Delay-Tolerant Networking UDP Convergence Layer Protocol Version 2
draft-ietf-dtn-udpcl-00
| Document | Type | Active Internet-Draft (dtn WG) | |
|---|---|---|---|
| Authors | Brian Sipos , Joshua Deaton | ||
| Last updated | 2024-11-07 | ||
| Replaces | draft-sipos-dtn-udpcl | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Additional resources |
GitHub Repository
Mailing list discussion |
||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-dtn-udpcl-00
Delay-Tolerant Networking B. Sipos
Internet-Draft JHU/APL
Intended status: Standards Track J. Deaton
Expires: 11 May 2025 SAIC
7 November 2024
Delay-Tolerant Networking UDP Convergence Layer Protocol Version 2
draft-ietf-dtn-udpcl-00
Abstract
This document describes a UDP convergence layer (UDPCL) for Delay-
Tolerant Networking (DTN). This version of the UDPCL protocol
clarifies requirements of RFC7122, adds discussion of multicast
addressing, congestion signaling, and updates to the Bundle Protocol
(BP) contents, encodings, and convergence layer requirements in BP
version 7. Specifically, the UDPCL uses CBOR-encoded BPv7 bundles as
its service data unit being transported and provides an unreliable
transport of such bundles. This version of UDPCL also includes
security and extensibility mechanisms.
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 11 May 2025.
Copyright Notice
Copyright (c) 2024 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
Sipos & Deaton Expires 11 May 2025 [Page 1]
Internet-Draft DTN UDPCLv2 November 2024
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
1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Use of CDDL . . . . . . . . . . . . . . . . . . . . . . . 5
1.3. Requirements Language . . . . . . . . . . . . . . . . . . 5
1.4. Definitions Specific to the UDPCL Protocol . . . . . . . 6
2. General Protocol Description . . . . . . . . . . . . . . . . 7
2.1. Convergence Layer Services . . . . . . . . . . . . . . . 8
2.2. PKIX Environments and CA Policy . . . . . . . . . . . . . 9
2.3. UDP Conversation Stability . . . . . . . . . . . . . . . 9
2.4. Path Characterization . . . . . . . . . . . . . . . . . . 10
2.5. Fragmentation Policies . . . . . . . . . . . . . . . . . 10
2.6. Error Checking Policies . . . . . . . . . . . . . . . . . 11
2.7. Congestion Control Policies . . . . . . . . . . . . . . . 11
3. UDPCL Operation . . . . . . . . . . . . . . . . . . . . . . . 12
3.1. IP Header . . . . . . . . . . . . . . . . . . . . . . . . 12
3.2. UDP Header . . . . . . . . . . . . . . . . . . . . . . . 13
3.3. UDPCL Packets . . . . . . . . . . . . . . . . . . . . . . 14
3.3.1. Redundant Transmission . . . . . . . . . . . . . . . 15
3.4. UDPCL Messages . . . . . . . . . . . . . . . . . . . . . 15
3.5. UDPCL Extension Items . . . . . . . . . . . . . . . . . . 17
3.5.1. Extension Support . . . . . . . . . . . . . . . . . . 18
3.5.2. Transfer . . . . . . . . . . . . . . . . . . . . . . 18
3.5.3. Sender Listen . . . . . . . . . . . . . . . . . . . . 20
3.5.4. Sender Node ID . . . . . . . . . . . . . . . . . . . 21
3.5.5. DTLS Initiation (STARTTLS) . . . . . . . . . . . . . 21
3.5.6. Peer Probe . . . . . . . . . . . . . . . . . . . . . 22
3.5.7. Peer Confirmation . . . . . . . . . . . . . . . . . . 24
3.5.8. ECN Counts . . . . . . . . . . . . . . . . . . . . . 25
3.6. Identified Transfers . . . . . . . . . . . . . . . . . . 26
3.6.1. Bundle Transfer ID . . . . . . . . . . . . . . . . . 26
3.6.2. Segmentation and Reassembly . . . . . . . . . . . . . 27
3.7. Path Characterization Procedures . . . . . . . . . . . . 28
3.7.1. Packetization Layer Path MTU Discovery . . . . . . . 28
3.7.2. Delay Time Estimation . . . . . . . . . . . . . . . . 29
3.7.3. Throughput and Loss Estimation . . . . . . . . . . . 29
3.7.4. Congestion Control Feedback . . . . . . . . . . . . . 30
3.8. UDPCL Security . . . . . . . . . . . . . . . . . . . . . 31
3.8.1. Entity Identification . . . . . . . . . . . . . . . . 31
3.8.2. Certificate Profile for UDPCL . . . . . . . . . . . . 32
3.8.3. DTLS Handshake . . . . . . . . . . . . . . . . . . . 32
3.8.4. DTLS Authentication . . . . . . . . . . . . . . . . . 32
Sipos & Deaton Expires 11 May 2025 [Page 2]
Internet-Draft DTN UDPCLv2 November 2024
3.8.5. Policy Recommendations . . . . . . . . . . . . . . . 32
3.8.6. Example Secured and Bidirectional Transfers . . . . . 33
4. Implementation Status . . . . . . . . . . . . . . . . . . . . 34
5. Security Considerations . . . . . . . . . . . . . . . . . . . 35
5.1. Threat: Passive Leak of Node Data . . . . . . . . . . . . 35
5.2. Threat: Passive Leak of Bundle Data . . . . . . . . . . . 35
5.3. Threat: Transport Security Stripping . . . . . . . . . . 36
5.4. Threat: Weak DTLS Configurations . . . . . . . . . . . . 36
5.5. Threat: Untrusted End-Entity Certificate . . . . . . . . 36
5.6. Threat: Certificate Validation Vulnerabilities . . . . . 37
5.7. Threat: BP Node Impersonation . . . . . . . . . . . . . . 37
5.8. Threat: Off-Path Packet Injection . . . . . . . . . . . . 38
5.9. Threat: Denial of Service . . . . . . . . . . . . . . . . 38
5.10. Mandatory-to-Implement DTLS . . . . . . . . . . . . . . . 39
5.11. Alternate Uses of DTLS . . . . . . . . . . . . . . . . . 39
5.11.1. DTLS Without Authentication . . . . . . . . . . . . 39
5.11.2. Non-Certificate DTLS Use . . . . . . . . . . . . . . 39
5.12. Predictability of Transfer IDs . . . . . . . . . . . . . 40
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 40
6.1. IP Multicast Addresses . . . . . . . . . . . . . . . . . 40
6.2. UDP Port Number . . . . . . . . . . . . . . . . . . . . . 41
6.3. UDPCL Extension Types . . . . . . . . . . . . . . . . . . 42
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 43
7.1. Normative References . . . . . . . . . . . . . . . . . . 43
7.2. Informative References . . . . . . . . . . . . . . . . . 46
Appendix A. Significant changes from RFC7122 . . . . . . . . . . 48
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 49
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 49
1. Introduction
This document describes the UDP convergence-layer protocol for Delay-
Tolerant Networking (DTN). DTN is an end-to-end architecture
providing communications in and/or through highly stressed
environments, including those with intermittent connectivity, long
and/or variable delays, and high bit error rates. More detailed
descriptions of the rationale and capabilities of these networks can
be found in "Delay-Tolerant Networking Architecture" [RFC4838].
An important goal of the DTN architecture is to accommodate a wide
range of networking technologies and environments. The protocol used
for DTN communications is the Bundle Protocol version 7 (BPv7)
[RFC9171], an application-layer protocol that is used to construct a
store-and-forward overlay network. BPv7 requires the services of a
"convergence-layer adapter" (CLA) to send and receive bundles using
the service of some "native" link, network, or Internet protocol.
This document describes one such convergence-layer adapter that uses
the well-known User Datagram Protocol (UDP). This convergence layer
Sipos & Deaton Expires 11 May 2025 [Page 3]
Internet-Draft DTN UDPCLv2 November 2024
is referred to as UDP Convergence Layer (UDPCL). For the remainder
of this document, the abbreviation "BP" without the version suffix
refers to BPv7.
The locations of the UDPCL and the Bundle Protocol in the Internet
model protocol stack (described in [RFC1122]) are shown in Figure 1.
In particular, when BP is using UDP as its bearer with UDPCL as its
convergence layer, both BP and UDPCL reside at the application layer
of the Internet model.
+-------------------------+
| DTN Application | -\
+-------------------------+ |
| Bundle Protocol (BP) | -> Application Layer
+-------------------------+ |
| UDP Conv. Layer (UDPCL) | |
+-------------------------+ |
| DTLS (optional) | -/
+-------------------------+
| UDP | ---> Transport Layer
+-------------------------+
| IPv4/IPv6 | ---> Network Layer
+-------------------------+
| Link-Layer Protocol | ---> Link Layer
+-------------------------+
Figure 1: The Locations of the Bundle Protocol and the UDP
Convergence-Layer Protocol above the Internet Protocol Stack
1.1. Scope
This document describes the format of the protocol data units passed
between entities participating in UDPCL communications. This
document does not address:
* The format of protocol data units of the Bundle Protocol, as those
are defined elsewhere in [RFC9171]. This includes the concept of
bundle fragmentation and bundle encapsulation. The UDPCL
transfers bundles as opaque data blocks.
* Mechanisms for locating or identifying other bundle entities
(peers) within a network or across an internet. The mapping of a
Node ID to a potential convergence layer (CL) protocol and network
address is left to implementation and configuration of the BP
Agent (BPA) and its various potential routing strategies, as is
the mapping of a DNS name and/or address to a choice of an end-
entity certificate to authenticate a node to its peers.
Sipos & Deaton Expires 11 May 2025 [Page 4]
Internet-Draft DTN UDPCLv2 November 2024
* Logic for routing bundles along a path toward a bundle's endpoint.
This CL protocol is involved only in transporting bundles between
adjacent entities in a routing sequence.
* Logic for performing rate control and congestion control of bundle
transfers, both incoming and outgoing from a UDPCL entity. The
signaling defined in Section 3.5.8 and Section 3.7.4 can support a
congestion control mechanism, but it is an implementation matter
to choose and configure such a mechanism.
* Policies or mechanisms for issuing Public Key Infrastructure Using
X.509 (PKIX) certificates; provisioning, deploying, or accessing
certificates and private keys; deploying or accessing certificate
revocation lists (CRLs); or configuring security parameters on an
individual entity or across a network.
* Uses of Datagram Transport Layer Security (DTLS) which are not
based on PKIX certificate authentication (see Section 5.11.2) or
in which authentication of both entities is not possible (see
Section 5.11.1).
Any UDPCL implementation requires a BP agent to perform those above
listed functions in order to perform end-to-end bundle delivery.
