draft-ietf-intarea-frag-fragile-06.txt   draft-ietf-intarea-frag-fragile-07.txt 
Internet Area WG R. Bonica Internet Area WG R. Bonica
Internet-Draft Juniper Networks Internet-Draft Juniper Networks
Intended status: Best Current Practice F. Baker Intended status: Best Current Practice F. Baker
Expires: August 2, 2019 Unaffiliated Expires: August 3, 2019 Unaffiliated
G. Huston G. Huston
APNIC APNIC
R. Hinden R. Hinden
Check Point Software Check Point Software
O. Troan O. Troan
Cisco Cisco
F. Gont F. Gont
SI6 Networks SI6 Networks
January 29, 2019 January 30, 2019
IP Fragmentation Considered Fragile IP Fragmentation Considered Fragile
draft-ietf-intarea-frag-fragile-06 draft-ietf-intarea-frag-fragile-07
Abstract Abstract
This document describes IP fragmentation and explains how it reduces This document describes IP fragmentation and explains how it reduces
the reliability of Internet communication. the reliability of Internet communication.
This document also proposes alternatives to IP fragmentation and This document also proposes alternatives to IP fragmentation and
provides recommendations for developers and network operators. provides recommendations for developers and network operators.
Status of This Memo Status of This Memo
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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 August 2, 2019. This Internet-Draft will expire on August 3, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 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
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1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. IP Fragmentation . . . . . . . . . . . . . . . . . . . . . . 3 2. IP Fragmentation . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Links, Paths, MTU and PMTU . . . . . . . . . . . . . . . 3 2.1. Links, Paths, MTU and PMTU . . . . . . . . . . . . . . . 3
2.2. Fragmentation Procedures . . . . . . . . . . . . . . . . 5 2.2. Fragmentation Procedures . . . . . . . . . . . . . . . . 5
2.3. Upper-Layer Reliance on IP Fragmentation . . . . . . . . 6 2.3. Upper-Layer Reliance on IP Fragmentation . . . . . . . . 6
3. Requirements Language . . . . . . . . . . . . . . . . . . . . 7 3. Requirements Language . . . . . . . . . . . . . . . . . . . . 7
4. Reduced Reliability . . . . . . . . . . . . . . . . . . . . . 7 4. Reduced Reliability . . . . . . . . . . . . . . . . . . . . . 7
4.1. Policy-Based Routing . . . . . . . . . . . . . . . . . . 7 4.1. Policy-Based Routing . . . . . . . . . . . . . . . . . . 7
4.2. Network Address Translation (NAT) . . . . . . . . . . . . 8 4.2. Network Address Translation (NAT) . . . . . . . . . . . . 8
4.3. Stateless Firewalls . . . . . . . . . . . . . . . . . . . 9 4.3. Stateless Firewalls . . . . . . . . . . . . . . . . . . . 9
4.4. Stateless Load Balancers . . . . . . . . . . . . . . . . 9 4.4. Equal Cost Multipath, Link Aggregate Groups and Stateless
4.5. Equal Cost Multipath (ECMP) . . . . . . . . . . . . . . . 10 Load-Balancers . . . . . . . . . . . . . . . . . . . . . 9
4.6. IPv4 Reassembly Errors at High Data Rates . . . . . . . . 10 4.5. IPv4 Reassembly Errors at High Data Rates . . . . . . . . 10
4.7. Security Vulnerabilities . . . . . . . . . . . . . . . . 10 4.6. Security Vulnerabilities . . . . . . . . . . . . . . . . 10
4.8. PMTU Blackholing Due to ICMP Loss . . . . . . . . . . . . 11 4.7. PMTU Blackholing Due to ICMP Loss . . . . . . . . . . . . 11
4.8.1. Transient Loss . . . . . . . . . . . . . . . . . . . 12 4.7.1. Transient Loss . . . . . . . . . . . . . . . . . . . 12
4.8.2. Incorrect Implementation of Security Policy . . . . . 12 4.7.2. Incorrect Implementation of Security Policy . . . . . 12
4.8.3. Persistent Loss Caused By Anycast . . . . . . . . . . 13 4.7.3. Persistent Loss Caused By Anycast . . . . . . . . . . 13
