< draft-ietf-bier-path-mtu-discovery-08.txt		draft-ietf-bier-path-mtu-discovery-09.txt >
	BIER Working Group G. Mirsky		BIER Working Group G. Mirsky
	Internet-Draft ZTE Corp.		Internet-Draft ZTE Corp.
	Intended status: Standards Track T. Przygienda		Intended status: Standards Track T. Przygienda
	Expires: November 22, 2020 Juniper Networks		Expires: May 23, 2021 Juniper Networks
	A. Dolganow		A. Dolganow
	Individual contributor		Individual contributor
	May 21, 2020		November 19, 2020
	Path Maximum Transmission Unit Discovery (PMTUD) for Bit Index Explicit		Path Maximum Transmission Unit Discovery (PMTUD) for Bit Index Explicit
	Replication (BIER) Layer		Replication (BIER) Layer
	draft-ietf-bier-path-mtu-discovery-08		draft-ietf-bier-path-mtu-discovery-09
	Abstract		Abstract
	This document describes Path Maximum Transmission Unit Discovery		This document describes Path Maximum Transmission Unit Discovery
	(PMTUD) in Bit Indexed Explicit Replication (BIER) layer.		(PMTUD) in Bit Indexed Explicit Replication (BIER) layer.
	Status of This Memo		Status of This Memo
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
	skipping to change at page 1, line 35 ¶		skipping to change at page 1, line 35 ¶
	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 November 22, 2020.		This Internet-Draft will expire on May 23, 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
	carefully, as they describe your rights and restrictions with respect		carefully, as they describe your rights and restrictions with respect
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	1.1. Conventions used in this document . . . . . . . . . . . . 3		1.1. Conventions used in this document . . . . . . . . . . . . 3
	1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3		1.1.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . 3
	1.1.2. Requirements Language . . . . . . . . . . . . . . . . 3		1.1.2. Requirements Language . . . . . . . . . . . . . . . . 3
	2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3		2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3
	3. PMTUD Mechanism for BIER . . . . . . . . . . . . . . . . . . 4		3. PMTUD Mechanism for BIER . . . . . . . . . . . . . . . . . . 4
	3.1. Data TLV for BIER Ping . . . . . . . . . . . . . . . . . 6		3.1. Data TLV for BIER Ping . . . . . . . . . . . . . . . . . 6
	4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7		4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
	5. Security Considerations . . . . . . . . . . . . . . . . . . . 7		5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
	6. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . 7		6. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . 7
	7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7		7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
	7.1. Normative References . . . . . . . . . . . . . . . . . . 7		7.1. Normative References . . . . . . . . . . . . . . . . . . 7
	7.2. Informative References . . . . . . . . . . . . . . . . . 8		7.2. Informative References . . . . . . . . . . . . . . . . . 8
	skipping to change at page 2, line 35 ¶		skipping to change at page 2, line 35 ¶
	In packet switched networks, when a host seeks to transmit data to a		In packet switched networks, when a host seeks to transmit data to a
	target destination, the data is transmitted as a set of packets. In		target destination, the data is transmitted as a set of packets. In
	many cases, it is more efficient to use the largest size packets that		many cases, it is more efficient to use the largest size packets that
	are less than or equal to the least Maximum Transmission Unit (MTU)		are less than or equal to the least Maximum Transmission Unit (MTU)
	for any forwarding device along the routed path to the IP destination		for any forwarding device along the routed path to the IP destination
	for these packets. Such "least MTU" is known as Path MTU (PMTU).		for these packets. Such "least MTU" is known as Path MTU (PMTU).
	Fragmentation or packet drop, silent or not, may occur on hops along		Fragmentation or packet drop, silent or not, may occur on hops along
	the route where an MTU is smaller than the size of the datagram. To		the route where an MTU is smaller than the size of the datagram. To
	avoid any of the listed above behaviors, the packet source must find		avoid any of the listed above behaviors, the packet source must find
	the value of the least MTU, i.e. PMTU, that will be encountered along		the value of the least MTU, i.e., PMTU, that will be encountered
	the route that a set of packets will follow to reach the given set of		along the route that a set of packets will follow to reach the given
	destinations. Such MTU determination along a specific path is		set of destinations. Such MTU determination along a specific path is
	referred to as path MTU discovery (PMTUD).		referred to as path MTU discovery (PMTUD).
