DNS

Directory Name Service

Core Network →
Introduced in R99 Also in: Core Network, Management, Security

DNS is a hierarchical, distributed naming system used in 3GPP networks to translate domain names into IP addresses for service discovery, network element location, and traffic routing.

Category
Core Network
Introduced
R99
Where
Services › Codecs
Also touches
3 segments
Specifications
56 specs
DNS Description Purpose Related Classification Detected Changes Specifications

Description

The Directory Name Service (DNS) in 3GPP is a critical infrastructure component based on the Internet Engineering Task Force (IETF) standards, specifically RFC 1034 and RFC 1035. It operates as a distributed database that resolves Fully Qualified Domain Names (FQDNs) into corresponding IP addresses and other resource records, such as NAPTR (Naming Authority Pointer) and SRV (Service) records. Within the 3GPP architecture, DNS is used extensively by core network functions for dynamic discovery and selection of peer network elements. For instance, during the establishment of a Packet Data Network (PDN) connection, the Packet Data Network Gateway (PGW) or Session Management Function (SMF) may be selected based on DNS queries that consider the Access Point Name (APN), subscriber's location, and network policies. The system employs a hierarchical structure with root servers, top-level domains, and authoritative name servers specific to the operator's network (e.g., epc.mnc<MNC>.mcc<MCC>.3gppnetwork.org). DNS queries are initiated by various network functions, including the Mobility Management Entity (MME), Serving GPRS Support Node (SGSN), Home Subscriber Server (HSS), and Policy and Charging Rules Function (PCRF), to locate services like the PGW/SMF, HSS/UDM, or application servers. The resolution process involves recursive and iterative queries, with caching mechanisms at resolvers to improve efficiency and reduce latency. DNS is also pivotal for inter-operator connectivity, enabling the resolution of FQDNs for roaming scenarios and interconnection between different Public Land Mobile Networks (PLMNs). In 5G systems, DNS remains essential for service-based architecture (SBA), where Network Function (NF) instances register their profiles and endpoints in the Network Repository Function (NRF), and consumer NFs use DNS-based service discovery to find appropriate producer NFs based on service names, NF types, and other selection criteria.

Purpose & Motivation

DNS was introduced to solve the problem of static, hard-coded network element addressing, which was inflexible and difficult to manage in large-scale, dynamic mobile networks. Prior to its adoption, network configurations required manual updates of IP addresses in network elements, leading to operational complexity, scalability issues, and increased risk of errors during network expansions or failures. The primary motivation was to enable automated, dynamic discovery and selection of network functions, which is essential for load balancing, redundancy, and efficient resource utilization. DNS provides a standardized, scalable mechanism for service and node discovery across the core network, supporting features like APN resolution, PGW/SMF selection, and inter-operator roaming. It abstracts the underlying network topology, allowing operators to deploy and relocate network functions without reconfiguring every dependent element. This flexibility is crucial for the evolution towards cloud-native, virtualized networks and 5G's service-based architecture, where network functions can be instantiated and scaled elastically. DNS also facilitates the implementation of advanced traffic steering policies, network slicing, and multi-vendor interoperability by providing a common resolution framework.

Classification

Part ofFQDN
Specific typesEASDFNAPTRTLD
Related approachesAPNPGWSMF

Detected Changes Across Releases

from 3GPP Change Requests

Specific changes extracted from the „Change history“ tables of 3GPP specifications (20 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.

Rel-15 1 change

In Release 15, 3GPP introduced new DNS records to enable the selection of a network node with a specific network capability, particularly for the Dedicated Core Network feature. This enhancement allows the DNS function to resolve queries based on the required network capability, directing user equipment to an appropriate core network node. The specific technical mechanism involves defining new DNS record types to carry the network capability information for node selection.

  • DNS records for selecting a node with a network capability in a Dedidated Core Network TS 29.303CR0109
Rel-16 5 changes

In Release 16, the enhancements for DNS included provisioning DNS server security information to the UE and defining DNS procedures to support Ethernet PDN types. It also introduced mechanisms for using a Fully Qualified Domain Name (FQDN) for N3IWF selection to enable a UE to access PLMN services via an SNPN and vice-versa.