1.2. Use of CDDL
This document defines CBOR structure using the Concise Data
Definition Language (CDDL) of [RFC8610]. The entire CDDL structure
can be extracted from the XML version of this document using the
XPath expression:
'//sourcecode[@type="cddl"]'
The following initial fragment defines the top-level symbols of this
document's CDDL.
start = udpcl-ext-map
1.3. Requirements Language
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.
Sipos & Deaton Expires 11 May 2025 [Page 5]
Internet-Draft DTN UDPCLv2 November 2024
1.4. Definitions Specific to the UDPCL Protocol
This section contains definitions specific to the UDPCL protocol.
UDPCL Entity: This is the notional UDPCL application that initiates
UDPCL transfers. This design, implementation, configuration, and
specific behavior of such an entity is outside of the scope of
this document. However, the concept of an entity has utility
within the scope of this document as the container and initiator
of transfers. The relationship between a UDPCL entity and UDPCL
sessions is defined as follows:
* A UDPCL Entity MAY actively perform any number of transfers and
SHOULD do so whenever the entity has a bundle to forward to
another entity in the network.
* A UDPCL Entity MAY support zero or more passive listening
elements that listen for transfers from other entities in the
network, including non-unicast transfers.
These relationships are illustrated in Figure 2. For the
remainder of this document, the term "entity" without the prefix
"UDPCL" refers to a UDPCL entity.
UDP Conversation: This refers to datagrams exchanged between two
network peers, with each peer identified by a (unicast IP address,
UDP port) tuple. Because UDP is connectionless, there is no
notion of a conversation being "opened" or "closed" and some
conversations are uni-directional.
Transfer: This refers to the procedures and mechanisms for
conveyance of an individual bundle from one entity to one or more
destinations. This version of UDPCL includes a segmentation
mechanism to allow transfers which are larger than the allowable
UDP datagram size.
Transmit: This refers to a transfer outgoing from an entity as seen
from that transmitting entity.
Receive: This refers to a transfer incoming to an entity as seen
from that receiving entity.
Sipos & Deaton Expires 11 May 2025 [Page 6]
Internet-Draft DTN UDPCLv2 November 2024
+----------------------------------------+
| UDPCL Entity |
| | +----------------+
| +--------------------------------+ | | |-+
| | Actively Initiated Transfer #1 |--------->| Other | |
| +--------------------------------+ | | UDPCL Entity's | |
| ... | | Passive | |
| +--------------------------------+ | | Listener | |
| | Actively Initiated Transfer #n |--------->| | |
| | | | | |
| | Sender Listen |<---------| | |
| +--------------------------------+ | +----------------+ |
| | +-----------------+
| +---------------------------+ |
| | +---------------------------+ | +----------------+
| | | Optional Passive | | | |-+
| +-| Listener(s) |<---------+ Other | |
| +---------------------------+ | | UDPCL Entity's | |
| ^ | | Active | |
| | | | Initiator(s) | |
| +-------------| | |
+----------------------------------------+ +----------------+ |
+-----------------+
Figure 2: The relationships between UDPCL entities
2. General Protocol Description
The service of this protocol is the transmission of DTN bundles via
the User Datagram Protocol (UDP). This document specifies the
optional segmentation of bundles, procedures for DTLS setup and
teardown, and a set of messages and entity requirements. The general
operation of the protocol is as follows.
Fundamentally, the UDPCL is a (logically) unidirectional "transmit
and forget" protocol which itself maintains no long-term state and
provides no feedback from the receiver to the transmitter. The only
long-term state related to UDPCL is used by DTLS in its session
keeping (which is bound to a UDP conversation). An entity receiving
a bundle from a particular source address-and-port does not imply
that the transmitter is willing to accept bundle transfers on that
same address-and-port. It is the obligation of a BP agent and its
routing schemes to determine a bundle return path (if such a path
even exists).
Sipos & Deaton Expires 11 May 2025 [Page 7]
Internet-Draft DTN UDPCLv2 November 2024
2.1. Convergence Layer Services
This version of the UDPCL provides the following services to support
the over-laying Bundle Protocol agent. In all cases, this is not an
API definition but a logical description of how the CL can interact
with the BP agent. Each of these interactions can be associated with
any number of additional metadata items as necessary to support the
operation of the CL or BP agent.
Begin Transmission: The principal purpose of the UDPCL is to allow a
BP agent to transmit bundle data to one or more other entities.
The receiver of each transfer is identified by an (destination)
IPv4 or IPv6 address, a UDP port number, and an optional local
interface identifier (see Section 3 for details). The CL does not
necessarily perform any transmission queueing (see Section 2.7),
but might block while transmissions are being processed at the UDP
layer. Any queueing of transmissions is the obligation of the BP
agent.
Transmission Started: The UDPCL entity indicates to the BP agent
when a bundle transmission begins sending UDP datagrams. Once
started, there is no notion of a UDPCL transmission failure; a BP
agent has to rely on bundle-level status reporting to track bundle
progress through the network. Because of potential queueing or
DTLS setup time, this can be delayed from the BP agent providing
the bundle-to-transmit.
Transmission Finished: The UDPCL entity indicates to the BP agent
when a bundle has been fully transmitted. This is not a positive
indication that any next-hop receiver has either received or
processed the transfer.
Reception Started: The UDPCL entity indicates to the BP agent when a
bundle transfer has begun, which can include information about the
total size of a segmented transfer.
Reception Success: The UDPCL entity indicates to the BP agent when a
bundle has been fully transferred from a peer entity. The
transmitter of each transfer is identified by a (source) IP
address, a UDP port number, and an optional local interface
identifier (see Section 3 for details).
Reception Failure: The UDPCL entity indicates to the BP agent on
certain reasons for reception failure, notably upon an unfinished
transfer timeout (see Section 3.5.2).
Attempt DTLS Session: The UDPCL allows a BP agent to preemptively
Sipos & Deaton Expires 11 May 2025 [Page 8]
Internet-Draft DTN UDPCLv2 November 2024
attempt to establish a DTLS session with a peer entity (see
Section 3.5.5 and Section 3.8). Each session attempt can send a
different set of session negotiation parameters as directed by the
BP agent.
Close DTLS Session: The UDPCL allows a BP agent to preemptively
close an established DTLS session with a peer entity. The closure
request is on a per-session basis.
DTLS Session State Changed: The UDPCL entity indicates to the BP
agent when a DTLS session state changes. The possible DTLS
session states are defined in [RFC9147].
Begin Sender Listen: The UDPCL allows a BP agent to indicate when
packets on a particular address-and-port is listened for (see
Section 3.5.3). The Sender Listen interval is configurable for
each peer address-and-port.
End Sender Listen: The UDPCL allows a BP agent to indicate when
packets on a particular address-and-port are no longer be
accepted.
Sender Listen Received: The UDPCL entity indicates to the BP agent
when a Sender Listen extension has been received from a peer. The
Sender Node ID, if present, is part of this indication.
2.2. PKIX Environments and CA Policy
This specification gives requirements about how to use PKIX
certificates issued by a Certificate Authority (CA), but does not
define any mechanisms for how those certificates come to be. The
UDPCL uses the exact same mechanisms and makes the same assumptions
as TCPCL in Section 3.4 of [RFC9174].
2.3. UDP Conversation Stability
Unlike the loose UDPCL definition in [RFC7122], the requirements in
this document ensure that traffic between two peers with stable IP
addresses also use stable UDP port numbers. This enables the UDPCL
to be more compatible with network address translation (NAT)
middleboxes and, where necessary, enables the UDPCL to be used along
with protocols such as Session Traversal Utilities for NAT (STUN)
[RFC8489] and Interactive Connectivity Establishment (ICE) [RFC8445].
Sipos & Deaton Expires 11 May 2025 [Page 9]
Internet-Draft DTN UDPCLv2 November 2024
There is a trade-off between stability of UDP conversations and a
possible need to protect from off-path data injection, as described
in Section 5.8, so the conversation long-term stability (in
Section 3.1 and Section 3.2) is recommended while specific cases of
short-term consistency Section 3.5.2, Section 3.5.3, and
Section 3.5.6 are required.
2.4. Path Characterization
The earlier UDPCL definition in [RFC7122] assumed that BP node
operators had deep visibility into the IP networks over which bundles
would be transferred, specifically that the IP paths between UDPCL
sender and receiver had well-characterized parameters for: path
maximum transmit unit (PMTU), one-way delay time, one-way throughput
limit, and packet loss statistics (both due to congestion and to link
errors).
In situations where node operators do not have prior information
about those parameters, this version of the UDPCL supports mechanisms
to measure or estimate them. These mechanisms are defined in detail
under Section 3.7.
2.5. Fragmentation Policies
It is a implementation matter for a sending entity to determine the
PMTU to be used as a target upper-bound UDP datagram size.
The priority order of fragmentation is the following:
1. When possible, bundles too large to fit in one PMTU-sized packet
MAY be fragmented at the BP layer. Bundle payload fragmentation
does not help a large bundle if extension blocks are a major
contributor to bundle size, so in some circumstances BP layer
fragmentation will not reduce the bundle size sufficiently. It
is outside the scope of UDPCL to manage BP agent fragmentation
policies; encoded bundles are received from the BP agent either
already fragmented or not.
2. When a PMTU is available to a peer, bundles too large to fit in
one PMTU-sized packet SHALL be segmented as a UDPCL transfer (see
Section 3.6). Segmentation at this level treats bundle transfers
as opaque data, so it is independent of bundle block sizes or
counts. When a PMTU is available, IPv4 packets sent by a UDPCL
entity SHOULD have the DF bit set to allow detection of PMTU
issues.
Sipos & Deaton Expires 11 May 2025 [Page 10]
Internet-Draft DTN UDPCLv2 November 2024
3. All IPv6 packets and all IPv4 packets which do not have the DF
bit set which are larger than the link MTU will be fragmented by
the transmitting entity to fit within one link MTU. Because of
the issues listed in Section 3.2 of [RFC8085] and [RFC8900], it
is best to avoid IP fragmentation as much as possible.
A UDPCL entity SHOULD NOT proactively drop an outgoing transfer due
to datagram size. If intermediate network nodes drop IP packets it
is an implementation matter to receive network feedback (e.g. ICMP
_Fragmentation Needed_ of [RFC792] or ICMPv6 _Packet Too Big_ of
Section 3.2 of [RFC4443]). The UDPCL itself provides no transfer
acknowledgement mechanism or other protocol-level reception feedback
other than the optional Packetization Layer Path MTU Discovery
procedure, which is why an accurate PMTU for a peer is critical
information.
2.6. Error Checking Policies
The core Bundle Protocol specification assumes that bundles are
transferring over an erasure channel, i.e., a channel that either
delivers packets correctly or not at all.
A UDP transmitter SHALL NOT disable UDP checksums. A UDP receiver
SHALL NOT disable the checking of received UDP checksums.
