Extensions to Compress and Derive Fields in HTTP Datagrams
draft-rosomakho-masque-connect-ip-optimizations-01
This document is an Internet-Draft (I-D).
Anyone may submit an I-D to the IETF.
This I-D is not endorsed by the IETF and has no formal standing in the
IETF standards process.
| Document | Type | Active Internet-Draft (candidate for masque WG) | |
|---|---|---|---|
| Authors | Yaroslav Rosomakho , Tommy Pauly | ||
| Last updated | 2026-04-21 (Latest revision 2026-02-27) | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | Call For Adoption By WG Issued | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-rosomakho-masque-connect-ip-optimizations-01
Multiplexed Application Substrate over QUIC Encryption Y. Rosomakho
Internet-Draft Zscaler
Intended status: Standards Track T. Pauly
Expires: 31 August 2026 Apple
27 February 2026
Extensions to Compress and Derive Fields in HTTP Datagrams
draft-rosomakho-masque-connect-ip-optimizations-01
Abstract
This document defines extensions for HTTP Datagram-based protocols
that improve transmission efficiency by introducing templates for
compressing or deriving datagram fields.
These templates allow endpoints to define parts of datagrams that are
static and can be removed, and other parts that can be derived (such
as packet lengths and checksum values).
Additionally, this document defines a checksum offload procedure
enabling receivers to complete Internet checksums using sender-
provided partial values.
These optimisations reduce per-packet overhead, processing cost, and
increase the effective maximum transmission unit (MTU) when datagrams
are encapsulated in QUIC DATAGRAM frames.
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://yaroslavros.github.io/connect-ip-optimizations/draft-
rosomakho-masque-connect-ip-optimizations.html. Status information
for this document may be found at https://datatracker.ietf.org/doc/
draft-rosomakho-masque-connect-ip-optimizations/.
Discussion of this document takes place on the Multiplexed
Application Substrate over QUIC Encryption 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/yaroslavros/connect-ip-optimizations.
Rosomakho & Pauly Expires 31 August 2026 [Page 1]
Internet-Draft HTTP Datagram Compression February 2026
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 31 August 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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 5
3. Negotiation of Capabilities . . . . . . . . . . . . . . . . . 6
3.1. Header Definition . . . . . . . . . . . . . . . . . . . . 6
3.2. Negotiation Behavior . . . . . . . . . . . . . . . . . . 6
3.2.1. Templates . . . . . . . . . . . . . . . . . . . . . . 7
3.2.2. Derived Fields . . . . . . . . . . . . . . . . . . . 7
3.2.3. Checksum Offload . . . . . . . . . . . . . . . . . . 7
3.3. Example . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Processing Context Capsules . . . . . . . . . . . . . . . . . 8
4.1. Processing Context Overview . . . . . . . . . . . . . . . 8
4.1.1. Processing Context Construction . . . . . . . . . . . 8
4.1.2. Processing Context Acknowledgement . . . . . . . . . 8
4.1.3. Processing Context Closure . . . . . . . . . . . . . 9
4.2. Template Capsules . . . . . . . . . . . . . . . . . . . . 9
Rosomakho & Pauly Expires 31 August 2026 [Page 2]
Internet-Draft HTTP Datagram Compression February 2026
4.2.1. TEMPLATE_ASSIGN Capsule . . . . . . . . . . . . . . . 9
4.2.2. TEMPLATE_ACK Capsule . . . . . . . . . . . . . . . . 10
4.2.3. TEMPLATE_CLOSE Capsule . . . . . . . . . . . . . . . 11
4.3. Derived Field Capsules . . . . . . . . . . . . . . . . . 11
4.3.1. DERIVED_ASSIGN Capsule . . . . . . . . . . . . . . . 11
4.3.2. DERIVED_ACK Capsule . . . . . . . . . . . . . . . . . 12
4.3.3. DERIVED_CLOSE Capsule . . . . . . . . . . . . . . . . 12
4.4. Checksum Offload Capsules . . . . . . . . . . . . . . . . 12
4.4.1. CHECKSUM_ASSIGN Capsule . . . . . . . . . . . . . . . 12
4.4.2. CHECKSUM_ACK Capsule . . . . . . . . . . . . . . . . 13
4.4.3. CHECKSUM_CLOSE Capsule . . . . . . . . . . . . . . . 13
5. Processing Context Operation . . . . . . . . . . . . . . . . 14
5.1. Sender behavior . . . . . . . . . . . . . . . . . . . . . 14
5.1.1. Template Contexts . . . . . . . . . . . . . . . . . . 14
5.1.2. Derived Field Contexts . . . . . . . . . . . . . . . 14
5.1.3. Checksum Offload Contexts . . . . . . . . . . . . . . 15
5.1.4. Context Selection . . . . . . . . . . . . . . . . . . 15
5.2. Receiver behavior . . . . . . . . . . . . . . . . . . . . 15
5.2.1. Template Reconstruction . . . . . . . . . . . . . . . 15
5.2.2. Derived Field Processing . . . . . . . . . . . . . . 16
5.2.3. Checksum Offload Processing . . . . . . . . . . . . . 16
6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 16
6.1. CONNECT-IP: TCP over IPv6 with template, derived fields and
checksum offload . . . . . . . . . . . . . . . . . . . . 17
6.2. CONNECT-ETHERNET: UDP over IPv4 with template and derived
fields . . . . . . . . . . . . . . . . . . . . . . . . . 22
7. Security Considerations . . . . . . . . . . . . . . . . . . . 27
7.1. Resource Exhaustion . . . . . . . . . . . . . . . . . . . 27
7.2. Amplification . . . . . . . . . . . . . . . . . . . . . . 27
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
8.1. HTTP Capsule Types Registration . . . . . . . . . . . . . 27
8.2. HTTP Field Name Registration . . . . . . . . . . . . . . 28
8.3. HTTP Datagram Derived Field Types Registry . . . . . . . 29
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.1. Normative References . . . . . . . . . . . . . . . . . . 30
9.2. Informative References . . . . . . . . . . . . . . . . . 31
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 32
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32
1. Introduction
The CONNECT-IP method [CONNECT-IP] allows an HTTP client to establish
an IP tunnel through an HTTP proxy and exchange IP packets using
either HTTP/3 Datagrams (Section 2.1 of [HTTP-DATAGRAMS]) or DATAGRAM
capsules (Section 3.5 of [HTTP-DATAGRAMS]). Similarly, CONNECT-
ETHERNET [CONNECT-ETHERNET] allows sending Ethernet frames over HTTP
Datagrams. These protocols send complete packets or frames by
default, including all transport and network headers. This is a
Rosomakho & Pauly Expires 31 August 2026 [Page 3]
Internet-Draft HTTP Datagram Compression February 2026
simple approach, but incurs per-packet overhead due to the repeated
transmission of largely invariant header fields.
