draft-ietf-dtn-tcpclv4-21.txt		draft-ietf-dtn-tcpclv4-22.txt
	Delay-Tolerant Networking B. Sipos		Delay-Tolerant Networking B. Sipos
	Internet-Draft RKF Engineering		Internet-Draft RKF Engineering
	Intended status: Standards Track M. Demmer		Intended status: Standards Track M. Demmer
	Expires: December 11, 2020 UC Berkeley		Expires: April 29, 2021 UC Berkeley
	J. Ott		J. Ott
	Aalto University		Aalto University
	S. Perreault		S. Perreault
	June 9, 2020		October 26, 2020
	Delay-Tolerant Networking TCP Convergence Layer Protocol Version 4		Delay-Tolerant Networking TCP Convergence Layer Protocol Version 4
	draft-ietf-dtn-tcpclv4-21		draft-ietf-dtn-tcpclv4-22
	Abstract		Abstract
	This document describes a TCP-based convergence layer (TCPCL) for		This document describes a TCP-based convergence layer (TCPCL) for
	Delay-Tolerant Networking (DTN). This version of the TCPCL protocol		Delay-Tolerant Networking (DTN). This version of the TCPCL protocol
	resolves implementation issues in the earlier TCPCL Version 3 of		resolves implementation issues in the earlier TCPCL Version 3 of
	RFC7242 and updates to the Bundle Protocol (BP) contents, encodings,		RFC7242 and updates to the Bundle Protocol (BP) contents, encodings,
	and convergence layer requirements in BP Version 7. Specifically,		and convergence layer requirements in BP Version 7. Specifically,
	the TCPCLv4 uses CBOR-encoded BPv7 bundles as its service data unit		the TCPCLv4 uses CBOR-encoded BPv7 bundles as its service data unit
	being transported and provides a reliable transport of such bundles.		being transported and provides a reliable transport of such bundles.
	skipping to change at page 1, line 42 ¶		skipping to change at page 1, line 42 ¶
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at https://datatracker.ietf.org/drafts/current/.		Drafts is at https://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on December 11, 2020.		This Internet-Draft will expire on April 29, 2021.
	Copyright Notice		Copyright Notice
	Copyright (c) 2020 IETF Trust and the persons identified as the		Copyright (c) 2020 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(https://trustee.ietf.org/license-info) in effect on the date of		(https://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	skipping to change at page 2, line 37 ¶		skipping to change at page 2, line 37 ¶
	3.6. Transfer Segmentation Policies . . . . . . . . . . . . . 21		3.6. Transfer Segmentation Policies . . . . . . . . . . . . . 21
	3.7. Example Message Exchange . . . . . . . . . . . . . . . . 22		3.7. Example Message Exchange . . . . . . . . . . . . . . . . 22
	4. Session Establishment . . . . . . . . . . . . . . . . . . . . 23		4. Session Establishment . . . . . . . . . . . . . . . . . . . . 23
	4.1. TCP Connection . . . . . . . . . . . . . . . . . . . . . 24		4.1. TCP Connection . . . . . . . . . . . . . . . . . . . . . 24
	4.2. Contact Header . . . . . . . . . . . . . . . . . . . . . 25		4.2. Contact Header . . . . . . . . . . . . . . . . . . . . . 25
	4.3. Contact Validation and Negotiation . . . . . . . . . . . 26		4.3. Contact Validation and Negotiation . . . . . . . . . . . 26
	4.4. Session Security . . . . . . . . . . . . . . . . . . . . 27		4.4. Session Security . . . . . . . . . . . . . . . . . . . . 27
	4.4.1. Entity Identification . . . . . . . . . . . . . . . . 28		4.4.1. Entity Identification . . . . . . . . . . . . . . . . 28
	4.4.2. TLS Handshake . . . . . . . . . . . . . . . . . . . . 29		4.4.2. TLS Handshake . . . . . . . . . . . . . . . . . . . . 29
	4.4.3. TLS Authentication . . . . . . . . . . . . . . . . . 30		4.4.3. TLS Authentication . . . . . . . . . . . . . . . . . 30
	4.4.4. Example TLS Initiation . . . . . . . . . . . . . . . 31		4.4.4. Example TLS Initiation . . . . . . . . . . . . . . . 32
	4.5. Message Header . . . . . . . . . . . . . . . . . . . . . 32		4.5. Message Header . . . . . . . . . . . . . . . . . . . . . 33
	4.6. Session Initialization Message (SESS_INIT) . . . . . . . 34		4.6. Session Initialization Message (SESS_INIT) . . . . . . . 34
	4.7. Session Parameter Negotiation . . . . . . . . . . . . . . 35		4.7. Session Parameter Negotiation . . . . . . . . . . . . . . 36
	4.8. Session Extension Items . . . . . . . . . . . . . . . . . 36		4.8. Session Extension Items . . . . . . . . . . . . . . . . . 37
	5. Established Session Operation . . . . . . . . . . . . . . . . 37		5. Established Session Operation . . . . . . . . . . . . . . . . 38
	5.1. Upkeep and Status Messages . . . . . . . . . . . . . . . 37		5.1. Upkeep and Status Messages . . . . . . . . . . . . . . . 38
	5.1.1. Session Upkeep (KEEPALIVE) . . . . . . . . . . . . . 37		5.1.1. Session Upkeep (KEEPALIVE) . . . . . . . . . . . . . 38
	5.1.2. Message Rejection (MSG_REJECT) . . . . . . . . . . . 38		5.1.2. Message Rejection (MSG_REJECT) . . . . . . . . . . . 39
	5.2. Bundle Transfer . . . . . . . . . . . . . . . . . . . . . 39		5.2. Bundle Transfer . . . . . . . . . . . . . . . . . . . . . 40
	5.2.1. Bundle Transfer ID . . . . . . . . . . . . . . . . . 40		5.2.1. Bundle Transfer ID . . . . . . . . . . . . . . . . . 41
	5.2.2. Data Transmission (XFER_SEGMENT) . . . . . . . . . . 40		5.2.2. Data Transmission (XFER_SEGMENT) . . . . . . . . . . 41
	5.2.3. Data Acknowledgments (XFER_ACK) . . . . . . . . . . . 42		5.2.3. Data Acknowledgments (XFER_ACK) . . . . . . . . . . . 43
	5.2.4. Transfer Refusal (XFER_REFUSE) . . . . . . . . . . . 43		5.2.4. Transfer Refusal (XFER_REFUSE) . . . . . . . . . . . 44
	5.2.5. Transfer Extension Items . . . . . . . . . . . . . . 46		5.2.5. Transfer Extension Items . . . . . . . . . . . . . . 47
	6. Session Termination . . . . . . . . . . . . . . . . . . . . . 48		6. Session Termination . . . . . . . . . . . . . . . . . . . . . 49
	6.1. Session Termination Message (SESS_TERM) . . . . . . . . . 48		6.1. Session Termination Message (SESS_TERM) . . . . . . . . . 49
	6.2. Idle Session Shutdown . . . . . . . . . . . . . . . . . . 51		6.2. Idle Session Shutdown . . . . . . . . . . . . . . . . . . 52
	7. Implementation Status . . . . . . . . . . . . . . . . . . . . 51		7. Implementation Status . . . . . . . . . . . . . . . . . . . . 52
	8. Security Considerations . . . . . . . . . . . . . . . . . . . 51		8. Security Considerations . . . . . . . . . . . . . . . . . . . 52
	8.1. Threat: Passive Leak of Node Data . . . . . . . . . . . . 52		8.1. Threat: Passive Leak of Node Data . . . . . . . . . . . . 53
	8.2. Threat: Passive Leak of Bundle Data . . . . . . . . . . . 52		8.2. Threat: Passive Leak of Bundle Data . . . . . . . . . . . 53
	8.3. Threat: TCPCL Version Downgrade . . . . . . . . . . . . . 52		8.3. Threat: TCPCL Version Downgrade . . . . . . . . . . . . . 53
	8.4. Threat: Transport Security Stripping . . . . . . . . . . 52		8.4. Threat: Transport Security Stripping . . . . . . . . . . 53
	8.5. Threat: Weak TLS Configurations . . . . . . . . . . . . . 53		8.5. Threat: Weak TLS Configurations . . . . . . . . . . . . . 54
	8.6. Threat: Certificate Validation Vulnerabilities . . . . . 53		8.6. Threat: Certificate Validation Vulnerabilities . . . . . 54
	8.7. Threat: Symmetric Key Limits . . . . . . . . . . . . . . 53		8.7. Threat: Symmetric Key Limits . . . . . . . . . . . . . . 54