Even when UDP checksums are enabled, a small probability of UDP
packet corruption remains. In some environments, it could be
acceptable for a BPA to occasionally receive corrupted input for some
blocks. In general, however, a BPA is RECOMMENDED to ensure the a
bundle's blocks are covered by a CRC so that next-hop receivers can
verify the block contents.
2.7. Congestion Control Policies
The applications using UDPCL for bundle transport SHALL conform to
the congestion control requirements of Section 3.1 of [RFC8085]. The
application SHALL either perform active congestion control of bundles
or behave as the Low Data-Volume application as defined in
Section 3.1.3 of [RFC8085].
When nodes have bidirectional IP capability with a peer, the ECN
marking and feedback mechanism of Section 3.7.4 can be used to
provide Active Queue Management (AQM) of UDP traffic (and thus BP
traffic) to the peer providing feedback. It is an implementation
matter to ensure that traffic patterns which require UDPCL queuing
and rate control are paired with a UDPCL entity capable of AQM and
peers which provide requisite ECN feedback.
Sipos & Deaton Expires 11 May 2025 [Page 11]
Internet-Draft DTN UDPCLv2 November 2024
When nodes have bidirectional BP transfer capability, the bundle
deletion reason code "traffic pared" can be used by a receiving agent
to signal to the bundle source application that throttling of bundles
along that BP path needs to occur.
3. UDPCL Operation
This section defines the UDPCL protocol and its interactions with
under-layers (IP and UDP) and over-layers (BP), as illustrated in
Figure 1. The section is organized from the network layer up toward
the BP layer. It also discusses behavior within the UDPCL layer,
which is illustrated in Figure 3.
+-------------------------------------------+
| Identified Transfer | Extension Signaling | <- Sequencing /
+-------------------------------------------+ segmentation
\ /
------ -----------------
\ /
+-------------------------------------------+
| Bundle | Extension Map | ... | Padding | <- Messaging
+-------------------------------------------+
| UDPCL Packet | <- Packetization
+-------------------------------------------+
Figure 3: Breakdown of sub-layers within the UDPCL
3.1. IP Header
The earlier UDPCL specification in [RFC7122] did not include guidance
on IP addressing, interface sourcing, or potential use of multicast,
though the architecture of [RFC4838] explicitly includes multicast
and anycast as expected network modes.
For each forwarding transfer the BP agent determines the mapping from
destination EID to next-hop CL parameters, including next-hop
destination address and source interface. Some EIDs represent
singleton destinations and others non-singleton destinations as
defined in Section 4.2.5.1 of [RFC9171]. The singleton-ness of an
EID does not necessarily correspond with the unicast-ness of its
forwarding, as some bundle routing schemes involve attempting
multiple parallel paths to a singleton endpoint and some involve
forwarding non-singleton-destination traffic to known individual BP
neighbors along unicast paths.
For unicast transfers to a single node, the destination address SHALL
be a non-multicast IPv4 or IPv6 address (which includes link-local
addresses). For unicast transfers, the source interface address MAY
Sipos & Deaton Expires 11 May 2025 [Page 12]
Internet-Draft DTN UDPCLv2 November 2024
be supplied by the BP agent or otherwise determined by the operating
system IP routing. When performing unicast transfers, a UDPCL entity
SHOULD require DTLS use (see Section 3.8) or restrict the network to
one protected by IPsec or some other under-layer security mechanism
(e.g., a virtual private network).
For multicast transfers to any number of nodes, the destination
address SHALL be a multicast IPv4 [IANA-IPv4-MCAST] or IPv6
[IANA-IPv6-MCAST] address. The well-known multicast addresses
defined in Section 6.1 SHALL be used as a default in the absence of
any network-specific configuration. For multicast transfers, the
source interface address MUST be supplied by the BP agent rather than
inferred by the UDPCL entity. For multicast transfers the UDPCL does
not define any security mechanism.
When supported by an implementation, the UDPCL SHOULD accept and
provide information on the local interface from which a transmission
is sent or to which a reception was received. For IPv6 this
corresponds with the IPV6_PKTINFO ancillary data API of Section 6.1
of [RFC3542]; for IPv4 this is an implementation-specific detail
supported by IP_PKTINFO ancillary data on some operating systems.
Identifying an interface for transmission or reception allows a BPA
to provide fine-grained control and visibility when UDPCL is used for
IP multicast or when link-local addressing is in use.
The IPv4 header bit _don't fragment_ (DF) is used as discussed in
Section 2.5.
The IPv4 and IPv6 header field for Explicit Congestion Notification
(ECN) is used as discussed in Section 2.7 and Section 3.7.4.
3.2. UDP Header
UDP port number 4556 has been assigned by IANA [IANA-PORTS] as the
Registered Port number for the UDPCL and SHALL be used as a default
for both source and destination. Other source or destination port
numbers MAY be used per local configuration. Determining a passive
entity's destination port number (if different from the registered
UDPCL port number) is up to the implementation.
Sipos & Deaton Expires 11 May 2025 [Page 13]
Internet-Draft DTN UDPCLv2 November 2024
If the default source port is not used, typically an operating system
assigned number in the UDP Ephemeral range (49152-65535) is used.
For repeated messaging to the same destination address-and-port, the
active entity SHOULD reuse the same source address-and-port. For
feedback messaging, the passive entity SHALL respond to the same
address-and-port that solicited the feedback and use the same source
address-and-port which was listed on. Reusing source address-and-
port allows simplifies network monitoring and analysis and also
enables bi-directional messaging as defined in Section 3.5.3,
Section 3.7.1, and Section 3.7.4.
3.3. UDPCL Packets
The lowest layer of UDPCL communication are individual-datagram
packets. To exchange UDPCL data, an active entity SHALL transmit a
UDP datagram to a listening passive entity in accordance with
[RFC0768], typically by using the services provided by the operating
system. For backward compatibility with [RFC7122], UDPCL has no
explicit message type identifier.
Each UDP datagram SHALL contain one or more UDPCL message as defined
in Section 3.4. Each type of message defines additional restrictions
on how it can be used in a packet.
The following are special cases of UDPCL packet uses.
Unframed Transfer: An unframed transfer packet SHALL consist of a
single encoded BPv6 or BPv7 bundle with no padding. This provides
backward compatibility with [RFC7122] and a allows a trivial use
of UDPCL which is just embedding an encoded bundle in a UDP
datagram.
Keepalive: A keepalive packet SHALL consist of exactly four octets
of padding with no preceding message. This behavior maintains
backward compatibility with [RFC7122].
DTLS Record: In addition to the UDPCL-specific messaging,
immediately after a DTLS Initiation (see Section 3.5.5) the DTLS
handshake sequence will begin. Packets with a leading octet value
of 0x16 SHALL be treated as a DTLS handshake record in accordance
with Section 4.1 of [RFC9147].
If the datagram with the DTLS Initiation extension is not received
by an entity, the entity SHOULD still detect the DTLS handshake
records and start the handshake sequence at that point. Packets
with a leading octet value of 0x14--0x1A or 0x20--0x3F SHALL be
treated as a DTLS sequencing failure; DTLS non-handshake records
SHOULD never be seen by the UDPCL messaging layer.
Sipos & Deaton Expires 11 May 2025 [Page 14]
Internet-Draft DTN UDPCLv2 November 2024
3.3.1. Redundant Transmission
Because the UDPCL uses unreliable UDP as its transmission layer, an
entity with information about the loss characteristics of the path to
a peer entity can intentionally perform duplicate transmissions to
improve the chances that the packet, message, or whole transfer will
arrive at the receiver. It is an implementation matter to determine
when to perform redundant transmission, and could be based on the
interface, peer network or address, or properties of the UDPCL packet
itself.
The number of duplicate transmissions for a packet is referred to as
its Redundancy Factor. A Redundancy Factor of one means to perform
no duplicate transmission. A larger Redundancy Factor will result in
more network resources used (and possibly wasted).
The time interval between original and each duplicate transmission is
referred to as its Redundancy Delay. A larger Redundancy Delay will
result in more entity resources used keeping packet contents in
memory for retransmission. To avoid a receiver mishandling redundant
packets containing Transfer items (see Section 3.6.2) the Redundancy
Delay SHOULD be no longer than the receiver's transfer timeout, if
known, or one minute (60 seconds).
For paths where losses over time are bursty, a low redundancy factor
but high redundancy delay will ensure that the duplicated packets are
transmitted over a longer span of time and (hopefully) do not have a
correlated probability of loss.
To avoid unnecessary processing on the receiver's BP Agent, when
redundant transmission is used the identified transfer (Section 3.6)
mechanism SHALL be used even for single-segment transfers. This
allows the UDPCL entity can discard any duplicate receptions before
they reach the BP Agent. If redundant transmission is used with an
unframed transfer the UDPCL has no ability to discard any duplicate
receptions and all duplicates will be seen by the receiving BP Agent.
3.4. UDPCL Messages
The middle layer of UDPCL communication are unframed, but self-
delimited, messages. Specific message types MAY be concatenated
together into a single packet, each message type indicates any
restrictions on how it can be used within a packet.
For backward compatibility with [RFC7122], UDPCL has no explicit
message type identifier. The message type is inferred by the
inspecting the data contents according to the following rules:
Sipos & Deaton Expires 11 May 2025 [Page 15]
Internet-Draft DTN UDPCLv2 November 2024
Bundle: When sent outside of an explicit identified transfer
(Section 3.6) an encoded bundle is treated as a separate message
type. This is for compatibility with [RFC7122] but comes at the
expense of the UDPCL not being able to de-duplicate any redundant
transfers (Section 3.3.1).
BPv6 Bundle: All encoded BP version 6 bundles begin with the
version identifier octet 0x06 in accordance with [RFC5050]. A
message with a leading octet value of 0x06 SHALL be treated as
a BPv6 bundle. Multiple BPv6 Bundles SHOULD NOT be present in
one UDPCL packet to maintain compatibility with [RFC7122].
BPv7 Bundle: All encoded BP version 7 bundles begin with a CBOR
array head in accordance with [RFC9171]. A message with a
leading octet value indicating CBOR array (major type 4) SHALL
be treated as a BPv7 bundle.
BPv7 bundles transmitted via UDPCL SHALL NOT include any
leading CBOR tag. If the BP agent provides bundles with such
tags the transmitting UDPCL entity SHALL remove them.
Extension Map: All UDPCL extensions SHALL be contained in a CBOR map
in accordance with the definitions of Section 3.5. The encoded
Extension Map SHALL NOT have any CBOR tags. A message with a
leading octet value indicating CBOR map (major type 5) SHALL be
treated as an Extension Map.
Padding: Padding data SHALL be a sequence of octets all with value
0x00. A message with a leading octet value of 0x00 SHALL be
treated as padding.
Padding is used to ensure a UDP datagram is exactly a desired
size. Because padding has no intrinsic length indication, if
present it SHALL be the last contents of any UDPCL packet. A
receiving UDPCL entity SHALL ignore all padding, including any
trailing non-zero octets.
