SRR shaping

Unanswered Question
Sep 19th, 2008
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Hi there,


I am learning the basics of QoS on the 3560 platform. To begin I applied the "auto qos voip trust" command on two interfaces. This command enabled some basic mls qos statements in the config.


The specific interface looked like this:


interface GigabitEthernet0/20

srr-queue bandwidth share 10 10 60 20

srr-queue bandwidth shape 10 0 0 0

queue-set 2

mls qos trust cos

auto qos voip trust

end


Then, I wanted to understand the SRR shaping command. So what i did was, configure two interfaces, with two hosts, and removed the SRR share commands. The two interfaces, with the two hosts (same VLAN), now look like this:


interface GigabitEthernet0/1

duplex full

speed 100

queue-set 2

mls qos trust cos

auto qos voip trust

spanning-tree portfast

end

!

interface GigabitEthernet0/2

duplex full

speed 100

srr-queue bandwidth shape 10 100 220 120

queue-set 2

mls qos trust cos

auto qos voip trust

spanning-tree portfast

end


With this config i did some bandwidth tests, by copying a big file between G0/1 and G0/2. Copying a file from G0/1 to G0/2 resulted in a speed of 0.83mbit


Copying a file from G0/2 to G0/1 resulted in a full speed bandwidth of 100mbit.


This behavior is exactly the opposite of what i expected to get with this config. Apparently the "srr-queue bandwidth shape" statement on G0/2 did reduce the inbound traffic (download). From what I've learned from the docs, SRR shaping applies to the egress queues, also called outbound, so from port G0/2 to G0/1 and not vice versa?


Any hints will be appreciated..

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gogasca Fri, 09/19/2008 - 11:14
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Your concern makes sense to me, afaik SRR bandwidth shape is for egress queues.

Can we see the following:


show mls qos

show mls qos interface (interface #)

show mls qos interface [interface #] queueing


and the sh run and sh ver.

Which COS value the file is set to? 0, 3 ?

If you remove mls qos trust cos or add mls qos trust dscp? same behaviour?


Thanks



diondohmen Sun, 09/21/2008 - 23:18
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gogasca, thanks for your reply.


I don't do anything with the CoS/DSCP value, so it hits Q4, 1/120 of the total bandwidth.


I've included a txt with all of the requested show commands.



Pavel Bykov Tue, 09/23/2008 - 21:07
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Well, SRR is set up in the inverse proportion. So you have set up "10" for the first queue, which means 1/10, or 10%. 10% of 1 gigabit is 100 Mbps...


So, isn't everything working correctly?

Also, did you check your settings with show mls qos commands? Do you have mls qos enabled globaly?

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