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QoS Lan configuration reference

July 23rd, 2012 | Posted by Jaime Diez in CCIE Voice | Cisco

I didn’t know how to approach this post because of its depth; therefore, I thought that giving an example would be a good idea keeping the post short and just as a brief reference on how to configure QoS. So, here I go.

Before you continue reading, you should have a good understanding of the QoS stages and the different mechanisms, because I am not going to explain the theory which can be found on my previous post.

The whole configuration posted here is based on the Cisco Catalyst 3750 which is on the lab exam.

I always keep in mind the stages to follow the same steps while I am configuring.

Classification > Policing/Marking > InputQ Mapping/Input queuing > Ingress scheduling > Stack Ring > OutputQ mapping/Output queuing > Egress Scheduling

Bellow a little diagram that it is always easier to remember and understand.

QoS Catalyst 3750

Here the example commented with some lines omitted. Please bear in mind, that these examples don’t cover all the posibilities.

 !— Policing/Marking
mls qos map policed-dscp  46 to 0 !—  how traffic is marked if it is policed
mls qos map cos-dscp 0 8 16 26 32 46 48 56 !—  map cos values to dscp values, should match with dscp-cos map
!— Ingress Scheduling
mls qos srr-queue input bandwidth 90 10 !— Q1, Q2 values are weights, minimum bandwidth guarantee if there is congestion
!— Input Queuing
mls qos srr-queue input threshold 1 8 16 !—  queue 1 threshold 1 and 2, thresold 3 non-configurable 100
mls qos srr-queue input threshold 2 34 66 !— queue 2…
mls qos srr-queue input buffers 67 33 !— buffer allocation Q1 and Q2
!— InputQ Mapping
mls qos srr-queue input cos-map queue 1 threshold 2  1 !— CoS 1 will be dropped when Q1 is at level T2=16%
mls qos srr-queue input cos-map queue 1 threshold 3  0 !— CoS 0 will be dropped when Q1 is at level T3=100%
mls qos srr-queue input cos-map queue 2 threshold 1  2
mls qos srr-queue input cos-map queue 2 threshold 2  4 6 7 !— CoS 4,6,7 will be dropped when Q2 is at level T2=66%
mls qos srr-queue input cos-map queue 2 threshold 3  3 5
mls qos srr-queue input dscp-map queue 1 threshold 2  9 10 11 12 13 14 15 !— DSCPs will be dropped when Q1 is at level T2=16%
mls qos srr-queue input dscp-map queue 1 threshold 3  0 1 2 3 4 5 6 7
mls qos srr-queue input dscp-map queue 1 threshold 3  32
mls qos srr-queue input dscp-map queue 2 threshold 1  16 17 18 19 20 21 22 23
mls qos srr-queue input dscp-map queue 2 threshold 2  33 34 35 36 37 38 39 48
mls qos srr-queue input dscp-map queue 2 threshold 2  49 50 51 52 53 54 55 56
mls qos srr-queue input dscp-map queue 2 threshold 2  57 58 59 60 61 62 63
mls qos srr-queue input dscp-map queue 2 threshold 3  24 25 26 27 28 29 30 31
mls qos srr-queue input dscp-map queue 2 threshold 3  40 41 42 43 44 45 46 47
!— OutputQ Mapping
mls qos srr-queue output cos-map queue 1 threshold 3  5 !— CoS 5 will be dropped when Q1 is at level T3=100%(queue-set 1)
mls qos srr-queue output cos-map queue 2 threshold 3  3 6 7
mls qos srr-queue output cos-map queue 3 threshold 3  2 4
mls qos srr-queue output cos-map queue 4 threshold 2  1 !— CoS 1 will be dropped when Q4 is at level T2=50%(queue-set 1)
mls qos srr-queue output cos-map queue 4 threshold 3  0
mls qos srr-queue output dscp-map queue 1 threshold 3  40 41 42 43 44 45 46 47
mls qos srr-queue output dscp-map queue 2 threshold 3  24 25 26 27 28 29 30 31
mls qos srr-queue output dscp-map queue 2 threshold 3  48 49 50 51 52 53 54 55
mls qos srr-queue output dscp-map queue 2 threshold 3  56 57 58 59 60 61 62 63
mls qos srr-queue output dscp-map queue 3 threshold 3  16 17 18 19 20 21 22 23
mls qos srr-queue output dscp-map queue 3 threshold 3  32 33 34 35 36 37 38 39
mls qos srr-queue output dscp-map queue 4 threshold 1  8 !— DSCP 8 will be dropped when Q4 is at level T1=20%(queue-set 1)
mls qos srr-queue output dscp-map queue 4 threshold 2  9 10 11 12 13 14 15
mls qos srr-queue output dscp-map queue 4 threshold 3  0 1 2 3 4 5 6 7
!— Output Queuing
!— 2 queue sets configurable, just one applied per port
mls qos queue-set output 1 threshold 1 138 138 92 138 !— qs1 Q1, T1 138%, T2 138%, T3 100%(omitted), reserved 92%, max 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 !— buffer allocation Q1, Q2, Q3, Q4
mls qos queue-set output 2 buffers 16 6 17 61

