Hello @_Chris_ ,
QoS on LAN switches was platform dependent and this is the case of C3560.
In a nutshell a C3560 does not use modular QoS like routers and more modern switches ( C3650 , C3850 do for example) so you cannot see anything with a show policy-map interface command because the device does not use Modular QoS.
QoS on C3560 is more near the hardware level with two input queues and 4 output queues.
From a hiearchical point of view the commands can be seen in the following way:
a)
mls qos
this global command enables the QoS on the switch that by default is disabled.
b) global commands for various mappings
The C3560 is a multilayer switch the key concept here is the internal DSCP value that is associated to a packet.
The device can at the port level be configured to trust the received value or to set a new one.
However, the input queues and the output queues refer to OSI layer 2 CoS the three bits of 802.1p in 802.1Q header.
From this fact it derives a long list of mapping commands.
Each queue has different thresholds in terms of number of packets stored in the queue. This is called WTD weighted Tail Drop when going over a threshold a specific frame will be dropped.
mls qos srr-queue input cos-map queue 1 threshold 2 1
this command associates to queue 1 threshold 2 frames with CoS 1
a more complex mapping happens for DSCP values that are 6 bits wide
>> mls qos srr-queue input dscp-map queue 1 threshold 2 9 10 11 12 13 14 15
in this case DSCP values 9 to 15 are associated to input queue 1 threshold 2.
Similarly mappings happen for the output queues
mls qos srr-queue output dscp-map queue 1 threshold 3 40 41 42 43 44 45 46 47
the output queues can use SRR Shared round robin or shaped round robin or a combination of both.
The Shaped round robin applies an upper limit to the queue, shared round robin is totally elastic and the amount of traffic serviced depends on the ratio of the weights rather then their absolute values.
Actually the device supports two sets of output queues and this is handy for uplinks versus access ports.
c) see interface config
interface GigabitEthernet0/2
description Workstations and IP Phones
switchport access vlan 2
switchport mode access
switchport voice vlan 10
srr-queue bandwidth share 10 10 60 20
srr-queue bandwidth shape 10 0 0 0
priority-queue out
mls qos trust cos
auto qos trust
macro description cisco-phone
This port at QoS level does the following:
in input it trusts the CoS settings that are seen on the voice vlan tagged frames
mls qos trust cos
in the output direction we see that
there is a priority queue enabled likely used for VOIP frames
prioroty-queue out
The SRR is a combination of shared and shaped round robin
srr-queue bandwidth share 10 10 60 20
srr-queue bandwidth shape 10 0 0 0
likely queue 1 is the priority queue and will be serviced first and it also shaped.
Of the remaining queues queue 3 has 6 more times probability to be serviced then queue 2 and 3 times then queue 4.
Cisco introduced auto QoS as a way to help engineers when dealing with QoS on LAN switches.
To be honest if you are going to replace the device with a new one you will get modular QoS so the suggestion is to try to understand your QoS configuration but do not waste too much time on it.
Hope to help
Giuseppe
