Resource Records for EUI-48 and EUI-64 Addresses in the DNS

The Domain Name System (DNS) is described in and . This base specification defines many resource record (RR) types, and subsequent specifications have defined others. Each defined RR type provides a means of encoding particular data in the DNS. 48-bit Extended Unique Identifier (EUI-48) and 64-bit Extended Unique Identifier (EUI-64) are address formats specified by the IEEE for use in various layer-2 networks, e.g., Ethernet. This document defines two new RR types, EUI48 and EUI64, for encoding EUI-48 and EUI-64 addresses in the DNS. There are potentially severe privacy implications resulting from the indiscriminate publication of link-layer addresses in the DNS (see ). This document recommends that EUI-48 or EUI-64 addresses SHOULD NOT be published in the public DNS. This document specifies an interoperable encoding of these address types for use in private DNS namespaces, where the privacy implications can be constrained and mitigated.

This document uses capitalized keywords such as MUST and MAY to describe the requirements for using the registered RR types. The intended meaning of those keywords in this document are the same as those described in . Although these keywords are often used to specify normative requirements in IETF Standards, their use in this document does not imply that this document is a standard of any kind.

The EUI48 resource record (RR) is used to store a single EUI-48 address in the DNS. The Type value for the EUI48 RR is 108 (decimal). The EUI48 RR is class independent. The EUI48 RR has no special Time-to-Live (TTL) requirements.

The RDATA for an EUI48 RR consists of a single, 6-octet Address field, encoded in network (big-endian) order.

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | EUI-48 Address | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The Address field MUST be represented as six two-digit hexadecimal numbers separated by hyphens. The hexadecimal digits "A" through "F" MAY be represented in either upper or lower case.

The following EUI48 RR stores the EUI-48 unicast address 00-00-5e-00-53-2a.

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

The EUI64 RR is used to store a single EUI-64 address in the DNS. The Type value for the EUI64 RR is 109 (decimal). The EUI64 RR is class independent. The EUI64 RR has no special TTL requirements.

The RDATA for an EUI64 RR consists of a single, 8-octet Address field, encoded in network (big-endian) order.

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | EUI-64 Address | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The Address field MUST be represented as eight two-digit hexadecimal numbers separated by hyphens. The hexadecimal digits "A" through "F" MAY be represented in either upper or lower case.

The following EUI64 RR stores the EUI-64 unicast address 00&nbhy;00&nbhy;5e&nbhy;ef&nbhy;10&nbhy;00&nbhy;00&nbhy;2a.

host.example. 86400 IN EUI64 00-00-5e-ef-10-00-00-2a

Canadian cable Internet subscribers are assigned IP addresses using DHCP, using a DHCP server operated by a cable company. In the case where a cable company provides last-mile connectivity to a subscriber on behalf of a third-party company (reseller), the DHCP server assigns addresses from a pool supplied by the reseller. The reseller retains knowledge of the EUI-48 address of the DOCSIS modem supplied to the subscriber but has no direct knowledge of the IP addresses assigned. In order for the reseller to be able to map the IP address assigned to a subscriber to that EUI-48 address (and hence to the subscriber identity), the cable company can make available information from the DHCP server that provides (EUI-48, IP) address mapping. Cable companies in Canada are required to make this address mapping available using the DNS. Zones containing the relevant information are published on DNS servers, access to which is restricted to the resellers corresponding to particular sets of subscribers. Subscriber address information is not published in the public DNS. Existing DNS schemas for the representation of (EUI-48, IP) mapping used by Canadian cable companies are varied and inefficient; in the absence of an RR type for direct encoding of EUI-48 addresses, addresses are variously encoded into owner names or are published in TXT records. The specification in this document facilitates a more efficient, consistent, and reliable representation of (EUI-48, IP) mapping than was previously available.

The specification of the new RR types in this document has no effect on the address resolution behavior of any previously existing network processes or protocols. Proposals or specifications to modify or augment address resolution processes or protocols by making use of these RR types should specify how any address conflicts or use of multiple EUI48/EUI64 RRs are handled.

IANA has assigned the RR type value 108 (decimal) for EUI48 and 109 (decimal) for EUI64. The corresponding entries in the "Resource Record (RR) TYPEs" subregistry (http://www.iana.org/assignments/dns-parameters/) match the following data: Type Value Meaning Reference EUI48 108 an EUI-48 address this document EUI64 109 an EUI-64 address this document

There are privacy concerns with the publication of link-layer addresses in the DNS. EUI-48 and EUI-64 addresses with the Local/Global bit zero (referred to in as the universal/local bit) are intended to represent unique identifiers for network connected equipment, notwithstanding many observed cases of duplication due to manufacturing errors, unauthorized use of Organizationally Unique Identifiers (OUIs), and address spoofing through configuration of network interfaces. Publication of EUI-48 or EUI-64 addresses in the DNS may result in privacy issues in the form of unique trackable identities that in some cases may be permanent. For example, although IP addresses and DNS names for network devices typically change over time, EUI-48 and EUI-64 addresses configured on the same devices are normally far more stable (in many cases, effectively invariant). Publication of EUI-48 addresses associated with user devices in a way that could be mapped to assigned IP addresses would allow the behavior of those users to be tracked by third parties, regardless of where and how the user's device is connected to the Internet. This might well result in a loss of privacy for the user. The publication of EUI-48 or EUI-64 addresses associated with deployed equipment, using the mechanism described in this document or any other mechanism, has the potential to facilitate Media Access Control (MAC) cloning -- that is, facilitate link-layer attacks against deployed devices, e.g., to disrupt service or intercept data. These concerns can be mitigated by restricting access to DNS zones containing EUI48 or EUI64 RRs to specific, authorized clients and by provisioning them in DNS zones that exist in private namespaces only. This document recommends that EUI-48 or EUI-64 addresses SHOULD NOT be published in the public DNS.

The author acknowledges the contributions of Olafur Gudmundsson, Mark Smith, Andrew Sullivan, Roy Arends, Michael StJohns, Donald Eastlake III, Randy Bush, and John Klensin.