Other HTTP Datagram-based protocols share similar properties:
datagrams often contain structured packets where many header fields
remain constant across a flow while only a subset of bytes change
between packets. Transmitting complete packets therefore wastes
bandwidth and processing resources.
This document introduces a set of optional extensions that define
Processing Contexts for HTTP Datagram payloads. A Processing Context
describes transformations applied to a received datagram payload
prior to delivery to the target protocol and may reference a parent
context, forming a processing chain.
Reusable templates allow endpoints to associate a Context Identifier
with a reusable packet layout consisting of static and variable byte
regions. Once a template has been installed using reliable Capsules,
datagrams referencing the same Context Identifier carry only the
variable portions of the packet. This reduces the size of
transmitted datagrams and processing overhead, while remaining
compatibile with intermediaries that are unaware of these
optimisations.
Derived field processing allows the receiver to reconstruct certain
header fields (for example packet length fields and complete
checksums) based on the size and structure of the reconstructed
packet. This eliminates the need for the sender to transmit such
fields for every packet.
In addition, this document defines a checksum offload procedure
enabling endpoints to cooperatively compute Internet checksums, where
the sender provides a partial checksum and the receiver completes the
computation after reconstruction. This mirrors hardware checksum-
offload behavior used on network interfaces and tunnel devices,
reducing per-packet CPU cost for encapsulating or decapsulating
CONNECT-IP and CONNECT-ETHERNET traffic.
When HTTP Datagrams are encapsulated in QUIC DATAGRAM frames, these
optimisations also increase the effective maximum transmission unit
(MTU) by reducing the number of bytes carried inside each QUIC
packet.
Rosomakho & Pauly Expires 31 August 2026 [Page 4]
Internet-Draft HTTP Datagram Compression February 2026
All extensions are negotiated during the HTTP request/response
handshake and signalled using Capsules on the reliable control
stream. Endpoints can always fall back to transmitting complete
datagrams using Context Identifier 0, which represents unoptimised
datagrams containing the full payload as defined by the underlying
HTTP Datagram protocol.
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.
The following terms are used in this document:
Context Identifier (Context ID): A numeric identifier associated
with a Processing Context. Context ID encoding and allocation
follow the rules defined in Section 4 of [CONNECT-UDP]. Context
ID 0 indicates that the datagram payload is delivered without
additional processing as defined by the underlying HTTP Datagram
protocol.
Processing Context: A set of rules describing how an HTTP Datagram
payload is transformed before delivery to the target protocol. A
Processing Context may reference a parent context, forming a
processing chain. Processing Contexts are immutable once created.
Template: A reusable packet layout consisting of a sequence of
static and variable segments. Static segments contain bytes
removed from optimized datagrams, while variable segments
correspond to bytes still carried in the datagram payload.
Derived Field: A header field whose value is generated by the
receiver during reconstruction and written into the reconstructed
packet rather than being transmitted in the datagram payload.
Derived fields include length fields and complete checksums.
Checksum Offload: A capability allowing the receiver to complete the
Internet checksum according to [INCREMENTAL-CHECKSUM] using a
sender-provided partial checksum after reconstruction of the
packet.
Capsule: A reliable control-stream message, as defined in Section 3
of [HTTP-DATAGRAMS], used in this specification to signal
creation, acknowledgement, or deletion of Processing Contexts.
Rosomakho & Pauly Expires 31 August 2026 [Page 5]
Internet-Draft HTTP Datagram Compression February 2026
3. Negotiation of Capabilities
Endpoints negotiate support for HTTP Datagram processing contexts
during the HTTP request/response handshake by using the http-
datagram-contexts HTTP header field, whose value is a Structured
Field Dictionary as defined in Section 3.2 of [STRUCTURED-HTTP].
3.1. Header Definition
http-datagram-contexts = sf-dictionary
Figure 1: http-datagram-contexts header field
This document defines the following optional dictionary keys:
max-templates (Integer): Maximum number of concurrently active
template contexts the sender is willing to maintain for templates
created by the peer. Absence of this key or value of 0 indicates
that the sender does not support reusable templates.
max-templates-segments (Integer): Maximum number of static segments
accepted within a single template. Absence of this key or value
of 0 indicates that the sender does not impose a limit on number
of static segments in a single template.
derived (Inner List): A list of supported Derived Field Types as
defined in Section 8.3.
checksum (Boolean): Indicates support for the checksum offload
procedure defined in this document. A value of ?1 means the
endpoint is willing to complete checksums using sender-provided
partial values. If omitted or set to ?0, checksum offload is not
supported.
mtu (Integer): Upper limit on maximum reconstructed packet size the
receiver is willing to accept.
Endpoints MUST ignore unknown dictionary members. The absence of a
member implies that the corresponding capability is not supported for
contexts created by the peer.
3.2. Negotiation Behavior
Capabilities are directional. Each endpoint advertises the
processing contexts it is willing to receive and maintain for
datagrams sent by the peer. An endpoint MAY create a context only if
the peer advertised support for the corresponding capability.
Rosomakho & Pauly Expires 31 August 2026 [Page 6]
Internet-Draft HTTP Datagram Compression February 2026
3.2.1. Templates
If the peer advertises the max-templates value greater than 0, the
endpoint MAY create template contexts up to that limit using capsules
defined in Section 4.
An endpoint MUST NOT create templates exceeding the peer's advertised
max-template-segments limit when that parameter is present.
If the peer advertises an mtu limit, the sender MUST NOT transmit a
datagram that would reconstruct into a packet larger than the
advertised limit after all processing contexts have been applied.
3.2.2. Derived Fields
An endpoint MAY create a derived context only if every operation in
the capsule appears in the peer's derived list.
3.2.3. Checksum Offload
An endpoint MAY create a checksum offload context only if the peer
advertised checksum=?1.
3.3. Example
HTTP/3 sample request (client to proxy):
:method = CONNECT
:protocol = connect-ip
:scheme = https
:path = /.well-known/masque/ip/*/*/
:authority = proxy.example.net
capsule-protocol = ?1
http-datagram-contexts = max-templates=20000, max-templates-segments=32, derived=(0 2 4), checksum=?1, mtu=1500
Figure 2: CONNECT-IP with http-datagram-contexts request example
HTTP/3 sample response (proxy to client):
:status = 200
capsule-protocol = ?1
http-datagram-contexts = max-templates=65535, derived=(0 1), checksum=?0, mtu=1500
Figure 3: CONNECT-IP with http-datagram-contexts response example
In this example, both peers support reusable templates. The proxy
supports a subset of derived fields (ipv4-total-length, ipv4-udp-
length and ipv4-header-checksum) and the checksum offload. The
Rosomakho & Pauly Expires 31 August 2026 [Page 7]
Internet-Draft HTTP Datagram Compression February 2026
client supports a different subset of derived fields (ipv4-total-
length and ipv6-payload-length) without the checksum offload. Both
endpoints indicate that the maximum packet size after reconstruction
must not exceed 1500 bytes.
