Internet-Draft CONNECT-ETHERNET October 2023
Sedeño Expires 21 April 2024 [Page]
Workgroup:
Multiplexed Application Substrate over QUIC Encryption
Internet-Draft:
draft-ietf-masque-connect-ethernet-01
Published:
Intended Status:
Standards Track
Expires:
Author:
A. R. Sedeño
Google LLC

Proxying Ethernet in HTTP

Abstract

This document describes how to proxy Ethernet frames in HTTP. This protocol is similar to IP proxying in HTTP, but for Layer 2 instead of Layer 3. More specifically, this document defines a protocol that allows an HTTP client to create Layer 2 Ethernet tunnel through an HTTP server to an attached physical or virtual Ethernet segment.

About This Document

This note is to be removed before publishing as an RFC.

The latest revision of this draft can be found at https://ietf-wg-masque.github.io/draft-ietf-masque-connect-ethernet/draft-ietf-masque-connect-ethernet.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-ietf-masque-connect-ethernet/.

Discussion of this document takes place on the MASQUE Working Group mailing list (mailto:masque@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/masque/. Subscribe at https://www.ietf.org/mailman/listinfo/masque/.

Source for this draft and an issue tracker can be found at https://github.com/ietf-wg-masque/draft-ietf-masque-connect-ethernet.

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 21 April 2024.

Table of Contents

1. Introduction

HTTP provides the CONNECT method (see Section 9.3.6 of [HTTP]) for creating a TCP [TCP] tunnel to a destination, a similar mechanism for UDP [CONNECT-UDP], and an additional mechanism for IP [CONNECT-IP]. However, these mechanisms can't carry layer 2 frames without further encapsulation inside of IP, for instance with EtherIP [ETHERIP], GUE [GUE] or L2TP [L2TP] [L2TPv3], which imposes an additional MTU cost.

This document describes a protocol for exchanging Ethernet frames with an HTTP server. Either participant in the HTTP connection can then relay Ethernet frames to and from a local or virtual interface, allowing the bridging of two Ethernet broadcast domains to establish a Layer 2 VPN. This can simplify connectivity to network-connected appliances that are configured to only interact with peers on the same Ethernet broadcast domain.

This protocol supports all existing versions of HTTP by using HTTP Datagrams [HTTP-DGRAM]. When using HTTP/2 [HTTP/2] or HTTP/3 [HTTP/3], it uses HTTP Extended CONNECT as described in [EXT-CONNECT2] and [EXT-CONNECT3]. When using HTTP/1.x [HTTP/1.1], it uses HTTP Upgrade as defined in Section 7.8 of [HTTP].

2. Conventions and Definitions

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, we use the term "Ethernet proxy" to refer to the HTTP server that responds to the Ethernet proxying request. The term "client" is used in the HTTP sense; the client constructs the Ethernet proxying request. If there are HTTP intermediaries (as defined in Section 3.7 of [HTTP]) between the client and the Ethernet proxy, those are referred to as "intermediaries" in this document. The term "Ethernet proxying endpoints" refers to both the client and the Ethernet proxy.

This document uses terminology from [QUIC]. Where this document defines protocol types, the definition format uses the notation from Section 1.3 of [QUIC]. This specification uses the variable-length integer encoding from Section 16 of [QUIC]. Variable-length integer values do not need to be encoded in the minimum number of bytes necessary.

Note that, when the HTTP version in use does not support multiplexing streams (such as HTTP/1.1), any reference to "stream" in this document represents the entire connection.

3. Configuration of Clients

Clients are configured to use Ethernet proxying over HTTP via a URL.

Examples are shown below:

https://example.org/.well-known/masque/ethernet/
https://proxy.example.org:4443/masque/ethernet/
https://proxy.example.org:4443/masque/ethernet/
https://masque.example.org/?user=bob

4. Tunnelling Ethernet over HTTP

To allow negotiation of a tunnel for Ethernet over HTTP, this document defines the "connect-ethernet" HTTP upgrade token. The resulting Ethernet tunnels use the Capsule Protocol (see Section 3.2 of [HTTP-DGRAM]) with HTTP Datagrams in the format defined in Section 6.

