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QoSInterface Config

service-policy [input|output] [policy]

Applies a QoS policy map to an interface for inbound or outbound traffic classification, marking, policing, shaping, or queuing.

Syntax·Interface Config
service-policy [input|output] [policy]

When to Use This Command

  • Apply a policy to shape outbound traffic on a WAN interface to 10 Mbps.
  • Apply a policy to police inbound traffic and drop packets exceeding a rate limit.
  • Apply a policy to mark VoIP traffic with DSCP EF on an access port.
  • Apply a policy to prioritize critical traffic over best-effort on a trunk interface.

Command Examples

Apply output shaping policy to a WAN interface

interface GigabitEthernet0/0 service-policy output SHAPE-10M
Router# show policy-map interface GigabitEthernet0/0
 GigabitEthernet0/0

 Service-policy output: SHAPE-10M

   Class-map: class-default (match-any)
     0 packets, 0 bytes
     5 minute offered rate 0 bps, drop rate 0 bps
     Match: any
     queue limit 64 packets
     (queue depth/total drops/no-buffer drops) 0/0/0
     (pkts output/bytes output) 0/0
     shape (average) cir 10000000, bc 40000, be 40000
       target shape rate 10000000

   Class-map: VOICE (match-any)
     0 packets, 0 bytes
     5 minute offered rate 0 bps, drop rate 0 bps
     Match: ip dscp ef (46)
     queue limit 40 packets
     (queue depth/total drops/no-buffer drops) 0/0/0
     (pkts output/bytes output) 0/0
     shape (average) cir 1000000, bc 4000, be 4000
       target shape rate 1000000

The output shows two class-maps: 'class-default' (all traffic) and 'VOICE' (DSCP EF). For each class, it displays packet/byte counts, offered rate, drop rate, queue depth, and shaping parameters (CIR, Bc, Be). The 'target shape rate' is the actual enforced rate.

Apply input police policy to a LAN interface

interface GigabitEthernet0/1 service-policy input POLICE-10M
Router# show policy-map interface GigabitEthernet0/1
 GigabitEthernet0/1

 Service-policy input: POLICE-10M

   Class-map: class-default (match-any)
     100 packets, 12000 bytes
     5 minute offered rate 50000 bps, drop rate 1000 bps
     Match: any
     police:
       cir 10000000 bps, bc 312500 bytes
       conformed 90 packets, 10800 bytes; actions:
         transmit
       exceeded 10 packets, 1200 bytes; actions:
         drop
       violated 0 packets, 0 bytes; actions:
         drop
       conformed 45000 bps, exceed 5000 bps, violate 0 bps

The output shows the policer applied to all traffic. 'conformed' packets are within CIR and are transmitted; 'exceeded' packets exceed CIR but are within burst; 'violated' packets exceed both. Actions for each category are displayed. Rates in bps help verify if policing is working correctly.

Understanding the Output

The 'show policy-map interface' command displays per-class statistics for the applied policy. Key fields: 'Service-policy [input|output]: [policy-name]' indicates direction and policy name. Each class-map shows matched traffic (packets/bytes), offered rate (average input rate), drop rate (packets dropped). For shaping: 'shape (average) cir' shows configured CIR, and 'target shape rate' is the actual enforced rate. For policing: 'conformed', 'exceeded', 'violated' counts and actions (transmit/drop). 'conformed rate' and 'exceed rate' help verify if traffic is within limits. Queue depth indicates congestion. Good values: low drop rate, conformed rate close to CIR. Bad values: high drop rate, excessive exceeded packets, queue depth consistently high.

CCNA Exam Tips

1.

Remember that 'service-policy' is applied in interface configuration mode, not global.

2.

Know that 'input' and 'output' are the only direction keywords; you cannot apply a policy in both directions on the same interface with one command.

3.

The exam may test that a policy map must be created with 'policy-map' before applying it with 'service-policy'.

4.

Be aware that 'service-policy' can be used with both MQC (Modular QoS CLI) and legacy QoS; CCNA focuses on MQC.

Common Mistakes

Applying a policy without first creating the policy map and class maps, resulting in an error.

Using 'service-policy' in global configuration mode instead of interface configuration mode.

Forgetting to specify the direction (input or output), which causes the command to be rejected.

Applying a policy that references a class map that does not exist, leading to an incomplete configuration.

Related Commands

policy-map [name]

Creates or modifies a QoS policy-map that defines a set of class-maps and associated actions (e.g., bandwidth, priority, drop) to apply to traffic on Cisco IOS routers.

show class-map

Displays the configuration and match criteria of all class maps or a specific class map, used to verify QoS classification rules.

show policy-map interface

Displays the current QoS policy applied to an interface, including per-class statistics such as packets matched, bytes, and actions taken, used to verify and troubleshoot QoS configurations.

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