RFC 8822 | 5G WWC User Plane Encapsulation | April 2021 |
Allan, et al. | Informational | [Page] |
As part of providing wireline access to the 5G Core (5GC), deployed wireline networks carry user data between 5G residential gateways and the 5G Access Gateway Function (AGF). The encapsulation method specified in this document supports the multiplexing of traffic for multiple PDU sessions within a VLAN-delineated access circuit, permits legacy equipment in the data path to inspect certain packet fields, carries 5G QoS information associated with the packet data, and provides efficient encoding. It achieves this by specific points of similarity with the Point-to-Point Protocol over Ethernet (PPPoE) data packet encapsulation (RFC 2516).¶
This document is not an Internet Standards Track specification; it is published for informational purposes.¶
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are candidates for any level of Internet Standard; see Section 2 of RFC 7841.¶
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc8822.¶
Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved.¶
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Converged 5G ("fifth generation") wireline networks carry user data between 5G residential gateways (5G-RGs) and the 5G Access Gateway Function (identified as a Wireline-AGF (W-AGF) by 3GPP in [TS23316]) across deployed access networks based on Broadband Forum [TR101] and [TR178]. This form of wireline access is considered to be trusted non-3GPP access by the 5G system.¶
The transport encapsulation used needs to meet a variety of requirements, including the following:¶
A data encapsulation that uses a common Ethertype and has certain fields appearing at the same offset as the PPPoE data encapsulation [RFC2516] can address these requirements. This data encapsulation is referred to as the 5G WWC user plane encapsulation or 5WE. Currently deployed access nodes do not police the VER, TYPE, or CODE fields of an RFC 2516 PPPoE header and only perform limited policing of stateful functions with respect to the procedures documented in RFC 2516. Therefore, these fields have a different definition for 5WE and are used to:¶
This 5G-specific redesign of fields not inspected by deployed equipment results in an encapsulation uniquely applicable to the requirements for the communication of PDU session traffic between the subscriber premises and the 5G system over wireline networks. The 6-byte RFC 2516 data packet header followed by a 2-byte PPP protocol ID is also the most frugal of the encapsulations that are currently supported by legacy access equipment that could be adapted to meet these requirements.¶
This encapsulation is expected to be used in environments where RFC 2516 is deployed. Therefore, implementations MUST examine the version number:¶
In both cases, frames for the supported version number should have session IDs corresponding to established sessions for the respective protocol models. A 5WE frame with an unrecognized session ID MUST be silently discarded.¶
This encapsulation may have MTU issues when used for Ethernet multiplexing in networks where the underlying Ethernet payload is limited to 1500 bytes.¶
This encapsulation is not suitable for other network environments, e.g., general use over the public Internet.¶
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.¶
This document uses the following acronyms:¶
The Ethernet payload [IEEE802] for PPPoE [RFC2516] is indicated by an Ethertype of 0x8864. The information following that Ethertype uses a value of 2 in the VER field for the repurposing of the PPPoE data encapsulation as the 5G WWC user plane encapsulation (5WE). The 5G WWC user plane encapsulation is structured as follows:¶
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | VER | TYPE | QFI |R|0| SESSION_ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LENGTH | PROTOCOL ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | DATA PAYLOAD ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-¶
The description of each field is as follows:¶
The 16-bit identifier of the data payload type encoded using values from the IANA "PPP DLL Protocol Numbers" registry <https://www.iana.org/assignments/ppp-numbers>.¶
The following values are valid in this field for 5G WWC use:¶
Packets received that do not contain one of the above protocol IDs are silently discarded.¶
5G NAS procedures used for session life-cycle maintenance employ ciphering and integrity protection [TS23502]. They can be considered a more secure session establishment discipline than existing RFC 2516 procedures, at least against on-path attackers. The design of the 5WE encapsulation will not circumvent existing anti-spoofing and other security procedures in deployed equipment. The existing access equipment will be able to identify fields that they normally process and police as per existing RFC 2516 traffic.¶
Therefore, the security of a fixed access network using 5WE will be equivalent or superior to current practice.¶
5WE-encapsulated traffic is used on what the 5GC considers to be trusted non-3GPP interfaces; therefore, it is not ciphered. 5WE is not suitable for use over an untrusted non-3GPP interface.¶
The security requirements of the 5G system are documented in [TS33501].¶
IANA has created the following registry on the "Point-to-Point (PPP) Protocol Field Assignments" page:¶
VER | Description | Reference |
---|---|---|
0 | Reserved | [RFC8822] |
1 | PPPoE | [RFC2516] |
2 | 5G WWC User Plane Encapsulation | [RFC8822] |
3-15 | unassigned |
IANA has added this document as an additional reference for Ethertype 0x8864 in the "Ether Types" registry on the IANA "IEEE 802 Numbers" page <https://www.iana.org/assignments/ieee-802-numbers>.¶
This memo is a result of comprehensive discussions by the Broadband Forum's Wireline Wireless Convergence Work Area. The authors would also like to thank Joel Halpern and Dirk Von Hugo for their detailed review of this document.¶