A summary of how a receiving UDPCL entity can interpret the first
octet of a UDPCL packet is listed in Table 1. When inspecting using
CBOR major types, the range of values is caused by the CBOR head
encoding of [RFC8949].
Sipos & Deaton Expires 11 May 2025 [Page 16]
Internet-Draft DTN UDPCLv2 November 2024
+===============+=============+========================+
| Octet Value | Message | Message Extent |
| | Content | |
+===============+=============+========================+
| 0x00 | Padding | Remainder of packet |
+---------------+-------------+------------------------+
| 0x06 | BPv6 Bundle | Remainder of packet |
| | | (to be decoded by BPA) |
+---------------+-------------+------------------------+
| 0x14--0x1A or | DTLS Record | Remainder of packet |
| | | |
| 0x20--0x3F | | |
+---------------+-------------+------------------------+
| 0x80--0x9F | BPv7 Bundle | Remainder of packet |
| | (CBOR | (to be decoded by BPA) |
| | array) | |
+---------------+-------------+------------------------+
| 0xA0--0xBF | Extension | End of map item, |
| | Map (CBOR | possibly followed by |
| | map) | other map or padding |
+---------------+-------------+------------------------+
| others | unused | |
+---------------+-------------+------------------------+
Table 1: First-Octet Contents
3.5. UDPCL Extension Items
Extensions to UDPCL are encoded per-datagram in a single CBOR map as
defined in Section 3.4. Each UDPCL extension item SHALL be
identified by a unique Extension ID used as a key in the Extension
Map. Extension ID values SHALL be a CBOR int item which fits within a
signed 16-bit integer. Extension ID assignments are listed in
Section 6.3.
Unless prohibited by particular extension type requirements, a single
Extension Map MAY contain any combination of extension items.
Receivers SHALL ignore extension items with unknown Extension ID and
continue to process known extension items.
Sipos & Deaton Expires 11 May 2025 [Page 17]
Internet-Draft DTN UDPCLv2 November 2024
; Map structure requiring non-zero-int keys.
; CDDL cannot enforce type-specific requirements about other items
; being present (or not present) in the same map.
udpcl-ext-map = $udpcl-ext-map .within udpcl-ext-map-structure
$udpcl-ext-map = {
+ $$udpcl-ext-item
}
udpcl-ext-map-structure = {
+ ext-key => any
}
ext-key = ((-32768 .. 32767) .within int) .ne 0
Figure 4: Extension Map structure CDDL
The following subsections define the initial UDPCL extension types.
3.5.1. Extension Support
This extension allows an entity to signal its support for receiving
specific UDPCL extension types.
The Extension Support value SHALL be a CBOR array of int items. Each
item SHALL represent an extension type code which is able to be
handled by the entity sending the Extension Support.
The minimum set of Extension Support SHOULD contain values 1 through
8 inclusive, which are the extension types defined in this document.
$$udpcl-ext-item //= (
1: [ + ext-key ]
)
Figure 5: Extension Support CDDL
This extension type is expected to be used along with Sender Listen
for announcing presence to (potential) peer entities.
If an entity receives an extension type which it cannot handle, that
entity MAY send an Extension Support item in response. The
enveloping UDPCL packet SHALL use the source address-and-port that
sent the unhandled extension type as the destination of the packet.
3.5.2. Transfer
This extension item allows CL-layer segmentation of bundle transfers
as defined in Section 3.6.
Sipos & Deaton Expires 11 May 2025 [Page 18]
Internet-Draft DTN UDPCLv2 November 2024
The Transfer value SHALL be an untagged CBOR array of two or four
items. The items are defined in the following order:
Transfer ID: This field SHALL be a CBOR uint item no larger than
32-bits, which is used to correlate multiple segments.
Total Length: This optional field SHALL be a CBOR uint item no
larger than 32-bits, which is used to indicate the total length
(in octets) of the transfer. If multiple Transfer items for the
same Transfer ID are received with differing Total Length values,
the receiver SHALL treat the transfer as being malformed and
refuse to handle any further segments associated with the
transfer. If a transfer requires only a single segment, this
field SHALL be omitted and the total length treated as the size of
the Segment Data.
Segment Offset: This optional field SHALL be a CBOR uint item no
larger than 32-bits, which is used to indicate the offset (in
octets) into the transfer for the start of this segment. If a
transfer requires only a single segment, this field SHALL be
omitted and the segment offset treated as zero.
Segment Data: This field SHALL be a CBOR bstr item no larger than
2^32-1 octets, in which the segment data is contained. The bstr
itself indicates the length of the segment data.
$$udpcl-ext-item //= (
2: [
transfer-id: uint .size 4,
?(
total-length: uint .size 4,
segment-offset: uint .size 4,
),
segment-data: bstr,
]
)
Figure 6: Transfer CDDL
Multiple Transfer items MAY be present in the same UDPCL packet by
concatenating multiple Extension Map into one packet.
A transmitting entity SHALL use the same source and destination
address-and-port for all UDPCL packets comprising a single segmented
transfer. This is more strict than the requirements of Section 3.2
to ensure consistent reassembly behavior in Section 3.6.2.
Sipos & Deaton Expires 11 May 2025 [Page 19]
Internet-Draft DTN UDPCLv2 November 2024
3.5.3. Sender Listen
This extension item indicates that the transmitter is listening for
UDPCL packets on the source address-and-port used to transmit the
message containing this extension item. This is different from
simply listening on a UDP port (either the default or any other) when
the entity is behind a NAT or firewall which will not allow
unsolicited UDP/IP datagrams. Although the packet containing this
extension is not retransmitted, the time interval is finite and the
extension is sent repeatedly while the transmitter continues to
listen for packets. There is no positive indication that packets are
no longer accepted; the Sender Listen just stops being transmitted.
The Sender Listen value SHALL be an untagged uint value representing
the interval of time (in milliseconds) that the entity is willing to
accept UDPCL packets on the source address-and-port used for the
associated transmitted message. After transmitting a Sender Listen,
the entity SHALL listen for and accept datagrams on the source
address-and-port used for the associated transmitted message. As
long as the entity is still willing to accept packets, at the end of
one accept interval the entity SHALL transmit another Sender Listen
item. This repetition continues until the entity is no longer
willing to listen for packets.
A receiving entity SHOULD treat a peer as no longer listening after
an implementation-defined timeout since the last received Sender
Listen item. A RECOMMENDED Sender Listen timeout is three (3) times
the associated time duration; this allows a single dropped datagram
to not interrupt a continuous sequence.
$$udpcl-ext-item //= (
3: time-duration,
)
time-duration = uint
Figure 7: Sender Listen CDDL
Unlike the generic source port requirement in Section 3.2, when
repeated Sender Listen are transmitted in a sequence a consistent
source address-and-port SHALL be used.
The Sender Listen interval SHOULD be no shorter than 1 second and no
longer than 60 seconds.
Sipos & Deaton Expires 11 May 2025 [Page 20]
Internet-Draft DTN UDPCLv2 November 2024
An entity SHOULD include an Extension Support and Sender Node ID item
along with a Sender Listen item if the conditions of those extension
types are met. An entity MAY include any other extension type along
with a Sender Listen item. An entity SHALL NOT transmit a Sender
Listen item before or along with a DTLS Initiate if DTLS is desired
for a conversation.
This extension is not a neighbor discovery mechanism and does not
indicate an entity listening generally on a particular UDP port.
Sender Listen applies only to UDP datagrams from the the peer
address-and-port.
3.5.4. Sender Node ID
This extension item indicates the Node ID of the transmitter. For
DTLS-secured sessions (see Section 3.8.4) this extension can be used
to disambiguate an end-entity certificate which has multiple NODE-ID
values.
The Sender Node ID value SHALL be an untagged tstr value containing a
Node ID. Every Node ID SHALL be a URI consistent with the
requirements of [RFC3986] and the URI schemes of the IANA "Bundle
Protocol URI Scheme Type" registry [IANA-BUNDLE].
$$udpcl-ext-item //= (
4: nodeid,
)
nodeid = tstr
Figure 8: Sender Node ID CDDL
An entity SHOULD NOT include a Sender Node ID item if a DTLS session
has already been established and the presented end-entity certificate
contains a single NODE-ID. In this case there is no ambiguity about
which Node ID is identified by the certificate.
If an entity receives a peer Node ID which is not authenticated (by
the procedure of Section 3.8.4) that Node ID SHOULD NOT be used by a
BP agent for any discovery or routing functions. Trusting an
unauthenticated Node ID can lead to the threat described in
Section 5.7.
3.5.5. DTLS Initiation (STARTTLS)
This extension item indicates that the transmitter is about to begin
a DTLS handshake sequence in accordance with Section 3.8.
Sipos & Deaton Expires 11 May 2025 [Page 21]
Internet-Draft DTN UDPCLv2 November 2024
The DTLS Initiation value SHALL be an untagged null value. There are
no DTLS parameters actually transmitted as part of this extension, it
only serves to indicate to the recipient that the next datagram will
be a DTLS ClientHello. Although the datagram containing this
extension is not retransmitted, the DTLS handshake itself will
retransmit ClientHello messages until confirmation is received.
$$udpcl-ext-item //= (
5: null
)
Figure 9: DTLS Initiation CDDL
If the entity is configured to enable exchanging messages according
to DTLS 1.3 [RFC9147] or any successors which are compatible with
that DTLS ClientHello, the first message in any sequence to a unicast
recipient SHALL be an Extension Map with the DTLS Initiation item.
The RECOMMENDED policy is to enable DTLS for all unicast recipients,
even if security policy does not allow or require authentication.
This follows the opportunistic security model of [RFC7435], though an
active attacker could interfere with the exchange in such cases (see
Section 5.3).
The Extension Map containing a DTLS Initiation item SHALL NOT contain
any other items. A DTLS Initiation item SHALL NOT be present in any
message transmitted within a DTLS session. A receiver of a DTLS
Initiation item within a DTLS session SHALL ignore it. Between
transmitting a DTLS Initiation item and finishing a DTLS handshake
(either success or failure) an entity SHALL NOT transmit any other
UDP datagrams in that same conversation.
3.5.6. Peer Probe
This extension item provides the Probe Packet functionality of
Section 4.1 of [RFC8899] in order to support path MTU discovery
mechanism of Section 3.7.1.
The Peer Probe value SHALL be an array of three items. The items are
defined in the following order:
Nonce: The first item SHALL be a uint nonce for correlating with
Peer Confirmation extensions.
Sequence Number: The second item SHALL be a uint sequence number for
the specific Probe packet.
Confirmation Delay: The second item SHALL be a uint representing the
desired confirmation delay time (in milliseconds).