4.9. Blackholing Due To Filtering or Loss . . . . . . . . . . 13 4.8. Blackholing Due To Filtering or Loss . . . . . . . . . . 13
5. Alternatives to IP Fragmentation . . . . . . . . . . . . . . 14 5. Alternatives to IP Fragmentation . . . . . . . . . . . . . . 14
5.1. Transport Layer Solutions . . . . . . . . . . . . . . . . 14 5.1. Transport Layer Solutions . . . . . . . . . . . . . . . . 14
5.2. Application Layer Solutions . . . . . . . . . . . . . . . 15 5.2. Application Layer Solutions . . . . . . . . . . . . . . . 15
6. Applications That Rely on IPv6 Fragmentation . . . . . . . . 16 6. Applications That Rely on IPv6 Fragmentation . . . . . . . . 16
6.1. DNS . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 6.1. DNS . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
6.2. OSPF . . . . . . . . . . . . . . . . . . . . . . . . . . 17 6.2. OSPF . . . . . . . . . . . . . . . . . . . . . . . . . . 17
6.3. Packet-in-Packet Encapsulations . . . . . . . . . . . . . 17 6.3. Packet-in-Packet Encapsulations . . . . . . . . . . . . . 17
6.4. Licklider Transmission Protocol (LTP) . . . . . . . . . . 17 6.4. Licklider Transmission Protocol (LTP) . . . . . . . . . . 18
7. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 18 7. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 18
7.1. For Application and Protocol Developers . . . . . . . . . 18 7.1. For Application and Protocol Developers . . . . . . . . . 18
7.2. For System Developers . . . . . . . . . . . . . . . . . . 18 7.2. For System Developers . . . . . . . . . . . . . . . . . . 18
7.3. For Middle Box Developers . . . . . . . . . . . . . . . . 18 7.3. For Middle Box Developers . . . . . . . . . . . . . . . . 19
7.4. For Network Operators . . . . . . . . . . . . . . . . . . 19 7.4. For ECMP, LAG and Load-Balancer Developers And Operators 19
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 7.5. For Network Operators . . . . . . . . . . . . . . . . . . 19
9. Security Considerations . . . . . . . . . . . . . . . . . . . 19 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19 9. Security Considerations . . . . . . . . . . . . . . . . . . . 20
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20
11.1. Normative References . . . . . . . . . . . . . . . . . . 19 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
11.1. Normative References . . . . . . . . . . . . . . . . . . 20
11.2. Informative References . . . . . . . . . . . . . . . . . 21 11.2. Informative References . . . . . . . . . . . . . . . . . 21
Appendix A. Contributors' Address . . . . . . . . . . . . . . . 24 Appendix A. Contributors' Address . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction 1. Introduction
Operational experience [Kent] [Huston] [RFC7872] reveals that IP Operational experience [Kent] [Huston] [RFC7872] reveals that IP
fragmentation reduces the reliability of Internet communication. fragmentation reduces the reliability of Internet communication.
This document describes IP fragmentation and explains how it reduces This document describes IP fragmentation and explains how it reduces
the reliability of Internet communication. This document also the reliability of Internet communication. This document also
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o The Destination IP Address and Destination Port on each inbound o The Destination IP Address and Destination Port on each inbound
packet. packet.
A+P [RFC6346] and Carrier Grade NAT (CGN) [RFC6888] are two common A+P [RFC6346] and Carrier Grade NAT (CGN) [RFC6888] are two common
NAT strategies. In both approaches the NAT device must virtually NAT strategies. In both approaches the NAT device must virtually
reassemble fragmented packets in order to translate and forward each reassemble fragmented packets in order to translate and forward each
fragment. fragment.
