< draft-ietf-dnsop-avoid-fragmentation-02.txt		draft-ietf-dnsop-avoid-fragmentation-03.txt >
	Network Working Group K. Fujiwara		Network Working Group K. Fujiwara
	Internet-Draft JPRS		Internet-Draft JPRS
	Intended status: Best Current Practice P. Vixie		Intended status: Best Current Practice P. Vixie
	Expires: March 19, 2021 Farsight		Expires: 27 May 2021 Farsight
	September 15, 2020		23 November 2020
	Fragmentation Avoidance in DNS		Fragmentation Avoidance in DNS
	draft-ietf-dnsop-avoid-fragmentation-02		draft-ietf-dnsop-avoid-fragmentation-03
	Abstract		Abstract
	EDNS0 enables a DNS server to send large responses using UDP and is		EDNS0 enables a DNS server to send large responses using UDP and is
	widely deployed. Path MTU discovery remains widely undeployed due to		widely deployed. Path MTU discovery remains widely undeployed due to
	security issues, and IP fragmentation has exposed weaknesses in		security issues, and IP fragmentation has exposed weaknesses in
	application protocols. Currently, DNS is known to be the largest		application protocols. Currently, DNS is known to be the largest
	user of IP fragmentation. It is possible to avoid IP fragmentation		user of IP fragmentation. It is possible to avoid IP fragmentation
	in DNS by limiting response size where possible, and signaling the		in DNS by limiting response size where possible, and signaling the
	need to upgrade from UDP to TCP transport where necessary. This		need to upgrade from UDP to TCP transport where necessary. This
	skipping to change at page 1, line 38 ¶		skipping to change at page 1, line 38 ¶
	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 March 19, 2021.		This Internet-Draft will expire on 27 May 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/
	(https://trustee.ietf.org/license-info) in effect on the date of		license-info) in effect on the date of publication of this document.
	publication of this document. Please review these documents		Please review these documents carefully, as they describe your rights
	carefully, as they describe your rights and restrictions with respect		and restrictions with respect to this document. Code Components
	to this document. Code Components extracted from this document must		extracted from this document must include Simplified BSD License text
	include Simplified BSD License text as described in Section 4.e of		as described in Section 4.e of the Trust Legal Provisions and are
	the Trust Legal Provisions and are provided without warranty as		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
	2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3		2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
	3. Proposal to avoid IP fragmentation in DNS . . . . . . . . . . 4		3. Proposal to avoid IP fragmentation in DNS . . . . . . . . . . 4
	3.1. Recommendations for UDP requestors . . . . . . . . . . . 4		3.1. Recommendations for UDP responders . . . . . . . . . . . 4
	3.2. Recommendations for UDP responders . . . . . . . . . . . 4		3.2. Recommendations for UDP requestors . . . . . . . . . . . 5
	4. Maximum DNS/UDP payload size . . . . . . . . . . . . . . . . 5		4. Maximum DNS/UDP payload size . . . . . . . . . . . . . . . . 5
	5. Incremental deployment . . . . . . . . . . . . . . . . . . . 6		5. Incremental deployment . . . . . . . . . . . . . . . . . . . 6
	6. Request to zone operators and DNS server operators . . . . . 6		6. Request to zone operators and DNS server operators . . . . . 7
	7. Considerations . . . . . . . . . . . . . . . . . . . . . . . 6		7. Considerations . . . . . . . . . . . . . . . . . . . . . . . 7
	7.1. Protocol compliance . . . . . . . . . . . . . . . . . . . 6		7.1. Protocol compliance . . . . . . . . . . . . . . . . . . . 7
	8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7		8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
	9. Security Considerations . . . . . . . . . . . . . . . . . . . 7		9. Security Considerations . . . . . . . . . . . . . . . . . . . 7
	10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7		10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
	11. References . . . . . . . . . . . . . . . . . . . . . . . . . 7		11. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
	11.1. Normative References . . . . . . . . . . . . . . . . . . 7		11.1. Normative References . . . . . . . . . . . . . . . . . . 7
	11.2. Informative References . . . . . . . . . . . . . . . . . 8		11.2. Informative References . . . . . . . . . . . . . . . . . 9
	Appendix A. How to retrieve path MTU value to a destination from		Appendix A. How to retrieve path MTU value to a destination from
	applications . . . . . . . . . . . . . . . . . . . . 9		applications . . . . . . . . . . . . . . . . . . . . . . 10
	Appendix B. Minimal-responses . . . . . . . . . . . . . . . . . 9		Appendix B. Minimal-responses . . . . . . . . . . . . . . . . . 10
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
	1. Introduction		1. Introduction
	DNS has EDNS0 [RFC6891] mechanism. It enables a DNS server to send		DNS has EDNS0 [RFC6891] mechanism. It enables a DNS server to send
	large responses using UDP. EDNS0 is now widely deployed, and DNS		large responses using UDP. EDNS0 is now widely deployed, and DNS
	(over UDP) is said to be the biggest user of IP fragmentation.		(over UDP) is said to be the biggest user of IP fragmentation.
