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QoSClass-map Config

match dscp [value]

Matches packets based on the DSCP value in the IP header for classification in a class map.

Syntax·Class-map Config
match dscp [value]

When to Use This Command

  • Classify VoIP traffic marked with DSCP EF for priority queuing.
  • Identify video conferencing traffic using DSCP AF41 for bandwidth guarantee.
  • Match network control traffic with DSCP CS6 for low-latency treatment.
  • Filter traffic with specific DSCP values for remarking or policing.

Command Examples

Match DSCP EF for VoIP traffic

match dscp ef

This command matches packets with DSCP value EF (46), commonly used for voice traffic.

Match multiple DSCP values for video and voice

match dscp ef af41

Matches packets with DSCP EF (46) or AF41 (34), used for voice and video respectively.

Understanding the Output

This command does not produce output directly; it is used within a class-map configuration. To verify, use 'show class-map' to see the match criteria. The class map will list the DSCP values matched. A correct configuration shows the expected DSCP values; missing or incorrect values indicate a configuration error.

CCNA Exam Tips

1.

CCNA exam tip: DSCP values are often tested with their decimal equivalents (e.g., EF=46, AF41=34).

2.

CCNA exam tip: Remember that 'match dscp' is used in class-map config mode, not globally.

3.

CCNA exam tip: You can match up to 8 DSCP values in a single match statement.

4.

CCNA exam tip: DSCP matching is case-insensitive (e.g., 'ef' or 'EF').

Common Mistakes

Mistake 1: Using 'match ip dscp' instead of 'match dscp' in class-map config mode.

Mistake 2: Forgetting to enter class-map configuration mode before using the command.

Mistake 3: Matching DSCP values that are not standard or mis-typing the value (e.g., 'af41' vs 'af4').

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.

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