Virtual reassembly in the network is problematic, because it is Virtual reassembly in the network is problematic, because it is
computationally expensive and because it is prone to attacks computationally expensive and because it is prone to attacks
(Section 4.7). (Section 4.6).
4.3. Stateless Firewalls 4.3. Stateless Firewalls
IP fragmentation causes problems for stateless firewalls whose rules IP fragmentation causes problems for stateless firewalls whose rules
include TCP and UDP ports. Because port information is not available include TCP and UDP ports. Because port information is not available
in the trailing fragments the firewall is limited to the following in the trailing fragments the firewall is limited to the following
options: options:
o Accept all trailing fragments, possibly admitting certain classes o Accept all trailing fragments, possibly admitting certain classes
of attack. of attack.
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o Block all trailing fragments, possibly blocking legitimate o Block all trailing fragments, possibly blocking legitimate
traffic. traffic.
Neither option is attractive. Neither option is attractive.
This problem does not occur in stateful firewalls or Network Address This problem does not occur in stateful firewalls or Network Address
Translation (NAT) devices. Such devices maintain state so that they Translation (NAT) devices. Such devices maintain state so that they
can afford identical treatment to each fragment that belongs to a can afford identical treatment to each fragment that belongs to a
packet. packet.
4.4. Stateless Load Balancers 4.4. Equal Cost Multipath, Link Aggregate Groups and Stateless Load-
Balancers
IP fragmentation causes problems for stateless load balancers. In IP fragmentation causes problems for Equal Cost Multipath (ECMP),
order to assign a packet or packet fragment to a link, the load- Link Aggregate Groups (LAG) and other stateless load-balancing
balancer executes an algorithm. The following paragraphs describe a technologies. In order to assign a packet or packet fragment to a
commonly deployed load-balancing algorithm. link, an intermediate node executes a hash (i.e., load-balancing)
algorithm. The following paragraphs describe a commonly deployed
hash algorithm.
If the packet or packet fragment contains a transport-layer header, If the packet or packet fragment contains a transport-layer header,
the load balancing algorithm accepts the following 5-tuple as input: the algorithm accepts the following 5-tuple as input:
o IP Source Address. o IP Source Address.
o IP Destination Address. o IP Destination Address.
o IPv4 Protocol or IPv6 Next Header. o IPv4 Protocol or IPv6 Next Header.
o transport-layer source port. o transport-layer source port.
o transport-layer destination port. o transport-layer destination port.
If the packet or packet fragment does not contain a transport-layer If the packet or packet fragment does not contain a transport-layer
header, the load balancing algorithm accepts only the following header, the algorithm accepts only the following 3-tuple as input:
3-tuple as input:
o IP Source Address. o IP Source Address.
o IP Destination Address. o IP Destination Address.
o IPv4 Protocol or IPv6 Next Header. o IPv4 Protocol or IPv6 Next Header.
Therefore, non-fragmented packets belonging to a flow can be assigned Therefore, non-fragmented packets belonging to a flow can be assigned
to one link while fragmented packets belonging to the same flow can to one link while fragmented packets belonging to the same flow can
be divided between that link and another. This can cause suboptimal be divided between that link and another. This can cause suboptimal
load balancing. load-balancing.
4.5. Equal Cost Multipath (ECMP) [RFC6438] offers a partial solution to this problem for IPv6 devices
only. According to [RFC6438]:
IP fragmentation causes problems for routers that support Equal Cost "At intermediate routers that perform load distribution, the hash
Multipath (ECMP). Many routers that support ECMP execute the algorithm used to determine the outgoing component-link in an ECMP
algorithm described in Section 4.4. Therefore, the exhibit they same and/or LAG toward the next hop MUST minimally include the 3-tuple
problematic behaviors described in Section 4.4. {dest addr, source addr, flow label} and MAY also include the
remaining components of the 5-tuple."