	However, "Fragmentation Considered Poisonous" [Herzberg2013] proposed		However, "Fragmentation Considered Poisonous" [Herzberg2013] proposed
	effective off-path DNS cache poisoning attack vectors using IP		effective off-path DNS cache poisoning attack vectors using IP
	fragmentation. "IP fragmentation attack on DNS" [Hlavacek2013] and		fragmentation. "IP fragmentation attack on DNS" [Hlavacek2013] and
	skipping to change at page 3, line 38 ¶		skipping to change at page 3, line 44 ¶
	that the size of the IP and TCP headers is known, as well as the far		that the size of the IP and TCP headers is known, as well as the far
	end's MSS parameter and the interface or path MTU, so that the		end's MSS parameter and the interface or path MTU, so that the
	segment size can be chosen so as to keep the each IP datagram below a		segment size can be chosen so as to keep the each IP datagram below a
	target size. This takes advantage of the elasticity of TCP's		target size. This takes advantage of the elasticity of TCP's
	packetizing process as to how much queued data will fit into the next		packetizing process as to how much queued data will fit into the next
	segment. In contrast, DNS over UDP has little datagram size		segment. In contrast, DNS over UDP has little datagram size
	elasticity and lacks insight into IP header and option size, and so		elasticity and lacks insight into IP header and option size, and so
	must make more conservative estimates about available UDP payload		must make more conservative estimates about available UDP payload
	space.		space.
	This document proposes to avoid IP fragmentation in DNS/UDP.		This document proposes to set IP_DONTFRAG / IPV6_DONTFRAG in DNS/UDP
			responses in order to avoid IP fragmentation, and describes how to
			avoid packet losses due to IP_DONTFRAG / IPV6_DONTFRAG.
	2. Terminology		2. Terminology
	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		"OPTIONAL" in this document are to be interpreted as described in
	BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all		BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all
	capitals, as shown here.		capitals, as shown here.
	"Requestor" refers to the side that sends a request. "Responder"		"Requestor" refers to the side that sends a request. "Responder"
	skipping to change at page 4, line 4 ¶		skipping to change at page 4, line 16 ¶
	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		"OPTIONAL" in this document are to be interpreted as described in
	BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all		BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all
	capitals, as shown here.		capitals, as shown here.
	"Requestor" refers to the side that sends a request. "Responder"		"Requestor" refers to the side that sends a request. "Responder"
	refers to an authoritative, recursive resolver or other DNS component		refers to an authoritative, recursive resolver or other DNS component
	that responds to questions. (Quoted from EDNS0 [RFC6891])		that responds to questions. (Quoted from EDNS0 [RFC6891])
	"Path MTU" is the minimum link MTU of all the links in a path between		"Path MTU" is the minimum link MTU of all the links in a path between
	a source node and a destination node. (Quoted from [RFC8201])		a source node and a destination node. (Quoted from [RFC8201])
	"Path MTU discovery" is defined by [RFC1191], [RFC8201] and		"Path MTU discovery" is defined by [RFC1191], [RFC8201] and
	[RFC8899].		[RFC8899].
	Many of the specialized terms used in this document are defined in		Many of the specialized terms used in this document are defined in
	DNS Terminology [RFC8499].		DNS Terminology [RFC8499].