	8.8. Threat: BP Node Impersonation . . . . . . . . . . . . . . 53		8.8. Threat: BP Node Impersonation . . . . . . . . . . . . . . 54
	8.9. Threat: Denial of Service . . . . . . . . . . . . . . . . 54		8.9. Threat: Denial of Service . . . . . . . . . . . . . . . . 55
	8.10. Alternate Uses of TLS . . . . . . . . . . . . . . . . . . 55		8.10. Alternate Uses of TLS . . . . . . . . . . . . . . . . . . 56
	8.10.1. TLS Without Authentication . . . . . . . . . . . . . 55		8.10.1. TLS Without Authentication . . . . . . . . . . . . . 56
	8.10.2. Non-Certificate TLS Use . . . . . . . . . . . . . . 55		8.10.2. Non-Certificate TLS Use . . . . . . . . . . . . . . 56
	8.11. Predictability of Transfer IDs . . . . . . . . . . . . . 55		8.11. Predictability of Transfer IDs . . . . . . . . . . . . . 56
	9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 56		9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 57
	9.1. Port Number . . . . . . . . . . . . . . . . . . . . . . . 56		9.1. Port Number . . . . . . . . . . . . . . . . . . . . . . . 57
	9.2. Protocol Versions . . . . . . . . . . . . . . . . . . . . 56		9.2. Protocol Versions . . . . . . . . . . . . . . . . . . . . 57
	9.3. Session Extension Types . . . . . . . . . . . . . . . . . 57		9.3. Session Extension Types . . . . . . . . . . . . . . . . . 58
	9.4. Transfer Extension Types . . . . . . . . . . . . . . . . 58		9.4. Transfer Extension Types . . . . . . . . . . . . . . . . 59
	9.5. Message Types . . . . . . . . . . . . . . . . . . . . . . 59		9.5. Message Types . . . . . . . . . . . . . . . . . . . . . . 60
	9.6. XFER_REFUSE Reason Codes . . . . . . . . . . . . . . . . 60		9.6. XFER_REFUSE Reason Codes . . . . . . . . . . . . . . . . 61
	9.7. SESS_TERM Reason Codes . . . . . . . . . . . . . . . . . 61		9.7. SESS_TERM Reason Codes . . . . . . . . . . . . . . . . . 62
	9.8. MSG_REJECT Reason Codes . . . . . . . . . . . . . . . . . 62		9.8. MSG_REJECT Reason Codes . . . . . . . . . . . . . . . . . 63
	10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 63		10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 64
	11. References . . . . . . . . . . . . . . . . . . . . . . . . . 63		11. References . . . . . . . . . . . . . . . . . . . . . . . . . 64
	11.1. Normative References . . . . . . . . . . . . . . . . . . 63		11.1. Normative References . . . . . . . . . . . . . . . . . . 64
	11.2. Informative References . . . . . . . . . . . . . . . . . 65		11.2. Informative References . . . . . . . . . . . . . . . . . 66
	Appendix A. Significant changes from RFC7242 . . . . . . . . . . 66		Appendix A. Significant changes from RFC7242 . . . . . . . . . . 67
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 68		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 69
	1. Introduction		1. Introduction
	This document describes the TCP-based convergence-layer protocol for		This document describes the TCP-based convergence-layer protocol for
	Delay-Tolerant Networking. Delay-Tolerant Networking is an end-to-		Delay-Tolerant Networking. Delay-Tolerant Networking is an end-to-
	end architecture providing communications in and/or through highly		end architecture providing communications in and/or through highly
	stressed environments, including those with intermittent		stressed environments, including those with intermittent
	connectivity, long and/or variable delays, and high bit error rates.		connectivity, long and/or variable delays, and high bit error rates.
	More detailed descriptions of the rationale and capabilities of these		More detailed descriptions of the rationale and capabilities of these
	networks can be found in "Delay-Tolerant Network Architecture"		networks can be found in "Delay-Tolerant Network Architecture"
	skipping to change at page 21, line 23 ¶		skipping to change at page 21, line 23 ¶
	Many other policies can be established in a TCPCL network between the		Many other policies can be established in a TCPCL network between the
	two extremes of single persistent sessions and only ephemeral		two extremes of single persistent sessions and only ephemeral
	sessions. Different policies can be applied to each peer entity and		sessions. Different policies can be applied to each peer entity and
	to each bundle as it needs to be transferred (e.g for quality of		to each bundle as it needs to be transferred (e.g for quality of
	service). Additionally, future session extension types can apply		service). Additionally, future session extension types can apply
	further nuance to session policies and policy negotiation.		further nuance to session policies and policy negotiation.
	3.6. Transfer Segmentation Policies		3.6. Transfer Segmentation Policies
	Each TCPCL session allows a negotiated transfer segmentation polcy to		Each TCPCL session allows a negotiated transfer segmentation policy
	be applied in each transfer direction. A receiving node can set the		to be applied in each transfer direction. A receiving node can set
	Segment MRU in its SESS_INIT message to determine the largest		the Segment MRU in its SESS_INIT message to determine the largest
	acceptable segment size, and a transmitting node can segment a		acceptable segment size, and a transmitting node can segment a
	transfer into any sizes smaller than the receiver's Segment MRU. It		transfer into any sizes smaller than the receiver's Segment MRU. It
	is a network administration matter to determine an appropriate		is a network administration matter to determine an appropriate
	segmentation policy for entities operating TCPCL, but guidance given		segmentation policy for entities operating TCPCL, but guidance given
	here can be used to steer policy toward performance goals. It is		here can be used to steer policy toward performance goals. It is
	also advised to consider the Segment MRU in relation to chunking/		also advised to consider the Segment MRU in relation to chunking/
	packetization performed by TLS, TCP, and any intermediate network-		packetization performed by TLS, TCP, and any intermediate network-
	layer nodes.		layer nodes.
	Minimum Overhead: For a simple network expected to exchange		Minimum Overhead: For a simple network expected to exchange
	skipping to change at page 25, line 15 ¶		skipping to change at page 25, line 15 ¶
	4.2. Contact Header		4.2. Contact Header
	This section describes the format of the Contact Header and the		This section describes the format of the Contact Header and the
	meaning of its fields.		meaning of its fields.
	If an entity is capable of exchanging messages according to TLS 1.3		If an entity is capable of exchanging messages according to TLS 1.3
	[RFC8446] or any successors which are compatible with that TLS		[RFC8446] or any successors which are compatible with that TLS
	ClientHello, the the CAN_TLS flag within its Contact Header SHALL be		ClientHello, the the CAN_TLS flag within its Contact Header SHALL be
	set to 1. This behavior prefers the use of TLS when possible, even		set to 1. This behavior prefers the use of TLS when possible, even
	if security policy does not allow or require authentication. This		if security policy does not allow or require authentication. This
	follows the opportunistic security model of [RFC7435].		follows the opportunistic security model of [RFC7435], though an
			active attacker could interfere with the exchange in such cases.