	[RFC8279] introduces and explains Bit Index Explicit Replication		[RFC8279] introduces and explains Bit Index Explicit Replication
	(BIER) architecture and how it supports forwarding of multicast data		(BIER) architecture and how it supports the forwarding of multicast
	packets. A BIER domain consists of Bit-Forwarding Routers (BFRs)		data packets. A BIER domain consists of Bit-Forwarding Routers
	that are uniquely identified by their respective BFR-ids. An ingress		(BFRs) that are uniquely identified by their respective BFR-ids. An
	border router (acting as a Bit Forwarding Ingress Router (BFIR))		ingress border router (acting as a Bit Forwarding Ingress Router
	inserts a Forwarding Bit Mask (F-BM) into a packet. Each targeted		(BFIR)) inserts a Forwarding Bit Mask (F-BM) into a packet. Each
	egress node (referred to as a Bit Forwarding Egress Router (BFER)) is		targeted egress node (referred to as a Bit Forwarding Egress Router
	represented by Bit Mask Position (BMP) in the BMS. A transit or		(BFER)) is represented by Bit Mask Position (BMP) in the BMS. A
	intermediate BIER node, referred to as BFR, forwards BIER		transit or intermediate BIER node, referred to as BFR, forwards BIER
	encapsulated packets to BFERs, identified by respective BMPs,		encapsulated packets to BFERs, identified by respective BMPs,
	according to a Bit Index Forwarding Table (BIFT).		according to a Bit Index Forwarding Table (BIFT).
	1.1. Conventions used in this document		1.1. Conventions used in this document
	1.1.1. Terminology		1.1.1. Acronyms
	BFR: Bit-Forwarding Router		BFR: Bit-Forwarding Router
	BFER: Bit-Forwarding Egress Router		BFER: Bit-Forwarding Egress Router
	BFIR: Bit-Forwarding Ingress Router		BFIR: Bit-Forwarding Ingress Router
	BIER: Bit Index Explicit Replication		BIER: Bit Index Explicit Replication
	BIFT: Bit Index Forwarding Tree		BIFT: Bit Index Forwarding Tree
	skipping to change at page 3, line 39 ¶		skipping to change at page 3, line 39 ¶
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and		"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
	"OPTIONAL" in this document are to be interpreted as described in BCP		"OPTIONAL" in this document are to be interpreted as described in BCP
	14 [RFC2119] [RFC8174] when, and only when, they appear in all		14 [RFC2119] [RFC8174] when, and only when, they appear in all
	capitals, as shown here.		capitals, as shown here.
	2. Problem Statement		2. Problem Statement
	[I-D.ietf-bier-oam-requirements] sets forth the requirement to define		[I-D.ietf-bier-oam-requirements] sets forth the requirement to define
	PMTUD protocol for BIER domain. This document describes the		PMTUD protocol for BIER domain. This document describes the
	extension to [I-D.ietf-bier-ping] for use in BIER PMTUD solution.		extension to [I-D.ietf-bier-ping] for use in the BIER PMTUD solution.
	Current PMTUD mechanisms ([RFC1191], [RFC8201], and [RFC4821]) are		Current PMTUD mechanisms ([RFC1191], [RFC8201], and [RFC4821]) are
	primarily targeted to work on point-to-point, i.e. unicast paths.		primarily targeted to work on point-to-point, i.e. unicast paths.
	These mechanisms use packet fragmentation control by disabling		These mechanisms use packet fragmentation control by disabling
	fragmentation of the probe packet. As a result, a transient node		fragmentation of the probe packet. As a result, a transient node
	that cannot forward a probe packet that is bigger than its link MTU		that cannot forward a probe packet that is bigger than its link MTU
	sends to the packet source an error notification, otherwise the		sends to the packet source an error notification, otherwise the
	packet destination may respond with a positive acknowledgment. Thus,		packet destination may respond with a positive acknowledgment. Thus,
	possibly through a series of iterations, varying the size of the		possibly through a series of iterations, varying the size of the
	probe packet, the packet source discovers the PMTU of the particular		probe packet, the packet source discovers the PMTU of the particular
	skipping to change at page 4, line 38 ¶		skipping to change at page 4, line 38 ¶
	----- \ -----		----- \ -----
	--| G |		--| G |
	-----		-----
	Figure 1: Multicast network		Figure 1: Multicast network
	3. PMTUD Mechanism for BIER		3. PMTUD Mechanism for BIER
	A BFIR selects a set of BFERs for the specific multicast		A BFIR selects a set of BFERs for the specific multicast
	distribution. Such a BFIR determines, by explicitly controlling a		distribution. Such a BFIR determines, by explicitly controlling a
	subset of targeted BFERs and transmitting series of probe packets,		subset of targeted BFERs and transmitting a series of probe packets,
	the MTU of that multicast distribution tree. In case of ECMP, BFIR		the MTU of that multicast distribution tree. In the case of ECMP,
	MAY test each path by variating the value in Entropy field. The		BFIR MAY test each path by variating the value in the Entropy field.