Sipos & Deaton Expires 11 May 2025 [Page 22]
Internet-Draft DTN UDPCLv2 November 2024
$$udpcl-ext-item //= (
6: [
nonce,
seqno,
confirm-delay
],
)
; A correlator nonce for confirmations
nonce = uint
seqno = uint
confirm-delay = uint
Figure 10: Peer Probe CDDL
When the Peer Probe item is present in a UDPCL packet, the Extension
Map SHALL be the only message in the packet and it SHALL be followed
by padding to a specific total size. A transmitting entity SHALL use
the same source and destination address-and-port for all UDPCL
packets containing a Peer Probe with the same nonce value. This is
more strict than the requirements of Section 3.2 to ensure consistent
confirmation behavior defined below.
The nonce value SHALL be used to correlate multiple Probe packets
into a single sequence. If an entity receives multiple unique nonce
values from the same source address-and-port and the number of unique
nonce values exceeds an upper limit, the receiving entity SHALL
ignore the Probe. The upper limit is implementation defined but
SHOULD be no less than one unique nonce at-a-time.
If the confirmation delay time is above an upper limit the receiving
entity SHALL ignore the Probe. The upper limit is implementation
defined but SHOULD be no shorter than one minute (60 seconds).
If an entity receives multiple instances of Peer Probe with the same
nonce and sequence number values, the duplicates SHALL NOT be
ignored. This makes the last duplicate transmission of the last
probe the basis of Peer Confirmation timing.
Sipos & Deaton Expires 11 May 2025 [Page 23]
Internet-Draft DTN UDPCLv2 November 2024
After an entity receives and validates a packet with a Peer Probe
extension item it SHALL wait for the indicated confirmation delay
time before sending a Peer Confirmation item. The enveloping UDPCL
packet SHALL use the source address-and-port that sent the last Probe
item as the destination of the Confirmation. Once the Peer
Confirmation packet is sent, the entity SHALL remove state associated
with the Peer Probe items being confirmed. This bounds the state on
a confirming entity and makes each Peer Confirmation with the same
nonce value incremental and not additive (_i.e._, there will never be
two Confirmations with the same nonce covering the same sequence
numbers, except for duplicate transmissions).
3.5.7. Peer Confirmation
This extension item provides the Confirmation functionality of
Section 4.2 of [RFC8899] in order to support path MTU discovery
mechanism of Section 3.7.1.
The Peer Confirmation value SHALL be an array of two items. The
items are defined in the following order:
Nonce: The first item SHALL be a uint nonce for correlating with
Peer Probe items.
Seen Sequence Range: The second item SHALL be an array of pairs of
uint values representing the range of sequence numbers of received
Probe packets with the same nonce value.
The encoding of ranges is a compressed form in which each pair of
values indicates:
1. The non-zero offset from the previous one-past-end-of-interval,
or the offset from zero if there is no preceding interval
2. The length of this interval, which is inclusive of the first and
last contained sequence number so will always be positive
Sipos & Deaton Expires 11 May 2025 [Page 24]
Internet-Draft DTN UDPCLv2 November 2024
$$udpcl-ext-item //= (
7: [
nonce,
seen-range
],
)
; Range of sequence numbers seen
seen-range = [ + seen-interval-pair ]
seen-interval-pair = (
offset: uint,
length: uint .gt 0,
)
Figure 11: Peer Confirmation CDDL
When an entity receives a packet with a Peer Confirmation extension
item it SHALL wait for the same confirmation delay used in each Probe
item for multiple Confirmation items with the same nonce. Upon
reception of all Confirmation items within the waiting delay, the
entity SHALL treat the largest value of the seen range as the PMTU to
the corresponding peer entity.
3.5.8. ECN Counts
This extension item provides the ECN Feedback functionality of
Section 4.2 of [RFC9331] in order to support congestion control
feedback of Section 3.7.4.
The ECN Counts value SHALL be an array of three items. The items are
defined in the following order:
ECT(0) Count: The first item SHALL be a uint count of packets marked
with ECT(0) received from the peer, wrapped to 32-bits.
ECT(1) Count: The second item SHALL be a uint count of packets
marked with ECT(1) received from the peer, wrapped to 32-bits.
CE Count: The third item SHALL be a uint count of packets marked
with CE received from the peer, wrapped to 32-bits.
Sipos & Deaton Expires 11 May 2025 [Page 25]
Internet-Draft DTN UDPCLv2 November 2024
$$udpcl-ext-item //= (
8: [
ect0: ecn-count,
ect1: ecn-count,
ce: ecn-count
],
)
; Wraps around at 32-bits
ecn-count = uint .size 4
Figure 12: ECN Counts CDDL
Because this extension type will only be used for feedback to a
specific transmitting peer, it SHALL NOT be present in any UDPCL
packet with an IP multicast destination.
3.6. Identified Transfers
This version of UDPCL supports CL-layer identification of bundles and
segmentation of bundles larger than the PMTU would otherwise allow.
Policies related to segmentation at or fragmentation above, or below
the UDPCL layer are defined in Section 2.5. The entire segmented
bundle is referred to as a Transfer and individual segments of a
transfer are encoded as Transfer extension items in accordance with
Section 3.5.2.
This mechanism also allows a bundle transfer to be transmitted along
with additional extension items, which the unframed bundle-in-
datagram data does not. This specification does not define any
extension items which augment an associated transfer.
3.6.1. Bundle Transfer ID
Each Transfer item contains a Transfer ID which is used to correlate
messages for a single bundle transfer. A Transfer ID does not
attempt to address uniqueness of the bundle data itself and has no
relation to concepts such as bundle fragmentation. Each invocation
of UDPCL by the BP agent, requesting transmission of a bundle
(fragmentary or otherwise), can cause the initiation of a single
UDPCL transfer.
Sipos & Deaton Expires 11 May 2025 [Page 26]
Internet-Draft DTN UDPCLv2 November 2024
Because UDPCL operation is connectionless, Transfer IDs from each
entity SHALL be unique for the operating duration of the entity. In
practice, the ID needs only be unique for the longest receiver de-
duplication and reassembly time window; but because that information
is not part of the protocol there is no way for an transmitting
entity to know the reassembly time window of any receiver (see
Section 3.6.2). When there are bidirectional bundle transfers
between UDPCL entities, an entity SHOULD NOT rely on any relation
between Transfer IDs originating from each side of the conversation.
Although there is not a strict requirement for Transfer ID initial
values or ordering (see Section 5.12), in the absence of any other
mechanism for generating Transfer IDs an entity SHALL use the
following algorithm: the initial Transfer ID from each entity is
zero; subsequent Transfer ID values are incremented from the prior
Transfer ID value by one; upon exhaustion of the entire 32-bit
Transfer ID space, the subsequent Transfer ID value is zero.
3.6.2. Segmentation and Reassembly
The full data content of a transfer SHALL be an unframed (BPv6 or
BPv7) bundle as defined in Section 3.4. A receiving entity SHALL
discard any reassembled transfer which does not properly contain a
bundle as defined in Section 3.4.
A transmitting entity MAY produce a Transfer with a single segment
(i.e., a Segment Data size identical to the Total Length) in which
case the redundant Transfer fields are omitted. A transmitting
entity SHALL NOT produce Transfer segments with overlapping span. A
transmitting entity SHOULD transmit Transfer segments in order of
Segment Offset; this makes the behavior deterministic.
A receving entity SHALL maintain transfer reassembly state based on
the tuple of packet source address-and-port and the Transfer ID sent
by that source. This relies on the stability of source port numbers
at least for the duration of a single transfer, as required by
Section 3.5.2. See Section 2.3 for options and implications of
source port number use.
Because of the nature of UDP transport, there is no guaranteed order
or timing of received Transfer items. A receiving entity SHALL
consider a transport as finished when Segment Data has been received
which fully covers the Total Length of the transfer.
A receiving entity SHALL discard any Transfer item containing
different CBOR types than defined in this document. A receiving
entity SHALL discard any Transfer item containing a segment with a
span overlapping any other in the reassembly state. That includes
Sipos & Deaton Expires 11 May 2025 [Page 27]
Internet-Draft DTN UDPCLv2 November 2024
overlapping span because of a redundant transmission (see
Section 3.3.1). Because there is no feedback indication at the UDPCL
layer, a transmitter has no indication when a Transfer item is
discarded by the receiver.
A receiving entity SHOULD discard unfinished reassembly state after
an implementation-defined timeout since the last received segment.
This timeout is purely receiver-side and represents the maximum
allowed time between sequential received datagrams (in any order),
which will be short if the datagrams take a similar network path. A
receiving entity SHALL NOT discard reassembly state upon successful
completion of a transfer, in case the transmitting entity is sending
redundant packets (Section 3.3.1) which need to be discarded.
Entities SHOULD choose a transfer timeout interval no longer than one
minute (60 seconds). Discarding an unfinished transfer causes no
indication to the transmitting entity, but does indicate this to the
receiving BP agent.
3.7. Path Characterization Procedures
The procedures defined in this section allow pairs of UDPCL entities
to characterize IP path parameters between them when those parameters
are either unknown or for troubleshooting when actual network
performance deviates from expectations.
These procedures not mandated to be used operationally, but when the
associated characterization is desired these are the procedures which
SHALL be used.
3.7.1. Packetization Layer Path MTU Discovery
This version of UDPCL is compatible with the requirements of
Packetization Layer Path MTU Discovery (PLPMTUD) from [RFC8899].
Specifically the UDPCL supports the requirements of Section 6.1 of
[RFC8899] by using the Peer Probe extension item to perform the probe
behavior and Peer Confirmation extension item for the confirmation
behavior. Because the Peer Confirmation acknowledges a possibly
large range of Peer Probe packets, this makes the UDPCL less
sensitive to large or time-variable path delays than if each Probe
was separately acknowledged.
The use of PLPMTUD is especially helpful when DTLS is used to secure
UDPCL conversations, as the DTLS confidentiality mechanism and
associated record layer reduces the maximum packet size (MPS) by an
amount depending upon the negotiated ciphersuite.
Sipos & Deaton Expires 11 May 2025 [Page 28]
Internet-Draft DTN UDPCLv2 November 2024
In case one or more Peer Probe items are sent but no corresponding
Peer Confirmation is ever received, this might indicate that the peer
has not implemented or enabled PLPMTUD and SHOULD NOT be treated as
an indication that the peer is unreachable.
3.7.2. Delay Time Estimation
The round-trip time (RTT) between two entities can be estimated by
sending a sequence of small sized Peer Probe items, each in its own
UDPCL packet, with a small or zero Confirmation Delay and measuring
the time taken to receive the corresponding Peer Confirmation item.
The sequence MAY be as short as a single packet to get a point
estimate of RTT. Otherwise, the inter-packet interval at the sender
SHALL be larger than the Confirmation Delay contained in each item.
This will cause each probe packet to correspond with a single related
confirmation packet allowing either a time-series estimation or an
average-over-time estimation of RTT.
Because there is no explicit time tagging of the acknowledgement, the
one-way delay can be assumed to be one half of the RTT total.
