Network Working Group D. Eastlake Internet-Draft Independent Intended status: Standards Track 8 June 2026 Expires: 10 December 2026 MAC Address for Layer 3 Link Local Discovery Protocol (LLDP) draft-eastlake-lldp-mac-06 Abstract IEEE 802 has defined a number of protocols which can operate between adjacent Ethernet stations at Layer 2, including bridges, and may be useful between Layer 3 aware stations such as IP routers and hosts. An example is the Link Layer Discovery Protocol (IEEE Std 802.1AB, LLDP). This document specifies a MAC address that can be used for this purpose for interoperability despite intervening bridges. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 10 December 2026. Copyright Notice Copyright (c) 2026 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Eastlake Expires 10 December 2026 [Page 1] Internet-Draft L3 LLDP MAC Address June 2026 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Notations Used in This Document . . . . . . . . . . . . . 2 2. Network Layers and MAC Addresses . . . . . . . . . . . . . . 3 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 4. Security Considerations . . . . . . . . . . . . . . . . . . . 5 5. Normative References . . . . . . . . . . . . . . . . . . . . 5 6. Informative References . . . . . . . . . . . . . . . . . . . 5 Appendix A. IANA EUI-48 Assignment Request . . . . . . . . . . . 6 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction IEEE 802 [IEEE802] has defined a number of protocols which operate between adjacent Ethernet stations at Layer 2, including bridges, such as the Link Layer Discovery Protocol ([IEEE802.1AB] LLDP) and the Link Aggregation Control Protocol ([IEEE802.1AX] LACP). LLDP and other such protocols may be useful between adjacent Layer 3 [ISO] aware stations such as IP routers and hosts. This document specifies a MAC address that can be used for that purpose despite intervening bridges. 1.1. Notations Used in This Document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. In this document the terms/acronyms listed below have the indicated meaning: "LACP" Link Aggregation Control Protocol [IEEE802.1AX]. "Layer 2" Layer 2 in the ISO model [ISO]. "Layer 3" Layer 3 in the ISO model [ISO]. "LLDP" Link Layer Discovery Protocol [IEEE802.1AB]. "MAC" Media Access Control [RFC9542] (not Message Authentication Code). "PDU" Protocol Data Unit. Eastlake Expires 10 December 2026 [Page 2] Internet-Draft L3 LLDP MAC Address June 2026 2. Network Layers and MAC Addresses LLDP [IEEE802.1AB] is a Layer 2 [ISO] protocol providing for the unacknowledged announcement of information by an Ethernet station to other stations on the same Ethernet link. There are proposals, such as [LLDP], for the use of LLDP between L3 aware stations such as IP adjacent routers. As illustrated in the figure below, uses of LLDP and similar protocols between Ethernet stations have a scope of adjacency controlled by the multicast destination MAC address [RFC9542] of the Ethernet frame used to transmit the LLDP PDU. * Customer bridges use 0x0180C2000000 for LLDP and the like. Frames sent to that address are transparently forwarded through any lower level bridges, such as the provider bridges shown below. On the other hand, IP routers do not forward frames sent to unknown multicast addresses unless configured to do so. Thus, frames sent to this address by the customer bridge shown near the bottom of the figure will not reach either of the customer bridges shown higher up in the figure due to the intervening IP router. * Provider bridges use 0x0180C2000008 for LLDP. Frames sent to that address are transparently forwarded by lower level bridges (not shown in the figure) and are blocked by higher level bridges, such as customer bridges. They are also blocked as described in the previous point by IP routers. LLDP or similar Ethernet frames intended to be between adjacent IP routers or between a host and its first hop IP router need to avoid use of a destination MAC address that might be intercepted by any intervening bridge. The multicast destination MAC addresses used by bridges are the block from 0x0180C2000000 to 0x0180C200003F but it would