To initiate an Ethernet tunnel associated with a single HTTP stream, a client issues a request containing the "connect-ethernet" upgrade token.

By virtue of the definition of the Capsule Protocol (see Section 3.2 of [HTTP-DGRAM]), Ethernet proxying requests do not carry any message content. Similarly, successful Ethernet proxying responses also do not carry any message content.

Ethernet proxying over HTTP MUST be operated over TLS or QUIC encryption, or another equivalent encryption protocol, to provide confidentiality, integrity, and authentication.

4.1. Ethernet Proxy Handling

Upon receiving an Ethernet proxying request:

  • if the recipient is configured to use another HTTP proxy, it will act as an intermediary by forwarding the request to another HTTP server. Note that such intermediaries may need to re-encode the request if they forward it using a version of HTTP that is different from the one used to receive it, as the request encoding differs by version (see below).

  • otherwise, the recipient will act as an Ethernet proxy. The Ethernet proxy can choose to reject the Ethernet proxying request or establish an Ethernet tunnel.

The lifetime of the Ethernet tunnel is tied to the Ethernet proxying request stream.

A successful response (as defined in Sections 4.3 and 4.5) indicates that the Ethernet proxy has established an Ethernet tunnel and is willing to proxy Ethernet frames. Any response other than a successful response indicates that the request has failed; thus, the client MUST abort the request.

4.2. HTTP/1.1 Request

When using HTTP/1.1 [HTTP/1.1], an Ethernet proxying request will meet the following requirements:

  • the method SHALL be "GET".

  • the request SHALL include a single Host header field containing the host and optional port of the Ethernet proxy.

  • the request SHALL include a Connection header field with value "Upgrade" (note that this requirement is case-insensitive as per Section 7.6.1 of [HTTP]).

  • the request SHALL include an Upgrade header field with value "connect-ethernet".

An Ethernet proxying request that does not conform to these restrictions is malformed. The recipient of such a malformed request MUST respond with an error and SHOULD use the 400 (Bad Request) status code.

For example, if the client is configured with the URL "https://example.org/.well-known/masque/ethernet/" and wishes to open an Ethernet tunnel, it could send the following request.

GET https://example.org/.well-known/masque/ethernet/ HTTP/1.1
Host: example.org
Connection: Upgrade
Upgrade: connect-ethernet
Capsule-Protocol: ?1
Figure 1: Example HTTP/1.1 Request

4.3. HTTP/1.1 Response

The server indicates a successful response by replying with the following requirements:

  • the HTTP status code on the response SHALL be 101 (Switching Protocols).

  • the response SHALL include a Connection header field with value "Upgrade" (note that this requirement is case-insensitive as per Section 7.6.1 of [HTTP]).

  • the response SHALL include a single Upgrade header field with value "connect-ethernet".

  • the response SHALL meet the requirements of HTTP responses that start the Capsule Protocol; see Section 3.2 of [HTTP-DGRAM].

If any of these requirements are not met, the client MUST treat this proxying attempt as failed and close the connection.

For example, the server could respond with:

HTTP/1.1 101 Switching Protocols
Connection: Upgrade
Upgrade: connect-ethernet
Capsule-Protocol: ?1
Figure 2: Example HTTP/1.1 Response

4.4. HTTP/2 and HTTP/3 Requests

When using HTTP/2 [HTTP/2] or HTTP/3 [HTTP/3], Ethernet proxying requests use HTTP Extended CONNECT. This requires that servers send an HTTP Setting as specified in [EXT-CONNECT2] and [EXT-CONNECT3] and that requests use HTTP pseudo-header fields with the following requirements:

  • The :method pseudo-header field SHALL be "CONNECT".

  • The :protocol pseudo-header field SHALL be "connect-ethernet".

  • The :authority pseudo-header field SHALL contain the authority of the IP proxy.

  • The :path and :scheme pseudo-header fields SHALL NOT be empty. Their values SHALL contain the scheme and path from the configured URL; see Section 3.