	critical step is that in case of failure at an intermediate BFR to		The critical step is that in case of failure at an intermediate BFR
	forward towards the subset of targeted downstream BFERs, the BFR		to forward towards the subset of targeted downstream BFERs, the BFR
	responds with a partial (compared to the one it received in the		responds with a partial (compared to the one it received in the
	request) bitmask towards the originating BFIR in error notification.		request) bitmask towards the originating BFIR in error notification.
	That allows for retransmission of the next probe with smaller MTU		That allows for retransmission of the next probe with a smaller MTU
	address only towards the failed downstream BFERs instead of all BFERs		address only towards the failed downstream BFERs instead of all BFERs
	addressed in the previous probe. In the scenario discussed in		addressed in the previous probe. In the scenario discussed in
	Section 2 the second and all following (if needed) probes will be		Section 2 the second and all following (if needed) probes will be
	sent only to the node D since MTU discovery of E, F, and G has been		sent only to the node D since MTU discovery of E, F, and G has been
	completed already by the first probe successfully.		completed already by the first probe successfully.
	[I-D.ietf-bier-ping] introduced BIER Ping as a transport-independent		[I-D.ietf-bier-ping] introduced BIER Ping as a transport-independent
	OAM mechanism to detect and localize failures in the BIER data plane.		OAM mechanism to detect and localize failures in the BIER data plane.
	This document specifies how BIER Ping can be used to perform		This document specifies how BIER Ping can be used to perform
	efficient PMTUD in the BIER domain.		efficient PMTUD in the BIER domain.
	skipping to change at page 5, line 52 ¶		skipping to change at page 5, line 52 ¶
	been sent. In this case, the bit corresponding to the BFER MUST		been sent. In this case, the bit corresponding to the BFER MUST
	be cleared from the BMS;		be cleared from the BMS;
	o a negative Echo Reply with bit string listing unreached BFERs and		o a negative Echo Reply with bit string listing unreached BFERs and
	recommended MTU value MTU'. The BFIR MUST add the bit string to		recommended MTU value MTU'. The BFIR MUST add the bit string to
	its BMS and set the size of the next probe as min(MTU, MTU')		its BMS and set the size of the next probe as min(MTU, MTU')
	If upon expiration of the Echo Request timer BFIR didn't receive any		If upon expiration of the Echo Request timer BFIR didn't receive any
	Echo Replies, then the size of the probe SHOULD be decreased. There		Echo Replies, then the size of the probe SHOULD be decreased. There
	are scenarios when an implementation of the PMTUD would not decrease		are scenarios when an implementation of the PMTUD would not decrease
	the size of the probe. For example, if upon expiration of the Echo		the size of the probe. For example, suppose upon expiration of the
	Request timer BFIR didn't receive any Echo Reply, then BFIR MAY		Echo Request timer BFIR didn't receive any Echo Reply. In that case,
	continue to retransmit the probe using the initial size and MAY apply		BFIR MAY continue to retransmit the probe using the initial size and
	probe delay retransmission procedures. The algorithm used to delay		MAY apply probe delay retransmission procedures. The algorithm used
	retransmission procedures on BFIR is outside the scope of this		to delay retransmission procedures on BFIR is outside the scope of
	specification. The BFIR sends probes using BMS and locally defined		this specification. The BFIR sends probes using BMS and locally
	retransmission procedures until either the bit string is clear, i.e.		defined retransmission procedures until either the bit string is
	contains no set bits, or until the BFIR retransmission procedure		clear, i.e., contains no set bits, or until the BFIR retransmission
	terminates and PMTU discovery is declared unsuccessful. In case of		procedure terminates and PMTU discovery is declared unsuccessful. In
	convergence of the procedure, the size of the last probe indicates		the case of convergence of the procedure, the size of the last probe
	the PMTU size that can be used for all BFERs in the initial BMS		indicates the PMTU size that can be used for all BFERs in the initial
	without incurring fragmentation.		BMS without incurring fragmentation.
