How ENS Domains Work: A Complete Technical Guide to Ethereum Name Service

Understanding the Core Architecture of ENS

The Ethereum Name Service (ENS) transforms long hexadecimal wallet addresses into human-readable names like alice.eth. Unlike the Domain Name System (DNS) that maps domain names to IP addresses, ENS maps names to blockchain addresses, content hashes, and metadata through smart contracts on Ethereum. At its foundation, ENS consists of two primary smart contracts: the ENS Registry and the Resolver.

The ENS Registry is a single smart contract that stores a list of all domains and subdomains, along with their owner, resolver, and Time-to-Live (TTL). Ownership is managed via ERC-721 compliant NFTs, meaning each .eth domain is a unique non-fungible token you can transfer or sell. The Resolver contract handles the actual translation: when someone queries vitalik.eth, the registry points to a resolver that returns the associated Ethereum address. This separation allows for flexible resolution logic — a single domain can resolve to different addresses depending on the context (e.g., ETH transfers vs. IPFS content).

ENS uses a hierarchical naming system similar to DNS. The root node is owned by the ENS DAO, which governs the .eth top-level domain. Below that, domain owners can create unlimited subdomains (e.g., pay.alice.eth) without paying additional registration fees. Each subdomain operates as an independent NFT with its own ownership and resolver.

The Registration Process: From Auction to Permanent Ownership

ENS domains follow a distinct registration lifecycle designed to prevent squatting and ensure fair distribution. Here’s the technical breakdown:

1. Availability Check: Before starting, verify the domain is not registered. ENS uses a commit-reveal scheme to prevent front-running during registration. You hash the domain name and your address, then submit a commit transaction. After waiting at least 60 seconds (the commit delay), you proceed to step 2.
2. Reveal and Register: Submit a second transaction containing the actual domain name and the same secret used in the commit. The smart contract verifies the hash matches, then mints the ERC-721 token and sets the registration period (typically 1 year minimum). The registration fee consists of a one-time upfront cost plus annual renewal fees based on character length.
3. Set Resolver and Records: After registration, set a resolver contract for your domain. Most users deploy the default public resolver, then add records: ETH address, BTC address, IPFS content hash, text records (email, URL, social handles), and more. Each record type costs additional gas.

Pricing follows a tiered model: domains with 3+ characters cost roughly $5/year in ETH, while 3-character domains (e.g., abc.eth) cost approximately $160/year due to scarcity. Premium 1-2 character names only become available via an English auction when released by the ENS DAO. For collectors seeking shorter addresses, the ENS 3-digit names market offers an alternative path through secondary trading rather than direct registration.

Renewal is critical — if a domain expires, it enters a 90-day grace period where only the owner can renew. After that, a 28-day "premium" period follows where anyone can claim it by paying the registration cost plus a premium fee that decays to zero. Understanding this lifecycle prevents accidental loss of domains.

Resolution Mechanics: How Lookups Work Under the Hood

When a wallet or dApp needs to resolve alice.eth, the process involves three smart contract calls:

1. Node Derivation: The domain name is hashed using a specific algorithm (namehash) that converts human-readable names to a fixed-length bytes32 node. Example: namehash('alice.eth') produces a unique identifier.
2. Registry Query: The ENS Registry is called with this node. It returns the resolver contract address and the owner. If the domain is unregistered, the resolver returns address(0).
3. Resolver Call: The caller then queries the resolver contract, typically calling addr(bytes32 node) for ETH address resolution or text(bytes32 node, string key) for metadata. The resolver returns the stored value or reverts if the record doesn't exist.

This two-step architecture enables upgrades without changing the registry. If a better resolver standard emerges, existing domains can point to new resolver contracts without re-registering. Popular resolvers include the Public Resolver (supports all common records) and reverse resolvers that map addresses back to ENS names.

Gas costs vary: a simple ETH address resolution costs ~40,000 gas on Ethereum mainnet, while resolving multiple records (e.g., ETH + BTC + Avatar) can cost 100,000+ gas. Layer 2 solutions and off-chain resolvers (ENSIP-10) are reducing these costs, but for high-frequency applications, caching resolved names in off-chain databases remains standard practice.

Subdomains, Records, and Advanced Features

ENS supports a rich ecosystem of record types beyond simple address resolution. Each domain can store:

• Cryptocurrency addresses: Over 50 supported chains including BTC, LTC, DOGE, and all EVM-compatible chains. Each uses its own coin type identifier (e.g., 60 for ETH, 0 for BTC).
• Content hashes: IPFS or Swarm content hashes enable decentralized websites. A browser with ENS support can load alice.eth as an IPFS-hosted site.
• Text records: Key-value pairs for metadata like email, url, avatar, description. The ENS Avatar standard (ERC-721 metadata) lets NFTs serve as profile pictures.
• ABI records: Store contract ABIs for enabling human-readable contract interactions.

Subdomains provide powerful delegation: as alice.eth owner, you can mint pay.alice.eth and set its resolver to point to a different address. This enables hierarchical control without paying registration fees — ideal for organizations managing multiple wallets. However, the parent domain owner retains the ability to reclaim the subdomain if desired.

ENS also integrates with DNS names through the ENSDNSSEC oracle. Owners of traditional DNS domains (like example.com) can import them to ENS by proving ownership via DNSSEC. This bridges Web2 and Web3 identity, allowing example.com to resolve to an Ethereum address.

Governance and the Future of ENS

The ENS system is governed by the ENS DAO, a decentralized autonomous organization that controls the registry's root node and the treasury of registration fees. Token holders (ENS tokens) vote on proposals ranging from fee adjustments to protocol upgrades. Active participation remains key to shaping the ecosystem — you can Join the ENS DAO to contribute to governance decisions that determine the future of naming on Ethereum.

Key upgrades under discussion include:

• Gas optimization via EIP-3668: Off-chain lookups (CCIP Read) allow resolvers to serve data from Layer 2 or off-chain databases, reducing mainnet costs by up to 90%.
• Multi-chain resolution: Expanding ENS to work across all EVM and non-EVM chains without requiring separate registrations.
• DNS integration expansion: More TLDs beyond .com and .org as DNSSEC adoption grows.
• Name wrapper contracts: Standardizing how domains and subdomains interact, including explicit expiration dates for subdomains.

For developers, building with ENS requires understanding these tradeoffs: mainnet security vs. L2 speed, public resolver simplicity vs. custom resolver flexibility, and the cost of storing records on-chain vs. off-chain. The ENS documentation provides reference implementations for the namehash algorithm and resolver interface (EIP-137).

As Web3 adoption matures, ENS is evolving from a niche naming service into infrastructure — integrated by wallets (MetaMask, Rainbow), dApps (Uniswap, OpenSea), and browsers (Brave, Chrome via plugins). Understanding how it works at the protocol level is essential for anyone building or investing in decentralized identity solutions.