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About DNS discovery

Understand how a node retrieves peer connection details from an ENR tree published in DNS.​

Built upon the foundation of EIP-1459: Node Discovery via DNS, DNS Discovery allows the retrieval of an ENR tree from the TXT field of a domain name. This approach enables the storage of essential node connection details, including IP, port, and multiaddr. This bootstrapping method allows anyone to register and publish a domain name for the network, promoting increased decentralisation.

How DNS discovery works​

sequenceDiagram
    Node->>DNS Server: (1) Lookup TXT example.com
    DNS Server-->>Node: (2) enrtree-root:v1 e=U3...3Y ...
    Node->>DNS Server: (3) Lookup TXT U3...3Y.example.com
    DNS Server-->>Node: (4) enrtree-branch:DU...VQ,J3..HU,IC...WE
    Node->> DNS Server: (5) Lookup TXT DU...VQ.example.com
    DNS Server-->>Node: (6) enr:-M-4QLdAB-Kyz...Wt1Mg8
    Node ->> Node: (7) Decode ENR: Peer's connection details
  1. DNS lookup query to retrieve TXT data stored on example.com domain.
  2. enrtree-root is returned, and the value of e is the enr-root, the root hash of the node subtree.
  3. DNS lookup query to retrieve TXT data stored on <enr-root>.example.com domain.
  4. enrtree-branch is returned; this tree contains hashes of node subtrees.
  5. DNS lookup query to retrieve TXT data stored on DU...VQ.example.com domain, the first leaf of enrtree-branch.
  6. enr record is returned.
  7. Returned value is decoded, and peer connection details such as IP address and port are learned.

Pros and cons​

Pros:

  • Low latency, low resource requirements.
  • Easy bootstrap list updates by modifying the domain name, eliminating the need for code changes.
  • Ability to reference a larger list of nodes by including other domain names in the code or ENR tree.

Cons:

  • Vulnerable to censorship: Domain names can be blocked or restricted.
  • Limited scalability: The listed nodes are at risk of being overwhelmed by receiving all queries. Also, operators must provide their ENR to the domain owner for listing.