QoS explanation in CIsco 3750 switch

[george85]

Hello guys,

I am trying to understand in 3750 switch how will behave with the below QoS configuration?

The below configuration is for input marked traffic that is coming from a device (host) with the appropriate dscp priotiry in to the switch.

For queue 1 how can distinguish in what threshold the packet will drop ? I have lost the concept i guess.

mls qos srr-queue input threshold 1 80 90
mls qos srr-queue input dscp-map queue 1 threshold 1 40 41 42 43 44 45 47
mls qos srr-queue input dscp-map queue 1 threshold 2 18 36
mls qos srr-queue input dscp-map queue 1 threshold 3 24 34

Also in Interface

interface FastEthernet1/0/x
srr-queue bandwidth share 10 40 20 30
srr-queue bandwidth shape 10 0 0 0

The switch has more configuration but for out traffic. Probably ill open a new thread for that.

BR

George

[Joseph W. Doherty]

"For queue 1 how can distinguish in what threshold the packet will drop ?"

First you determine which threshold (WTD1, WTD2 or queue full limit) the packet's ToS will use.

So, for example:

mls qos srr-queue input dscp-map queue 1 threshold 2 18 36

DSCP values of 18 or 36 will use the WTD2 setting.

Then the you need to see what the WTD2 (percentage) setting is.

mls qos srr-queue input threshold 1 80 90

BTW, generally you very, very rarely need to configure a 3750s ingress queues (from their defaults).