4. Processing Context Capsules
This specification defines multiple capsule types to construct,
acknowledge, and delete processing contexts.
4.1. Processing Context Overview
4.1.1. Processing Context Construction
Processing contexts are created using capsules that define a new
unique non-zero Context ID encoded as a variable-length integer. A
Context ID MUST NOT be reused. As specified in Section 4 of
[CONNECT-UDP], even-numbered Context IDs are allocated by the client
and odd-numbered by the proxy.
Each processing context MAY reference an already-defined parent
context using Next Context ID encoded as a variable-length integer.
A context MUST reference only a Context ID previously defined by the
peer. Forward references are not permitted. Processing context
without a parent is identified by Next Context ID set to 0. A
processing chain MUST NOT contain more than one context of the same
type. A receiver that detects such a condition MUST treat the
context as malformed and follow the error-handling procedure defined
in Section 3.3 of [HTTP-DATAGRAMS].
A receiver of an *_ASSIGN capsule with an invalid Context ID or
unknown Next Context ID MUST treat it as malformed and follow the
error-handling procedure defined in Section 3.3 of [HTTP-DATAGRAMS].
4.1.2. Processing Context Acknowledgement
For each *_ASSIGN capsule received, the receiver MUST transmit the
corresponding *_ACK capsule after successfully installing the
context.
Endpoints MAY transmit datagrams referencing contexts prior to
receiving the *_ACK. A receiver MAY buffer datagrams referencing
unknown Context IDs but MUST bound buffering by time and memory.
A receiver of an *_ACK capsule with an unknown Context ID or any data
after Context ID MUST treat it as malformed and follow the error-
handling procedure defined in Section 3.3 of [HTTP-DATAGRAMS].
Rosomakho & Pauly Expires 31 August 2026 [Page 8]
Internet-Draft HTTP Datagram Compression February 2026
4.1.3. Processing Context Closure
Processing Contexts are retired by sending corresponding *_CLOSE
capsule. Closing a context implicitly closes all contexts that
reference it directly or transitively.
A receiver of a *_CLOSE capsule SHOULD retain the closed context and
its descendants for a short period to allow in-flight datagrams to
arrive, but MUST bound the retention time and memory usage.
*_CLOSE capsules with unknown Context ID or any data after Context ID
MUST be treated as malformed. Receiver of such capsules MUST follow
the error-handling procedure defined in Section 3.3 of
[HTTP-DATAGRAMS].
4.2. Template Capsules
4.2.1. TEMPLATE_ASSIGN Capsule
TEMPLATE_ASSIGN Capsule {
Type (i) = 0x3ee3143f,
Length (i),
Context ID (i),
Next Context ID (i),
Static Segment (..) ...
}
Figure 4: TEMPLATE_ASSIGN Capsule Format
The TEMPLATE_ASSIGN capsule contains a sequence of one or more Static
Segments.
Static Segment {
Segment Offset (i),
Segment Length (i),
Segment Payload (..),
}
Figure 5: Static Segment Format
Each Static Segment contains following fields:
Segment Offset: Byte offset from the start of the reconstructed
packet, encoded as a variable-length integer
Segment Length: Length of the Segement Payload field, encoded as a
variable-length integer
Rosomakho & Pauly Expires 31 August 2026 [Page 9]
Internet-Draft HTTP Datagram Compression February 2026
Segment Payload: Static bytes to insert at the Segment Offset
4.2.1.1. Parsing and validation
The receiver parses a TEMPLATE_ASSIGN capsule by reading, in order:
the Context ID, the Next Context ID, and one or more static segments
whose encodings consume exactly the remaining length of the capsule.
Context ID and Next Context ID processing is described in
Section 4.1.1.
Each Static Segment consists of a Segment Offset, a Segment Length,
and exactly Segment Length octets of Segment Payload. Static
segments MUST appear in strictly increasing Segment Offset order and
MUST NOT overlap. There MUST be at least 1 byte between consecutive
segments.
A receiver that advertised a max-templates-segments limit MUST ensure
that the template does not contain more static segments. A receiver
that advertised a mtu limit in http-datagram-contexts MUST ensure
that the sum of Segment Offset and Segment Length of the final
segment does not exceed the MTU limit. Final reconstructed packet
size validation is performed during packet reconstruction
(Section 5.2). The capsule MUST end immediately after the last
static segment.
If any of the capsule fields are malformed upon reception, the
receiver of the capsule MUST follow the error-handling procedure
defined in Section 3.3 of [HTTP-DATAGRAMS].
A receiver that has already accepted the maximum number of templates
it advertised via the max-templates member in http-datagram-contexts
MUST treat any additional TEMPLATE_ASSIGN capsule an error and MUST
follow the same error-handling procedure.
Per-packet validation uses the reconstruction procedure described in
Section 5.2.
4.2.2. TEMPLATE_ACK Capsule
TEMPLATE_ACK Capsule {
Type (i) = 0x3ee31440,
Length (i),
Context ID (i),
}
Figure 6: TEMPLATE_ACK Capsule Format
Processing of the TEMPLATE_ACK capsule is described in Section 4.1.2
Rosomakho & Pauly Expires 31 August 2026 [Page 10]
Internet-Draft HTTP Datagram Compression February 2026
4.2.3. TEMPLATE_CLOSE Capsule
TEMPLATE_CLOSE Capsule {
Type (i) = 0x3ee31441,
Length (i),
Context ID (i),
}
Figure 7: TEMPLATE_CLOSE Capsule Format
Processing of the TEMPLATE_CLOSE capsule is described in
Section 4.1.3
4.3. Derived Field Capsules
4.3.1. DERIVED_ASSIGN Capsule
DERIVED_ASSIGN Capsule {
Type (i) = 0x3ee31442,
Length (i),
Context ID (i),
Next Context ID (i),
Derived Field Type (i) ...
}
Figure 8: DERIVED_ASSIGN Capsule Format
The DERIVED_ASSIGN capsule defines a processing context that
generates and inserts one or more derived fields into the
reconstructed packet. The sender does not transmit these fields in
the datagram payload.
4.3.1.1. Parsing and validation
The receiver parses a DERIVED_ASSIGN capsule by reading, in order:
the Context ID, the Next Context ID, and one or more Derived Field
Type values encoded as variable-length integers. Context ID and Next
Context ID processing is described in Section 4.1.1.
If a Derived Field Type is not present in the receiver's advertised
derived capability list in http-datagram-contexts or if any Derived
Field Type appears more than once in the capsule, the receiver MUST
treat the capsule as malformed and follow the error-handling
procedure defined in Section 3.3 of [HTTP-DATAGRAMS].
