Handling IDNs: Legacy TLD vs New gTLD Technical Considerations

Internationalized Domain Names have played a significant role in expanding internet accessibility by allowing domain names to be registered in scripts other than Latin characters. This has enabled a more inclusive online presence for speakers of languages such as Arabic, Chinese, Cyrillic, and many others. However, the implementation and management of IDNs have presented technical challenges, particularly in ensuring compatibility, security, and stability across different top-level domains. Legacy TLDs such as com, net, and org have had to adapt their long-established infrastructures to accommodate IDNs, whereas new gTLDs were introduced with IDN capabilities as a foundational feature. The technical considerations involved in handling IDNs differ between these two groups, influencing everything from encoding standards to DNS resolution and security mechanisms.

Legacy TLDs were initially designed to support only ASCII-based domain names using the traditional Latin character set. When IDNs were first introduced, legacy registries faced the challenge of retrofitting their existing infrastructure to handle Unicode characters while maintaining backward compatibility with systems that only supported ASCII. The solution came in the form of Punycode, an encoding mechanism that translates Unicode characters into an ASCII-compatible format that can be processed by the Domain Name System. For example, the domain name “例子.com” (which uses Chinese characters) is stored in the DNS as “xn--fsq.com.” This approach allows IDNs to coexist within the existing DNS framework, but it introduced additional complexity in domain management, particularly regarding normalization, display consistency, and user experience.

New gTLDs, launched under ICANN’s new domain expansion program, were designed with IDN support as a core functionality. Unlike legacy TLDs that had to integrate IDNs into pre-existing systems, new gTLD operators could implement IDN capabilities from the outset, ensuring that their registries were built to handle Unicode-based registrations efficiently. Many new gTLDs were specifically created to support non-Latin scripts, including fully internationalized domain extensions such as “.онлайн” (Cyrillic for “.online”) and “.みんな” (Japanese for “everyone”). This has allowed for a more seamless integration of IDNs without the transitional issues faced by legacy registries. However, despite their advantages in native IDN support, new gTLD registries have still encountered challenges in standardizing IDN policies and ensuring consistent implementation across different languages and scripts.

One of the major technical challenges in handling IDNs is the prevention of homographic attacks, where visually similar characters from different scripts are used to create deceptive domain names. For example, the Cyrillic character “а” (U+0430) looks identical to the Latin character “a” (U+0061), which could be exploited to register domains that appear to be legitimate but actually lead to phishing sites or malicious content. Legacy TLDs, having adopted IDN support later in their operational history, implemented strict registration policies to prevent homographic spoofing, often restricting IDN registrations to single-script domains or predefined character sets that minimize visual confusion. This approach reduces the risk of abuse but also limits the flexibility of IDN domain registrations.

New gTLDs have implemented a variety of policies to address homographic security concerns, ranging from registry-level restrictions to automated script validation tools that detect and block deceptive domain registrations. Some new gTLD operators have introduced policies that allow IDNs only in specific languages, ensuring that registrants cannot mix characters from different scripts within the same domain name. Additionally, many new gTLDs have integrated machine learning-based anomaly detection systems that flag suspicious IDN registrations for further review. While these measures have helped mitigate security risks, they have also introduced challenges in ensuring that legitimate multilingual users can register domains that accurately reflect their brand or identity.

Another technical consideration in handling IDNs is DNS resolution performance and compatibility across different applications and networks. Legacy TLDs, having been built on infrastructure optimized for ASCII-based queries, had to upgrade their DNS servers to fully support IDN queries while ensuring that legacy resolvers and mail servers could still function properly. Some older software applications and email clients still struggle with IDN resolution, particularly when Punycode conversion is not properly implemented. This has led to inconsistent user experiences where an IDN may work seamlessly in one environment but fail in another. To address this, legacy TLD registries have worked closely with browser developers, email service providers, and cybersecurity organizations to promote best practices for IDN compatibility and universal acceptance.

New gTLDs, benefiting from launching in a more IDN-aware ecosystem, have been able to optimize their DNS configurations for IDN resolution from the beginning. Many operate on modern cloud-based DNS platforms that include built-in support for Unicode-based queries, reducing the need for extensive compatibility adjustments. However, new gTLD operators have still faced challenges in ensuring that IDN domains function correctly across all internet services, particularly in legacy network environments where non-ASCII domain names may not be fully supported. To improve adoption and usability, new gTLD registries have engaged in industry-wide efforts to encourage email providers, web hosting services, and content management systems to enhance their IDN compatibility.

The implementation of IDN variants is another area where technical considerations differ between legacy and new gTLDs. Many languages have multiple ways to represent the same word or phrase using different character variants, which can lead to potential conflicts or unintended domain duplications. Legacy TLD registries have approached this issue by introducing variant blocking mechanisms, where registering one IDN variant automatically prevents the registration of visually or linguistically similar variants by other parties. This helps prevent cybersquatting and domain confusion but can also lead to challenges in cases where legitimate users may want access to different variants of the same domain name.

New gTLDs, operating under ICANN’s IDN Variant Program, have adopted more sophisticated variant management strategies that allow for controlled activation of IDN variants under predefined policies. Some new gTLD registries use bundling techniques, where multiple variants of an IDN are linked to a single registration, ensuring that all relevant versions of a domain name are assigned to the same registrant. This approach provides better protection against domain name abuse while maintaining linguistic and cultural relevance for IDN users. However, managing IDN variants at scale requires complex registry policies and ongoing collaboration with language experts to ensure that variant rules align with linguistic best practices.

Despite the advancements in IDN handling, both legacy and new gTLDs continue to face challenges in driving broader adoption and ensuring seamless user experiences. Legacy TLDs have had to invest in continuous infrastructure upgrades to maintain compatibility with evolving IDN standards, while new gTLDs have focused on refining policies and security measures to accommodate diverse scripts and languages. As IDN adoption grows, the need for standardized technical solutions, improved application support, and enhanced security frameworks will remain crucial in ensuring that IDNs fulfill their promise of making the internet truly multilingual and globally accessible.

The contrasting technical approaches of legacy and new gTLDs in handling IDNs reflect the broader evolution of internet infrastructure, where long-established systems must adapt to new demands while newer architectures are designed with inclusivity and scalability in mind. As more users register and use IDNs, continued collaboration between registries, registrars, technology providers, and policy organizations will be essential in overcoming the remaining technical and operational hurdles. The future of IDNs will depend on ongoing improvements in DNS security, application compatibility, and user education, ensuring that domain names can effectively represent the linguistic and cultural diversity of the global internet community.

Internationalized Domain Names have played a significant role in expanding internet accessibility by allowing domain names to be registered in scripts other than Latin characters. This has enabled a more inclusive online presence for speakers of languages such as Arabic, Chinese, Cyrillic, and many others. However, the implementation and management of IDNs have presented technical…