	3. Proposal to avoid IP fragmentation in DNS		3. Proposal to avoid IP fragmentation in DNS
	The methods to avoid IP fragmentation in DNS are described below:		The methods to avoid IP fragmentation in DNS are described below:
	3.1. Recommendations for UDP requestors		3.1. Recommendations for UDP responders
	o UDP requestors SHOULD send DNS responses with IP_DONTFRAG /		* UDP responders SHOULD send DNS responses with IP_DONTFRAG /
	IPV6_DONTFRAG [RFC3542] options.		IPV6_DONTFRAG [RFC3542] options.
	o UDP requestors MAY probe to discover the real MTU value per		* If the UDP responder detects immediate error that the UDP packet
			cannot be sent beyond the path MTU size (EMSGSIZE), the UDP
			responder MAY recreate response packets fit in path MTU size, or
			TC bit set.
			* UDP responders MAY probe to discover the real MTU value per
	destination. If the path MTU discovery failed or is impossible,		destination. If the path MTU discovery failed or is impossible,
	use the default path MTU described in Section 4.		use the default path MTU described in Section 4.
	o UDP reqoestors SHOULD use the requestor's payload size to limit		* UDP responders SHOULD compose UDP responses that result in IP
	the path MTU value minus the IP header length and UDP header		packets that do not exceed the path MTU to the requestor. Of
	length. Of course, as in the conventional case, a specified value		course, as in the conventional case, a specified value (1220 or
	(1220 or 1232) as the requestor's payload size may be used.		1232) as the DNS packet size limit may be used.
	o UDP requestors MAY drop fragmented DNS/UDP responses without IP
	reassembly to avoid cache poisoning attacks.
	o DNS responses may be dropped by IP fragmentation. Upon a timeout,		The cause and effect of the TC bit is unchanged from EDNS0
	UDP requestors may retry using TCP or UDP, per local policy.		[RFC6891].
	3.2. Recommendations for UDP responders		3.2. Recommendations for UDP requestors
	o UDP responders SHOULD send DNS responses with IP_DONTFRAG /		* UDP requestors SHOULD send DNS responses with IP_DONTFRAG /
	IPV6_DONTFRAG [RFC3542] options.		IPV6_DONTFRAG [RFC3542] options.
	o UDP responders MAY probe to discover the real MTU value per		* UDP requestors MAY probe to discover the real MTU value per
	destination. If the path MTU discovery failed or is impossible,		destination. If the path MTU discovery failed or is impossible,
	use the default path MTU described in Section 4.		use the default path MTU described in Section 4.
	o UDP responders SHOULD compose UDP responses that result in IP		* UDP reqoestors SHOULD use the requestor's payload size to limit
	packets that do not exceed the path MTU to the requestor. Of		the path MTU value minus the IP header length and UDP header
	course, as in the conventional case, a specified value (1220 or		length. Of course, as in the conventional case, a specified value
	1232) as the DNS packet size limit may be used.		(1220 or 1232) as the requestor's payload size may be used.
	The cause and effect of the TC bit is unchanged from EDNS0		* UDP requestors MAY drop fragmented DNS/UDP responses without IP
	[RFC6891].		reassembly to avoid cache poisoning attacks.
			* DNS responses may be dropped by IP fragmentation. Upon a timeout,
			UDP requestors may retry using TCP or UDP, per local policy.
	4. Maximum DNS/UDP payload size		4. Maximum DNS/UDP payload size
	Default path MTU value for IPv6 is XXXX. Default path MTU value for		Default path MTU value for IPv6 is XXXX. Default path MTU value for
	IPv4 is XXXX.		IPv4 is XXXX.
	Discussions under here will be deleted when the discussion is over.		Discussions under here will be deleted when the discussion is over.
	There are many discussions for default path MTU values.		There are many discussions for default path MTU values.
	o The minimum MTU for an IPv6 interface is 1280 octets (see		* The minimum MTU for an IPv6 interface is 1280 octets (see
	Section 5 of [RFC8200]). Then, we can use it as default path MTU		Section 5 of [RFC8200]). Then, we can use it as default path MTU
	value for IPv6.		value for IPv6.
