ME-3400, drop with port shaping

Unanswered Question
Jun 3rd, 2008

Hello.

We have a ME-3400 with IOS Metro IP.

The giga0/1 and gi0/3 ports are configured all the same with qos policing (input policy-map) and port shaping+Class Based Priority queueing (output policy-map).

We have no drop on gi0/1 output.

On gi0/3 output the drop is about 1-2% although the traffic (for example 10Mbps) is much less than the port shaped bandwidth (for example 200Mbps).

Can anyone help me?

Thank you.

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Pavel Bykov Tue, 06/03/2008 - 04:08

Hello, sure we can.

1. Check the output policy map using "show policy-map interface gi 0/3 output" command. This should say exactly where packets are dropped.

2. Check the parameters. In the output the first line should say the following:

Service-policy output: XYZ

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

8645541 packets

Match: any

Traffic Shaping

Average Rate Traffic Shaping

CIR 11111120 (bps)

Output Queue:

Max queue-limit default threshold: 48

Tail Packets Drop: 0

Service-policy : ABC

Class-map: core-queue1 (match-any)

3321747 packets

Match: cos 5

Priority

police cir 1000000 bc 31250

conform-action transmit

exceed-action drop

conform: 0 (packets) exceed: 0 (packets)

Output Queue:

Max queue-limit default threshold: 48

Tail Packets Drop: 0

The bold values are critical - low buffers means high drop probability.

Remember - interface never sends data at any other rate than it's physical rate, meaning "LOAD" is just an average of how many bytes transferred over what time.

So if 1000 packets will arrive in one milisecond, and then you have no traffic for 10 seconds, average will be low load, but 1000 packets will not fit in 48 buffers and 952 packets will be dropped.

Increase buffers! use the following guideline: calculate how many packets can be sent in 10ms window, and increase the buffers accordingly. E.G for 100Mbps 1 Mb can be sent in 10ms, which is 1Mbps/8 = 125000 BYTES. With "packet" size of 250 (buffers are per packet but their size is limited) that's 500 buffer places, or 500 packets buffer.

3. Always pay attention to BC and TC values

Bursts will definitely be your problem

pbenin Tue, 06/03/2008 - 04:27

Hello "slidersv" and thank you 4 your attention.

I agree with you about BC and TC values, but it seems the buffer size (queue drop threshold) for the class-default in parent policy-map cannot be increased.

How can I modify the queue drop threshold - or the BC and TC values - in Policy-map PARENT-OUT ?

Thx.

This is our configuration:

policy-map PARENT-OUT

class class-default

shape average 200000000

service-policy CHILD-OUT

policy-map CHILD-OUT

class GOLD

police cir 4000000

priority

class class-default

queue-limit 272

And this is the "show policy-map" command with drops:

Service-policy output: PARENT-OUT

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

69129893 packets

Match: any

Traffic Shaping

Average Rate Traffic Shaping

CIR 200000000 (bps)

Output Queue:

Max queue-limit default threshold: 48

Tail Packets Drop: 953573

Service-policy : CHILD-OUT

Class-map: GOLD (match-any)

9668289 packets

Match: ip dscp ef (46)

police cir 4000000 bc 125000

conform-action transmit

exceed-action drop

conform: 9669394 (packets) exceed: 0 (packets)

Priority

Output Queue:

Max queue-limit default threshold: 48

Tail Packets Drop: 0

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

54789505 packets

Match: any

Tail Packets Drop: 953573

Queue Limit

queue-limit 272 (packets)

Output Queue:

Max queue-limit default threshold: 272

Tail Packets Drop: 953573

Pavel Bykov Tue, 06/03/2008 - 05:47

Hello.

Try setting queue-limit under every class-map, not on interface:

e.g.

policy-map child-out

class class-default

queue-limit 500

Hope this helps

pbenin Tue, 06/03/2008 - 05:55

Hi.

I try this:

policy-map CHILD-OUT

class GOLD

police cir 4000000

priority

class class-default

queue-limit 544

No improvement.

Sorry.

:-((

Pavel Bykov Wed, 06/04/2008 - 22:51

And I presume that "show interface gi0/3" output does not show any errors? What is the total load of Gigabit?

pbenin Wed, 06/04/2008 - 22:55

Exactly, no errors on gi0/3.

The load is about 6/255.

:-((

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