4.6. IPv4 Reassembly Errors at High Data Rates If the algorithm includes only the 3-tuple {dest addr, source addr,
flow label}, it will assign all fragments belonging to a packet to
the same link.
4.5. IPv4 Reassembly Errors at High Data Rates
IPv4 fragmentation is not sufficiently robust for use under some IPv4 fragmentation is not sufficiently robust for use under some
conditions in today's Internet. At high data rates, the 16-bit IP conditions in today's Internet. At high data rates, the 16-bit IP
identification field is not large enough to prevent frequent identification field is not large enough to prevent frequent
incorrectly assembled IP fragments, and the TCP and UDP checksums are incorrectly assembled IP fragments, and the TCP and UDP checksums are
insufficient to prevent the resulting corrupted datagrams from being insufficient to prevent the resulting corrupted datagrams from being
delivered to higher protocol layers. [RFC4963] describes some easily delivered to higher protocol layers. [RFC4963] describes some easily
reproduced experiments demonstrating the problem, and discusses some reproduced experiments demonstrating the problem, and discusses some
of the operational implications of these observations. of the operational implications of these observations.
These reassembly issues are not easily reproducible in IPv6 because These reassembly issues are not easily reproducible in IPv6 because
the IPv6 identification field is 32 bits long. the IPv6 identification field is 32 bits long.
4.7. Security Vulnerabilities 4.6. Security Vulnerabilities
Security researchers have documented several attacks that exploit IP Security researchers have documented several attacks that exploit IP
fragmentation. The following are examples: fragmentation. The following are examples:
o Overlapping fragment attacks [RFC1858][RFC3128][RFC5722] o Overlapping fragment attacks [RFC1858][RFC3128][RFC5722]
o Resource exhaustion attacks (such as the Rose Attack) o Resource exhaustion attacks (such as the Rose Attack)
o Attacks based on predictable fragment identification values o Attacks based on predictable fragment identification values
[RFC7739] [RFC7739]
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for an attacker to forge malicious IP fragments that would cause the for an attacker to forge malicious IP fragments that would cause the
reassembly procedure for legitimate packets to fail. reassembly procedure for legitimate packets to fail.
NIDS aims at identifying malicious activity by analyzing network NIDS aims at identifying malicious activity by analyzing network
traffic. Ambiguity in the possible result of the fragment reassembly traffic. Ambiguity in the possible result of the fragment reassembly
process may allow an attacker to evade these systems. Many of these process may allow an attacker to evade these systems. Many of these
systems try to mitigate some of these evasion techniques (e.g. By systems try to mitigate some of these evasion techniques (e.g. By
computing all possible outcomes of the fragment reassembly process, computing all possible outcomes of the fragment reassembly process,
at the expense of increased processing requirements). at the expense of increased processing requirements).
4.8. PMTU Blackholing Due to ICMP Loss 4.7. PMTU Blackholing Due to ICMP Loss
As mentioned in Section 2.3, upper-layer protocols can be configured As mentioned in Section 2.3, upper-layer protocols can be configured
to rely on PMTUD. Because PMTUD relies upon the network to deliver to rely on PMTUD. Because PMTUD relies upon the network to deliver
ICMP PTB messages, those protocols also rely on the networks to ICMP PTB messages, those protocols also rely on the networks to
deliver ICMP PTB messages. deliver ICMP PTB messages.
According to [RFC4890], ICMP PTB messages must not be filtered. According to [RFC4890], ICMP PTB messages must not be filtered.
However, ICMP PTB delivery is not reliable. It is subject to both However, ICMP PTB delivery is not reliable. It is subject to both
transient and persistent loss. transient and persistent loss.