Per-packet validation uses the reconstruction procedure described in
Section 5.2.
Rosomakho & Pauly Expires 31 August 2026 [Page 11]
Internet-Draft HTTP Datagram Compression February 2026
4.3.2. DERIVED_ACK Capsule
DERIVED_ACK Capsule {
Type (i) = 0x3ee31443,
Length (i),
Context ID (i),
}
Figure 9: DERIVED_ACK Capsule Format
Processing of the DERIVED_ACK capsule is described in Section 4.1.2
4.3.3. DERIVED_CLOSE Capsule
DERIVED_CLOSE Capsule {
Type (i) = 0x3ee31444,
Length (i),
Context ID (i),
}
Figure 10: DERIVED_CLOSE Capsule Format
Processing of the DERIVED_CLOSE capsule is described in Section 4.1.3
4.4. Checksum Offload Capsules
4.4.1. CHECKSUM_ASSIGN Capsule
CHECKSUM_ASSIGN Capsule {
Type (i) = 0x3ee31445,
Length (i),
Context ID (i),
Next Context ID (i),
Checksum Field Offset (i),
Checksum Start Offset (i),
}
Figure 11: CHECKSUM_ASSIGN Capsule Format
The CHECKSUM_ASSIGN capsule defines a processing context that
completes an Internet checksum for the reconstructed packet using a
sender-provided partial checksum.
In addition to Context ID and Next Context ID CHECKSUM_ASSIGN capsule
contains following fields encoded as variable-length integers:
Checksum Field Offset: Byte offset of the 16-bit Internet checksum
field within the reconstructed packet
Rosomakho & Pauly Expires 31 August 2026 [Page 12]
Internet-Draft HTTP Datagram Compression February 2026
Checksum Start Offset: Byte offset where checksum coverage begins.
Coverage runs from this offset to the end of the reconstructed
packet.
4.4.1.1. Parsing and validation
The receiver parses a CHECKSUM_ASSIGN capsule by reading, in order:
the Context ID, the Next Context ID, Checksum Field Offset and
Checksum Start Offset. Context ID and Next Context ID processing is
described in Section 4.1.1.
If the peer did not advertise checksum=?1 in http-datagram-contexts,
the receiver MUST treat the capsule as malformed and follow the
error-handling procedure defined in Section 3.3 of [HTTP-DATAGRAMS].
If Checksum Start Offset is 0, the receiver MUST treat the capsule as
malformed and follow the same error-handling procedure.
Per-packet validation uses the reconstruction procedure described in
Section 5.2.
4.4.2. CHECKSUM_ACK Capsule
CHECKSUM_ACK Capsule {
Type (i) = 0x3ee31446,
Length (i),
Context ID (i),
}
Figure 12: CHECKSUM_ACK Capsule Format
Processing of the CHECKSUM_ACK capsule is described in Section 4.1.2
4.4.3. CHECKSUM_CLOSE Capsule
CHECKSUM_CLOSE Capsule {
Type (i) = 0x3ee31447,
Length (i),
Context ID (i),
}
Figure 13: CHECKSUM_CLOSE Capsule Format
Processing of the CHECKSUM_CLOSE capsule is described in
Section 4.1.3
Rosomakho & Pauly Expires 31 August 2026 [Page 13]
Internet-Draft HTTP Datagram Compression February 2026
5. Processing Context Operation
This section defines how endpoints construct and consume HTTP
Datagram payloads using Processing Contexts.
A datagram carries a Context Identifier that selects the initial
Processing Context. A context MAY reference a parent context using
Next Context ID. The complete behavior is defined by recursively
following parent contexts until reaching Context ID 0.
Context ID 0 indicates that no processing is applied and the payload
is delivered unchanged to the underlying HTTP Datagram protocol.
5.1. Sender behavior
When sending a datagram using a Processing Context, the sender
constructs the payload so that the receiver can reconstruct the final
packet after applying the processing chain.
The sender MUST use a Context ID only after the corresponding
*_ASSIGN capsule has been transmitted.
5.1.1. Template Contexts
If the selected context chain contains a Template context, the sender
constructs the datagram payload as the concatenation of all variable
byte regions not covered by static segments.
Variable regions are emitted in strictly increasing offset order
starting at offset 0.
If the context chain contains no Template context, the payload MUST
be the complete packet.
5.1.2. Derived Field Contexts
Derived fields are not transmitted by the sender. When a derived
context is in use, the sender MUST remove the octets corresponding to
derived fields from the datagram payload. These octets are supplied
by the receiver during reconstruction.
The sender MUST construct the payload as if the derived field octets
were not part of the variable regions. That is, the payload MUST
contain only the remaining variable octets in strictly increasing
offset order.
Rosomakho & Pauly Expires 31 August 2026 [Page 14]
Internet-Draft HTTP Datagram Compression February 2026
5.1.3. Checksum Offload Contexts
If the context chain contains a checksum offload context, the sender
MUST place a precomputed partial Internet checksum value into the
checksum field at Checksum Field Offset in the reconstructed packet
image prior to transmission. This value is combined with the
receiver computation as described in Section 5.2.
5.1.4. Context Selection
If a packet does not match any available context, the sender MUST use
Context ID 0 and transmit the complete packet.
5.2. Receiver behavior
Upon receiving an HTTP Datagram with a non-zero Context ID, the
receiver retrieves the referenced Processing Context and recursively
resolves its parent contexts until Context ID 0 is reached.
If any referenced context is unknown, the receiver MAY buffer the
datagram as described in Section 4.1.2 or drop it.
If multiple processing contexts are present in a chain, the receiver
MUST apply them in the following order:
1. Template reconstruction (if present)
2. Derived field processing (if present)
3. Checksum offload processing (if present)
5.2.1. Template Reconstruction
If a Template context is present, the receiver reconstructs the
packet as follows:
1. Allocate a buffer large enough to contain the reconstructed
packet.
2. Insert static segment bytes at their specified offsets.
3. Fill all remaining gaps using bytes from the datagram payload in
strictly increasing offset order.
If payload bytes are exhausted before all gaps have been filled the
datagram MUST be dropped.
Rosomakho & Pauly Expires 31 August 2026 [Page 15]
Internet-Draft HTTP Datagram Compression February 2026
Packets larger than the advertised mtu in http-datagram-contexts MUST
be dropped.
5.2.2. Derived Field Processing
For each derived field present in the context chain, the receiver
computes the field value and inserts it into the reconstructed packet
at the location defined by the derived field type.
Derived fields are inserted into the packet image and therefore
increase the reconstructed packet size. The receiver MUST compute
derived field values based on the final reconstructed packet size and
structure.
Initial field definitions are specified in Section 8.3.
If the required header cannot be located, the packet MUST be dropped.