	Thus we conclude that in order to comply with the requirement in		Thus we conclude that in order to comply with the requirement in
	[I-D.ietf-bier-oam-requirements]:		[I-D.ietf-bier-oam-requirements]:
	o a BFR SHOULD support PMTUD;		o a BFR SHOULD support PMTUD;
	o a BFR MAY use defined per BIER sub-domain MTU value as initial MTU		o a BFR MAY use defined per BIER sub-domain MTU value as initial MTU
	value for discovery or use it as MTU for this BIER sub-domain to		value for discovery or use it as MTU for this BIER sub-domain to
	reach BFERs;		reach BFERs;
	o a BFIR MUST have a locally defined of PMTUD probe retransmission		o a BFIR MUST have a locally defined PMTUD probe retransmission
	procedure.		procedure.
	3.1. Data TLV for BIER Ping		3.1. Data TLV for BIER Ping
	There needs to be a control for probe size in order to support the		There needs to be a control for probe size in order to support the
	BIER PMTUD. Data TLV format is presented in Figure 2.		BIER PMTUD. Data TLV format is presented in Figure 2.
	0 1 2 3		0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1		0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	skipping to change at page 7, line 7 ¶		skipping to change at page 7, line 7 ¶
	o Type: indicates Data TLV, to be allocated by IANA Section 4.		o Type: indicates Data TLV, to be allocated by IANA Section 4.
	o Length: the length of the Data field in octets.		o Length: the length of the Data field in octets.
	o Data: n octets (n = Length) of arbitrary data. The receiver		o Data: n octets (n = Length) of arbitrary data. The receiver
	SHOULD ignore it.		SHOULD ignore it.
	4. IANA Considerations		4. IANA Considerations
	IANA is requested to assign new Type value for Data TLV Type from its		IANA is requested to assign a new Type value for Data TLV Type from
	registry of TLV and sub-TLV Types of BIER Ping as follows:		its registry of TLV and sub-TLV Types of BIER Ping as follows:
	+-------+-------------+---------------+		+-------+-------------+---------------+
	| Value | Description | Reference |		| Value | Description | Reference |
	+-------+-------------+---------------+		+-------+-------------+---------------+
	| TBA1 | Data | This document |		| TBA1 | Data | This document |
	+-------+-------------+---------------+		+-------+-------------+---------------+
	Table 1: Data TLV Type		Table 1: Data TLV Type
	5. Security Considerations		5. Security Considerations
	skipping to change at page 8, line 13 ¶		skipping to change at page 8, line 13 ¶
	May 2017, <https://www.rfc-editor.org/info/rfc8174>.		May 2017, <https://www.rfc-editor.org/info/rfc8174>.
	[RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,		[RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,
	"Path MTU Discovery for IP version 6", STD 87, RFC 8201,		"Path MTU Discovery for IP version 6", STD 87, RFC 8201,
	DOI 10.17487/RFC8201, July 2017,		DOI 10.17487/RFC8201, July 2017,
	<https://www.rfc-editor.org/info/rfc8201>.		<https://www.rfc-editor.org/info/rfc8201>.
	7.2. Informative References		7.2. Informative References
	[I-D.ietf-bier-oam-requirements]		[I-D.ietf-bier-oam-requirements]
	Mirsky, G., Nainar, N., Chen, M., and J. Networks,		Mirsky, G., Nainar, N., Chen, M., and S. Pallagatti,
	"Operations, Administration and Maintenance (OAM)		"Operations, Administration and Maintenance (OAM)
	Requirements for Bit Index Explicit Replication (BIER)		Requirements for Bit Index Explicit Replication (BIER)
	Layer", draft-ietf-bier-oam-requirements-10 (work in		Layer", draft-ietf-bier-oam-requirements-11 (work in
	progress), May 2020.		progress), November 2020.
	[RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,		[RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
	Przygienda, T., and S. Aldrin, "Multicast Using Bit Index		Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
	Explicit Replication (BIER)", RFC 8279,		Explicit Replication (BIER)", RFC 8279,
	DOI 10.17487/RFC8279, November 2017,		DOI 10.17487/RFC8279, November 2017,
	<https://www.rfc-editor.org/info/rfc8279>.		<https://www.rfc-editor.org/info/rfc8279>.
	Authors' Addresses		Authors' Addresses
	Greg Mirsky		Greg Mirsky
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