Transient loss of ICMP PTB messages can cause transient PMTU black Transient loss of ICMP PTB messages can cause transient PMTU black
holes. When the conditions contributing to transient loss abate, the holes. When the conditions contributing to transient loss abate, the
network regains its ability to deliver ICMP PTB messages and network regains its ability to deliver ICMP PTB messages and
connectivity between the source and destination nodes is restored. connectivity between the source and destination nodes is restored.
Section 4.8.1 of this document describes conditions that lead to Section 4.7.1 of this document describes conditions that lead to
transient loss of ICMP PTB messages. transient loss of ICMP PTB messages.
Persistent loss of ICMP PTB messages can cause persistent black Persistent loss of ICMP PTB messages can cause persistent black
holes. Section 4.8.2 and Section 4.8.3 of this document describe holes. Section 4.7.2 and Section 4.7.3 of this document describe
conditions that lead to persistent loss of ICMP PTB messages. conditions that lead to persistent loss of ICMP PTB messages.
The problem described in this section is specific to PMTUD. It does The problem described in this section is specific to PMTUD. It does
not occur when the upper-layer protocol obtains its PMTU estimate not occur when the upper-layer protocol obtains its PMTU estimate
from PLPMTUD or from any other source. from PLPMTUD or from any other source.
4.8.1. Transient Loss 4.7.1. Transient Loss
The following factors can contribute to transient loss of ICMP PTB The following factors can contribute to transient loss of ICMP PTB
messages: messages:
o Network congestion. o Network congestion.
o Packet corruption. o Packet corruption.
o Transient routing loops. o Transient routing loops.
o ICMP rate limiting. o ICMP rate limiting.
The effect of rate limiting may be severe, as RFC 4443 recommends The effect of rate limiting may be severe, as RFC 4443 recommends
strict rate limiting of IPv6 traffic. strict rate limiting of IPv6 traffic.
4.8.2. Incorrect Implementation of Security Policy 4.7.2. Incorrect Implementation of Security Policy
Incorrect implementation of security policy can cause persistent loss Incorrect implementation of security policy can cause persistent loss
of ICMP PTB messages. of ICMP PTB messages.
Assume that a Customer Premise Equipment (CPE) router implements the Assume that a Customer Premise Equipment (CPE) router implements the
following zone-based security policy: following zone-based security policy:
o Allow any traffic to flow from the inside zone to the outside o Allow any traffic to flow from the inside zone to the outside
zone. zone.
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allows the ICMP PTB to flow from the outside zone to the inside zone. allows the ICMP PTB to flow from the outside zone to the inside zone.
If not, the implementation discards the ICMP PTB message. If not, the implementation discards the ICMP PTB message.
When a incorrect implementation of the above-mentioned security When a incorrect implementation of the above-mentioned security
policy receives an ICMP PTB message, it discards the packet because policy receives an ICMP PTB message, it discards the packet because
its source address is not associated with an existing flow. its source address is not associated with an existing flow.
The security policy described above is implemented incorrectly on The security policy described above is implemented incorrectly on
many consumer CPE routers. many consumer CPE routers.
4.8.3. Persistent Loss Caused By Anycast 4.7.3. Persistent Loss Caused By Anycast
Anycast can cause persistent loss of ICMP PTB messages. Consider the Anycast can cause persistent loss of ICMP PTB messages. Consider the
example below: example below:
A DNS client sends a request to an anycast address. The network A DNS client sends a request to an anycast address. The network
routes that DNS request to the nearest instance of that anycast routes that DNS request to the nearest instance of that anycast
address (i.e., a DNS Server). The DNS server generates a response address (i.e., a DNS Server). The DNS server generates a response
and sends it back to the DNS client. While the response does not and sends it back to the DNS client. While the response does not
exceed the DNS server's PMTU estimate, it does exceed the actual exceed the DNS server's PMTU estimate, it does exceed the actual
PMTU. PMTU.