	o Most of the Internet and especially the inner core has an MTU of		* Most of the Internet and especially the inner core has an MTU of
	at least 1500 octets. An operator of a full resolver would be		at least 1500 octets. An operator of a full resolver would be
	well advised to measure their path MTU to several authority name		well advised to measure their path MTU to several authority name
	servers and to a random sample of their expected stub resolver		servers and to a random sample of their expected stub resolver
	client networks, to find the upper boundary on IP/UDP packet size		client networks, to find the upper boundary on IP/UDP packet size
	in the average case. This limit should not be exceeded by most		in the average case. This limit should not be exceeded by most
	messages received or transmitted by a full resolver, or else		messages received or transmitted by a full resolver, or else
	fallback to TCP will occur too often. An operator of		fallback to TCP will occur too often. An operator of
	authoritative servers would also be well advised to measure their		authoritative servers would also be well advised to measure their
	path MTU to several full-service resolvers. The Linux tool		path MTU to several full-service resolvers. The Linux tool
	"tracepath" can be used to measure the path MTU to well known		"tracepath" can be used to measure the path MTU to well known
	authority name servers such as [a-m].root-servers.net or [a-		authority name servers such as [a-m].root-servers.net or [a-
	m].gtld-servers.net. If the reported path MTU is for example no		m].gtld-servers.net. If the reported path MTU is for example no
	smaller than 1460, then the maximum DNS/UDP payload would be 1432		smaller than 1460, then the maximum DNS/UDP payload would be 1432
	for IP4 (which is 1460 - IP4 header(20) - UDP header(8)) and 1412		for IP4 (which is 1460 - IP4 header(20) - UDP header(8)) and 1412
	for IP6 (which is 1460 - IP6 header(40) - UDP header(8)). To		for IP6 (which is 1460 - IP6 header(40) - UDP header(8)). To
	allow for possible IP options and distant tunnel overhead, a		allow for possible IP options and distant tunnel overhead, a
	useful default for maximum DNS/UDP payload size would be 1400.		useful default for maximum DNS/UDP payload size would be 1400.
	o [RFC4035] defines that "A security-aware name server MUST support		* [RFC4035] defines that "A security-aware name server MUST support
	the EDNS0 message size extension, MUST support a message size of		the EDNS0 message size extension, MUST support a message size of
	at least 1220 octets". Then, the smallest number of the maximum		at least 1220 octets". Then, the smallest number of the maximum
	DNS/UDP payload size is 1220.		DNS/UDP payload size is 1220.
	o DNS flag day 2020 proposed 1232 as an EDNS buffer size.		* In order to avoid IP fragmentation, [DNSFlagDay2020] proposed that
	[DNSFlagDay2020] By the above reasoning, this proposal is either		the UDP requestors set the requestor's payload size to 1232, and
	too small or too large.		the UDP responders compose UDP responses fit in 1232 octets. The
			size 1232 is based on an MTU of 1280, which is required by the
			IPv6 specification [RFC8200], minus 48 octets for the IPv6 and UDP
			headers.
	It is considered that these arguments are diverted from IPv6		By the above reasoning, this proposal is either too small or too
	values because most IPv4 links have path MTU values larger than or		large.
	equal to the minimum MTU value of IPv6.
	5. Incremental deployment		5. Incremental deployment
	The proposed method supports incremental deployment.		The proposed method supports incremental deployment.
	When a full-service resolver implements the proposed method, its stub		When a full-service resolver implements the proposed method, its stub
	resolvers (clients) and the authority server network will no longer		resolvers (clients) and the authority server network will no longer
	observe IP fragmentation or reassembly from that server, and will		observe IP fragmentation or reassembly from that server, and will
	fall back to TCP when necessary.		fall back to TCP when necessary.
	skipping to change at page 6, line 25 ¶		skipping to change at page 7, line 11 ¶
	service resolvers (clients) will no longer observe IP fragmentation		service resolvers (clients) will no longer observe IP fragmentation
	or reassembly from that server, and will fall back to TCP when		or reassembly from that server, and will fall back to TCP when
	necessary.		necessary.
	6. Request to zone operators and DNS server operators		6. Request to zone operators and DNS server operators
	Large DNS responses are the result of zone configuration. Zone		Large DNS responses are the result of zone configuration. Zone
	operators SHOULD seek configurations resulting in small responses.		operators SHOULD seek configurations resulting in small responses.
	For example,		For example,
	o Use smaller number of name servers (13 may be too large)		* Use smaller number of name servers (13 may be too large)
	o Use smaller number of A/AAAA RRs for a domain name		* Use smaller number of A/AAAA RRs for a domain name
	o Use 'minimal-responses' configuration: Some implementations have		* Use 'minimal-responses' configuration: Some implementations have
	'minimal responses' configuration that causes DNS servers to make		'minimal responses' configuration that causes DNS servers to make
	response packets smaller, containing only mandatory and required		response packets smaller, containing only mandatory and required
	data (Appendix B).		data (Appendix B).
	o Use smaller signature / public key size algorithm for DNSSEC.		* Use smaller signature / public key size algorithm for DNSSEC.
