Cisco SG200-50 Switch QoS - Not seeing DSCP codes putting packets in priority queues

[pwillemann]

I have created a Java program which sends packets with DSCP markings from a computer on one subnet to a computer on another subnet.  I used Wireshark to verify the packets preserve the DSCP marking from the source to the destination.   The source machine sends the packets to a Cisco SG200-50 switch and then the packets get sent to an old Cisco 2811 router which disseminates them to the destination machine.  The router has a very old IOS, so that's why I added the switch in front of the router.  The DSCP markings do not have any effect on packets going to the correct priority queues in the switch.

The packets arrive at the destination machine in the same order as they where sent, however this is not what I expected.  My packets can have one of 3 DSCP codes (46, 22 or 0)  I expected the "46" packets, then the "22" packets and finally the "0" packets.  I am definitely a router/switch newbie, but based on the switch administrator's guide it looks like I have everything setup under the Quality of Service heading as it should be.

1. My Qos Mode is enabled and my Trust Mode is DSCP.
2. All the interfaces/ports, including the two I use (GE2 and GE3) have their QoS state enabled.
3. I set the Scheduling Method to WRR for the 4 queues, however whatever I try for the Scheduling method doesn't seem to matter.
4. I took the Defaults for the DSCP to Queue table.
5. In the Bandwidth table I configured an egress shaping rate for the ports (GE2 and GE3).  Whatever I do here doesn't matter though.
6. I set the Egress shaping for the 4 queues for each port.  Queue 4 has the biggest CIR, followed by 3, then 2 and then 1.

At this point my question is basically what am I missing?  Am I able to do what I want?  Did I forget some other SG200-50 switch configuration option?  I appreciate any guidance you can give me to steer me in the right direction so I can solve this annoying problem.

Thanks

[Brandon Svec]

This is kind of a wild guess, but I think your expectation is incorrect.  As I understand, the qos mechanism in the switch will only take effect if there is congestion or some metric has been met.  In the scenario you describe there is no reason to reorder or drop any packets.

During periods with light traffic, that is, when no congestion exists, packets are sent out the interface as soon as they arrive. During periods of transmit congestion at the outgoing interface, packets arrive faster than the interface can send them. If you use congestion management features, packets accumulating at an interface are queued until the interface is free to send them; they are then scheduled for transmission according to their assigned priority and the queueing mechanism configured for the interface. The router determines the order of packet transmission by controlling which packets are placed in which queue and how queues are serviced with respect to each other.

from: http://www.cisco.com/c/en/us/td/docs/ios/12_2/qos/configuration/guide/fqos_c/qcfconmg.html

Hopefully someone with more knowledge will chime in..

[pwillemann]

Ok, this makes some sense to me.  I kind of thought that doing the egress shaping might cause this "bottleneck." It seems like I should flood the switch with lots of traffic to see the desired effects.  I will try that and see what happens.  I guess I just need to figure out how much traffic to send.
 

[pwillemann]

I decided to adjust my GE2 and GE3 port settings to the lowest values allowed by the switch.  I have my packet creator program send 1000 packets to the switch.  The sending program takes about a second to send the data.  On my receiving laptop I print out the receiving packets and a corresponding number which represents the order it was sent.  This takes several minutes, which tells me I have effectively clamped down the bandwidth on the switch.  So far, despite my best efforts the packets arrive in the order in which they were sent.  From my perspective it appears that DSCP seems to be ignored.  There appears to be something that I fundamentally don't understand.

Questions:

1. Should I more than one sending machine?
2. Can I really do what I want to do with my current configuration?

Thank you very much for spending the time to read this.

[pwillemann]

I decided to adjust my GE2 and GE3 port settings to the lowest values allowed by the switch.  I have my packet creator program send 1000 packets to the switch.  The sending program takes about a second to send the data.  On my receiving laptop I print out the receiving packets and a corresponding number which represents the order it was sent.  This takes several minutes, which tells me I have effectively clamped down the bandwidth on the switch.  So far, despite my best efforts the packets arrive in the order in which they were sent.  From my perspective it appears that DSCP seems to be ignored.  There appears to be something that I fundamentally don't understand.

Questions:

1. Should I use more than one sending machine?
2. Can I really do what I want to do with my current configuration?

Thank you very much for spending the time to read this.