  • Provisioning of DNS server security information to the UE TS 24.501CR2345
  • N3IWF FQDN configured in a UE to support access to PLMN/SNPN services via SNPN/PLMN TS 24.502CR0079
  • Provisioning of DNS server security information to the UE-25.401 TS 24.501CR2483
  • FQDN for N3IWF selection to access PLMN services via an SNPN TS 24.502CR0102
  • DNS procedures to support Ethernet PDN TS 29.303CR0121
Rel-17 6 changes

In Release 17, new DNS-related enhancements included the ability for (re)configuring DNS server addresses and the introduction of a UE capability for DNS server security information. The release also specified a DNS procedure to resolve the Alternative PGW-C/SMF FQDN and allowed for the use of a USS FQDN as a service-level-AA server address. Furthermore, clarifications were provided on TAC determination for an FQDN.

  • (Re)configuring DNS server addresses TS 24.501CR3385
  • DNS server security information UE capability TS 24.501CR3696
  • USS FQDN as service-level-AA server address TS 24.501CR4175
  • Clarification on TAC determination for FQDN TS 24.502CR0191
  • DNS procedure to resolve the Alternative PGW-C/SMF FQDN TS 29.303CR0135
  • Align examples for DNs and URIs in clause 4.2 with object class naming conventions TS 32.158CR0053
Rel-18 6 changes

In Release 18, the DNS function was enhanced with new security information for DNS servers and a new prefixed FQDN mechanism for N3IWF selection. Corrections and clarifications were made to the procedures for DNS over (D)TLS and for using DNS to obtain a target UE via a UE-to-UE relay. Additionally, a correction was applied to the USS FQDN.

  • DNS server security information TS 24.302CR0729
  • Prefixed OI/TAI Identifier FQDN for N3IWF selection TS 24.502CR0223
  • Correction to DNS over (D)TLS TS 24.501CR5726
  • Remove NOTE on DNS over (D)TLS TS 24.501CR6244
  • Clarification on using DNS to obtain target end UE via UE-to-UE relay TS 24.554CR0603
  • Correction on USS FQDN TS 24.501CR4721
Rel-19 2 changes

In Release 19, the enhancements for the DNS function specifically support 5G ProSe (Proximity Services) by enabling DNS-based discovery of a target User Equipment in a multi-hop Layer 3 UE-to-UE relay procedure. Furthermore, the release introduces the capability to associate a DNS entry with the specific Relay Service Code (RSC) used for the layer-3 UE-to-UE relay operation.

  • DNS-based discovery of target 5G ProSe end UE in 5G ProSe multi-hop L3 U2U relay procedure TS 24.554CR0702
  • Associating the DNS entry with the used RSC for layer-3 UE-to-UE relay TS 24.554CR0714

Explore further

Broader topics and technologies where DNS plays a role.

Topics
OAM (Operations & Maintenance)Authentication (5G-AKA, EAP)Service Based ArchitectureEPC (Evolved Packet Core)Mission Critical (MCPTT)Roaming & Interconnect
Technologies
5G

Defining Specifications

3GPP specifications that define or reference DNS, with the latest known release. Sourced from the 3GPP document catalog — see methodology.

