QOS configuration on Cisco routers and switches

Below are some useful QOS  information on Cisco routers and switches

Recommended QOS bandwidth is about %33 for voice traffic
and leave %25 for best effort QOS
To change the best effort traffic use the below command on interface configuration:


To change the minimum and maximum packet thresholds for the DSCP value
Router(config-if)#random-detect ?
Router(config-if)#random-detect dscp/precidence ?
Router(config-if)#random-detect ecn (make the router ecn compatible and devices can use the last 2 bits of dscp for ecn congestion)

Some QOS Acronyms:
CIR=B(c)xT(c) Commited Information Rate
T(c)  timeslot
B(c) Committed Burst
B(e) Committed exeeded
D(e) Discard eligible
BECN  Backwards explicit congestion notification    For TCP
FECN  Forwards explicit congestion notificatclass   For UDP

Configure traffic shaping for frame relay

Router(config)#Policy-map SHAPRE_TR
Router(config-pmap)#class ALL_TR
Router(config-pmap-c)#shape adaptive <CIR>     # BECN
Router(config-pmap-c)#shape fecn-adapt         # FECN

PPP Fragmentation:

Router(config)#int s0/0
Router(config-if)#encapsulation ppp
Router(config-if)#ppp multilink
Router(config-if)#no ip addr
Router(config-if)#ppp multilink group 1
Router(config)#int multilink 1
Router(config-if)#ip address
Router(config-if)#bandwidth 512
Router(config-if)#ppp multilink fragment delay 10        # Max delay of Cisco 10 to 15 ms
Router(config-if)#ppp multilink interleave
Router(config-if)#ppp multilink group 1

To verify
show ppp multilink

For frame relay fragmentation:

map-class frame-relay FRAGMENT
fame-relay fragment ?

QOS on Cisco switches:

Router(config)#mls qos
Router(config)#mls qos map

Router(config)#int fa0/0
Router(config-if)#mls qos trust ?
Router(config-if)#mls qos cos ?

Weighted Round Roubin on Cisco switches(switches have normally 1 priority queue and 3 -4 wrr queue)

Router(config)#int fa0/1
Router(config-if)#wrr-queue cos-map <queue-number> <cos-value>
Router(config-if)#wrr-queue bandwidth <bw_for_queue1> <bw_for_quqe2> ?
Router(config-if)#priority-queue out    #will make last queue the priority queue

Configure SAA (Service Assurance agent)
rtr 100
type tcpConnect dest-ipaddr dest-port 80
rtr 200
type echo protocol ipICmpEcho

rtr schedule 100 start-time ?
rtr reaction-configuration 100 react ?

Check responses with SAA:
show rtr ?
show rtr collection-statistics 100
show rtr distribution-statistics 100 tabular

If SAA pro does not respond and you want to use SRST method for VOIP calls
voice-port 0/1/0
busyout monitor probe codec g729ar8 loss 2 delay 150

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