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EUI48 record

Stores an IEEE EUI-48 link-layer identifier in DNS for controlled private-namespace mappings and operational inventory workflows.

Written and maintained by Ben Ennis

Last reviewed July 27, 2026 · How we verify this

Zone-file example

device.example. 86400 IN EUI48 00-00-5e-00-53-2a

Typical uses

  • Mapping a managed cable modem or network device identifier to an address
  • Supporting restricted inventory lookups in a private DNS namespace
  • Replacing ad hoc EUI-48 encodings in owner names or TXT records
  • Correlating a device identity with DHCP or access-network records

When it breaks, check

  • Presentation format is exactly six two-digit hexadecimal fields separated by hyphens
  • The record does not alter ordinary address resolution or create an A or AAAA answer
  • Multiple records require an explicit consumer policy for conflicts and selection
  • Do not publish customer or device identifiers in public DNS; use an access-controlled private zone

What the EUI48 record does

An EUI48 record gives a consistent DNS representation to a six-octet link-layer identifier. An operator can use it in a private namespace where a DHCP or access provider needs to associate a managed device with an assigned IP address. The record is an inventory or correlation primitive; clients still need an A, AAAA, PTR, or provider-specific lookup to obtain an address.

The identifier is encoded in network byte order and shown as six hexadecimal pairs separated by hyphens. EUI48 does not make an address routable, prove device ownership, or update a lease. If an application consumes several records, its specification must define duplicate and conflict behavior rather than relying on DNS answer order.

Zone-file and wire format

EUI48 RDATA is a single six-octet address. In a zone file, write six two-digit hexadecimal fields separated by hyphens; uppercase and lowercase hexadecimal are both allowed. The bytes are in network order. The value below is an illustrative unicast identifier and is not a recommendation to publish a production device identifier.

device.example. 86400 IN EUI48 00-00-5e-00-53-2a

Common uses

Use EUI48 only for an explicit operational mapping in a private, access-controlled DNS zone. A cable or access provider can use it beside DHCP records when a reseller knows a modem identifier but needs a controlled DNS lookup for the assigned address. Keep the data source, retention period, and authorized readers documented. For ordinary host discovery, use A, AAAA, or PTR instead.

Troubleshooting

When a lookup fails, first confirm that the client can reach the private authoritative zone and that the query name is correct. Then verify the six-field syntax, compare the record with the inventory or DHCP source, and check whether more than one EUI48 value was published. A successful EUI48 response does not prove that an address mapping is current. Investigate stale TTLs and the separate address record or database. If the identifier appears in public DNS, remove it and review zone access, logs, and any downstream copies.

dig device.example EUI48 +noall +answer

# Query the authoritative private server without recursion.
dig @ns1.example.net device.example EUI48 +norecurse +noall +answer

The defining RFC

EUI48 is defined by RFC 7043, section 3, which specifies the six-octet presentation format and private-namespace guidance. Its privacy and security considerations are in section 8. See the IANA DNS Parameters registry for the assigned type.

Reference and tooling

Every record type and its assigned numeric value is listed in theIANA DNS Parameters registry. To query a live zone from the browser, use theDNS lookup tool. If the record you are chasing is TLS-related, the TLS inspector andCertificate Transparency lookup are usually the next two stops.

Other record types