be best to be conservative and avoid all addresses from 0x0180C2000000 to 0x0180C2FFFFFF. An address meeting this criterion is specified in Section 3 below and its use is RECOMMENDED. Eastlake Expires 10 December 2026 [Page 3] Internet-Draft L3 LLDP MAC Address June 2026 +-------+ | Host | +-------+ | +---------+ |L3 Router| +---------+ . \ . +---------------+ . |Customer Bridge| . +---------------+ . : \ . : +---------------+ . : |Provider Bridge| . : +---------------+ . : | . : +---------------+ . : |Provider Bridge| . : +---------------+ . : / . +---------------+ . |Customer Bridge| . +---------------+ . / +---------+ |L3 Router| +---------+ . \ . +---------------+ . |Customer Bridge| . +---------------+ . / +-------+ | Host | +-------+ Figure 1: Network Layer Bridging Example Note: The above figure is simplified. For example, where one or two customer bridges or provider bridges are shown, there could be zero or some larger number. There could also be one or more bridges between the host shown at the top of the figure and its first hop IP router. Only two levels of bridge are shown (customer and provider) but IEEE Std 802.1Q [IEEE_802.1Q_2022] specifies additional levels of bridges. Eastlake Expires 10 December 2026 [Page 4] Internet-Draft L3 LLDP MAC Address June 2026 3. IANA Considerations IANA is requested to assign a 48-bit multicast MAC address [00-00-0E- 90-00-04 suggested] under the IANA OUI for use with Link Layer Discovery Protocol and similar protocols between Layer 3 routers as per the request in Appendix A. The entry in the "IANA Multicast 48-bit MAC Addresses" registry is as follows: Addresses Usage Reference --------- -------------- --------------- [tbd] Layer 3 LLDP [this document] 4. Security Considerations Layer 2 packets can be spoofed by any entity having access to the links involved. The use of a multicast address not normally filtered by bridges can lead to wide dissemination of such packets. Consideration should be given to protecting such packets with IEEE Std 802.1AE [IEEE_802.1AE_2018] or some similar security protocol. 5. Normative References [IEEE802.1AB] 802, IEEE., "IEEE Standard for Local and metropolitan area networks - Station and Media Access Control Connectivity Discovery", IEEE Std 802.1AB-2016, 29 January 2016. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC9542] Eastlake 3rd, D., Abley, J., and Y. Li, "IANA Considerations and IETF Protocol and Documentation Usage for IEEE 802 Parameters", BCP 141, RFC 9542, DOI 10.17487/RFC9542, April 2024, . 6. Informative References Eastlake Expires 10 December 2026 [Page 5] Internet-Draft L3 LLDP MAC Address June 2026 [IEEE_802.1AE_2018] IEEE, "IEEE Standard for Local and metropolitan area networks-Media Access Control (MAC) Security", IEEE 802- 1ae-2018, DOI 10.1109/IEEESTD.2018.8585421, 21 December 2018, . [IEEE802] 802, IEEE., "IEEE 802 LAN/MAN Standards Committee", IEEE Std 802, . [IEEE802.1AX] 802, IEEE., "IEEE Standard for Local and metropolitan area networks - Link Aggregation", IEEE Std 802.1AX-2014. [IEEE_802.1Q_2022] IEEE, "IEEE Standard for Local and Metropolitan Area Networks--Bridges and Bridged Networks", IEEE 802-1q-2022, DOI 10.1109/IEEESTD.2022.10004498, 30 December 2022, . [ISO] ISO/IEC, "Information technology - Open Systems Interconnection - Basic Reference Model: The Basic Model", ISO/IEC 7498-1:1994(E), 15 June 1996. [LLDP] Lindem, A., Patel, K., Zandi, S., Haas, J., and X. Xu, "BGP Logical Link Discovery Protocol (LLDP) Peer Discovery", Work in progress, . Appendix A. IANA EUI-48 Assignment Request (not yet submitted) Applicant Name: Donald E. Eastlake 3rd Applicant Email: d3e3e3@gmail.com Applicant Telephone: +1-508-333-2270 Use Name: L3-LLDP Document: [this document] Specify whether this is an application for EUI-48 or EUI-64 identifiers: EUI-48 Size of Block requested: 1 Eastlake Expires 10 December 2026 [Page 6] Internet-Draft L3 LLDP MAC Address June 2026 Specify multicast, unicast, or both: multicast Author's Address Donald E. Eastlake 3rd Independent 2386 Panoramic Circle Apopka, Florida 32703 United States of America Email: d3e3e3@gmail.com Eastlake Expires 10 December 2026 [Page 7]