EF (match-all)

120258 packets, 23706082 bytes

30 second offered rate 0 bps, drop rate 0 bps

Match: dscp ef (46)

Priority: 25% (12500 kbps), burst bytes 312500, b/w exceed drops: 0

Class-map: AF41 (match-any)

20185 packets, 2771873 bytes

30 second offered rate 2000 bps, drop rate 0 bps

Match: dscp af41 (34)

20185 packets, 2771873 bytes

30 second rate 2000 bps

Match: access-group 120

0 packets, 0 bytes

30 second rate 0 bps

Queueing

queue limit 64 packets

(queue depth/total drops/no-buffer drops) 0/0/0

(pkts output/bytes output) 20185/2771873

bandwidth 40% (20000 kbps)

QoS Set

dscp af41

Packets marked 20185

Class-map: AF21 (match-all)

28576958 packets, 22389554081 bytes

30 second offered rate 4721000 bps, drop rate 13000 bps

Match: dscp af21 (18)

Queueing

queue limit 64 packets

(queue depth/total drops/no-buffer drops) 0/55112/0

(pkts output/bytes output) 28521846/22322447962

bandwidth 34% (17000 kbps)

Class-map: class-default (match-any)

2872335 packets, 1249193172 bytes

30 second offered rate 2410000 bps, drop rate 0 bps

Match: any

queue limit 256 packets

(queue depth/total drops/no-buffer drops) 0/146/0

(pkts output/bytes output) 2872189/1248942723

QoS Set

dscp default

Packets marked 2871109

Exp-weight-constant: 9 (1/512)

Mean queue depth: 0 packets

class Transmitted Random drop Tail drop Minimum Maximum Mark

pkts/bytes pkts/bytes pkts/bytes thresh thresh prob

0 2872189/1248942723 134/64490 12/984 20 40 1/10

1 0/0 0/0 0/0 22 40 1/10

2 0/0 0/0 0/0 24 40 1/10

3 0/0 0/0 0/0 26 40 1/10

4 0/0 0/0 0/0 28 40 1/10

5 0/0 0/0 0/0 30 40 1/10

6 0/0 0/0 0/0 32 40 1/10

7 0/0 0/0 0/0 34 40 1/10

POLICY MAPS

show policy-map

Policy Map WAN_QOS

Class EF

priority 25 (%)

Class AF41

bandwidth 40 (%)

set dscp af41

Class AF21

bandwidth 34 (%)

Class class-default

set ip dscp default

queue-limit 256 packets

packet-based wred, exponential weight 9

class min-threshold max-threshold mark-probablity

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

0 - - 1/10

1 - - 1/10

2 - - 1/10

3 - - 1/10

4 - - 1/10

5 - - 1/10

6 - - 1/10

7 - - 1/10

Policy Map SHAPE

Class class-default

Average Rate Traffic Shaping

cir 50000000 (bps)

queue-limit 256 packets

service-policy WAN_QOS

Edison Ortiz · ‎02-21-2012

The drops seem to be happening with Class AF21. What type of traffic matches such DSCP value in your network?

You may have to increase the queue-limit under the class to something greater than 64 until the drops stop.

I don't think the shaper is causing the issue but if you want to isolate, you can apply the child policy-map to the interface and see if drops continue.

Regards,

Edison

View solution in original post

Edison Ortiz · ‎02-21-2012

The drops seem to be happening with Class AF21. What type of traffic matches such DSCP value in your network?

You may have to increase the queue-limit under the class to something greater than 64 until the drops stop.

I don't think the shaper is causing the issue but if you want to isolate, you can apply the child policy-map to the interface and see if drops continue.

Regards,

Edison

sketterman · ‎02-21-2012

I am putting the majority of my business WAN traffic in AF21 and setting my internet and a few bandwidth hogging servers in class-default. I increased my queue-limit on my AF21 class to 256 and I have already lost 2715 packets in 15 minutes.

I guess I dont understand why a drop-rate is being applied when the link isn't full, or the queue isn't even hitting it's minimum bandwidth limit of 17Mbs. Should I maybe increase my Bc value to something higher than the default 4ms?

---EDIT---

After the initial loss of packets, packet loss slowed down to almost nothing, so increasing the queue limit seems to have helped.

Edison Ortiz · ‎02-21-2012

Packets that match that class will be placed in queues before they are dequeued. If the numbers of queues aren't enough, you will get packet drops. This behavior will occur even if you aren't reaching the maximum available throughput of the link and often seen under bursty traffic conditions.

As you stated, the situation has been resolved so please mark the thread accordingly.

Regards,

Edison