5.2.3. Checksum Offload Processing
If a checksum offload context is present, the receiver completes the
Internet checksum after all derived fields have been inserted.
The receiver completes the checksum as follows:
1. Treat the checksum field as zero.
2. Compute the one's-complement sum from Checksum Start Offset to L.
3. Add (fold) the 16-bit value currently present at the checksum
field.
4. Write the final one's-complement result to the checksum field.
If any offset exceeds the reconstructed packet length, the packet
MUST be dropped.
6. Examples
This section illustrates how contexts are created and how senders
form compact payloads. All offsets and lengths are in bits in the
packet diagrams and field tables. All offsets and lengths are in
bytes in segment tables and sample capsules.
Rosomakho & Pauly Expires 31 August 2026 [Page 16]
Internet-Draft HTTP Datagram Compression February 2026
6.1. CONNECT-IP: TCP over IPv6 with template, derived fields and
checksum offload
Original sample [TCP] over [IPv6] packet layout is illustrated below.
In addition to basic IPv6 and TCP headers it contains Timestamp
option as defined in Section 3 of [TCP-PERF].
This packet is to be transmitted from the client to the proxy over
CONNECT-IP.
Rosomakho & Pauly Expires 31 August 2026 [Page 17]
Internet-Draft HTTP Datagram Compression February 2026
|0 7|8 15|16 23|16 31|
+--------+-------+-------+--------+----------------+----------------+
|0 1 1 0 | 0x00 | 0x4bcde | ^
|Version | Traffic Class | Flow Label | |
+--------+---------------+--------+----------------+----------------+ |
| 0x0020 | 0x06 | 0x79 | I
| Payload length | Next header | Hop limit | P
+---------------------------------+----------------+----------------+
| | H
| 2001:0db8:85a3:0000:0000:8a2e:0370:7334 | E
| Source Address | A
| | D
+-------------------------------------------------------------------+ E
| | R
| 2001:0db8:a42b:0000:0000:7c3a:143a:1529 | |
| Destination Address | |
| | v
+---------------------------------+---------------------------------+
| 0x0050 | 0xd475 | ^
| Source port | Destination port | |
+---------------------------------+---------------------------------+ |
| 0x6caa4bd7 | |
| Sequence number | |
+-------------------------------------------------------------------+ |
| 0x9b16794e | T
| Acknowledgment number | C
+--------+------------------------+---------------------------------+ P
|1 0 0 0 |0 0 0 0 0 0 0 1 0 0 0 0 | 0x041e |
|Hdr Len | TCP Flags | Window | H
+--------+------------------------+---------------------------------+ E
| 0x8f6b | 0x0000 | A
| Checksum | Urgent Pointer | D
+----------------+----------------+----------------+----------------+ E
| 0x01 | 0x01 | 0x08 | 0x0a | R
| No-Op Option | No-Op Option |TimeStamp Option| Length | |
+----------------+----------------+----------------+----------------+ |
| 0x119a5db3 | |
| Timestamp value | |
+-------------------------------------------------------------------+ |
| 0xd9b4d48d | |
| Timestamp echo reply | v
+-------------------------------------------------------------------+
Figure 14: Example TCP over IPv6 packet before optimization
Rosomakho & Pauly Expires 31 August 2026 [Page 18]
Internet-Draft HTTP Datagram Compression February 2026
This example assumes that the peer supports templates with at least
two segments per template, IPv6 payload length derived field and
checksum offloading. These capabilities were communicated using the
following http-datagram-contexts HTTP field in proxy response
confirming CONNECT-IP extended CONNECT.
http-datagram-contexts = max-templates=1, max-templates-segments=2, derived=(1), checksum=?1, mtu=1500
Figure 15: http-datagram-contexts response example
Since the proxy does not support TCP checksum derivation, but it
supports checksum offloading, the client calculates checksum of IPv6
pseudo-header and places it in the TCP checksum field. Context for
the offloaded checksum is defined using the CHECKSUM_ASSIGN capsule:
CHECKSUM_ASSIGN Capsule {
Type (i) = 0x3ee31445,
Length (i) = 4,
Context ID (i) = 2,
Next Context ID (i) = 0,
Checksum Field Offset (i) = 56,
Checksum Start Offset (i) = 40,
}
Figure 16: CHECKSUM_ASSIGN Capsule for example IPv6/TCP packet
Payload length field in IPv6 header can derived by the peer, so it is
removed before calculating static segments. Resulting context for
the derived field is defined using DERIVED_ASSIGN capsule:
DERIVED_ASSIGN Capsule {
Type (i) = 0x3ee31442,
Length (i) = 3,
Context ID (i) = 4,
Next Context ID (i) = 2,
Derived Field Type (i) = 1
}
Figure 17: DERIVED_ASSIGN Capsule for example IPv6/TCP packet
The table below illustrates fields present in IPv6 and TCP headers
after derived field was removed, their offsets in bits from the
beginning of the packet and whether they are likely to be static for
most packets of a given traffic flow
Rosomakho & Pauly Expires 31 August 2026 [Page 19]
Internet-Draft HTTP Datagram Compression February 2026
+======+===============+======+==============================+======+
|Offset|Field name |Length|Value |Static|
+======+===============+======+==============================+======+
|0 |Version |4 |0110b |Yes |
+------+---------------+------+------------------------------+------+
|4 |Traffic Class |8 |0x00 |Yes |
+------+---------------+------+------------------------------+------+
|12 |Flow label |20 |0x4bcde |Yes |
+------+---------------+------+------------------------------+------+
|32 |Next header |8 |0x06 |Yes |
+------+---------------+------+------------------------------+------+
|40 |Hop limit |8 |0x79 |Yes |
+------+---------------+------+------------------------------+------+
|48 |Source address |128 |2001:0db8:85a3::8a2e:0370:7334|Yes |
+------+---------------+------+------------------------------+------+
|176 |Destination |128 |2001:0db8:a42b::7c3a:143a:1529|Yes |
| |address | | | |
+------+---------------+------+------------------------------+------+
|304 |Source port |16 |0x0050 |Yes |
+------+---------------+------+------------------------------+------+
|320 |Destination |16 |0xd475 |Yes |
| |port | | | |
+------+---------------+------+------------------------------+------+
|336 |Sequence number|32 |0x6caa4bd7 |No |
+------+---------------+------+------------------------------+------+
|368 |Acknowledgement|32 |0x9b16794e |No |
| |number | | | |
+------+---------------+------+------------------------------+------+
|400 |TCP header |4 |1000b |Yes |
| |length | | | |
+------+---------------+------+------------------------------+------+
|404 |TCP Flags |12 |000000010000b |No |
+------+---------------+------+------------------------------+------+
|416 |Window |16 |0x041e |No |
+------+---------------+------+------------------------------+------+
|432 |Checksum |16 |0x8f6b |No |
+------+---------------+------+------------------------------+------+
|448 |Urgent pointer |16 |0x0000 |Yes |
+------+---------------+------+------------------------------+------+
|464 |No-Op option |8 |0x01 |Yes |
+------+---------------+------+------------------------------+------+
|472 |No-Op option |8 |0x01 |Yes |
+------+---------------+------+------------------------------+------+
|480 |Timestamp |8 |0x08 |Yes |
| |option | | | |
+------+---------------+------+------------------------------+------+
|488 |Timestamp |8 |0x0a |Yes |
| |option length | | | |
Rosomakho & Pauly Expires 31 August 2026 [Page 20]
Internet-Draft HTTP Datagram Compression February 2026
+------+---------------+------+------------------------------+------+
|496 |Timestamp value|32 |0x119a5db3 |No |
+------+---------------+------+------------------------------+------+
|528 |Timestamp echo |32 |0xd9b4d48d |No |
| |reply | | | |
+------+---------------+------+------------------------------+------+
Table 1: IPv6 and TCP header fields in example packet
Static segments model the invariant parts except for the isolated
4-bit TCP header length.
