DSCP stands for Differentiated Services Code Point. It is a field in the IP header that is used for packet classification and traffic management in networks. DSCP is part of the Differentiated Services (DiffServ) model, which is used to provide Quality of Service (QoS) in IP networks.

How DSCP Works

  1. IP Header Field: DSCP is a 6-bit field in the IP header, replacing the older Type of Service (ToS) field. This field is used to mark packets for different levels of service.

  2. Traffic Classification: Network devices, such as routers and switches, use the DSCP value to classify and manage network traffic. By examining the DSCP value, these devices can prioritize certain types of traffic over others.

  3. QoS Policies: Based on the DSCP value, network administrators can define QoS policies that determine how packets are treated as they traverse the network. This can include prioritizing latency-sensitive traffic like voice and video, or providing lower priority to bulk data transfers.

DSCP Values and Classes

The 6-bit DSCP field allows for 64 possible values (0-63), which are typically grouped into classes:

  1. Default Forwarding (DF): DSCP value 0. This is the default class for standard best-effort traffic.

  2. Expedited Forwarding (EF): DSCP value 46 (101110). This class is used for low-loss, low-latency traffic, such as voice over IP (VoIP).

  3. Assured Forwarding (AF): There are four classes (AF1x, AF2x, AF3x, AF4x), each with three drop precedence levels. For example, AF11, AF12, AF13; AF21, AF22, AF23, etc. These are used to provide different levels of assurance for traffic delivery.

  4. Class Selector (CS): CS0 through CS7 values are used to provide backward compatibility with the old IP precedence field. For example, CS1 (001000) can be used for low-priority traffic.

Example Use Cases

  1. Voice over IP (VoIP): VoIP traffic is sensitive to delay and jitter. By marking VoIP packets with the EF DSCP value, network devices can prioritize these packets to ensure clear, uninterrupted voice communication.

  2. Video Streaming: Video traffic can be marked with an appropriate AF class to ensure smooth playback without buffering, even during times of network congestion.

  3. Critical Business Applications: Traffic from critical business applications can be assigned higher priority using specific DSCP values to ensure they receive the necessary bandwidth and low latency.

Example Configuration

Here is an example of how DSCP might be configured on a Cisco router to mark VoIP traffic:

class-map match-all VOIP
  match ip dscp ef

policy-map QOS_POLICY
  class VOIP
    priority 1000
  class class-default

interface GigabitEthernet0/1
  service-policy output QOS_POLICY

In this configuration:

  • A class map VOIP matches packets with the DSCP value ef.
  • A policy map QOS_POLICY gives priority to the VOIP class.
  • The QOS_POLICY is applied to the output of the GigabitEthernet0/1 interface.


DSCP is a crucial part of modern QoS implementations, allowing for fine-grained control over how different types of traffic are treated in an IP network. By marking packets with appropriate DSCP values, network administrators can ensure that critical applications receive the necessary bandwidth and performance characteristics.

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Disclaimer: This post was generated with the help of ChatGPT