mls qos !— enables QoS

!
!— Classification/Policing/Marking
class-map match-all SCCP_SIGNALING
  match access-group name SCCP_SIGNALING
class-map match-all VOICE_MEDIA !— define class to classify traffic
  match access-group name VOICE_MEDIA !— match ACL
!
!
!— Classification/Policing/Marking
policy-map POLICY_VOICE !— policy traffic
  class VOICE_MEDIA !— select class to be policed
   set dscp ef !— mark traffic
    police 768000 8000 exceed-action policed-dscp-transmit !— mark traffic from DSCP 46 to 0(BE) if 768kbps is exceeded
  class SCCP_SIGNALING
   set dscp cs3
    police 256000 8000 exceed-action drop !— drop traffic if 256kbps bandwidth is exceeded
!
!
!— Classification
interface FastEthernet1/0/4
 switchport access vlan 101
 switchport mode access
 switchport voice vlan 102
 mls qos cos 1 !— untagged frames (from the PC) are tagged with CoS 1
 mls qos trust device cisco-phone !— trust cos if a Cisco Phone is detected via CDP
 mls qos trust cos !— trust cos value of tagged frames
 spanning-tree portfast
!
interface FastEthernet1/0/5
 switchport access vlan 101
 switchport mode access
 switchport voice vlan 102
 switchport priority extend cos 1 !— mark with CoS 1 every packet on the phone’s switchport
 mls qos trust cos
 spanning-tree portfast
!
!
interface FastEthernet1/0/7
!— Egress Scheduling – PQ Q1 – Overwriting order: Priority Queue > Shaped > Shared
 srr-queue bandwidth share 10 10 60 20 !— weight value, 10/(10+60+20)
 srr-queue bandwidth shape  10  0  0  0 !— absolute value, 1/10
 priority-queue out !— PQ enabled

interface FastEthernet1/0/8
 service-policy input POLICY_VOICE !— MQC 

!— Classification
 mls qos trust device cisco-phone
 mls qos trust cos

!— Classification/Policing/Marking
ip access-list extended SCCP_SIGNALING
 permit tcp any any eq 2000
ip access-list extended VOICE_MEDIA !— ACL used on the class-map, identify specific traffic based on protocols, ports…
 permit udp 192.168.102.0 0.0.0.255 any range 16385 32767  
!

Verification and troubleshooting commands

SW1-HQ-3750#show mls qos  !— Check if QoS is enabled globally
QoS is enabled
QoS ip packet dscp rewrite is enabled

Classification/Policing/Marking

SW1-HQ-3750#show mls qos int f1/0/5  !— QoS status on the specified port
FastEthernet1/0/5
trust state: trust cos
trust mode: trust cos
trust enabled flag: ena
COS override: dis
default COS: 0
DSCP Mutation Map: Default DSCP Mutation Map
Trust device: none
qos mode: port-based

SW1-HQ-3750#show policy-map POLICY_VOICE !— Policy actions
  Policy Map POLICY_VOICE
    Class VOICE_MEDIA
      set dscp ef
      police 768000 8000 exceed-action policed-dscp-transmit
    Class SCCP_SIGNALING
      set dscp cs3
      police 256000 8000 exceed-action drop

SW1-HQ-3750#show mls qos int f1/0/8 policers !— Policy status on the specified port
FastEthernet1/0/8
policymap=POLICY_VOICE

type=Single, id=1 rate=768000, qlimit=8000, drop=0
 markdown dscp=0
type=Single, id=2 rate=256000, qlimit=8000, drop=1
 markdown dscp=0