An Ethernet proxying request that does not conform to these restrictions is malformed; see Section 8.1.1 of [HTTP/2] and Section 4.1.2 of [HTTP/3].

For example, if the client is configured with the URL "https://example.org/.well-known/masque/ethernet/" and wishes to open an Ethernet tunnel, it could send the following request.

HEADERS
:method = CONNECT
:protocol = connect-ethernet
:scheme = https
:path = /.well-known/masque/ethernet/
:authority = example.org
capsule-protocol = ?1
Figure 3: Example HTTP/2 or HTTP/3 Request

4.5. HTTP/2 and HTTP/3 Responses

The server indicates a successful response by replying with the following requirements:

  • the HTTP status code on the response SHALL be in the 2xx (Successful) range.

  • the response SHALL meet the requirements of HTTP responses that start the Capsule Protocol; see Section 3.2 of [HTTP-DGRAM].

If any of these requirements are not met, the client MUST treat this proxying attempt as failed and abort the request. As an example, any status code in the 3xx range will be treated as a failure and cause the client to abort the request.

For example, the server could respond with:

HEADERS
:status = 200
capsule-protocol = ?1
Figure 4: Example HTTP/2 or HTTP/3 Response

5. Context Identifiers

The mechanism for proxying Ethernet in HTTP defined in this document allows future extensions to exchange HTTP Datagrams that carry different semantics from Ethernet frames. Some of these extensions can augment Ethernet payloads with additional data or compress Ethernet frame header fields, while others can exchange data that is completely separate from Ethernet payloads. In order to accomplish this, all HTTP Datagrams associated with Ethernet proxying requests streams start with a Context ID field; see Section 6.

Context IDs are 62-bit integers (0-262-1). Context IDs are encoded as variable-length integers; see Section 16 of [QUIC]. The Context ID value of 0 is reserved for Ethernet payloads, while non-zero values are dynamically allocated. Non-zero even-numbered Context-IDs are client allocated, and odd-numbered Context IDs are proxy-allocated. The Context ID namespace is tied to a given HTTP request; it is possible for a Context ID with the same numeric value to be simultaneously allocated in distinct requests, potentially with different semantics. Context IDs MUST NOT be re-allocated within a given HTTP request but MAY be allocated in any order. The Context ID allocation restrictions to the use of even-numbered and odd-numbered Context IDs exist in order to avoid the need for synchronization between endpoints. However, once a Context ID has been allocated, those restrictions do not apply to the use of the Context ID; it can be used by either the client or the Ethernet proxy, independent of which endpoint initially allocated it.

Registration is the action by which an endpoint informs its peer of the semantics and format of a given Context ID. This document does not define how registration occurs. Future extensions MAY use HTTP header fields or capsules to register Context IDs. Depending on the method being used, it is possible for datagrams to be received with Context IDs that have not yet been registered. For instance, this can be due to reordering of the packet containing the datagram and the packet containing the registration message during transmission.

6. HTTP Datagram Payload Format

When associated with Ethernet proxying request streams, the HTTP Datagram Payload field of HTTP Datagrams (see [HTTP-DGRAM]) has the format defined in Figure 5. Note that when HTTP Datagrams are encoded using QUIC DATAGRAM frames, the Context ID field defined below directly follows the Quarter Stream ID field which is at the start of the QUIC DATAGRAM frame payload.

Ethernet Proxying HTTP Datagram Payload {
  Context ID (i),
  Payload (..),
}
Figure 5: Ethernet Proxying HTTP Datagram Format

The Ethernet Proxying HTTP Datagram Payload contains the following fields:

Context ID:

A variable-length integer that contains the value of the Context ID. If an HTTP/3 datagram which carries an unknown Context ID is received, the receiver SHALL either drop that datagram silently or buffer it temporarily (on the order of a round trip) while awaiting the registration of the corresponding Context ID.

Payload:

The payload of the datagram, whose semantics depend on value of the previous field. Note that this field can be empty.

Ethernet frames are encoded using HTTP Datagrams with the Context ID set to zero. When the Context ID is set to zero, the Payload field contains a full Layer 2 Ethernet Frame (from the MAC destination field until the last byte of the Frame check sequence field).