	Upon receipt of the Contact Header, both entities perform the		Upon receipt of the Contact Header, both entities perform the
	validation and negotiation procedures defined in Section 4.3. After		validation and negotiation procedures defined in Section 4.3. After
	receiving the Contact Header from the other entity, either entity MAY		receiving the Contact Header from the other entity, either entity MAY
	refuse the session by sending a SESS_TERM message with an appropriate		refuse the session by sending a SESS_TERM message with an appropriate
	reason code.		reason code.
	The format for the Contact Header is as follows:		The format for the Contact Header is as follows:
	1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3		1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
	skipping to change at page 26, line 11 ¶		skipping to change at page 26, line 11 ¶
	to the descriptions in Table 1. All reserved header flag bits		to the descriptions in Table 1. All reserved header flag bits
	SHALL be set to 0 by the sender. All reserved header flag bits		SHALL be set to 0 by the sender. All reserved header flag bits
	SHALL be ignored by the receiver.		SHALL be ignored by the receiver.
	+----------+--------+-----------------------------------------------+		+----------+--------+-----------------------------------------------+
	| Name | Code | Description |		| Name | Code | Description |
	+----------+--------+-----------------------------------------------+		+----------+--------+-----------------------------------------------+
	| CAN_TLS | 0x01 | If bit is set, indicates that the sending |		| CAN_TLS | 0x01 | If bit is set, indicates that the sending |
	| | | peer is capable of TLS security. |		| | | peer is capable of TLS security. |
	| | | |		| | | |
	| Reserved | others |		| Reserved | others | |
	+----------+--------+-----------------------------------------------+		+----------+--------+-----------------------------------------------+
	Table 1: Contact Header Flags		Table 1: Contact Header Flags
	4.3. Contact Validation and Negotiation		4.3. Contact Validation and Negotiation
	Upon reception of the Contact Header, each node follows the following		Upon reception of the Contact Header, each node follows the following
	procedures to ensure the validity of the TCPCL session and to		procedures to ensure the validity of the TCPCL session and to
	negotiate values for the session parameters.		negotiate values for the session parameters.
	skipping to change at page 28, line 28 ¶		skipping to change at page 28, line 28 ¶
	defines a prioritized list of what a certificate can identify about a		defines a prioritized list of what a certificate can identify about a
	TCPCL entity:		TCPCL entity:
	Node ID: The ideal certificate identity is the Node ID of the entity		Node ID: The ideal certificate identity is the Node ID of the entity
	using the NODE-ID definition below. When the Node ID is		using the NODE-ID definition below. When the Node ID is
	identified, there is no need for any lower-level identification to		identified, there is no need for any lower-level identification to
	take place.		take place.
	DNS Name: If CA policy forbids a certificate to contain an arbitrary		DNS Name: If CA policy forbids a certificate to contain an arbitrary
	NODE-ID but allows a DNS-ID to be identified then one or more		NODE-ID but allows a DNS-ID to be identified then one or more
	stable host names can be identified in the certificate. The use		stable DNS names can be identified in the certificate. The use of
	of wildcard DNS-ID is discouraged due to the complex rules for		wildcard DNS-ID is discouraged due to the complex rules for
	matching and dependence on implementation support for wildcard		matching and dependence on implementation support for wildcard
	matching (see Section 6.4.3 of [RFC6125]).		matching (see Section 6.4.3 of [RFC6125]).
	Network Address: If no stable host name is available but a stable		Network Address: If no stable DNS name is available but a stable
	network address is available and CA policy allows a certificate to		network address is available and CA policy allows a certificate to
	contain a NETWORK-ID (as defined below) then one or more network		contain a IPADDR-ID (as defined below) then one or more network
	addresses can be identified in the certificate.		addresses can be identified in the certificate.
	When only a DNS-ID or NETWORK-ID can be identified by a certificate,		When only a DNS-ID or IPADDR-ID can be identified by a certificate,
	it is implied that an entity which authenticates using that		it is implied that an entity which authenticates using that
	certificate is trusted to provide a valid Node ID in its SESS_INIT;		certificate is trusted to provide a valid Node ID in its SESS_INIT;
	the certificate itself does not actually authenticate that Node ID.		the certificate itself does not actually authenticate that Node ID.
	The RECOMMENDED security policy of an entity is to validate a peer		The RECOMMENDED security policy of an entity is to validate a peer
	which authenticates its Node ID regardless of an authenticated host		which authenticates its Node ID regardless of an authenticated DNS
	name or address, and only consider the host/address authentication in		name or address, and only consider the host/address authentication in
	the absence of an authenticated Node ID.		the absence of an authenticated Node ID.
	This specification defines a NODE-ID of a certificate as being the		This specification defines a NODE-ID of a certificate as being the
	subjectAltName entry of type uniformResourceIdentifier whose value is		subjectAltName entry of type uniformResourceIdentifier whose value is
	a URI consistent with the requirements of [RFC3986] and the URI		a URI consistent with the requirements of [RFC3986] and the URI
	schemes of the IANA "Bundle Protocol URI Scheme Type" registry. This		schemes of the IANA "Bundle Protocol URI Scheme Type" registry. This
	is similar to the URI-ID of [RFC6125] but does not require any		is similar to the URI-ID of [RFC6125] but does not require any
	structure to the scheme-specific-part of the URI. Unless specified		structure to the scheme-specific-part of the URI. Unless specified
	otherwise by the definition of the URI scheme being authenticated,		otherwise by the definition of the URI scheme being authenticated,
	URI matching of a NODE-ID SHALL use the URI comparison logic of		URI matching of a NODE-ID SHALL use the URI comparison logic of
	[RFC3986] and scheme-based normalization of those schemes specified		[RFC3986] and scheme-based normalization of those schemes specified
	in [I-D.ietf-dtn-bpbis]. A URI scheme can refine this "exact match"		in [I-D.ietf-dtn-bpbis]. A URI scheme can refine this "exact match"
	logic with rules about how Node IDs within that scheme are to be		logic with rules about how Node IDs within that scheme are to be
	compared with the certificate-authenticated NODE-ID.		compared with the certificate-authenticated NODE-ID.
	This specification defines a NETWORK-ID of a certificate as being the		This specification defines a IPADDR-ID of a certificate as being the
	subjectAltName entry of type iPAddress whose value is encoded		subjectAltName entry of type iPAddress whose value is encoded
	according to [RFC5280].		according to [RFC5280].
	4.4.2. TLS Handshake		4.4.2. TLS Handshake
	The use of TLS is negotiated using the Contact Header as described in		The use of TLS is negotiated using the Contact Header as described in
	Section 4.3. After negotiating an Enable TLS parameter of true, and		Section 4.3. After negotiating an Enable TLS parameter of true, and
	before any other TCPCL messages are sent within the session, the		before any other TCPCL messages are sent within the session, the
	session entities SHALL begin a TLS handshake in accordance with		session entities SHALL begin a TLS handshake in accordance with
	[RFC8446]. By convention, this protocol uses the entity which		[RFC8446]. By convention, this protocol uses the entity which
	skipping to change at page 29, line 37 ¶		skipping to change at page 29, line 37 ¶
	The TLS handshake, if it occurs, is considered to be part of the		The TLS handshake, if it occurs, is considered to be part of the
	contact negotiation before the TCPCL session itself is established.		contact negotiation before the TCPCL session itself is established.