3.7.3. Throughput and Loss Estimation
The one-way packet loss between two entities can be estimated by
sending a sequence of equally-sized Peer Probe items, each in its own
UDPCL packet, over some short time interval and observing how many of
the probes have been seen in one or more corresponding Peer
Confirmation item. For relatively low loss rates, a BER can be
estimated by assuming each lost packet is caused by an equivalent to
a single random error.
Similarly, a sequence of relatively large-sized (for the expected
throughput order-of-magnitude) Peer Probe items, each in its own
UDPCL packet, and the total volume indicated by corresponding Peer
Confirmation items over some time interval can be used to estimate
the one-way throughput limit.
For both cases above, the Probe packets can be combined with ECN
markings as described in Section 3.7.4 to ensure that losses or
throughput limits are not related to intermediate queuing congestion.
Sipos & Deaton Expires 11 May 2025 [Page 29]
Internet-Draft DTN UDPCLv2 November 2024
3.7.4. Congestion Control Feedback
AQM can be performed using "classic" ECN of [RFC3168] or with more
advanced methods such as the ECN Protocol for Low Latency, Low Loss,
and Scalable Throughput (L4S) of [RFC9331]. These mechanisms allow
for endpoints to implement internet-friendly congestion control with
a small amount of application-level feedback of ECN data. The ECN
Counts extension of Section 3.5.8 allows a UDPCL entity to both
signal that it is ECN capable and to report ECN feedback in a way
compatible with both [RFC3168] and [RFC9331].
Because the information base defined below counts ECN values based on
UDP conversation, the feedback occurs at the level of the entire
conversation and not an individual message or bundle transfer within.
When present, any sending queues of a UDPCL entity SHALL be organized
around the UDP conversation.
When an entity has enabled a congestion control mechanism, it SHALL
mark outgoing IP packets with an ECN field of either ECT(0) or ECT(1)
codepoint if they contain bundle data (either from an unframed
transfer or an identified transfer Section 3.5.2). This marking is
the signal that the sending entity is ECN capable and desires to
receive ECN feedback.
When an entity has enabled ECN feedback and receives a UDPCL packet
with a unicast IP destination and an ECN field other than the _Not-
ECT_ codepoint, the ECN field of the IP packet SHALL be used to
update the entry of the ECN Feedback information table corresponding
to its UDP Conversation. When a new entry is needed in the ECN
Feedback information table, the counts SHALL be initialized to zero.
When an entity has ECN feedback for a peer, it SHALL send ECN Counts
extension items to that peer. The ECN Counts extension MAY be sent
periodically by a timer or when count values are increased above some
threshold. When triggered by timer, the minimum interval SHOULD be
no shorter than 1 second. When triggered by count change, the
minimum increase SHOULD be no a change in CE Count being
// TBD% of the sum of the changes of ECT(0) Count and ECT(1) Count.
The information base for ECN Feedback information is a logical table
containing the columns of Table 2.
Sipos & Deaton Expires 11 May 2025 [Page 30]
Internet-Draft DTN UDPCLv2 November 2024
+==============+============================================+
| Name | Description |
+==============+============================================+
| UDP | This is the four-tuple of address-and-port |
| Conversation | for the remote and local UDP endpoints. |
+--------------+--------------------------------------------+
| ECT(0) Count | This is the total number of IP packets |
| | received in the UDP Conversation with the |
| | ECN field containing the ECT(0) codepoint. |
+--------------+--------------------------------------------+
| ECT(1) Count | This is the total number of IP packets |
| | received in the UDP Conversation with the |
| | ECN field containing the ECT(0) codepoint. |
+--------------+--------------------------------------------+
| CE Count | This is the total number of IP packets |
| | received in the UDP Conversation with the |
| | ECN field containing the CE codepoint. |
+--------------+--------------------------------------------+
Table 2: ECN Feedback Information Columns
3.8. UDPCL Security
This version of the UDPCL supports establishing a DTLS session within
an existing UDP conversation. When DTLS is used within the UDPCL it
affects the entire conversation. There is no concept of a plaintext
message being sent in a conversation after a DTLS session is
established.
Once established, the lifetime of a DTLS session SHALL be bound by
the DTLS session ticket lifetime or either peer sending a Closure
Alert record.
Subsequent DTLS session attempts to the same passive entity MAY
attempt to use the DTLS session resumption feature. There is no
guarantee that the passive entity will accept the request to resume a
DTLS session, and the active entity cannot assume any resumption
outcome.
3.8.1. Entity Identification
The UDPCL uses DTLS for certificate exchange in both directions to
identify each entity and to allow each entity to authenticate its
peer. Each certificate can potentially identify multiple entities
and there is no problem using such a certificate as long as the
identifiers are sufficient to meet authentication policy (as
described in later sections) for the entity which presents it.
Sipos & Deaton Expires 11 May 2025 [Page 31]
Internet-Draft DTN UDPCLv2 November 2024
The types and priorities of identities used by DTLS in UDPCL is the
same as those for TLS in TCPCL as defined in Section 4.4.1 of
[RFC9174].
3.8.2. Certificate Profile for UDPCL
All end-entity certificates used by a UDPCL entity SHALL conform to
the profile defined in Section 4.4.2 of [RFC9174].
3.8.3. DTLS Handshake
The signaling for DTLS Initiation is described in Section 3.5.5.
After sending or receiving an Extension Map containing a DTLS
Initiation item, an entity SHALL begin the handshake procedure of
Section 5 of [RFC9147]. By convention, this protocol uses the entity
which sent the DTLS Initiation (the active peer) as the "client" role
of the DTLS handshake request.
Upon receiving an unexpected ClientHello record outside of a DTLS
session, an entity SHALL begin the DTLS handshake procedure as if a
DTLS Initiation had been received. This allows recovering from a
dropped packet containing DTLS Initiation.
3.8.4. DTLS Authentication
The function and mechanism of DTLS authentication in UDPCL is the
same as for TLS in TCPCL as defined in Section 4.4.4 of [RFC9174],
with the exception that Node ID Authentication is based on an
optional Sender Node ID extension (see Section 3.5.4) used to
disambiguate when an end-entity certificate contains multiple NODE-ID
values.
3.8.5. Policy Recommendations
The policy recommendations given here are are the same as those for
TCPCL in Section 4.4.5 of [RFC9174]. They are restated in this
document for clarity.
A RECOMMENDED security policy is to enable the use of OCSP checking
during DTLS handshake. A RECOMMENDED security policy is that if an
Extended Key Usage is present that it needs to contain "id-kp-
bundleSecurity" of [IANA-SMI] to be usable with UDPCL security. A
RECOMMENDED security policy is to require a validated NODE-ID and to
ignore any network-level DNS-ID or IPADDR-ID.
This policy relies on and informs the certificate requirements in
Section 3.8.2. This policy assumes that a DTN-aware CA (see
Section 2.2) will only issue a certificate for a Node ID when it has
Sipos & Deaton Expires 11 May 2025 [Page 32]
Internet-Draft DTN UDPCLv2 November 2024
verified that the private key holder actually controls the DTN node;
this is needed to avoid the threat identified in Section 5.7. This
policy requires that a certificate contain a NODE-ID and allows the
certificate to also contain network-level identifiers. A tailored
policy on a more controlled network could relax the requirement on
Node ID validation and allow just network-level identifiers to
authenticate a peer.
3.8.6. Example Secured and Bidirectional Transfers
This simple example shows a sequence of pre-transfer setup followed
by a set of (unrelated) bundle transfers. All messaging in this
example occurs between the same Entity A address-and-port and Entity
B address-and-port.
The example Entity A has a policy to only send or receive bundles
within a DTLS session, so any outgoing bundles to Entity B are queued
until the DTLS session is established. Because Entity A is willing
to accept transfers on its ephemeral UDP port, the first outgoing
message after the DTLS handshake contains the Sender Listen extension
(along with a Sender Node ID indicating its identity to Entity B).
Sipos & Deaton Expires 11 May 2025 [Page 33]
Internet-Draft DTN UDPCLv2 November 2024
Entity A Entity B
active peer passive peer
+-------------------------+
| Initiate DTLS Ext. | ->
+-------------------------+
+-------------------------+ +-------------------------+
| DTLS Negotiation | -> <- | DTLS Negotiation |
| (as client) | | (as server) |
+-------------------------+ +-------------------------+
DNS-ID and IPADDR-ID authentication occurs.
Secured UDPCL messaging can begin.
+-------------------------+
| Sender Listen Ext. | ->
| Sender Node ID Ext. |
+-------------------------+
NODE-ID authentication occurs.
DTLS session is established, transfers can begin.
+-------------------------+
| Unframed Transfer | -> +-------------------------+
+-------------------------+ <- | Unframed Transfer |
+-------------------------+ +-------------------------+
| Unframed Transfer | ->
+-------------------------+
Figure 13: An example of the flow of protocol messages on a
single UDP conversation between two entities
4. Implementation Status
This section is to be removed before publishing as an RFC.
[NOTE to the RFC Editor: please remove this section before
publication, as well as the reference to [RFC7942],
[github-dtn-demo-agent], and [github-dtn-wireshark].]
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
Sipos & Deaton Expires 11 May 2025 [Page 34]
Internet-Draft DTN UDPCLv2 November 2024
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations can
exist.
An example implementation of the this draft of UDPCL has been created
as a GitHub project [github-dtn-demo-agent] and is intended to use as
a proof-of-concept and as a possible source of interoperability
testing. This example implementation uses D-Bus as the CL-BP Agent
interface, so it only runs on hosts which provide the Python "dbus"
library.
A wireshark dissector for UDPCL has been created as a GitHub project
[github-dtn-wireshark] and has been kept in-sync with the latest
encoding of this specification.
5. Security Considerations
This section separates security considerations into threat categories
based on guidance of BCP 72 [RFC3552].
5.1. Threat: Passive Leak of Node Data
When used without DTLS security, the UDPCL can expose the Node ID and
other configuration data to passive eavesdroppers. This can occur
even if no bundle transfers are transmitted. This can be avoided by
always using DTLS, even if authentication is not available (see
Section 5.11).
5.2. Threat: Passive Leak of Bundle Data
UDPCL can be used to provide point-to-point unicast transport
security, but does not provide multicast security, security of data-
at-rest, and does not guarantee end-to-end bundle security. In those
cases the bundle security mechanisms defined in [RFC9172] are to be
used instead.
When used without DTLS security, the UDPCL exposes all bundle data to
passive eavesdroppers. This can be avoided by always using DTLS for
unicast messaging, even if authentication is not available (see
Section 5.11).
Sipos & Deaton Expires 11 May 2025 [Page 35]
Internet-Draft DTN UDPCLv2 November 2024
5.3. Threat: Transport Security Stripping
When security policy allows non-DTLS messaging, UDPCL does not
protect against active network attackers. It is possible for a on-
path attacker to drop or alter packets containing Extension Map and/
or DTLS handshake records, which will cause the receiver to not
negotiate a DTLS session. This leads to the "SSL Stripping" attack
described in [RFC7457].