Resulting static segments:
+=========+=========+===============+===============================+
| Segment | Segment | Segment | Segment Payload |
| Offset | Length | Contents | |
+=========+=========+===============+===============================+
| 0 | 42 | Version, | 0x6004bcde067920010db885a3... |
| | | Traffic | |
| | | Class, Flow | |
| | | Label, Next | |
| | | header, Hop | |
| | | limit, | |
| | | Source | |
| | | address, | |
| | | Destination | |
| | | address, | |
| | | Source port, | |
| | | Destination | |
| | | port | |
+---------+---------+---------------+-------------------------------+
| 56 | 6 | Urgent | 0x00000101080a |
| | | pointer, 2 | |
| | | No-Op TCP | |
| | | options, | |
| | | Timestamp | |
| | | option code | |
| | | and length | |
+---------+---------+---------------+-------------------------------+
Table 2: Static segments for example IPv6/TCP packet
Resulting TEMPLATE_ASSIGN capsule with client-allocated even context
id is illustrated below:
Rosomakho & Pauly Expires 31 August 2026 [Page 21]
Internet-Draft HTTP Datagram Compression February 2026
TEMPLATE_ASSIGN Capsule {
Type (i) = 0x3ee3143f,
Length (i) = 54,
Context ID (i) = 6,
Next Context ID (i) = 4,
Static Segment {
Segment Offset (i) = 0,
Segment Length (i) = 42,
Segment Payload = 0x6004bcde067920010db885a3000000008a2e0370733420010db8a42b000000007c3a143a15290050d475,
},
Static Segment {
Segment Offset (i) = 56,
Segment Length (i) = 6,
Segment Payload = 0x00000101080a,
}
}
Figure 18: TEMPLATE_ASSIGN Capsule for example IPv6/TCP packet
The resulting processing context chain reduces per-packet overhead by
removing 50 bytes of repeated header material, increasing the
effective MTU when datagrams are encapsulated in QUIC DATAGRAM
frames.
The sender concatenates all variable regions in increasing offset
order. Packets that do not match this template (for example packets
with IPv6 extension headers or without TCP options) are sent using
Context ID 0 or associated with a new context.
Upon receiving the datagram with Context ID 6, proxy re-assembles the
datagram by concatenating static and variable segments according to
the offsets, re-calculates Payload Length and inserts it into IPv6
header and completes the TCP checksum using the sender-provided
pseudo-header partial checksum.
6.2. CONNECT-ETHERNET: UDP over IPv4 with template and derived fields
Original sample [UDP] over [IPv4] Ethernet frame layout is
illustrated below.
This frame is to be transmitted from the proxy to the client over
CONNECT-ETHERNET.
Rosomakho & Pauly Expires 31 August 2026 [Page 22]
Internet-Draft HTTP Datagram Compression February 2026
|0 7|8 15|16 23|24 31|32 39|40 47|
+--------+--------+--------+--------+--------+--------+
| Destination MAC address |
| 00:00:5E:00:53:01 |
+--------+--------+--------+--------+--------+--------+
| Source MAC address |
| 00:00:5E:00:53:02 |
+--------+--------+--------+--------+--------+--------+
| 0x0800 |
| EtherType | ETHERNET HEADER
+-----------------+
|0 7|8 15|16 23|16 31|
+--------+-------+----------------+----------------+----------------+
|0 1 0 0 |0 1 0 1| 0x02 | 0x04cc | ^
|Version |Hdr Len| Traffic Class | Total length | |
+--------+-------+----------------+------+--------------------------+ I
| 0x0000 |0 1 0 |0 0 0 0 0 0 0 0 0 0 0 0 0 | P
| Identification |Flags | Fragment offset |
+----------------+----------------+------+--------------------------+ H
| 0x40 | 0x11 | 0xb21b | E
| TTL | Protocol | Header checksum | A
+----------------+----------------+---------------------------------+ D
| 192.0.2.1 | E
| Source Address | R
+-------------------------------------------------------------------+ |
| 192.0.2.2 | |
| Destination Address | v
+---------------------------------+---------------------------------+
| 0xc199 | 0x1151 | ^
| Source port | Destination port | |
+---------------------------------+---------------------------------+ |
| 0x04b8 | 0x72de | U
| Length | Checksum | D
+---------------------------------+---------------------------------+ P
| | |
| UDP payload (1200 bytes) | |
| ... | v
Figure 19: Example UDP over IPv4 Ethernet frame before optimization
This example assumes that the peer supports templates, IPv4 total
length, IPv4 header checksum, UDP length in IPv4 packet and UDP
checksum in IPv4 packet derived field. These capabilities were
communicated using the following http-datagram-contexts HTTP field in
client requesting CONNECT-ETHERNET extended CONNECT.