A downstream router drops the packet and sends an ICMP PTB message A downstream router drops the packet and sends an ICMP PTB message
the packet's source (i.e., the anycast address). The network routes the packet's source (i.e., the anycast address). The network routes
the ICMP PTB message to the anycast instance closest to the the ICMP PTB message to the anycast instance closest to the
downstream router. That anycast instance may not be the DNS server downstream router. That anycast instance may not be the DNS server
that originated the DNS response. It may be another DNS server with that originated the DNS response. It may be another DNS server with
the same anycast address. The DNS server that originated the the same anycast address. The DNS server that originated the
response may never receive the ICMP PTB message and may never update response may never receive the ICMP PTB message and may never update
its PMTU estimate. its PMTU estimate.
4.9. Blackholing Due To Filtering or Loss 4.8. Blackholing Due To Filtering or Loss
In RFC 7872, researchers sampled Internet paths to determine whether In RFC 7872, researchers sampled Internet paths to determine whether
they would convey packets that contain IPv6 extension headers. they would convey packets that contain IPv6 extension headers.
Sampled paths terminated at popular Internet sites (e.g., popular Sampled paths terminated at popular Internet sites (e.g., popular
web, mail and DNS servers). web, mail and DNS servers).
The study revealed that at least 28% of the sampled paths did not The study revealed that at least 28% of the sampled paths did not
convey packets containing the IPv6 Fragment extension header. In convey packets containing the IPv6 Fragment extension header. In
most cases, fragments were dropped in the destination autonomous most cases, fragments were dropped in the destination autonomous
system. In other cases, the fragments were dropped in transit system. In other cases, the fragments were dropped in transit
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Possible causes follow: Possible causes follow:
o Hardware inability to process fragmented packets. o Hardware inability to process fragmented packets.
o Failure to change vendor defaults. o Failure to change vendor defaults.
o Unintentional misconfiguration. o Unintentional misconfiguration.
o Intentional configuration (e.g., network operators consciously o Intentional configuration (e.g., network operators consciously
chooses to drop IPv6 fragments in order to address the issues chooses to drop IPv6 fragments in order to address the issues
raised in Section 4.1 through Section 4.8, above.) raised in Section 4.1 through Section 4.7, above.)
5. Alternatives to IP Fragmentation 5. Alternatives to IP Fragmentation
5.1. Transport Layer Solutions 5.1. Transport Layer Solutions
The Transport Control Protocol (TCP) [RFC0793]) can be operated in a The Transport Control Protocol (TCP) [RFC0793]) can be operated in a
mode that does not require IP fragmentation. mode that does not require IP fragmentation.
Applications submit a stream of data to TCP. TCP divides that stream Applications submit a stream of data to TCP. TCP divides that stream
of data into segments, with no segment exceeding the TCP Maximum of data into segments, with no segment exceeding the TCP Maximum
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must maintain state in order to achieve this goal. must maintain state in order to achieve this goal.
Price and performance considerations frequently motivate network Price and performance considerations frequently motivate network
operators to deploy stateless middle boxes. These stateless middle operators to deploy stateless middle boxes. These stateless middle
boxes may perform sub-optimally, process IP fragments in a manner boxes may perform sub-optimally, process IP fragments in a manner
that is not compliant with RFC 791 or RFC 8200, or even discard IP that is not compliant with RFC 791 or RFC 8200, or even discard IP
fragments completely. Such behaviors are NOT RECOMMENDED. If a fragments completely. Such behaviors are NOT RECOMMENDED. If a
middleboxes implements non-standard behavior with respect to IP middleboxes implements non-standard behavior with respect to IP
fragmentation, then that behavior MUST be clearly documented. fragmentation, then that behavior MUST be clearly documented.
7.4. For Network Operators 7.4. For ECMP, LAG and Load-Balancer Developers And Operators
In their default configuration, when the IPv6 Flow Label is not equal
to zero, IPv6 devices that implement ECMP, LAG or other load-
balancing technologies SHOULD accept only the following fields as
input to their hash algorithm:
o IP Source Address.
o IP Destination Address.
o Flow Label.