SW1-HQ-3750#show mls qos maps policed-dscp !— Policed DSCP action, for instance DSCP 46 to 0
   Policed-dscp map:
     d1 :  d2 0  1  2  3  4  5  6  7  8  9
     —————————————
      0 :    00 01 02 03 04 05 06 07 08 09
      1 :    10 11 12 13 14 15 16 17 18 19
      2 :    20 21 22 23 24 25 26 27 28 29
      3 :    30 31 32 33 34 35 36 37 38 39
      4 :    40 41 42 43 44 45 00 47 48 49
      5 :    50 51 52 53 54 55 56 57 58 59
      6 :    60 61 62 63

Map tables
SW1-HQ-3750#show mls qos maps cos-dscp !— cos to dscp mapping
   Cos-dscp map:
        cos:   0  1  2  3  4  5  6  7
     ——————————–
       dscp:   0  8 16 26 32 46 48 56

Ingress Queuing and Scheduling

SW1-HQ-3750#show mls qos input-queue !— Input queue configuration
Queue     :       1       2
———————————————-
buffers   :      67      33
bandwidth :      90      10
priority  :       0      10
threshold1:       8      34
threshold2:      16      66

SW1-HQ-3750#show mls qos maps cos-input-q !— Input queue COS mapping
   Cos-inputq-threshold map:
              cos:  0   1   2   3   4   5   6   7  
              ————————————
  queue-threshold: 1-3 1-2 2-1 2-3 2-2 2-3 2-2 2-2

SW1-HQ-3750#show mls qos maps dscp-input-q !— Input queue DSCP mapping
   Dscp-inputq-threshold map:
     d1 :d2    0     1     2     3     4     5     6     7     8     9
     ————————————————————
      0 :    01-03 01-03 01-03 01-03 01-03 01-03 01-03 01-03 01-01 01-02
      1 :    01-02 01-02 01-02 01-02 01-02 01-02 02-01 02-01 02-01 02-01
      2 :    02-01 02-01 02-01 02-01 02-03 02-03 02-03 02-03 02-03 02-03
      3 :    02-03 02-03 01-03 02-02 02-02 02-02 02-02 02-02 02-02 02-02
      4 :    02-03 02-03 02-03 02-03 02-03 02-03 02-03 02-03 02-02 02-02
      5 :    02-02 02-02 02-02 02-02 02-02 02-02 02-02 02-02 02-02 02-02
      6 :    02-02 02-02 02-02 02-02

Egress Queuing and Scheduling

SW1-HQ-3750#show mls qos queue-set 1 !— Output queue set 1 configuration
Queueset: 1
Queue     :       1       2       3       4
———————————————-
buffers   :      10      10      26      54
threshold1:     138     138      36      20
threshold2:     138     138      77      50
reserved  :      92      92     100      67
maximum   :     138     400     318     400

SW1-HQ-3750#show mls qos maps dscp-output-q !— Output queue DSCP mapping
   Dscp-outputq-threshold map:
     d1 :d2    0     1     2     3     4     5     6     7     8     9
     ————————————————————
      0 :    04-03 04-03 04-03 04-03 04-03 04-03 04-03 04-03 04-01 04-02
      1 :    04-02 04-02 04-02 04-02 04-02 04-02 03-03 03-03 03-03 03-03
      2 :    03-03 03-03 03-03 03-03 02-03 02-03 02-03 02-03 02-03 02-03
      3 :    02-03 02-03 03-03 03-03 03-03 03-03 03-03 03-03 03-03 03-03
      4 :    01-03 01-03 01-03 01-03 01-03 01-03 01-03 01-03 02-03 02-03
      5 :    02-03 02-03 02-03 02-03 02-03 02-03 02-03 02-03 02-03 02-03
      6 :    02-03 02-03 02-03 02-03

SW1-HQ-3750#show mls qos int f1/0/8 queueing !— Check port egress queuing
FastEthernet1/0/8
Egress Priority Queue : disabled
Shaped queue weights (absolute) :  25 0 0 0
Shared queue weights  :  25 25 25 25
The port bandwidth limit : 100  (Operational Bandwidth:100.0)
The port is mapped to qset : 1

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