	Specifics about sensitive data exposure are discussed in Section 8.		Specifics about sensitive data exposure are discussed in Section 8.
	The parameters within each TLS negotiation are implementation		The parameters within each TLS negotiation are implementation
	dependent but any TCPCL node SHALL follow all recommended practices		dependent but any TCPCL node SHALL follow all recommended practices
	of BCP 195 [RFC7525], or any updates or successors that become part		of BCP 195 [RFC7525], or any updates or successors that become part
	of BCP 195. Within each TLS handshake, the following requirements		of BCP 195. Within each TLS handshake, the following requirements
	apply (using the rough order in which they occur):		apply (using the rough order in which they occur):
	Client Hello: When a resolved host name was used to establish the		Client Hello: When a resolved DNS name was used to establish the TCP
	TCP connection, the TLS ClientHello SHOULD include a Server Name		connection, the TLS ClientHello SHOULD include a Server Name
	Indication (SNI) in accordance with [RFC6066] containing that host		Indication (SNI) in accordance with [RFC6066]. When present, the
	name (of the passive entity) which was resolved. Note: The SNI		"server_name" extension SHALL contain a "HostName" value taken
	text is the network-layer name for the passive entity, which is		from the DNS name (of the passive entity) which was resolved.
	not the Node ID of that entity.		Note: The 'HostName in the "server_name" extension is the network
			name for the passive entity, not the Node ID of that entity.
	Server Certificate: The passive entity SHALL supply a certificate		Server Certificate: The passive entity SHALL supply a certificate
	within the TLS handshake to allow authentication of its side of		within the TLS handshake to allow authentication of its side of
	the session. Unless prohibited by CA policy, the passive entity		the session. Unless prohibited by CA policy, the passive entity
	certificate SHALL contain a NODE-ID which authenticates the Node		certificate SHALL contain a NODE-ID which authenticates the Node
	ID of the peer. When assigned a stable host name, the passive		ID of the peer. When assigned a stable DNS name, the passive
	entity certificate SHOULD contain a DNS-ID which authenticates		entity certificate SHOULD contain a DNS-ID which authenticates
	that (fully qualified) name. When assigned a stable network		that (fully qualified) name. When assigned a stable network
	address, the passive entity certificate MAY contain a NETWORK-ID		address, the passive entity certificate MAY contain a IPADDR-ID
	which authenticates that address. The passive entity MAY use the		which authenticates that address. The passive entity MAY use the
	SNI host name to choose an appropriate server-side certificate		SNI DNS name to choose an appropriate server-side certificate
	which authenticates that host name.		which authenticates that DNS name.
	Certificate Request: During TLS handshake, the passive entity SHALL		Certificate Request: During TLS handshake, the passive entity SHALL
	request a client-side certificate.		request a client-side certificate.
	Client Certificate: The active entity SHALL supply a certificate		Client Certificate: The active entity SHALL supply a certificate
	chain within the TLS handshake to allow authentication of its side		chain within the TLS handshake to allow authentication of its side
	of the session. Unless prohibited by CA policy, the active entity		of the session. Unless prohibited by CA policy, the active entity
	certificate SHALL contain a NODE-ID which authenticates the Node		certificate SHALL contain a NODE-ID which authenticates the Node
	ID of the peer. When assigned a stable host name, the active		ID of the peer. When assigned a stable DNS name, the active
	entity certificate SHOULD contain a DNS-ID which authenticates		entity certificate SHOULD contain a DNS-ID which authenticates
	that (fully qualified) name. When assigned a stable network		that (fully qualified) name. When assigned a stable network
	address, the active entity certificate MAY contain a NETWORK-ID		address, the active entity certificate MAY contain a IPADDR-ID
	which authenticates that address.		which authenticates that address.
	All certificates supplied during TLS handshake SHALL conform to		All certificates supplied during TLS handshake SHALL conform to
	[RFC5280], or any updates or successors to that profile. When a		[RFC5280], or any updates or successors to that profile. When a
	certificate is supplied during TLS handshake, the full certification		certificate is supplied during TLS handshake, the full certification
	chain SHOULD be included unless security policy indicates that is		chain SHOULD be included unless security policy indicates that is
	unnecessary.		unnecessary.
	If a TLS handshake cannot negotiate a TLS connection, both entities		If a TLS handshake cannot negotiate a TLS connection, both entities
	of the TCPCL session SHALL close the TCP connection. At this point		of the TCPCL session SHALL close the TCP connection. At this point
	the TCPCL session has not yet been established so there is no TCPCL		the TCPCL session has not yet been established so there is no TCPCL
	session to terminate.		session to terminate.
	After a TLS connection is successfully established, the active entity		After a TLS connection is successfully established, the active entity
	SHALL send a SESS_INIT message to begin session negotiation. This		SHALL send a SESS_INIT message to begin session negotiation. This
	session negotiation and all subsequent messaging are secured.		session negotiation and all subsequent messaging are secured.
	4.4.3. TLS Authentication		4.4.3. TLS Authentication
	Using PKIX certificates exchanged during the TLS handshake, each of		Using PKIX certificates exchanged during the TLS handshake, each of
	the entities can attempt to authenticate its peer Node ID directly or		the entities can authenticate a peer Node ID directly or authenticate
	authenticate the peer host name or network address. The Node ID		the peer DNS name or network address. The logic for attempting
	exchanged in the Session Initialization is likely to be used by the		authentication is separate from the logic for handling the result of
	BP agent for making transfer and routing decisions, so attempting		authentication, which is based on local security policy.
	Node ID validation is required while attempting host name validation
	is optional. The logic for attempting validation is separate from
	the logic for handling the result of validation, which is based on
	local security policy.
	By using the SNI host name (see Section 4.4.2) a single passive		By using the SNI DNS name (see Section 4.4.2) a single passive entity
	entity can act as a convergence layer for multiple BP agents with		can act as a convergence layer for multiple BP agents with distinct
	distinct Node IDs. When this "virtual host" behavior is used, the		Node IDs. When this "virtual host" behavior is used, the DNS name is
	host name is used as the indication of which BP Node the active		used as the indication of which BP Node the active entity is
	entity is attempting to communicate with. A virtual host CL entity		attempting to communicate with. A virtual host CL entity can be
	can be authenticated by a certificate containing all of the host		authenticated by a certificate containing all of the DNS names and/or
	names and/or Node IDs being hosted or by several certificates each		Node IDs being hosted or by several certificates each authenticating
	authenticating a single host name and/or Node ID, using the SNI value		a single DNS name and/or Node ID, using the SNI value from the peer
	from the peer to select which certificate to use.		to select which certificate to use.
	Any certificate received during TLS handshake SHALL be validated up		Any certificate received during TLS handshake SHALL be validated up
	to one or more trusted CA certificates. If certificate validation		to one or more trusted CA certificates. If certificate validation
	fails or if security policy disallows a certificate for any reason,		fails or if security policy disallows a certificate for any reason,
	the entity SHALL terminate the session (with a reason code of		the entity SHALL terminate the session (with a reason code of
	"Contact Failure").		"Contact Failure").
			The result of authenticating a peer value against a certificate claim
			is one of:
			Absent: Indicating that the claim type is not present in the
			certificate and cannot be authenticated.
			Success: Indicating the claim type is present and matches the peer
			(Node ID / DNS name / address) value.
			Failure: Indicating the claim type is present but did not match the
			peer value.
