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## Understanding SRR

Hi all, I am trying to get my head around SRR but have hit a road block.

In regards to this command:

mls qos srr-queue output dscp-map queue 4 threshold 3  0 1 2 3 4 5 6 7

It looks the DSCP values (0 1 2 3 4 5 6 7) are being mapped to queue 4, threshold 3, so then which of the following lines does it get mapped to?

mls qos queue-set output 1 threshold 1 138 138 92 138
mls qos queue-set output 1 threshold 2 138 138 92 400
mls qos queue-set output 1 threshold 3 36 77 100 318
mls qos queue-set output 1 threshold 4 20 50 67 400
mls qos queue-set output 2 threshold 1 149 149 100 149
mls qos queue-set output 2 threshold 2 118 118 100 235
mls qos queue-set output 2 threshold 3 41 68 100 272
mls qos queue-set output 2 threshold 4 42 72 100 242
mls qos queue-set output 1 buffers 10 10 26 54
mls qos queue-set output 2 buffers 16 6 17 61

If I understand correctly, the queue 4 in the mls qos srr-queue output dscp-map queue 4 command maps to the threshold 4 in the mls qos queue-set output 2 threshold 4 and mls qos queue-set output 1 threshold 4 20 50 67 400 commands - is this correct? If so, what does the threshold 3 mean in the mls qos srr-queue output dscp-map queue 4 threshold 3 command?

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Hall of Fame Super Silver

## Re: Understanding SRR

Hello Parians,

taking in account the following:

>>

### WTD Thresholds

You can assign each packet that flows through the switch to a queue and  to a threshold. Specifically, you map DSCP or CoS values to an egress  queue and map DSCP or CoS values to a threshold ID. You use the mls qos srr-queue output dscp-map queue queue-id {dscp1...dscp8 | threshold threshold-id  dscp1...dscp8} or the  mls qos srr-queue output cos-map queue queue-id {cos1...cos8 | threshold threshold-id  cos1...cos8} global configuration  command. You can display the DSCP output queue threshold map and the  CoS output queue threshold map by using the show mls  qos maps privileged EXEC command.

see

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_46_se/configuration/guide/swqos.html#wp1157930

the line

mls qos queue-set output 1 threshold 1 138 138 92 138

mls qos queue-set output qset-id threshold queue-id  drop-threshold1 drop-threshold2 reserved-threshold maximum-threshold

the command sets parameters for queue-set 1 used outbound and sets thresholds for queue 1

>> If so, what does the threshold 3 mean in the mls qos srr-queue  output dscp-map queue 4 threshold 3 command?

means the following  subset DSCP values up to 8 are mapped to queue 4 to threshold 3.

note: what is missing is a parameter of queue-set id to say to what queue-set we are referring to.

But this means that DSCP mapping to queues is global and on each interface you can only choice if you want to use queue-set 1 or queue-set 2.

Hope to help

Giuseppe

2 REPLIES
Hall of Fame Super Silver

## Re: Understanding SRR

Hello Parians,

taking in account the following:

>>

### WTD Thresholds

You can assign each packet that flows through the switch to a queue and  to a threshold. Specifically, you map DSCP or CoS values to an egress  queue and map DSCP or CoS values to a threshold ID. You use the mls qos srr-queue output dscp-map queue queue-id {dscp1...dscp8 | threshold threshold-id  dscp1...dscp8} or the  mls qos srr-queue output cos-map queue queue-id {cos1...cos8 | threshold threshold-id  cos1...cos8} global configuration  command. You can display the DSCP output queue threshold map and the  CoS output queue threshold map by using the show mls  qos maps privileged EXEC command.

see

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_46_se/configuration/guide/swqos.html#wp1157930

the line

mls qos queue-set output 1 threshold 1 138 138 92 138

mls qos queue-set output qset-id threshold queue-id  drop-threshold1 drop-threshold2 reserved-threshold maximum-threshold

the command sets parameters for queue-set 1 used outbound and sets thresholds for queue 1

>> If so, what does the threshold 3 mean in the mls qos srr-queue  output dscp-map queue 4 threshold 3 command?

means the following  subset DSCP values up to 8 are mapped to queue 4 to threshold 3.

note: what is missing is a parameter of queue-set id to say to what queue-set we are referring to.

But this means that DSCP mapping to queues is global and on each interface you can only choice if you want to use queue-set 1 or queue-set 2.

Hope to help

Giuseppe

Community Member

## Re: Understanding SRR

Thanks for the reply and the information, it is much appreciated.

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