SpecificationTitleRelease
TR 21.905 vj00 3GPP Technical Terms and Definitions Rel-19
TR 22.975 v1310 UMTS Numbering and Addressing Requirements Rel-4
TS 23.060 vj00 GPRS Service Description Stage 2 Rel-19
TS 23.140 v1600 MMS Non-Realtime Service Definition Rel-6
TS 23.228 vj50 IMS Stage-2 Service Description Rel-19
TS 23.234 vd10 3GPP-WLAN Interworking Index Rel-13
TS 23.236 vj00 Intra Domain Connection of RAN Nodes to Multiple CN Nodes Rel-19
TS 23.271 vj00 LCS Stage 2 Specification Rel-19
TS 23.327 vd10 3GPP-WLAN Mobility Stage 2 Description Rel-13
TS 23.722 vf10 Common API Framework (CAPIF) for 3GPP Northbound APIs Rel-15
TR 23.758 vh00 Study on Edge Application Architecture Rel-17
TR 23.976 vj00 Push Service Requirements Analysis Rel-19
TR 23.981 vj00 IPv4 IMS Interworking and Migration Study Rel-19
TS 24.228 v1500 IP Multimedia Call Control Signaling Flows Rel-5
TS 24.229 vj50 IMS call control protocol based on SIP and SDP Rel-19
TS 24.234 vc20 3GPP-WLAN Interworking Network Selection Rel-12
TS 24.302 vj00 Access to EPC via non-3GPP networks; Stage 3 Rel-19
TS 24.501 vj50 5G NAS Protocols Specification Rel-19
TS 24.502 vj20 5G Core Access via Non-3GPP Networks; Stage 3 Rel-19
TS 24.525 vj00 Business Trunking Architecture & Requirements Rel-19
TS 24.543 vj50 SEAL Data Delivery Management Protocol Rel-19
TS 24.554 vj40 5G Proximity Services (ProSe) Protocols Rel-19
TS 24.802 vc10 IMS II-NNI Traversal Scenario Determination Study Rel-12
TS 26.247 vj00 3GPP Progressive Download & DASH over HTTP Rel-19
TS 26.512 vj10 5G Media Streaming Protocols & APIs Rel-19
TS 26.802 vj20 Multicast Enhancements for 5G Media Streaming Rel-19
TR 26.803 vh00 5G Media Streaming Extensions for Edge Processing Rel-17
TS 26.804 vj10 5G Media Streaming Extensions Study Rel-19
TR 26.805 vh01 Study on Media Production over 5G NPN Systems Rel-17
TS 26.891 vg00 Media Distribution Services in 5G System Rel-16
TR 26.928 vj00 Study on eXtended Reality (XR) in 5G Rel-19
TR 26.944 vj00 QoE, ESQoS and SQoS metrics for 3G multimedia services Rel-19
TS 27.060 vj00 TE-MT Interworking for Packet Domain Rel-19
TS 28.314 vk00 Management and Orchestration - Plug and Connect Rel-20
TS 29.061 vj00 Packet Domain Interworking for PLMN Rel-19
TS 29.161 vc00 3GPP-WLAN Interworking Requirements Rel-12
TS 29.201 vj00 RESTful Rx Interface for AF-PC Communication Rel-19
TS 29.303 vj10 DNS Procedures for Evolved Packet System Rel-19
TS 29.333 vj00 MRFC-MRFP Mp Interface Protocol Rel-19
TS 29.368 vj00 Tsp Reference Point Stage 3 Specification Rel-19
TS 29.819 vd00 Diameter Base Protocol Update Analysis Rel-13
TS 32.101 vj00 Management principles and high-level requirements Rel-19
TS 32.158 vk00 Management and Orchestration REST Solution Sets Rel-20
TS 32.300 vj00 3GPP Network Resource Naming Convention Rel-19
TS 32.501 vj00 Self-Configuration of Network Elements Concepts Rel-19
TS 32.502 vj00 Self-Configuration IRP Information Service Rel-19
TS 32.583 vj00 HNB OAM&P Procedure Flows for Type 1 Interface Rel-19
TS 32.593 vj00 HeNB OAM&P Procedure Flows for Type 1 Interface Rel-19
TS 32.833 vb00 Converged OSS End-to-End Management Study Rel-11
TS 33.222 vj00 Secure HTTP Access in GAA Rel-19
TS 33.320 vj00 H(e)NB Subsystem Security Architecture Rel-19
TR 33.739 vi10 Study on security enhancement of support for Rel-18
TS 33.823 vc20 GBA Web Browser Integration Study Rel-12
TS 43.318 vj00 Generic Access Network (GAN) Stage 2 Rel-19
TR 43.902 vj00 GAN Enhancements Feasibility Study Rel-19
TS 44.318 vj00 Generic Access Network (GAN) Interface Procedures Rel-19