	Notably, the signature size of ECDSA or EdDSA is smaller than RSA.		Notably, the signature size of ECDSA or EdDSA is smaller than RSA.
	7. Considerations		7. Considerations
	7.1. Protocol compliance		7.1. Protocol compliance
	In prior research ([Fujiwara2018] and dns-operations mailing list		In prior research ([Fujiwara2018] and dns-operations mailing list
	discussions), there are some authoritative servers that ignore EDNS0		discussions), there are some authoritative servers that ignore EDNS0
	requestor's UDP payload size, and return large UDP responses.		requestor's UDP payload size, and return large UDP responses.
	skipping to change at page 7, line 29 ¶		skipping to change at page 8, line 14 ¶
	[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,		[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
	DOI 10.17487/RFC1191, November 1990,		DOI 10.17487/RFC1191, November 1990,
	<https://www.rfc-editor.org/info/rfc1191>.		<https://www.rfc-editor.org/info/rfc1191>.
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119,		Requirement Levels", BCP 14, RFC 2119,
	DOI 10.17487/RFC2119, March 1997,		DOI 10.17487/RFC2119, March 1997,
	<https://www.rfc-editor.org/info/rfc2119>.		<https://www.rfc-editor.org/info/rfc2119>.
	[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>.
	[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.		[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
	Rose, "Protocol Modifications for the DNS Security		Rose, "Protocol Modifications for the DNS Security
	Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,		Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,
	<https://www.rfc-editor.org/info/rfc4035>.		<https://www.rfc-editor.org/info/rfc4035>.
	[RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS		[RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
	Security (DNSSEC) Hashed Authenticated Denial of		Security (DNSSEC) Hashed Authenticated Denial of
	Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008,		Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008,
	<https://www.rfc-editor.org/info/rfc5155>.		<https://www.rfc-editor.org/info/rfc5155>.
	[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms		[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
	for DNS (EDNS(0))", STD 75, RFC 6891,		for DNS (EDNS(0))", STD 75, RFC 6891,
	DOI 10.17487/RFC6891, April 2013,		DOI 10.17487/RFC6891, April 2013,
	<https://www.rfc-editor.org/info/rfc6891>.		<https://www.rfc-editor.org/info/rfc6891>.
	[RFC7739] Gont, F., "Security Implications of Predictable Fragment
	Identification Values", RFC 7739, DOI 10.17487/RFC7739,
	February 2016, <https://www.rfc-editor.org/info/rfc7739>.
	[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage		[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
	Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,		Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
	March 2017, <https://www.rfc-editor.org/info/rfc8085>.		March 2017, <https://www.rfc-editor.org/info/rfc8085>.
	[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC		[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
	2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,		2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
	May 2017, <https://www.rfc-editor.org/info/rfc8174>.		May 2017, <https://www.rfc-editor.org/info/rfc8174>.
	[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6		[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
	(IPv6) Specification", STD 86, RFC 8200,		(IPv6) Specification", STD 86, RFC 8200,
	skipping to change at page 8, line 27 ¶		skipping to change at page 9, line 5 ¶
	[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>.
	[RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS		[RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
	Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,		Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
	January 2019, <https://www.rfc-editor.org/info/rfc8499>.		January 2019, <https://www.rfc-editor.org/info/rfc8499>.
	[RFC8899] Fairhurst, G., Jones, T., Tuexen, M., Ruengeler, I., and		[RFC8899] Fairhurst, G., Jones, T., Tüxen, M., Rüngeler, I., and T.
	T. Voelker, "Packetization Layer Path MTU Discovery for		Völker, "Packetization Layer Path MTU Discovery for
	Datagram Transports", RFC 8899, DOI 10.17487/RFC8899,		Datagram Transports", RFC 8899, DOI 10.17487/RFC8899,
	September 2020, <https://www.rfc-editor.org/info/rfc8899>.		September 2020, <https://www.rfc-editor.org/info/rfc8899>.
	[RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, B., Troan, O.,		[RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O.,
	and F. Gont, "IP Fragmentation Considered Fragile",		and F. Gont, "IP Fragmentation Considered Fragile",
	BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020,		BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020,
	<https://www.rfc-editor.org/info/rfc8900>.		<https://www.rfc-editor.org/info/rfc8900>.