http-datagram-contexts = max-templates=1, max-templates-segments=1, derived=(0 2 4 7), mtu=1500
Rosomakho & Pauly Expires 31 August 2026 [Page 23]
Internet-Draft HTTP Datagram Compression February 2026
Figure 20: http-datagram-contexts request example
Total length and header checksum in IPv4 header as well as length and
checksum in UDP header can be derived by the peer, so these fields
are removed before calculating static segments. Resulting context
for the derived field is defined using DERIVED_ASSIGN capsule:
DERIVED_ASSIGN Capsule {
Type (i) = 0x3ee31442,
Length (i) = 6,
Context ID (i) = 1,
Next Context ID (i) = 0,
Derived Field Type (i) = 0
Derived Field Type (i) = 2
Derived Field Type (i) = 4
Derived Field Type (i) = 7
}
Figure 21: DERIVED_ASSIGN Capsule for example IPv4/UDP ethernet frame
Table below illustrates fields present in Ethernet, IPv4 and UDP
headers after derived fields were removed, their offsets in bits from
the beginning of the frame and if they are likely to be static for
most packets of a given traffic flow
Rosomakho & Pauly Expires 31 August 2026 [Page 24]
Internet-Draft HTTP Datagram Compression February 2026
+========+================+========+===================+========+
| Offset | Field name | Length | Value | Static |
+========+================+========+===================+========+
| 0 | Destination | 48 | 00:00:5E:00:53:01 | Yes |
| | MAC address | | | |
+--------+----------------+--------+-------------------+--------+
| 48 | Source MAC | 48 | 00:00:5E:00:53:02 | Yes |
| | address | | | |
+--------+----------------+--------+-------------------+--------+
| 96 | EtherType | 16 | 0x0800 | Yes |
+--------+----------------+--------+-------------------+--------+
| 112 | Version | 4 | 0100b | Yes |
+--------+----------------+--------+-------------------+--------+
| 116 | Header length | 4 | 0101b | Yes |
+--------+----------------+--------+-------------------+--------+
| 120 | Traffic Class | 8 | 0x02 | Yes |
+--------+----------------+--------+-------------------+--------+
| 128 | Identification | 16 | 0x0000 | Yes |
+--------+----------------+--------+-------------------+--------+
| 144 | Flags | 3 | 010b | Yes |
+--------+----------------+--------+-------------------+--------+
| 147 | Fragment | 13 | 0000000000000b | Yes |
| | offset | | | |
+--------+----------------+--------+-------------------+--------+
| 160 | TTL | 8 | 0x40 | Yes |
+--------+----------------+--------+-------------------+--------+
| 168 | Protocol | 8 | 0x11 | Yes |
+--------+----------------+--------+-------------------+--------+
| 176 | Source address | 32 | 192.0.2.1 | Yes |
+--------+----------------+--------+-------------------+--------+
| 208 | Destination | 32 | 192.0.2.2 | Yes |
| | address | | | |
+--------+----------------+--------+-------------------+--------+
| 240 | Source port | 16 | 0xc199 | Yes |
+--------+----------------+--------+-------------------+--------+
| 256 | Destination | 16 | 0x1151 | Yes |
| | port | | | |
+--------+----------------+--------+-------------------+--------+
| 272 | UDP payload | 9600 | ... | No |
+--------+----------------+--------+-------------------+--------+
Table 3: Ethernet, IPv4 and UDP header fields in example frame
A single static segment model can be used for the initial part of the
HTTP datagram after derived fields were removed:
Rosomakho & Pauly Expires 31 August 2026 [Page 25]
Internet-Draft HTTP Datagram Compression February 2026
+=======+=======+===============+======================================================================+
|Segment|Segment|Segment |Segment Payload |
|Offset |Length |Contents | |
+=======+=======+===============+======================================================================+
|0 |34 |Source MAC |0x00005E00530100005E00530208004502000040004011c0000201c0000202c1991151|
| | |address, | |
| | |Destination MAC| |
| | |address, | |
| | |EtherType, | |
| | |Version, Header| |
| | |length and | |
| | |Traffic Class, | |
| | |Identification,| |
| | |Flags, Fragment| |
| | |offset, TTL, | |
| | |Protocol, | |
| | |Source address,| |
| | |Destination | |
| | |address, Source| |
| | |port and | |
| | |Destination | |
| | |port | |
+-------+-------+---------------+----------------------------------------------------------------------+
Table 4: Static segment for example Ethernet/IPv4/UDP frame
Resulting TEMPLATE_ASSIGN capsule with proxy-allocated odd Context ID
is illustrated below:
TEMPLATE_ASSIGN Capsule {
Type (i) = 0x3ee3143f,
Length (i) = 38,
Context ID (i) = 3,
Next Context ID (i) = 1,
Static Segment {
Segment Offset (i) = 0,
Segment Length (i) = 34,
Segment Payload = 0x00005E00530100005E00530208004502000040004011c0000201c0000202c1991151,
}
}
Figure 22: TEMPLATE_ASSIGN Capsule for example IPv4/UDP ethernet
frame
The resulting processing context chain reduces per-frame overhead by
removing 34 bytes of repeated header material, increasing the
effective MTU when datagrams are encapsulated in QUIC DATAGRAM
frames.
Rosomakho & Pauly Expires 31 August 2026 [Page 26]
Internet-Draft HTTP Datagram Compression February 2026
The sender concatenates all variable regions in increasing offset
order.
Upon receiving the datagram with Context ID 3, client re-assembles
the datagram by appending variable segments to the static, re-
calculates derived fields and inserts them at appropriate locations
in the datagram.
7. Security Considerations
This specification changes how HTTP Datagrams are reconstructed but
does not weaken transport-layer integrity or confidentiality
protections provided by the underlying HTTP mapping. All Capsules
travel on the reliable control stream and inherit those protections.
7.1. Resource Exhaustion
Processing contexts introduce receiver state and reconstruction work.
An attacker could attempt to exhaust memory or CPU by creating
excessive numbers of templates and static segments, purposely sending
datagrams referencing not-yet-installed contexts and causing
excessive buffering of unknown Context IDs.
Implementations MUST enforce limits on number of active templates and
static segments and restrict memory used for buffering datagrams with
unknown contexts.
7.2. Amplification
Derived fields and template reconstruction increase the size of the
reconstructed packet relative to the received datagram payload. An
attacker could exploit this to amplify processing cost and perform a
denial-of-service attack.
Endpoints MUST ensure that reconstructed packet size does not exceed
the negotiated MTU and SHOULD apply rate limiting when expansion
ratios are abnormally high.
8. IANA Considerations
8.1. HTTP Capsule Types Registration
This specification registers the following values in the "HTTP
Capsule Types" registry:
Rosomakho & Pauly Expires 31 August 2026 [Page 27]
Internet-Draft HTTP Datagram Compression February 2026
+============+=================+
| Value | Capsule Type |
+============+=================+
| 0x3ee3143f | TEMPLATE_ASSIGN |
+------------+-----------------+
| 0x3ee31440 | TEMPLATE_ACK |
+------------+-----------------+
| 0x3ee31441 | TEMPLATE_CLOSE |
+------------+-----------------+
| 0x3ee31442 | DERIVED_ASSIGN |
+------------+-----------------+
| 0x3ee31443 | DERIVED_ACK |
+------------+-----------------+
| 0x3ee31444 | DERIVED_CLOSE |
+------------+-----------------+
| 0x3ee31445 | CHECKSUM_ASSIGN |
+------------+-----------------+
| 0x3ee31446 | CHECKSUM_ACK |
+------------+-----------------+
| 0x3ee31447 | CHECKSUM_CLOSE |
+------------+-----------------+
Table 5
All of these new entries use the following values for these fields:
Status: provisional (permanent if this document is approved)
Reference: This document
Change Controller: IETF
Contact: MASQUE Working Group masque@ietf.org
Notes: None
8.2. HTTP Field Name Registration
This specification registers the following value in the "HTTP Field
Name" registry:
* Field Name: http-datagram-contexts
* Status: provisional (permanent if approved)
* Structured Type: Dictionary
* Reference: This document
Rosomakho & Pauly Expires 31 August 2026 [Page 28]
Internet-Draft HTTP Datagram Compression February 2026
* Comments: None
8.3. HTTP Datagram Derived Field Types Registry
IANA is requested to create a new registry titled "HTTP Datagram
Derived Field Types". The registration policy is expert review as
specified in Section 4.5 of [IANA-POLICY]. This new registry governs
the Derived Field types that appear in DERIVED_ASSIGN capsule and
derived list of http-datagram-contexts dictionary.
