# How to Debug QOS on switches and routers

**URL:** <https://forum.networklessons.com/t/how-to-debug-qos-on-switches-and-routers/1615>\
**Category:** Quality of Service\
**Created:** [March 29, 2017, 5:33pm UTC](https://forum.networklessons.com/t/how-to-debug-qos-on-switches-and-routers/1615 "2017-03-29T17:33:58Z")\
**Posts on this page:** 1\
**Showing post:** 2

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**Author:** ![ReneMolenaar](https://cdn-forum.networklessons.com/user_avatar/forum.networklessons.com/renemolenaar/32/488_2.png) [@ReneMolenaar](https://forum.networklessons.com/u/ReneMolenaar)\
**Post date:** [July 6, 2017, 9:58am UTC](https://forum.networklessons.com/t/how-to-debug-qos-on-switches-and-routers/1615/2 "2017-07-06T09:58:58Z")

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Hi Steven,

A simple method to verify this is to do it on a hop-by-hop basis, first from source to destination and then for the return traffic as well. On your routers (and most switches), you can use a policy map with no actions just to use it as a counter:

```
SW1(config)#class-map EF  
SW1(config-cmap)#match dscp ef

SW1(config)#policy-map COUNTER
SW1(config-pmap)#class EF

SW1(config)#interface GigabitEthernet 0/1
SW1(config-if)#service-policy input COUNTER

```

And monitor:

```
SW1#show policy-map interface GigabitEthernet 0/1
 GigabitEthernet0/1 

  Service-policy input: COUNTER

    Class-map: EF (match-all)  
      0 packets, 0 bytes
      5 minute offered rate 0000 bps
      Match: dscp ef (46)

    Class-map: class-default (match-any)  
      0 packets, 0 bytes
      5 minute offered rate 0000 bps, drop rate 0000 bps
      Match: any

```

That is a simple way to test it. You can also use the show mls qos command on the 29xx/35xx switches to see incoming marked traffic:

```
SW1#show mls qos interface FastEthernet 0/1 statistics
FastEthernet0/1 (All statistics are in packets)

  dscp: incoming
-------------------------------

  0 - 4 : 0 0 0 0 0
  5 - 9 : 0 0 0 0 0
 10 - 14 : 0 0 0 0 0
 15 - 19 : 0 0 0 0 0
 20 - 24 : 0 0 0 0 0
 25 - 29 : 0 0 0 0 0
 30 - 34 : 0 0 0 0 0
 35 - 39 : 0 0 0 0 0
 40 - 44 : 0 0 0 0 0
 45 - 49 : 0 0 0 0 0
 50 - 54 : 0 0 0 0 0
 55 - 59 : 0 0 0 0 0
 60 - 64 : 0 0 0 0

```

Of course there are also some network monitoring tools that do this on a larger scale, checking your policy-maps or netflow.

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