srr-queue bandwidth limit 10 just can use half bandwidth

Unanswered Question
Jul 16th, 2009

Hope to get help..!

I use WS-C3560G-24TS and try both ios 12.2.50.SE1 and 12.2.46.SE but problem the same.

The config as following,

interface GigabitEthernet0/1

no switchport

ip address 1.1.1.2 255.255.255.0

load-interval 30

speed 10

srr-queue bandwidth limit 10

but I find the int g0/1 output traffic only can achieve about 500kbps then I try config below,

interface GigabitEthernet0/1

no switchport

ip address 1.1.1.2 255.255.255.0

load-interval 30

speed 100

srr-queue bandwidth limit 10

I find int g0/1 output traffic only can achieve about 5Mbps,but if I change "srr-queue bandwidth limit xx" command xx to 20-90,the int g0/1 can achieve normal traffic bps, for example,

interface GigabitEthernet0/1

no switchport

ip address 1.1.1.2 255.255.255.0

load-interval 30

speed 10

srr-queue bandwidth limit 20

the int g0/1 output can achieve 2Mbps that is correct,just only when limit set to 10%,the traffic only can achieve half of limit bandwidth.

Does any one can help..thanks..

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gnijs Thu, 07/16/2009 - 08:22

Really Strange. Have you tries 9 or 11 ?

If these are also correct and only 10 is faulty -> escalate to TAC

netstaradam Thu, 07/16/2009 - 16:05

I has tried bandwidth limit 11 but results the same just can use half bandwidth.

Joseph W. Doherty Thu, 07/16/2009 - 12:06

Perhaps explained by . . .

"Usage Guidelines

If you configure this command to 80 percent, the port is idle 20 percent of the time. The line rate drops to 80 percent of the connected speed. These values are not exact because the hardware adjusts the line rate in increments of six. "

ref: http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_50_se/command/reference/cli3.html#wp1947391

netstaradam Thu, 07/16/2009 - 16:07

Yes..but just can use half bandwidth that is seems very not exact..!

bridgepartners Thu, 12/22/2011 - 06:58

Getting half the expected bandwidth seems to be unexpected.

Although Cisco state 'These values are not exact because the hardware adjusts the line rate in increments of six' experimental results show a different pattern. Using the command "show mls qos int x/y/z queueing" you can determine the actual operational speed for a given bandwidth limit value (this is covered in this post).

My switches showed the following usable values for bandwidth limit:

SettingActual
10       11.12
12       15.79
16       20.00
21       23.81
24       27.28
28       30.44
31       33.34
34       36.00
37       38.47
39       40.75
41       42.86
43       44.83
45       46.67
47       48.39
49       50.00
60       60.00
70       70.38
80       80.00
90       90.00

Any other value will use the next lowest usable value. I have omitted some of the higher intermediate values for clarity.

Daniel Kleeman

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