7. Ethernet Frame Handling

This document defines a tunnelling mechanism that is conceptually an Ethernet link. Implementations might need to handle some of the responsibilities of an Ethernet switch or bridge if they do not delegate them to another implementation such as a kernel. Those responsibilities are beyond the scope of this document, and include, but are not limited to, the handling of broadcast packets and multicast groups.

8. Examples

Ethernet proxying in HTTP enables the bridging of Ethernet broadcast domains. These examples are provided to help illustrate some of the ways in which Ethernet proxying can be used.

8.1. Remote Access L2VPN

The following example shows a point to point VPN setup where a client appears to be connected to a remote Layer 2 network.

HOST 1 L2 Layer 2 Client Layer 2 Tunnel Proxy HOST 2 Broadcast Domain HOST 3
Figure 6: L2VPN Tunnel Setup

In this case, the client connects to the Ethernet proxy and immediately can start sending ethernet frames to the attached broadcast domain.

[[ From Client ]]             [[ From Ethernet Proxy ]]

SETTINGS
  H3_DATAGRAM = 1

                              SETTINGS
                                ENABLE_CONNECT_PROTOCOL = 1
                                H3_DATAGRAM = 1

STREAM(44): HEADERS
:method = CONNECT
:protocol = connect-ethernet
:scheme = https
:path = /.well-known/masque/ethernet/
:authority = proxy.example.com
capsule-protocol = ?1

                              STREAM(44): HEADERS
                              :status = 200
                              capsule-protocol = ?1

DATAGRAM
Quarter Stream ID = 11
Context ID = 0
Payload = Encapsulated Ethernet Frame

                              DATAGRAM
                              Quarter Stream ID = 11
                              Context ID = 0
                              Payload = Encapsulated Ethernet Frame
Figure 7: VPN Full-Tunnel Example

8.2. Site-to-Site L2VPN

The following example shows a site-to-site VPN setup where a client joins a locally attached broadcast domain to a remote broadcast domain through the Proxy.

L2 Client L2 Tunnel Proxy HOST A Layer 2 Layer 2 HOST 1 Broadcast Broadcast HOST B Domain Domain HOST 2 HOST C HOST 3
Figure 8: Site-to-site L2VPN Example

In this case, the client connects to the Ethernet proxy and immediately can start relaying Ethernet frames from its attached broadcast domain to the proxy. The difference between this example and Section 8.1 is limited to what the Client is doing with the the tunnel; the exchange between the Client and the Proxy is the same as in Figure 7 above.

9. Security Considerations

There are risks in allowing arbitrary clients to establish a tunnel to a Layer 2 network. Bad actors could abuse this capability to attack hosts on that network that they would otherwise be unable to reach. HTTP servers that support Ethernet proxying SHOULD restrict its use to authenticated users. Depending on the deployment, possible authentication mechanisms include mutual TLS between IP proxying endpoints, HTTP-based authentication via the HTTP Authorization header [HTTP], or even bearer tokens. Proxies can enforce policies for authenticated users to further constrain client behavior or deal with possible abuse. For example, proxies can rate limit individual clients that send an excessively large amount of traffic through the proxy.

Users of this protocol may send arbitrary Ethernet frames through the tunnel, including frames with falsified source MAC addresses. This could allow impersonation of other hosts, poisoning of ARP and CAM tables, and cause a denial of service to other hosts on the network. These are the same attacks available to an arbitrary client with physical access to the network.

10. IANA Considerations

10.1. HTTP Upgrade Token

This document will request IANA to register "connect-ethernet" in the HTTP Upgrade Token Registry maintained at <https://www.iana.org/assignments/http-upgrade-tokens>.

Value:

connect-ethernet

Description:

Proxying of Ethernet Payloads

Expected Version Tokens:

None

References:

This document

10.2. Updates to the MASQUE URI Suffixes Registry

This document will request IANA to register "ethernet" in the MASQUE URI Suffixes Registry maintained at $IANA_URL_TBD, created by CONNECT-IP [CONNECT-IP].