	Either during or immediately after the TLS handshake, the active		Either during or immediately after the TLS handshake, the active
	entity SHALL attempt to authenticate the host name (of the passive		entity SHALL authenticate the DNS name (of the passive entity) used
	entity) used to initiate the TCP connection using any DNS-ID of the		to initiate the TCP connection using any DNS-ID of the peer
	peer certificate. If host name validation fails (including failure		certificate. If the DNS name authentication result is Failure or if
	because the certificate does not contain any DNS-ID) and security		the result is Absent and security policy requires an authenticated
	policy disallows an unauthenticated host, the entity SHALL terminate		DNS name, the entity SHALL terminate the session (with a reason code
	the session (with a reason code of "Contact Failure").		of "Contact Failure").
	Either during or immediately after the TLS handshake, the active		Either during or immediately after the TLS handshake, the active
	entity SHALL attempt to authenticate the IP address of the other side		entity SHALL authenticate the IP address of the other side of the TCP
	of the TCP connection using any NETWORK-ID of the peer certificate.		connection using any IPADDR-ID of the peer certificate. Either
	Either during or immediately after the TLS handshake, the passive		during or immediately after the TLS handshake, the passive entity
	entity SHALL attempt to authenticate the IP address of the other side		SHALL authenticate the IP address of the other side of the TCP
	of the TCP connection using any NETWORK-ID of the peer certificate.		connection using any IPADDR-ID of the peer certificate. If the
	If host address validation fails (including failure because the		address authentication result is Failure or if the result is Absent
	certificate does not contain any NETWORK-ID) and security policy		and security policy requires an authenticated network address, the
	disallows an unauthenticated host, the entity SHALL terminate the		entity SHALL terminate the session (with a reason code of "Contact
	session (with a reason code of "Contact Failure").		Failure").
	Immediately before Session Parameter Negotiation, each side of the		Immediately before Session Parameter Negotiation, each side of the
	session SHALL perform Node ID validation of its peer as described		session SHALL authenticate the Node ID of the peer's SESS_INIT
	below. Node ID validation SHALL succeed if the associated		message using any NODE-ID of the peer certificate. If the Node ID
	certificate includes a NODE-ID whose value matches the Node ID of the		authentication result is Failure or if the result is Absent and
	TCPCL entity. If Node ID validation fails (including failure because		security policy requires an authenticated Node ID, the entity SHALL
	the certificate does not contain any NODE-ID) and security policy		terminate the session (with a reason code of "Contact Failure").
	disallows an unauthenticated Node ID, the entity SHALL terminate the
	session (with a reason code of "Contact Failure").
	4.4.4. Example TLS Initiation		4.4.4. Example TLS Initiation
	A summary of a typical TLS use is shown in the sequence in Figure 17		A summary of a typical TLS use is shown in the sequence in Figure 17
	below. In this example the active peer terminates the session but		below. In this example the active peer terminates the session but
	termination can be initiated from either peer.		termination can be initiated from either peer.
	Entity A Entity B		Entity A Entity B
	active peer passive peer		active peer passive peer
	skipping to change at page 32, line 22 ¶		skipping to change at page 32, line 28 ¶
	+-------------------------+		+-------------------------+
	| Contact Header | -> +-------------------------+		| Contact Header | -> +-------------------------+
	+-------------------------+ <- | Contact Header |		+-------------------------+ <- | Contact Header |
	+-------------------------+		+-------------------------+
	+-------------------------+ +-------------------------+		+-------------------------+ +-------------------------+
	| TLS Negotiation | -> <- | TLS Negotiation |		| TLS Negotiation | -> <- | TLS Negotiation |
	| (as client) | | (as server) |		| (as client) | | (as server) |
	+-------------------------+ +-------------------------+		+-------------------------+ +-------------------------+
	Host name validation occurs.		DNS name validation occurs.
	Secured TCPCL messaging can begin.		Secured TCPCL messaging can begin.
	+-------------------------+		+-------------------------+
	| SESS_INIT | -> +-------------------------+		| SESS_INIT | -> +-------------------------+
	+-------------------------+ <- | SESS_INIT |		+-------------------------+ <- | SESS_INIT |
	+-------------------------+		+-------------------------+
	Node ID validation occurs.		Node ID validation occurs.
	Session is established, transfers can begin.		Session is established, transfers can begin.
	skipping to change at page 33, line 20 ¶		skipping to change at page 34, line 8 ¶
	Figure 18: Format of the Message Header		Figure 18: Format of the Message Header
	The message header fields are as follows:		The message header fields are as follows:
	Message Type: Indicates the type of the message as per Table 2		Message Type: Indicates the type of the message as per Table 2
	below. Encoded values are listed in Section 9.5.		below. Encoded values are listed in Section 9.5.
	+--------------+------+---------------------------------------------+		+--------------+------+---------------------------------------------+
	| Name | Code | Description |		| Name | Code | Description |
	+--------------+------+---------------------------------------------+		+--------------+------+---------------------------------------------+
	| SESS_INIT | 0x07 | Contains the session parameter |		| SESS_INIT | 0x07 | Contains the session parameter inputs from |
	| | | inputs from one of the entities, |		| | | one of the entities, as described in |
	| | | as described in Section 4.6. |		| | | Section 4.6. |
	| | | |		| | | |
	| SESS_TERM | 0x05 | Indicates that one of the |		| SESS_TERM | 0x05 | Indicates that one of the entities |
	| | | entities participating in the session |		| | | participating in the session wishes to |
	| | | wishes to cleanly terminate the session, as |		| | | cleanly terminate the session, as described |
	| | | described in Section 6.1. |		| | | in Section 6.1. |
	| | | |		| | | |
	| XFER_SEGMENT | 0x01 | Indicates the transmission of |		| XFER_SEGMENT | 0x01 | Indicates the transmission of a segment of |
	| | | a segment of bundle data, as described in |		| | | bundle data, as described in Section 5.2.2. |
	| | | Section 5.2.2. |
	| | | |		| | | |
	| XFER_ACK | 0x02 | Acknowledges reception of a |		| XFER_ACK | 0x02 | Acknowledges reception of a data segment, |
	| | | data segment, as described in |		| | | as described in Section 5.2.3. |
	| | | Section 5.2.3. |
	| | | |		| | | |
	| XFER_REFUSE | 0x03 | Indicates that the |		| XFER_REFUSE | 0x03 | Indicates that the transmission of the |
	| | | transmission of the current bundle SHALL be |		| | | current bundle SHALL be stopped, as |
	| | | stopped, as described in |		| | | described in Section 5.2.4. |
	| | | Section 5.2.4. |
	| | | |		| | | |
	| KEEPALIVE | 0x04 | Used to keep TCPCL session |		| KEEPALIVE | 0x04 | Used to keep TCPCL session active, as |
	| | | active, as described in |		| | | described in Section 5.1.1. |
	| | | Section 5.1.1. |
	| | | |		| | | |
	| MSG_REJECT | 0x06 | Contains a TCPCL message |		| MSG_REJECT | 0x06 | Contains a TCPCL message rejection, as |
	| | | rejection, as described in |		| | | described in Section 5.1.2. |
	| | | Section 5.1.2. |
	+--------------+------+---------------------------------------------+		+--------------+------+---------------------------------------------+
	Table 2: TCPCL Message Types		Table 2: TCPCL Message Types
	4.6. Session Initialization Message (SESS_INIT)		4.6. Session Initialization Message (SESS_INIT)
	Before a session is established and ready to transfer bundles, the		Before a session is established and ready to transfer bundles, the
	session parameters are negotiated between the connected entities.		session parameters are negotiated between the connected entities.