Operators SHOULD deploy these devices in their default configuration.
7.5. For Network Operators
Operators MUST ensure proper PMTUD operation in their network, Operators MUST ensure proper PMTUD operation in their network,
including making sure the network generates PTB packets when dropping including making sure the network generates PTB packets when dropping
packets too large compared to outgoing interface MTU. packets too large compared to outgoing interface MTU.
As per RFC 4890, network operators MUST NOT filter ICMPv6 PTB As per RFC 4890, network operators MUST NOT filter ICMPv6 PTB
messages unless they are known to be forged or otherwise messages unless they are known to be forged or otherwise
illegitimate. As stated in Section 4.8, filtering ICMPv6 PTB packets illegitimate. As stated in Section 4.7, filtering ICMPv6 PTB packets
causes PMTUD to fail. Many upper-layer protocols rely on PMTUD. causes PMTUD to fail. Many upper-layer protocols rely on PMTUD.
As per RFC 8200, network operators MUST NOT deploy IPv6 links whose As per RFC 8200, network operators MUST NOT deploy IPv6 links whose
MTU is less than 1280 bytes. MTU is less than 1280 bytes.
Network operators SHOULD NOT filter IP fragments if they originated Network operators SHOULD NOT filter IP fragments if they originated
at a domain name server or are destined for a domain name server. at a domain name server or are destined for a domain name server.
8. IANA Considerations 8. IANA Considerations
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[RFC5927] Gont, F., "ICMP Attacks against TCP", RFC 5927, [RFC5927] Gont, F., "ICMP Attacks against TCP", RFC 5927,
DOI 10.17487/RFC5927, July 2010, DOI 10.17487/RFC5927, July 2010,
<https://www.rfc-editor.org/info/rfc5927>. <https://www.rfc-editor.org/info/rfc5927>.
[RFC6346] Bush, R., Ed., "The Address plus Port (A+P) Approach to [RFC6346] Bush, R., Ed., "The Address plus Port (A+P) Approach to
the IPv4 Address Shortage", RFC 6346, the IPv4 Address Shortage", RFC 6346,
DOI 10.17487/RFC6346, August 2011, DOI 10.17487/RFC6346, August 2011,
<https://www.rfc-editor.org/info/rfc6346>. <https://www.rfc-editor.org/info/rfc6346>.
[RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
for Equal Cost Multipath Routing and Link Aggregation in
Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011,
<https://www.rfc-editor.org/info/rfc6438>.
[RFC6888] Perreault, S., Ed., Yamagata, I., Miyakawa, S., Nakagawa, [RFC6888] Perreault, S., Ed., Yamagata, I., Miyakawa, S., Nakagawa,
A., and H. Ashida, "Common Requirements for Carrier-Grade A., and H. Ashida, "Common Requirements for Carrier-Grade
NATs (CGNs)", BCP 127, RFC 6888, DOI 10.17487/RFC6888, NATs (CGNs)", BCP 127, RFC 6888, DOI 10.17487/RFC6888,
April 2013, <https://www.rfc-editor.org/info/rfc6888>. April 2013, <https://www.rfc-editor.org/info/rfc6888>.
[RFC7588] Bonica, R., Pignataro, C., and J. Touch, "A Widely [RFC7588] Bonica, R., Pignataro, C., and J. Touch, "A Widely
Deployed Solution to the Generic Routing Encapsulation Deployed Solution to the Generic Routing Encapsulation
(GRE) Fragmentation Problem", RFC 7588, (GRE) Fragmentation Problem", RFC 7588,
DOI 10.17487/RFC7588, July 2015, DOI 10.17487/RFC7588, July 2015,
<https://www.rfc-editor.org/info/rfc7588>. <https://www.rfc-editor.org/info/rfc7588>.
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