When DTLS is available on an entity, it is strongly encouraged that
the security policy disallow non-DTLS messaging for unicast purposes.
This requires that the DTLS handshake occurs before any other UDPCL
messaging, regardless of the policy-driven parameters of the
handshake and policy-driven handling of the handshake outcome.
One mechanism to mitigate the possibility of DTLS stripping is the
use of DNS-based Authentication of Named Entities (DANE) [RFC6698]
toward the passive peer. This mechanism relies on DNS and is
unidirectional, so it doesn't help with applying policy toward the
active peer, but it can be useful in an environment using
opportunistic security. The configuration and use of DANE are
outside of the scope of this document.
The negotiated use of DTLS is identical behavior to STARTTLS use in
[RFC2595], [RFC4511], and others.
5.4. Threat: Weak DTLS Configurations
Even when using DTLS to secure the UDPCL session, the actual
ciphersuite negotiated between the DTLS peers can be insecure.
Recommendations for ciphersuite use are included in BCP 195
[RFC7525]. It is up to security policies within each UDPCL entity to
ensure that the negotiated DTLS ciphersuite meets transport security
requirements.
5.5. Threat: Untrusted End-Entity Certificate
The profile in Section 3.8.4 uses end-entity certificates chained up
to a trusted root CA. During DTLS handshake, either entity can send
a certificate set which does not contain the full chain, possibly
excluding intermediate or root CAs. In an environment where peers
are known to already contain needed root and intermediate CAs there
is no need to include those CAs, but this has a risk of an entity not
actually having one of the needed CAs.
Sipos & Deaton Expires 11 May 2025 [Page 36]
Internet-Draft DTN UDPCLv2 November 2024
5.6. Threat: Certificate Validation Vulnerabilities
Even when DTLS itself is operating properly an attacker can attempt
to exploit vulnerabilities within certificate check algorithms or
configuration to establish a secure DTLS session using an invalid
certificate. An invalid certificate exploit could lead to bundle
data leaking and/or denial of service to the Node ID being
impersonated.
There are many reasons, described in [RFC5280] and [RFC6125], why a
certificate can fail to validate, including using the certificate
outside of its valid time interval, using purposes for which it was
not authorized, or using it after it has been revoked by its CA.
Validating a certificate is a complex task and can require network
connectivity outside of the primary UDPCL network path(s) if a
mechanism such as OCSP [RFC6960] is used by the CA. The
configuration and use of particular certificate validation methods
are outside of the scope of this document.
5.7. Threat: BP Node Impersonation
The certificates exchanged by DTLS enable authentication of peer DNS
name and Node ID, but it is possible that a peer either not provide a
valid certificate or that the certificate does not validate either
the DNS-ID/IPADDR-ID or NODE-ID of the peer (see Section 2.2).
Having a CA-validated certificate does not alone guarantee the
identity of the network host or BP node from which the certificate is
provided; additional validation procedures in Section 3.8.3 bind the
DNS-ID/IPADDR-ID or NODE-ID based on the contents of the certificate.
The DNS-ID/IPADDR-ID validation is a weaker form of authentication,
because even if a peer is operating on an authenticated network DNS
name or IP address it can provide an invalid Node ID and cause
bundles to be "leaked" to an invalid node. Especially in DTN
environments, network names and addresses of nodes can be time-
variable so binding a certificate to a Node ID is a more stable
identity.
NODE-ID validation ensures that the peer to which a bundle is
transferred is in fact the node which the BP Agent expects it to be.
In circumstances where certificates can only be issued to DNS names,
Node ID validation is not possible but it could be reasonable to
assume that a trusted host is not going to present an invalid Node
ID. Determining when a DNS-ID/IPADDR-ID authentication can be
trusted to validate a Node ID is also a policy matter outside of the
scope of this document.
Sipos & Deaton Expires 11 May 2025 [Page 37]
Internet-Draft DTN UDPCLv2 November 2024
One mitigation to arbitrary entities with valid PKIX certificates
impersonating arbitrary Node IDs is the use of the PKIX Extended Key
Usage key purpose "id-kp-bundleSecurity" of [IANA-SMI]. When this
Extended Key Usage is present in the certificate, it represents a
stronger assertion that the private key holder is trusted to operate
as a DTN Node.
5.8. Threat: Off-Path Packet Injection
As described in Section 5.1 of [RFC8085], when each endpoint of a UDP
conversation uses a stable port number the conversation can be more
easily snooped and off-path packets can be injected to spoof UDPCL
traffic. When the requirements in Section 3.2 are followed UDPCL
traffic will use predictable, well-known port numbers and will be
subject to this threat.
One direct mitigation of this threat is to use DTLS to ensure that
off-path attackers cannot inject packets without being discovered and
those packets rejected at the destination.
Another mitigation is for a UDPCL entity to use the well-known UDPCL
port for passive listening but choose an ephemeral port to bind to
when acting as the active peer. This will enable some amount of
obfuscation while maintaining stable UDP conversations, but could
also make legitimate traffic analysis and troubleshooting more
difficult.
5.9. Threat: Denial of Service
The behaviors described in this section all amount to a potential
denial-of-service to a UDPCL entity. The denial-of-service could be
limited to an individual UDPCL entity, or could affect all entities
on a host or network segment.
An entity can send a large amount of data to a UDPCL entity,
requiring the receiving entity to handle the data. The victim entity
can block UDP packets from network peers which are thought to be
incorrectly behaving within network.
An entity can also send only one segment of a seemingly valid
transfer and never send the remaining segments, which will cause
resources on the receiver to be wasted on transfer reassembly state.
The victim entity can either block packets from network peers or
intentionally keep a short unfinished transfer timeout (see
Section 3.6.2).
Sipos & Deaton Expires 11 May 2025 [Page 38]
Internet-Draft DTN UDPCLv2 November 2024
The keepalive mechanism can be abused to waste throughput within a
network link which would otherwise be usable for bundle
transmissions.
5.10. Mandatory-to-Implement DTLS
Following IETF best current practice, DTLS is mandatory to implement
for all UDPCL implementations but DTLS is optional to use for a any
given transfer. The recommended configuration of Section 3.5.5 is to
always attempt DTLS, but entities are permitted to disable DTLS based
on local configuration. The configuration to enable or disable DTLS
for an entity or a session is outside of the scope of this document.
The configuration to disable DTLS is different from the threat of
DTLS stripping described in Section 5.3.
5.11. Alternate Uses of DTLS
This specification makes use of PKIX certificate validation and
authentication within DTLS. There are alternate uses of DTLS which
are not necessarily incompatible with the security goals of this
specification, but are outside of the scope of this document. The
following subsections give examples of alternate DTLS uses.
5.11.1. DTLS Without Authentication
In environments where PKI is available but there are restrictions on
the issuance of certificates (including the contents of
certificates), it can be possible to make use of DTLS in a way which
authenticates only the passive entity of a UDPCL transfer or which
does not authenticate either entity. Using DTLS in a way which does
not successfully authenticate some claim of both peer entities of a
UDPCL transfer is outside of the scope of this document but does have
similar properties to the opportunistic security model of [RFC7435].
5.11.2. Non-Certificate DTLS Use
In environments where PKI is unavailable, alternate uses of DTLS
which do not require certificates such as pre-shared key (PSK)
authentication [RFC5489] and the use of raw public keys [RFC7250] are
available and can be used to ensure confidentiality within UDPCL.
Using non-PKI node authentication methods is outside of the scope of
this document.
Sipos & Deaton Expires 11 May 2025 [Page 39]
Internet-Draft DTN UDPCLv2 November 2024
5.12. Predictability of Transfer IDs
The only requirement on Transfer IDs is that they are unique from the
transmitting peer only. The trivial algorithm of the first transfer
starting at zero and later transfers incrementing by one causes
absolutely predictable Transfer IDs. Even when UDPCL is not DTLS
secured and there is a on-path attacker altering UDPCL messages,
there is no UDPCL feedback mechanism to interrupt or refuse a
transfer so there is no benefit in having unpredictable Transfer IDs.
6. IANA Considerations
Registration procedures referred to in this section are defined in
[RFC8126].
6.1. IP Multicast Addresses
This document allocates new routable multicast addresses for use with
the UDPCL.
Within the IPv4 multicast address registry of [IANA-IPv4-MCAST], the
sub-registry titled "Internetwork Control Block" has been updated to
include the following address.
+==============+======================+
| Parameter | Value |
+==============+======================+
| Address(es): | TBA-IP4 |
+--------------+----------------------+
| Description: | All BP Nodes |
+--------------+----------------------+
| References: | [This specification] |
+--------------+----------------------+
Table 3
Within the IPv6 multicast address registry of [IANA-IPv6-MCAST], the
sub-registry titled "Variable Scope Multicast Addresses" has been
updated to include the following address.
Sipos & Deaton Expires 11 May 2025 [Page 40]
Internet-Draft DTN UDPCLv2 November 2024
+==============+======================+
| Parameter | Value |
+==============+======================+
| Address(es): | TBA-IP6 |
+--------------+----------------------+
| Description: | All BP Nodes |
+--------------+----------------------+
| References: | [This specification] |
+--------------+----------------------+
Table 4
6.2. UDP Port Number
Within the port registry of [IANA-PORTS], UDP port number 4556 has
been previously assigned as the default port for the UDP convergence
layer in [RFC7122]. This assignment to UDPCL is unchanged, but the
assignment reference is updated to this specification. There is no
UDPCL version indication on-the-wire but this specification is a
superset of [RFC7122] and is fully backward compatible.
Service Name:
dtn-bundle
Transport Protocol(s):
UDP
Assignee:
IESG <iesg@ietf.org>
Contact:
IETF Chair <chair@ietf.org>
Description:
DTN Bundle UDP CL Protocol
Reference:
[This specification]
Port Number:
4556
The related assignment for DCCP port 4556 (registered by [RFC7122])
is unchanged.
Sipos & Deaton Expires 11 May 2025 [Page 41]
Internet-Draft DTN UDPCLv2 November 2024
6.3. UDPCL Extension Types
EDITOR NOTE: sub-registry to-be-created upon publication of this
specification.
IANA will create, under the "Bundle Protocol" registry [IANA-BUNDLE],
a sub-registry titled "Bundle Protocol UDP Convergence-Layer
Extension Types" and initialize it with the contents of Table 5. For
positive code points the registration procedure is Specification
Required. Negative code points are reserved for use on private
networks for functions not published to the IANA.
Specifications of new extension types need to define the CBOR item
structure of the extension data as well as the purpose and
relationship of the new extension to existing session/transfer state
within the baseline UDPCL sequencing. Receiving entities will ignore
items with unknown Extension ID, and that behavior needs to be
considered by new extension types.