Table 1: New MASQUE URI Suffixes
Path Segment Description Reference
ethernet Ethernet Proxying This Document

11. References

11.1. Normative References

[CONNECT-IP]
Pauly, T., Ed., Schinazi, D., Chernyakhovsky, A., Kühlewind, M., and M. Westerlund, "Proxying IP in HTTP", RFC 9484, DOI 10.17487/RFC9484, , <https://www.rfc-editor.org/rfc/rfc9484>.
[CONNECT-UDP]
Schinazi, D., "Proxying UDP in HTTP", RFC 9298, DOI 10.17487/RFC9298, , <https://www.rfc-editor.org/rfc/rfc9298>.
[EXT-CONNECT2]
McManus, P., "Bootstrapping WebSockets with HTTP/2", RFC 8441, DOI 10.17487/RFC8441, , <https://www.rfc-editor.org/rfc/rfc8441>.
[EXT-CONNECT3]
Hamilton, R., "Bootstrapping WebSockets with HTTP/3", RFC 9220, DOI 10.17487/RFC9220, , <https://www.rfc-editor.org/rfc/rfc9220>.
[HTTP]
Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "HTTP Semantics", STD 97, RFC 9110, DOI 10.17487/RFC9110, , <https://www.rfc-editor.org/rfc/rfc9110>.
[HTTP-DGRAM]
Schinazi, D. and L. Pardue, "HTTP Datagrams and the Capsule Protocol", RFC 9297, DOI 10.17487/RFC9297, , <https://www.rfc-editor.org/rfc/rfc9297>.
[HTTP/1.1]
Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "HTTP/1.1", STD 99, RFC 9112, DOI 10.17487/RFC9112, , <https://www.rfc-editor.org/rfc/rfc9112>.
[HTTP/2]
Thomson, M., Ed. and C. Benfield, Ed., "HTTP/2", RFC 9113, DOI 10.17487/RFC9113, , <https://www.rfc-editor.org/rfc/rfc9113>.
[HTTP/3]
Bishop, M., Ed., "HTTP/3", RFC 9114, DOI 10.17487/RFC9114, , <https://www.rfc-editor.org/rfc/rfc9114>.
[L2TP]
Townsley, W., Valencia, A., Rubens, A., Pall, G., Zorn, G., and B. Palter, "Layer Two Tunneling Protocol "L2TP"", RFC 2661, DOI 10.17487/RFC2661, , <https://www.rfc-editor.org/rfc/rfc2661>.
[L2TPv3]
Lau, J., Ed., Townsley, M., Ed., and I. Goyret, Ed., "Layer Two Tunneling Protocol - Version 3 (L2TPv3)", RFC 3931, DOI 10.17487/RFC3931, , <https://www.rfc-editor.org/rfc/rfc3931>.
[QUIC]
Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based Multiplexed and Secure Transport", RFC 9000, DOI 10.17487/RFC9000, , <https://www.rfc-editor.org/rfc/rfc9000>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/rfc/rfc2119>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/rfc/rfc8174>.
[TCP]
Eddy, W., Ed., "Transmission Control Protocol (TCP)", STD 7, RFC 9293, DOI 10.17487/RFC9293, , <https://www.rfc-editor.org/rfc/rfc9293>.

11.2. Informative References

[ETHERIP]
Housley, R. and S. Hollenbeck, "EtherIP: Tunneling Ethernet Frames in IP Datagrams", RFC 3378, DOI 10.17487/RFC3378, , <https://www.rfc-editor.org/rfc/rfc3378>.
[GUE]
Herbert, T., Yong, L., and O. Zia, "Generic UDP Encapsulation", Work in Progress, Internet-Draft, draft-ietf-intarea-gue-09, , <https://datatracker.ietf.org/doc/html/draft-ietf-intarea-gue-09>.

Acknowledgments

Much of the initial version of this draft borrows heavily from [CONNECT-IP].

The author would like to thank Alexander Chernyakhovsky and David Schinazi for their advice while preparing this document.

Author's Address

Alejandro R Sedeño
Google LLC