This new registry contains five columns:
Type: A positive integer identifying the field type
Name: A short name of the field
Description: A description of the field
Protocols: A list of HTTP Upgrade Tokens that the derived field type
can apply
Reference: An optional reference defining the use of the entry.
The registry's initial entries are as follows:
+====+====================+=============+================+=========+
|Type|Name |Description |Protocols |Reference|
+====+====================+=============+================+=========+
|0 |ipv4-total-length |IPv4 Total |connect-ip, |This |
| | |Length field |connect-ethernet|document |
| | |derived from | | |
| | |reconstructed| | |
| | |packet size | | |
+----+--------------------+-------------+----------------+---------+
|1 |ipv6-payload-length |IPv6 Payload |connect-ip, |This |
| | |Length field |connect-ethernet|document |
| | |derived from | | |
| | |reconstructed| | |
| | |packet size | | |
+----+--------------------+-------------+----------------+---------+
|2 |ipv4-udp-length |UDP Length |connect-ip, |This |
| | |derived from |connect-ethernet|document |
| | |UDP header to| | |
| | |end of IPv4 | | |
| | |packet | | |
+----+--------------------+-------------+----------------+---------+
|3 |ipv6-udp-length |UDP Length |connect-ip, |This |
| | |derived from |connect-ethernet|document |
Rosomakho & Pauly Expires 31 August 2026 [Page 29]
Internet-Draft HTTP Datagram Compression February 2026
| | |UDP header to| | |
| | |end of IPv6 | | |
| | |packet | | |
+----+--------------------+-------------+----------------+---------+
|4 |ipv4-header-checksum|IPv4 header |connect-ip, |This |
| | |checksum |connect-ethernet|document |
| | |computed over| | |
| | |IPv4 header | | |
+----+--------------------+-------------+----------------+---------+
|5 |ipv4-tcp-checksum |TCP checksum |connect-ip, |This |
| | |computed over|connect-ethernet|document |
| | |IPv4 pseudo- | | |
| | |header and | | |
| | |segment | | |
+----+--------------------+-------------+----------------+---------+
|6 |ipv6-tcp-checksum |TCP checksum |connect-ip, |This |
| | |computed over|connect-ethernet|document |
| | |IPv6 pseudo- | | |
| | |header and | | |
| | |segment | | |
+----+--------------------+-------------+----------------+---------+
|7 |ipv4-udp-checksum |UDP checksum |connect-ip, |This |
| | |computed over|connect-ethernet|document |
| | |IPv4 pseudo- | | |
| | |header and | | |
| | |segment | | |
+----+--------------------+-------------+----------------+---------+
|8 |ipv6-udp-checksum |UDP checksum |connect-ip, |This |
| | |computed over|connect-ethernet|document |
| | |IPv6 pseudo- | | |
| | |header and | | |
| | |segment | | |
+----+--------------------+-------------+----------------+---------+
Table 6
9. References
9.1. Normative References
[CONNECT-ETHERNET]
Sedeño, A., "Proxying Ethernet in HTTP", Work in Progress,
Internet-Draft, draft-ietf-masque-connect-ethernet-08, 10
October 2025, <https://datatracker.ietf.org/doc/html/
draft-ietf-masque-connect-ethernet-08>.
Rosomakho & Pauly Expires 31 August 2026 [Page 30]
Internet-Draft HTTP Datagram Compression February 2026
[CONNECT-IP]
Pauly, T., Ed., Schinazi, D., Chernyakhovsky, A.,
Kühlewind, M., and M. Westerlund, "Proxying IP in HTTP",
RFC 9484, DOI 10.17487/RFC9484, October 2023,
<https://www.rfc-editor.org/rfc/rfc9484>.
[CONNECT-UDP]
Schinazi, D., "Proxying UDP in HTTP", RFC 9298,
DOI 10.17487/RFC9298, August 2022,
<https://www.rfc-editor.org/rfc/rfc9298>.
[HTTP-DATAGRAMS]
Schinazi, D. and L. Pardue, "HTTP Datagrams and the
Capsule Protocol", RFC 9297, DOI 10.17487/RFC9297, August
2022, <https://www.rfc-editor.org/rfc/rfc9297>.
[INCREMENTAL-CHECKSUM]
Rijsinghani, A., Ed., "Computation of the Internet
Checksum via Incremental Update", RFC 1624,
DOI 10.17487/RFC1624, May 1994,
<https://www.rfc-editor.org/rfc/rfc1624>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<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,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[STRUCTURED-HTTP]
Nottingham, M. and P. Kamp, "Structured Field Values for
HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
<https://www.rfc-editor.org/rfc/rfc8941>.
9.2. Informative References
[IANA-POLICY]
Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/rfc/rfc8126>.
[IPv4] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/rfc/rfc791>.
Rosomakho & Pauly Expires 31 August 2026 [Page 31]
Internet-Draft HTTP Datagram Compression February 2026
[IPv6] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/rfc/rfc8200>.
[TCP] Eddy, W., Ed., "Transmission Control Protocol (TCP)",
STD 7, RFC 9293, DOI 10.17487/RFC9293, August 2022,
<https://www.rfc-editor.org/rfc/rfc9293>.
[TCP-PERF] Borman, D., Braden, B., Jacobson, V., and R.
Scheffenegger, Ed., "TCP Extensions for High Performance",
RFC 7323, DOI 10.17487/RFC7323, September 2014,
<https://www.rfc-editor.org/rfc/rfc7323>.
[UDP] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
DOI 10.17487/RFC0768, August 1980,
<https://www.rfc-editor.org/rfc/rfc768>.
Acknowledgments
TODO acknowledge.
Authors' Addresses
Yaroslav Rosomakho
Zscaler
Email: yrosomakho@zscaler.com
Tommy Pauly
Apple
Email: tpauly@apple.com
Rosomakho & Pauly Expires 31 August 2026 [Page 32]