Expert(s) are encouraged to be biased towards approving registrations
unless they are abusive, frivolous, or actively harmful (not merely
aesthetically displeasing, or architecturally dubious).
Sipos & Deaton Expires 11 May 2025 [Page 42]
Internet-Draft DTN UDPCLv2 November 2024
+==============+==========================+======================+
| Extension ID | Name | References |
+==============+==========================+======================+
| -32768 to -1 | Private/Experimental Use | [This specification] |
+--------------+--------------------------+----------------------+
| 0 | Reserved | [This specification] |
+--------------+--------------------------+----------------------+
| 1 | Extension Support | Section 3.5.1 of |
| | | [this specification] |
+--------------+--------------------------+----------------------+
| 2 | Transfer | Section 3.5.2 of |
| | | [this specification] |
+--------------+--------------------------+----------------------+
| 3 | Sender Listen | Section 3.5.3 of |
| | | [this specification] |
+--------------+--------------------------+----------------------+
| 4 | Sender Node ID | Section 3.5.4 of |
| | | [this specification] |
+--------------+--------------------------+----------------------+
| 5 | DTLS Initiation | Section 3.5.5 of |
| | (STARTTLS) | [this specification] |
+--------------+--------------------------+----------------------+
| 6 | Peer Probe | Section 3.5.6 of |
| | | [this specification] |
+--------------+--------------------------+----------------------+
| 7 | Peer Confirmation | Section 3.5.7 of |
| | | [this specification] |
+--------------+--------------------------+----------------------+
| 8 | ECN Counts | Section 3.5.8 of |
| | | [this specification] |
+--------------+--------------------------+----------------------+
| 9 to 32767 | Unassigned | |
+--------------+--------------------------+----------------------+
Table 5: Extension Type Codes
7. References
7.1. Normative References
[IANA-BUNDLE]
IANA, "Bundle Protocol",
<https://www.iana.org/assignments/bundle/>.
[IANA-PORTS]
IANA, "Service Name and Transport Protocol Port Number
Registry", <https://www.iana.org/assignments/service-
names-port-numbers/>.
Sipos & Deaton Expires 11 May 2025 [Page 43]
Internet-Draft DTN UDPCLv2 November 2024
[IANA-IPv4-MCAST]
IANA, "IPv4 Multicast Address Space Registry",
<https://www.iana.org/assignments/multicast-addresses/>.
[IANA-IPv6-MCAST]
IANA, "IPv6 Multicast Address Space Registry",
<https://www.iana.org/assignments/ipv6-multicast-
addresses/>.
[IANA-SMI] IANA, "Structure of Management Information (SMI) Numbers",
<https://www.iana.org/assignments/smi-numbers/>.
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
DOI 10.17487/RFC0768, August 1980,
<https://www.rfc-editor.org/info/rfc768>.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/info/rfc1122>.
[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/info/rfc2119>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<https://www.rfc-editor.org/info/rfc3168>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC5050] Scott, K. and S. Burleigh, "Bundle Protocol
Specification", RFC 5050, DOI 10.17487/RFC5050, November
2007, <https://www.rfc-editor.org/info/rfc5050>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
Sipos & Deaton Expires 11 May 2025 [Page 44]
Internet-Draft DTN UDPCLv2 November 2024
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <https://www.rfc-editor.org/info/rfc6125>.
[RFC6960] Santesson, S., Myers, M., Ankney, R., Malpani, A.,
Galperin, S., and C. Adams, "X.509 Internet Public Key
Infrastructure Online Certificate Status Protocol - OCSP",
RFC 6960, DOI 10.17487/RFC6960, June 2013,
<https://www.rfc-editor.org/info/rfc6960>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", RFC 7525, DOI 10.17487/RFC7525, May 2015,
<https://www.rfc-editor.org/info/rfc7525>.
[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
March 2017, <https://www.rfc-editor.org/info/rfc8085>.
[RFC8126] 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/info/rfc8126>.
[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/info/rfc8174>.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/info/rfc8610>.
[RFC8899] Fairhurst, G., Jones, T., Tüxen, M., Rüngeler, I., and T.
Völker, "Packetization Layer Path MTU Discovery for
Datagram Transports", RFC 8899, DOI 10.17487/RFC8899,
September 2020, <https://www.rfc-editor.org/info/rfc8899>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/info/rfc8949>.
Sipos & Deaton Expires 11 May 2025 [Page 45]
Internet-Draft DTN UDPCLv2 November 2024
[RFC9147] Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,
<https://www.rfc-editor.org/info/rfc9147>.
[RFC9171] Burleigh, S., Fall, K., and E. Birrane, III, "Bundle
Protocol Version 7", RFC 9171, DOI 10.17487/RFC9171,
January 2022, <https://www.rfc-editor.org/info/rfc9171>.
[RFC9174] Sipos, B., Demmer, M., Ott, J., and S. Perreault, "Delay-
Tolerant Networking TCP Convergence-Layer Protocol Version
4", RFC 9174, DOI 10.17487/RFC9174, January 2022,
<https://www.rfc-editor.org/info/rfc9174>.
[RFC9331] De Schepper, K. and B. Briscoe, Ed., "The Explicit
Congestion Notification (ECN) Protocol for Low Latency,
Low Loss, and Scalable Throughput (L4S)", RFC 9331,
DOI 10.17487/RFC9331, January 2023,
<https://www.rfc-editor.org/info/rfc9331>.
7.2. Informative References
[RFC792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, DOI 10.17487/RFC0792, September 1981,
<https://www.rfc-editor.org/info/rfc792>.
[RFC2595] Newman, C., "Using TLS with IMAP, POP3 and ACAP",
RFC 2595, DOI 10.17487/RFC2595, June 1999,
<https://www.rfc-editor.org/info/rfc2595>.
[RFC3542] Stevens, W., Thomas, M., Nordmark, E., and T. Jinmei,
"Advanced Sockets Application Program Interface (API) for
IPv6", RFC 3542, DOI 10.17487/RFC3542, May 2003,
<https://www.rfc-editor.org/info/rfc3542>.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003,
<https://www.rfc-editor.org/info/rfc3552>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
Sipos & Deaton Expires 11 May 2025 [Page 46]
Internet-Draft DTN UDPCLv2 November 2024
[RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access
Protocol (LDAP): The Protocol", RFC 4511,
DOI 10.17487/RFC4511, June 2006,
<https://www.rfc-editor.org/info/rfc4511>.
[RFC4838] Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst,
R., Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant
Networking Architecture", RFC 4838, DOI 10.17487/RFC4838,
April 2007, <https://www.rfc-editor.org/info/rfc4838>.
[RFC5489] Badra, M. and I. Hajjeh, "ECDHE_PSK Cipher Suites for
Transport Layer Security (TLS)", RFC 5489,
DOI 10.17487/RFC5489, March 2009,
<https://www.rfc-editor.org/info/rfc5489>.
[RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Transport Layer Security (TLS)
Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
2012, <https://www.rfc-editor.org/info/rfc6698>.
[RFC7122] Kruse, H., Jero, S., and S. Ostermann, "Datagram
Convergence Layers for the Delay- and Disruption-Tolerant
Networking (DTN) Bundle Protocol and Licklider
Transmission Protocol (LTP)", RFC 7122,
DOI 10.17487/RFC7122, March 2014,
<https://www.rfc-editor.org/info/rfc7122>.
[RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
Weiler, S., and T. Kivinen, "Using Raw Public Keys in
Transport Layer Security (TLS) and Datagram Transport
Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
June 2014, <https://www.rfc-editor.org/info/rfc7250>.
[RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection
Most of the Time", RFC 7435, DOI 10.17487/RFC7435,
December 2014, <https://www.rfc-editor.org/info/rfc7435>.
[RFC7457] Sheffer, Y., Holz, R., and P. Saint-Andre, "Summarizing
Known Attacks on Transport Layer Security (TLS) and
Datagram TLS (DTLS)", RFC 7457, DOI 10.17487/RFC7457,
February 2015, <https://www.rfc-editor.org/info/rfc7457>.
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/info/rfc7942>.
Sipos & Deaton Expires 11 May 2025 [Page 47]
Internet-Draft DTN UDPCLv2 November 2024
[RFC8445] Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive
Connectivity Establishment (ICE): A Protocol for Network
Address Translator (NAT) Traversal", RFC 8445,
DOI 10.17487/RFC8445, July 2018,
<https://www.rfc-editor.org/info/rfc8445>.
[RFC8489] Petit-Huguenin, M., Salgueiro, G., Rosenberg, J., Wing,
D., Mahy, R., and P. Matthews, "Session Traversal
Utilities for NAT (STUN)", RFC 8489, DOI 10.17487/RFC8489,
February 2020, <https://www.rfc-editor.org/info/rfc8489>.
[RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O.,
and F. Gont, "IP Fragmentation Considered Fragile",
BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020,
<https://www.rfc-editor.org/info/rfc8900>.
[RFC9172] Birrane, III, E. and K. McKeever, "Bundle Protocol
Security (BPSec)", RFC 9172, DOI 10.17487/RFC9172, January
2022, <https://www.rfc-editor.org/info/rfc9172>.
[github-dtn-demo-agent]
Sipos, B., "UDPCL Example Implementation",
<https://github.com/BSipos-RKF/dtn-demo-agent/>.
[github-dtn-wireshark]
Sipos, B., "UDPCL Wireshark Dissector",
<https://github.com/BSipos-RKF/dtn-wireshark/>.
Appendix A. Significant changes from RFC7122
The areas in which changes from [RFC7122] have been made to existing
requirements:
* Made explicit references to UDP- and IP-related RFCs.
* Made more strict Keepalive and Padding requirements.
* Added Extension Map message type and initial extension types.
* Defined UDPCL security and made it mandatory-to-implement but
optional to use.
The areas in which extensions from [RFC7122] have been made as new
behaviors are:
* Added BPv7 bundle as a possible UDPCL payload.
Sipos & Deaton Expires 11 May 2025 [Page 48]
Internet-Draft DTN UDPCLv2 November 2024
* Added discussion about optional explicit redundancy in
transmission.
* Added discussion about optional path MTU discovery.
* Added discussion about optional congestion control feedback.
* Defined semantics for IP multicast addressing.
* Defined recommendations for UDP port use and re-use (port
stability).
Acknowledgments
Much pre-draft review was performed to make the document clear and
readable by Sarah Heiner of JHU/APL.
Authors' Addresses
Brian Sipos
The Johns Hopkins University Applied Physics Laboratory
11100 Johns Hopkins Rd.
Laurel, MD 20723
United States of America
Email: brian.sipos+ietf@gmail.com
Joshua Deaton
Science Applications International Corporation
Email: joshua.e.deaton@nasa.gov
Sipos & Deaton Expires 11 May 2025 [Page 49]