	The SESS_INIT message is used to convey the per-entity parameters		The SESS_INIT message is used to convey the per-entity parameters
	which are used together to negotiate the per-session parameters as		which are used together to negotiate the per-session parameters as
	skipping to change at page 34, line 40 ¶		skipping to change at page 35, line 30 ¶
	+-----------------------------+		+-----------------------------+
	| Session Extension |		| Session Extension |
	| Items (var.) |		| Items (var.) |
	+-----------------------------+		+-----------------------------+
	Figure 19: SESS_INIT Format		Figure 19: SESS_INIT Format
	The fields of the SESS_INIT message are:		The fields of the SESS_INIT message are:
	Keepalive Interval: A 16-bit unsigned integer indicating the minimum		Keepalive Interval: A 16-bit unsigned integer indicating the minimum
	interval, in seconds, to negotiate the Session Keepalive using the		interval, in seconds, to negotiate as the Session Keepalive using
	method of Section 4.7.		the method of Section 4.7.
	Segment MRU: A 64-bit unsigned integer indicating the largest		Segment MRU: A 64-bit unsigned integer indicating the largest
	allowable single-segment data payload size to be received in this		allowable single-segment data payload size to be received in this
	session. Any XFER_SEGMENT sent to this peer SHALL have a data		session. Any XFER_SEGMENT sent to this peer SHALL have a data
	payload no longer than the peer's Segment MRU. The two entities		payload no longer than the peer's Segment MRU. The two entities
	of a single session MAY have different Segment MRUs, and no		of a single session MAY have different Segment MRUs, and no
	relation between the two is required.		relation between the two is required.
	Transfer MRU: A 64-bit unsigned integer indicating the largest		Transfer MRU: A 64-bit unsigned integer indicating the largest
	allowable total-bundle data size to be received in this session.		allowable total-bundle data size to be received in this session.
	skipping to change at page 35, line 37 ¶		skipping to change at page 36, line 27 ¶
	Extension Item is within a consistent data container as described		Extension Item is within a consistent data container as described
	in Section 4.8. The full set of Session Extension Items apply for		in Section 4.8. The full set of Session Extension Items apply for
	the duration of the TCPCL session to follow. The order and		the duration of the TCPCL session to follow. The order and
	multiplicity of these Session Extension Items is significant, as		multiplicity of these Session Extension Items is significant, as
	defined in the associated type specification(s). If the content		defined in the associated type specification(s). If the content
	of the Session Extension Items data disagrees with the Session		of the Session Extension Items data disagrees with the Session
	Extension Length (e.g., the last Item claims to use more octets		Extension Length (e.g., the last Item claims to use more octets
	than are present in the Session Extension Length), the reception		than are present in the Session Extension Length), the reception
	of the SESS_INIT is considered to have failed.		of the SESS_INIT is considered to have failed.
			When the active entity initiates a TCPCL session, it is likely based
			on routing information which binds a Node ID to CL parameters. If
			the active entity receives a SESS_INIT with different Node ID than
			was intended for the TCPCL session, the session MAY be allowed to be
			established. If allowed, such a session SHALL be associated with the
			Node ID provided in the SESS_INIT message rather than any intended
			value.
	4.7. Session Parameter Negotiation		4.7. Session Parameter Negotiation
	An entity calculates the parameters for a TCPCL session by		An entity calculates the parameters for a TCPCL session by
	negotiating the values from its own preferences (conveyed by the		negotiating the values from its own preferences (conveyed by the
	SESS_INIT it sent to the peer) with the preferences of the peer node		SESS_INIT it sent to the peer) with the preferences of the peer node
	(expressed in the SESS_INIT that it received from the peer). The		(expressed in the SESS_INIT that it received from the peer). The
	negotiated parameters defined by this specification are described in		negotiated parameters defined by this specification are described in
	the following paragraphs.		the following paragraphs.
	Transfer MTU and Segment MTU: The maximum transmit unit (MTU) for		Transfer MTU and Segment MTU: The maximum transmit unit (MTU) for
	whole transfers and individual segments are identical to the		whole transfers and individual segments are identical to the
	Transfer MRU and Segment MRU, respectively, of the received		Transfer MRU and Segment MRU, respectively, of the received
	Contact Header. A transmitting peer can send individual segments		SESS_INIT message. A transmitting peer can send individual
	with any size smaller than the Segment MTU, depending on local		segments with any size smaller than the Segment MTU, depending on
	policy, dynamic network conditions, etc. Determining the size of		local policy, dynamic network conditions, etc. Determining the
	each transmitted segment is an implementation matter. If either		size of each transmitted segment is an implementation matter. If
	the Transfer MRU or Segment MRU is unacceptable, the entity SHALL		either the Transfer MRU or Segment MRU is unacceptable, the entity
	terminate the session with a reason code of "Contact Failure".		SHALL terminate the session with a reason code of "Contact
			Failure".
	Session Keepalive: Negotiation of the Session Keepalive parameter is		Session Keepalive: Negotiation of the Session Keepalive parameter is
	performed by taking the minimum of the two Contact Headers'		performed by taking the minimum of the two Keepalive Interval
	Keepalive Interval values. The Session Keepalive interval is a		values from the two SESS_INIT messages. The Session Keepalive
	parameter for the behavior described in Section 5.1.1. If the		interval is a parameter for the behavior described in
	Session Keepalive interval is unacceptable, the entity SHALL		Section 5.1.1. If the Session Keepalive interval is unacceptable,
	terminate the session with a reason code of "Contact Failure".		the entity SHALL terminate the session with a reason code of
	Note: a negotiated Session Keepalive of zero indicates that		"Contact Failure". Note: a negotiated Session Keepalive of zero
	KEEPALIVEs are disabled.		indicates that KEEPALIVEs are disabled.
	Once this process of parameter negotiation is completed (which		Once this process of parameter negotiation is completed (which
	includes a possible completed TLS handshake of the connection to use		includes a possible completed TLS handshake of the connection to use
	TLS), this protocol defines no additional mechanism to change the		TLS), this protocol defines no additional mechanism to change the
	parameters of an established session; to effect such a change, the		parameters of an established session; to effect such a change, the
	TCPCL session MUST be terminated and a new session established.		TCPCL session MUST be terminated and a new session established.
	4.8. Session Extension Items		4.8. Session Extension Items
	Each of the Session Extension Items SHALL be encoded in an identical		Each of the Session Extension Items SHALL be encoded in an identical
	skipping to change at page 37, line 23 ¶		skipping to change at page 38, line 23 ¶
	+---------------+---------------+---------------+---------------+		+---------------+---------------+---------------+---------------+
	Figure 20: Session Extension Item Format		Figure 20: Session Extension Item Format
	+----------+--------+-----------------------------------------------+		+----------+--------+-----------------------------------------------+
	| Name | Code | Description |		| Name | Code | Description |
	+----------+--------+-----------------------------------------------+		+----------+--------+-----------------------------------------------+
	| CRITICAL | 0x01 | If bit is set, indicates that the receiving |		| CRITICAL | 0x01 | If bit is set, indicates that the receiving |
	| | | peer must handle the extension item. |		| | | peer must handle the extension item. |
	| | | |		| | | |
	| Reserved | others |		| Reserved | others | |
	+----------+--------+-----------------------------------------------+		+----------+--------+-----------------------------------------------+
	Table 3: Session Extension Item Flags		Table 3: Session Extension Item Flags
	5. Established Session Operation		5. Established Session Operation
	This section describes the protocol operation for the duration of an		This section describes the protocol operation for the duration of an
	established session, including the mechanism for transmitting bundles		established session, including the mechanism for transmitting bundles
	over the session.		over the session.
