Wednesday, 21 March 2018

Example: Applying QoS on a Cisco 3650 / 3850

Note: In older models / OS's we needed to issue 'mls qos' in order to enable QoS on the switch - however with the 3650 QoS is enabled by default.

The aim is to tag voice traffic with DSCP that hits either gi0/1 or gi0/2 from VLAN 10 and ensuring data traffic is even spread between vlan20 and vlan30. Note: In most cases AutoQoS is a much better solution and greatly simplifies the configuration - however I created this lab to demonstrate a simple example manually:

vlan 10
desc priority traffic
name VLAN10

vlan 20
desc non-priority data traffic 1
name VLAN20

vlan 30
desc non-priority data traffic 1
name VLAN20

We'll need to use MQC (Modular QoS CLI) in order to apply the QoS - so let's firstly create our class map:

####### Set ingress service policy

class-map qos_vlan10_cm_in
match vlan 10
exit

class-map qos_vlan20_cm_in
match vlan 20
exit

class-map qos_vlan20_cm_in
match vlan 30
exit

policy-map qos_pm_in
class qos_vlan10_cm_in
set ip dscp 40
class qos_vlan20_cm_in
set ip dscp 0
class qos_vlan30_cm_in
set ip dscp 0
exit

int gi1/0/1
service-policy input qos_pm_in

int gi1/0/2
service-policy input qos_pm_in

And now for the egress QoS:

class-map qos_vlan10_cm_out
match ip dscp 40
exit

class-map qos_vlan20_cm_out
match ip dscp 0
exit

class-map qos_vlan30_cm_out
match ip dscp 0
exit

policy-map qos_pm_out
class qos_vlan10_cm_out
priority 1 percent 10
class qos_vlan20_cm_out
bandwidth percent 20
class qos_vlan30_cm_out
bandwidth percent 20
class class-default
bandwidth remaining percent 100
exit

# The 'bandwidth percent' command provides 20% of the interfaces bandwdith to vlan20 and 20% to vlan30 - however during times were there is no contention other classes can utilise additional bandwidth. I.e. The command doesn't reserve bandwidth. While the remaining 100% of the bandwidth is shared between other traffic.

# The 'priority level' command always ensures that traffic from VLAN10 is always served before anything else and reserves 10% of the link (i.e. 100 megabits) for the voice traffic - however it is not able to utilise any greater than 10%!

Finall apply the service policy to the outgoing interface with:

int gi1/0/24
service-policy output qos_pm_out









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