QoS DSCP Marking Reference

Report an Issue

Help us improve by telling us what went wrong.

Embed this Tool

Customize and copy the embed code for your website.

Master Traffic Prioritization with DSCP Marking

Not all network traffic deserves equal treatment. A VoIP call needs low latency and jitter, while a file download can tolerate delays without anyone noticing. Quality of Service (QoS) mechanisms make these distinctions possible, and the Differentiated Services Code Point (DSCP) is the field in the IP header that tells routers how to prioritize each packet. The QoS DSCP Marking Reference tool provides a comprehensive lookup and conversion reference for DSCP values, per-hop behaviors, and their practical applications in real networks.

DSCP replaced the older IP Precedence and Type of Service (ToS) fields, providing 64 possible codepoints (6 bits) for traffic classification. In practice, a handful of well-known markings handle the vast majority of use cases: EF (Expedited Forwarding) for voice, AF (Assured Forwarding) classes for business-critical data, CS (Class Selector) values for backward compatibility with IP Precedence, and the default marking (DSCP 0) for best-effort traffic. This QoS DSCP marking reference tool maps every codepoint to its name, per-hop behavior, decimal and binary values, and typical use case.

How to Use the DSCP Reference Tool

Look up any DSCP value by entering its decimal number (0-63), binary representation, per-hop behavior name (like EF or AF31), or common name. The tool returns the complete details: decimal value, binary, per-hop behavior class, drop probability (for AF classes), the equivalent IP Precedence and ToS byte values, and a description of the typical traffic type that uses this marking.

The tool also displays a complete DSCP table organized by per-hop behavior class, making it easy to see the relationship between the four AF classes, their three drop precedence levels within each class, and how they compare to EF and CS markings. This organized view is invaluable when designing a QoS policy from scratch, because it shows at a glance which markings are available and how they map to the priority hierarchy.

Network Engineers Who Live with QoS Daily

Voice and unified communications engineers configure DSCP EF (46) marking on every voice endpoint and ensure that every switch, router, and firewall in the path honors this marking with priority queuing and low-latency forwarding. The reference tool helps them verify that all devices are classifying and marking consistently. A single device that re-marks EF traffic to default can destroy call quality across an entire site.

WAN engineers implementing QoS policies on MPLS and SD-WAN links use the DSCP reference to align traffic classes between the enterprise edge and the service provider network. Service providers often define their own class-of-service mappings (e.g., real-time, business-critical, standard, best-effort), and the enterprise must mark traffic with the correct DSCP values to receive the intended treatment. Mismatched markings mean you're paying for premium QoS treatment that your traffic never actually receives.

Security engineers configuring firewalls and intrusion prevention systems need to understand DSCP markings to write policies that don't inadvertently strip or remark QoS bits. Some security devices default to clearing the DSCP field, which destroys end-to-end QoS. The reference tool helps these engineers understand what each marking means so they can create appropriate pass-through rules.

Enterprise QoS Design Scenario

A financial services firm is deploying a new SD-WAN connecting 15 branch offices to two data centers. The QoS policy must support five traffic classes: real-time voice (EF, DSCP 46), interactive video (AF41, DSCP 34), transactional data like trading applications (AF21, DSCP 18), bulk data transfers (AF11, DSCP 10), and best effort for everything else (DSCP 0). Using the DSCP marking reference, the network architect documents the complete marking scheme with decimal values, binary codes, and the bandwidth allocation percentages for each class on the SD-WAN links.

The architect then uses the tool to verify that the DSCP values chosen for each class are appropriate. EF is reserved for traffic that needs the lowest latency and should constitute no more than 30 percent of link bandwidth. AF41 with its high priority but lower than EF ensures video gets good treatment without starving voice. AF21 and AF11 provide differentiation between interactive and bulk business traffic. The tool confirms that these markings align with RFC 2474 and RFC 2597 definitions.

QoS Implementation Tips

Mark traffic as close to the source as possible. Ideally, endpoints themselves apply the correct DSCP marking (phones mark EF, video systems mark AF41). If endpoints can't be trusted to mark correctly, the access switch should classify and mark based on port, VLAN, or deep packet inspection. Relying on markings applied at the WAN edge means the entire LAN runs without QoS differentiation.

Be careful with DSCP trust boundaries. By default, many switches don't trust incoming DSCP markings from access ports, resetting everything to 0. Explicitly configure trust on ports connected to trusted devices (IP phones, servers) and leave it untrusted on user access ports where a misconfigured PC could mark all its traffic as EF. The QoS DSCP Marking Reference on ToolWard is always available in your browser for quick lookups during configuration sessions.