	skipping to change at page 42, line 19 ¶		skipping to change at page 43, line 19 ¶
	+----------+--------+-----------------------------------------------+		+----------+--------+-----------------------------------------------+
	| Name | Code | Description |		| Name | Code | Description |
	+----------+--------+-----------------------------------------------+		+----------+--------+-----------------------------------------------+
	| END | 0x01 | If bit is set, indicates that this is the |		| END | 0x01 | If bit is set, indicates that this is the |
	| | | last segment of the transfer. |		| | | last segment of the transfer. |
	| | | |		| | | |
	| START | 0x02 | If bit is set, indicates that this is the |		| START | 0x02 | If bit is set, indicates that this is the |
	| | | first segment of the transfer. |		| | | first segment of the transfer. |
	| | | |		| | | |
	| Reserved | others |		| Reserved | others | |
	+----------+--------+-----------------------------------------------+		+----------+--------+-----------------------------------------------+
	Table 5: XFER_SEGMENT Flags		Table 5: XFER_SEGMENT Flags
	The flags portion of the message contains two flag values in the two		The flags portion of the message contains two flag values in the two
	low-order bits, denoted 'START' and 'END' in Table 5. The 'START'		low-order bits, denoted 'START' and 'END' in Table 5. The 'START'
	flag SHALL be set to 1 when transmitting the first segment of a		flag SHALL be set to 1 when transmitting the first segment of a
	transfer. The 'END' flag SHALL be set to 1 when transmitting the		transfer. The 'END' flag SHALL be set to 1 when transmitting the
	last segment of a transfer. In the case where an entire transfer is		last segment of a transfer. In the case where an entire transfer is
	accomplished in a single segment, both the 'START' and 'END' flags		accomplished in a single segment, both the 'START' and 'END' flags
	skipping to change at page 47, line 11 ¶		skipping to change at page 48, line 11 ¶
	+---------------+---------------+---------------+---------------+		+---------------+---------------+---------------+---------------+
	Figure 25: Transfer Extension Item Format		Figure 25: Transfer Extension Item Format
	+----------+--------+-----------------------------------------------+		+----------+--------+-----------------------------------------------+
	| Name | Code | Description |		| Name | Code | Description |
	+----------+--------+-----------------------------------------------+		+----------+--------+-----------------------------------------------+
	| CRITICAL | 0x01 | If bit is set, indicates that the receiving |		| CRITICAL | 0x01 | If bit is set, indicates that the receiving |
	| | | peer must handle the extension item. |		| | | peer must handle the extension item. |
	| | | |		| | | |
	| Reserved | others |		| Reserved | others | |
	+----------+--------+-----------------------------------------------+		+----------+--------+-----------------------------------------------+
	Table 7: Transfer Extension Item Flags		Table 7: Transfer Extension Item Flags
	5.2.5.1. Transfer Length Extension		5.2.5.1. Transfer Length Extension
	The purpose of the Transfer Length extension is to allow entities to		The purpose of the Transfer Length extension is to allow entities to
	preemptively refuse bundles that would exceed their resources or to		preemptively refuse bundles that would exceed their resources or to
	prepare storage on the receiving node for the upcoming bundle data.		prepare storage on the receiving node for the upcoming bundle data.
	skipping to change at page 49, line 38 ¶		skipping to change at page 50, line 38 ¶
	Reason Code: A one-octet refusal reason code interpreted according		Reason Code: A one-octet refusal reason code interpreted according
	to the descriptions in Table 9.		to the descriptions in Table 9.
	+----------+--------+-----------------------------------------------+		+----------+--------+-----------------------------------------------+
	| Name | Code | Description |		| Name | Code | Description |
	+----------+--------+-----------------------------------------------+		+----------+--------+-----------------------------------------------+
	| REPLY | 0x01 | If bit is set, indicates that this message is |		| REPLY | 0x01 | If bit is set, indicates that this message is |
	| | | an acknowledgement of an earlier SESS_TERM |		| | | an acknowledgement of an earlier SESS_TERM |
	| | | message. |		| | | message. |
	| | | |		| | | |
	| Reserved | others |		| Reserved | others | |
	+----------+--------+-----------------------------------------------+		+----------+--------+-----------------------------------------------+
	Table 8: SESS_TERM Flags		Table 8: SESS_TERM Flags
	+--------------+------+---------------------------------------------+		+--------------+------+---------------------------------------------+
	| Name | Code | Description |		| Name | Code | Description |
	+--------------+------+---------------------------------------------+		+--------------+------+---------------------------------------------+
	| Unknown | 0x00 | A termination reason is not available. |		| Unknown | 0x00 | A termination reason is not available. |
	| | | |		| | | |
	| Idle timeout | 0x01 | The session is being closed due to |		| Idle timeout | 0x01 | The session is being closed due to |
	skipping to change at page 53, line 39 ¶		skipping to change at page 54, line 39 ¶
	used by the CA. The configuration and use of particular certificate		used by the CA. The configuration and use of particular certificate
	validation methods are outside of the scope of this document.		validation methods are outside of the scope of this document.
	8.7. Threat: Symmetric Key Limits		8.7. Threat: Symmetric Key Limits
	Even with a secure block cipher and securely-established session		Even with a secure block cipher and securely-established session
	keys, there are limits to the amount of plaintext which can be safely		keys, there are limits to the amount of plaintext which can be safely
	encrypted with a given set of keys as described in [AEAD-LIMITS].		encrypted with a given set of keys as described in [AEAD-LIMITS].
	When permitted by the negotiated TLS version (see [RFC8446]), it is		When permitted by the negotiated TLS version (see [RFC8446]), it is
	advisable to take advantage of session key updates to avoid those		advisable to take advantage of session key updates to avoid those
	limits. When key updates are not possible, renegotiation of the TLS		limits.
	connection or establishing new TCPCL/TLS session are alternatives to
	limit session key use.
	8.8. Threat: BP Node Impersonation		8.8. Threat: BP Node Impersonation
	The certificates exchanged by TLS enable authentication of peer host		The certificates exchanged by TLS enable authentication of peer DNS
	name and Node ID, but it is possible that a peer either not provide a		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		valid certificate or that the certificate does not validate either
	the host name or Node ID of the peer (see Section 3.4). Having a CA-		the DNS name or Node ID of the peer (see Section 3.4). Having a CA-
	validated certificate does not alone guarantee the identity of the		validated certificate does not alone guarantee the identity of the
	network host or BP node from which the certificate is provided;		network host or BP node from which the certificate is provided;
	additional validation procedures in Section 4.4.2 bind the host name		additional validation procedures in Section 4.4.2 bind the DNS name
	or node ID based on the contents of the certificate.		or node ID based on the contents of the certificate.
	The host name validation is a weaker form of authentication, because		The DNS name validation is a weaker form of authentication, because
	even if a peer is operating on an authenticated network host name it		even if a peer is operating on an authenticated network DNS name it
	can provide an invalid Node ID and cause bundles to be "leaked" to an		can provide an invalid Node ID and cause bundles to be "leaked" to an
	invalid node. Especially in DTN environments, network names and		invalid node. Especially in DTN environments, network names and
	addresses of nodes can be time-variable so binding a certificate to a		addresses of nodes can be time-variable so binding a certificate to a
	Node ID is a more stable identity.		Node ID is a more stable identity.
	Node ID validation ensures that the peer to which a bundle is		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.		transferred is in fact the node which the BP Agent expects it to be.
	It is a reasonable policy to skip host name validation if		It is a reasonable policy to skip DNS name validation if certificates
	certificates can be guaranteed to validate the peer's Node ID. In		can be guaranteed to validate the peer's Node ID. In circumstances
	circumstances where certificates can only be issued to network host		where certificates can only be issued to DNS names, Node ID
	names, Node ID validation is not possible but it could be reasonable		validation is not possible but it could be reasonable to assume that
	to assume that a trusted host is not going to present an invalid Node		a trusted host is not going to present an invalid Node ID.
