Packs drop on a non-congest link (for Voice)

whx007007007 · ‎10-07-2013

Hi Everyone

I have a question regarding QOS packs drop on a non-congest link

My router Gi0/0 connects to ISP and here's the QOS configuration under this port:

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

QOS:

class-map match-any h_out

match ip precedence 4

class-map match-any l_out

match ip precedence 2

class-map match-any Voice_out

match ip precedence 5

!

policy-map Traffice-priority

class Voice_out

priority 320

class h_out

bandwidth percent 24

class l_out

bandwidth percent 16

class class-default

bandwidth percent 38

policy-map SHAPER-WAN

class class-default

shape average 1500000

service-policy Traffice-priority

interface GigabitEthernet0/0

description "CE e1"

bandwidth 1544

ip address X.X.X.X Y.Y.Y.Y

load-interval 30

duplex full

speed 10

!

service-policy output SHAPER-WAN

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

Show Output:

Router#show policy-map interface gigabitEthernet 0/0

GigabitEthernet0/0

Service-policy output: SHAPER-WAN

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

19559 packets, 7543324 bytes

30 second offered rate 251000 bps, drop rate 47000 bps

Match: any

Queueing

queue limit 64 packets

(queue depth/total drops/no-buffer drops) 0/1110/0

(pkts output/bytes output) 18468/6056654

shape (average) cir 1500000, bc 6000, be 6000

target shape rate 1500000

Service-policy : Traffice-priority

queue stats for all priority classes:

queue limit 64 packets

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

(pkts output/bytes output) 15623/4935338

Class-map: Voice_out (match-any)

16733 packets, 6335376 bytes

30 second offered rate 207000 bps, drop rate 47000 bps ------------------------------->you can see that 30 second offered rate is 207000bps which is less than priority 320 kbps, why there are some drop from this class?

Match: ip precedence 5

16733 packets, 6335376 bytes

30 second rate 207000 bps

Match: ip dscp ef (46)

0 packets, 0 bytes

30 second rate 0 bps

Priority: 320 kbps, burst bytes 8000, b/w exceed drops: 1110

Class-map: h_out (match-any)

0 packets, 0 bytes

30 second offered rate 0 bps, drop rate 0 bps

Match: ip precedence 4

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) 0/0

bandwidth 24% (360 kbps)

Class-map: l_out (match-any)

0 packets, 0 bytes

30 second offered rate 0 bps, drop rate 0 bps

Match: ip precedence 2

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) 0/0

bandwidth 16% (240 kbps)

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

2826 packets, 1207948 bytes

30 second offered rate 46000 bps, drop rate 0 bps

Match: any

Queueing

queue limit 64 packets

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

(pkts output/bytes output) 2845/1121316

bandwidth 38% (570 kbps)

My question is marked as Red, could anyone share some thought about that ?

Thanks a lot

jamie.grive · ‎10-08-2013

Hmm - the configuration is good, the only thing I can think of is you are exhausting the shaper token buckets because of bursty traffic.

Is there any TCP traffic getting marked as Prec 5 that could be entering this queue?

Please try doubling the bucket sizes and seeing if that resolves - and then investigate what traffic might be causing this if that works.

Joseph W. Doherty · ‎10-08-2013

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In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

You're looking at a 30 average rate, but policing happens in milliseconds. I.e. your traffic goes overrate within a millisecond time window (looks like 200ms) it will be dropped.

whx007007007 · ‎10-08-2013

May I know where you find my traffic goes overrate within a millisecond time window? Thanks

Joseph W. Doherty · ‎10-08-2013

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

May I know where you find my  traffic goes overrate within a millisecond time window? Thanks

You infer that from knowing how it works and the fact it's recording drops, but also:

Class-map: Voice_out (match-any)

16733 packets, 6335376 bytes

30 second offered rate 207000 bps, drop rate 47000 bps ------------------------------->you can see that 30 second offered rate is 207000bps which is less than priority 320 kbps, why there are some drop from this class?

Match: ip precedence 5

16733 packets, 6335376 bytes

30 second rate 207000 bps

Match: ip dscp ef (46)

0 packets, 0 bytes

30 second rate 0 bps

Priority: 320 kbps, burst bytes 8000, b/w exceed drops: 1110