	11.2. Informative References		11.2. Informative References
	[Brandt2018]		[Brandt2018]
	Brandt, M., Dai, T., Klein, A., Shulman, H., and M.		Brandt, M., Dai, T., Klein, A., Shulman, H., and M.
	Waidner, "Domain Validation++ For MitM-Resilient PKI",		Waidner, "Domain Validation++ For MitM-Resilient PKI",
	Proceedings of the 2018 ACM SIGSAC Conference on Computer		Proceedings of the 2018 ACM SIGSAC Conference on Computer
	skipping to change at page 9, line 15 ¶		skipping to change at page 9, line 40 ¶
	[Herzberg2013]		[Herzberg2013]
	Herzberg, A. and H. Shulman, "Fragmentation Considered		Herzberg, A. and H. Shulman, "Fragmentation Considered
	Poisonous", IEEE Conference on Communications and Network		Poisonous", IEEE Conference on Communications and Network
	Security , 2013.		Security , 2013.
	[Hlavacek2013]		[Hlavacek2013]
	Hlavacek, T., "IP fragmentation attack on DNS", RIPE 67		Hlavacek, T., "IP fragmentation attack on DNS", RIPE 67
	Meeting , 2013, <https://ripe67.ripe.net/		Meeting , 2013, <https://ripe67.ripe.net/
	presentations/240-ipfragattack.pdf>.		presentations/240-ipfragattack.pdf>.
			[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>.
			[RFC7739] Gont, F., "Security Implications of Predictable Fragment
			Identification Values", RFC 7739, DOI 10.17487/RFC7739,
			February 2016, <https://www.rfc-editor.org/info/rfc7739>.
	Appendix A. How to retrieve path MTU value to a destination from		Appendix A. How to retrieve path MTU value to a destination from
	applications		applications
	Socket options: "IP_MTU (since Linux 2.2) Retrieve the current known		Socket options: "IP_MTU (since Linux 2.2) Retrieve the current known
	path MTU of the current socket. Valid only when the socket has been		path MTU of the current socket. Valid only when the socket has been
	connected. Returns an integer. Only valid as a getsockopt(2)."		connected. Returns an integer. Only valid as a getsockopt(2)."
	(Quoted from Debian GNU Linux manual: ip(7))		(Quoted from Debian GNU Linux manual: ip(7))
	"IPV6_MTU getsockopt(): Retrieve the current known path MTU of the		"IPV6_MTU getsockopt(): Retrieve the current known path MTU of the
	current socket. Only valid when the socket has been connected.		current socket. Only valid when the socket has been connected.
	skipping to change at page 10, line 4 ¶		skipping to change at page 10, line 37 ¶
	below-zone) glue in the additional data section. In case of non-		below-zone) glue in the additional data section. In case of non-
	existent domain name or non-existent type, the start of authority		existent domain name or non-existent type, the start of authority
	(SOA RR) will be placed in the Authority Section.		(SOA RR) will be placed in the Authority Section.
	In addition, if the zone is DNSSEC signed and a query has the DNSSEC		In addition, if the zone is DNSSEC signed and a query has the DNSSEC
	OK bit, signatures are added in answer section, or the corresponding		OK bit, signatures are added in answer section, or the corresponding
	DS RRSet and signatures are added in authority section. Details are		DS RRSet and signatures are added in authority section. Details are
	defined in [RFC4035] and [RFC5155].		defined in [RFC4035] and [RFC5155].
	Authors' Addresses		Authors' Addresses
	Kazunori Fujiwara		Kazunori Fujiwara
	Japan Registry Services Co., Ltd.		Japan Registry Services Co., Ltd.
	Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda		Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda, Chiyoda-ku, Tokyo
	Chiyoda-ku, Tokyo 101-0065		101-0065
	Japan		Japan
	Phone: +81 3 5215 8451		Phone: +81 3 5215 8451
	Email: fujiwara@jprs.co.jp		Email: fujiwara@jprs.co.jp
	Paul Vixie		Paul Vixie
	Farsight Security Inc		Farsight Security Inc
	177 Bovet Road, Suite 180		177 Bovet Road, Suite 180
	San Mateo, CA 94402		San Mateo, CA, 94402
	United States of America		United States of America
	Phone: +1 650 393 3994		Phone: +1 650 393 3994
	Email: vixie@fsi.io		Email: vixie@fsi.io
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