	ID. Determining of when a host name authentication can be trusted to		Determining of when a DNS name authentication can be trusted to
	validate a Node ID is also a policy matter outside the scope of this		validate a Node ID is also a policy matter outside the scope of this
	document.		document.
	8.9. Threat: Denial of Service		8.9. Threat: Denial of Service
	The behaviors described in this section all amount to a potential		The behaviors described in this section all amount to a potential
	denial-of-service to a TCPCL entity. The denial-of-service could be		denial-of-service to a TCPCL entity. The denial-of-service could be
	limited to an individual TCPCL session, could affect other well-		limited to an individual TCPCL session, could affect other well-
	behaving sessions on an entity, or could affect all sessions on a		behaving sessions on an entity, or could affect all sessions on a
	host.		host.
	skipping to change at page 55, line 30 ¶		skipping to change at page 56, line 30 ¶
	specification, but are outside of the scope of this document. The		specification, but are outside of the scope of this document. The
	following subsections give examples of alternate TLS uses.		following subsections give examples of alternate TLS uses.
	8.10.1. TLS Without Authentication		8.10.1. TLS Without Authentication
	In environments where PKI is available but there are restrictions on		In environments where PKI is available but there are restrictions on
	the issuance of certificates (including the contents of		the issuance of certificates (including the contents of
	certificates), it may be possible to make use of TLS in a way which		certificates), it may be possible to make use of TLS in a way which
	authenticates only the passive entity of a TCPCL session or which		authenticates only the passive entity of a TCPCL session or which
	does not authenticate either entity. Using TLS in a way which does		does not authenticate either entity. Using TLS in a way which does
	not authenticate both peer entities of each TCPCL session is outside		not successfully authenticate some claim of both peer entities of a
	of the scope of this document but does have similar properties to the		TCPCL session is outside of the scope of this document but does have
	opportunistic security model of [RFC7435].		similar properties to the opportunistic security model of [RFC7435].
	8.10.2. Non-Certificate TLS Use		8.10.2. Non-Certificate TLS Use
	In environments where PKI is unavailable, alternate uses of TLS which		In environments where PKI is unavailable, alternate uses of TLS which
	do not require certificates such as pre-shared key (PSK)		do not require certificates such as pre-shared key (PSK)
	authentication [RFC5489] and the use of raw public keys [RFC7250] are		authentication [RFC5489] and the use of raw public keys [RFC7250] are
	available and can be used to ensure confidentiality within TCPCL.		available and can be used to ensure confidentiality within TCPCL.
	Using non-PKI node authentication methods is outside of the scope of		Using non-PKI node authentication methods is outside of the scope of
	this document.		this document.
	skipping to change at page 57, line 18 ¶		skipping to change at page 58, line 18 ¶
	| 0 | Reserved | [RFC7242] |		| 0 | Reserved | [RFC7242] |
	| | | |		| | | |
	| 1 | Reserved | [RFC7242] |		| 1 | Reserved | [RFC7242] |
	| | | |		| | | |
	| 2 | Reserved | [RFC7242] |		| 2 | Reserved | [RFC7242] |
	| | | |		| | | |
	| 3 | TCPCL | [RFC7242] |		| 3 | TCPCL | [RFC7242] |
	| | | |		| | | |
	| 4 | TCPCLv4 | This specification. |		| 4 | TCPCLv4 | This specification. |
	| | | |		| | | |
	| 5-255 | Unassigned |		| 5-255 | Unassigned | |
	+-------+-------------+-----------------------------------+		+-------+-------------+-----------------------------------+
	9.3. Session Extension Types		9.3. Session Extension Types
	EDITOR NOTE: sub-registry to-be-created upon publication of this		EDITOR NOTE: sub-registry to-be-created upon publication of this
	specification.		specification.
	IANA will create, under the "Bundle Protocol" registry [IANA-BUNDLE],		IANA will create, under the "Bundle Protocol" registry [IANA-BUNDLE],
	a sub-registry titled "Bundle Protocol TCP Convergence-Layer Version		a sub-registry titled "Bundle Protocol TCP Convergence-Layer Version
	4 Session Extension Types" and initialize it with the contents of		4 Session Extension Types" and initialize it with the contents of
	skipping to change at page 63, line 34 ¶		skipping to change at page 64, line 34 ¶
	This specification is based on comments on implementation of		This specification is based on comments on implementation of
	[RFC7242] provided from Scott Burleigh.		[RFC7242] provided from Scott Burleigh.
	11. References		11. References
	11.1. Normative References		11.1. Normative References
	[I-D.ietf-dtn-bpbis]		[I-D.ietf-dtn-bpbis]
	Burleigh, S., Fall, K., and E. Birrane, "Bundle Protocol		Burleigh, S., Fall, K., and E. Birrane, "Bundle Protocol
	Version 7", draft-ietf-dtn-bpbis-25 (work in progress),		Version 7", draft-ietf-dtn-bpbis-26 (work in progress),
	May 2020.		July 2020.
	[IANA-BUNDLE]		[IANA-BUNDLE]
	IANA, "Bundle Protocol",		IANA, "Bundle Protocol",
	<https://www.iana.org/assignments/bundle/>.		<https://www.iana.org/assignments/bundle/>.
	[IANA-PORTS]		[IANA-PORTS]
	IANA, "Service Name and Transport Protocol Port Number		IANA, "Service Name and Transport Protocol Port Number
	Registry", <https://www.iana.org/assignments/service-		Registry", <https://www.iana.org/assignments/service-
	names-port-numbers/>.		names-port-numbers/>.
	skipping to change at page 65, line 26 ¶		skipping to change at page 66, line 26 ¶
	[github-dtn-bpbis-tcpcl]		[github-dtn-bpbis-tcpcl]
	Sipos, B., "TCPCL Example Implementation",		Sipos, B., "TCPCL Example Implementation",
	<https://github.com/BSipos-RKF/dtn-bpbis-tcpcl/>.		<https://github.com/BSipos-RKF/dtn-bpbis-tcpcl/>.
	[I-D.ietf-dtn-bibect]		[I-D.ietf-dtn-bibect]
	Burleigh, S., "Bundle-in-Bundle Encapsulation", draft-		Burleigh, S., "Bundle-in-Bundle Encapsulation", draft-
	ietf-dtn-bibect-03 (work in progress), February 2020.		ietf-dtn-bibect-03 (work in progress), February 2020.
	[I-D.ietf-dtn-bpsec]		[I-D.ietf-dtn-bpsec]
	Birrane, E. and K. McKeever, "Bundle Protocol Security		Birrane, E. and K. McKeever, "Bundle Protocol Security
	Specification", draft-ietf-dtn-bpsec-22 (work in		Specification", draft-ietf-dtn-bpsec-23 (work in
	progress), March 2020.		progress), October 2020.
	[RFC2595] Newman, C., "Using TLS with IMAP, POP3 and ACAP",		[RFC2595] Newman, C., "Using TLS with IMAP, POP3 and ACAP",
	RFC 2595, DOI 10.17487/RFC2595, June 1999,		RFC 2595, DOI 10.17487/RFC2595, June 1999,
	<https://www.rfc-editor.org/info/rfc2595>.		<https://www.rfc-editor.org/info/rfc2595>.
	[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC		[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
	Text on Security Considerations", BCP 72, RFC 3552,		Text on Security Considerations", BCP 72, RFC 3552,
	DOI 10.17487/RFC3552, July 2003,		DOI 10.17487/RFC3552, July 2003,
	<https://www.rfc-editor.org/info/rfc3552>.		<https://www.rfc-editor.org/info/rfc3552>.
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