Internet DRAFT - draft-peng-v6ops-hbh
draft-peng-v6ops-hbh
Network Working Group S. Peng
Internet-Draft Z. Li
Intended status: Informational Huawei Technologies
Expires: 24 February 2022 C. Xie
China Telecom
Z. Qin
China Unicom
G. Mishra
Verizon Inc.
23 August 2021
Processing of the Hop-by-Hop Options Header
draft-peng-v6ops-hbh-06
Abstract
This document describes the processing of the Hop-by-Hop Options
Header (HBH) in today's routers in the aspects of standards
specification, common implementations, and default operations. This
document outlines the reasons why the Hop-by-Hop Options Header is
rarely utilized in current networks. In addition, this document
describes how the HBH could be used as a powerful mechanism allowing
deployment and operations of new services requiring a more optimized
way to leverage network resources of an infrastructure. The Hop-by-
Hop Options Header is taken into consideration by several network
operators as a valuable container for carrying the information
facilitating the introduction of new services. The processing
requirments of the HBH and the migration strategies are also
suggested.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119] [RFC8174]
when, and only when, they appear in all capitals, as shown here.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 24 February 2022.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Modern Router Architecture . . . . . . . . . . . . . . . . . 4
3. Specification of RFC 8200 . . . . . . . . . . . . . . . . . . 7
4. Common Implementations . . . . . . . . . . . . . . . . . . . 8
4.1. Historical Reasons . . . . . . . . . . . . . . . . . . . 9
4.2. Consequences . . . . . . . . . . . . . . . . . . . . . . 9
5. Operators' Typical Processing . . . . . . . . . . . . . . . . 9
6. New Services . . . . . . . . . . . . . . . . . . . . . . . . 10
7. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 10
8. Migration Strategies . . . . . . . . . . . . . . . . . . . . 11
9. Security Considerations . . . . . . . . . . . . . . . . . . . 12
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
12.1. Normative References . . . . . . . . . . . . . . . . . . 12
12.2. Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
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1. Introduction
Due to historical reasons, such as incapable ASICs, limited IPv6
deployments, and few service requirements, the most common Hop-by-Hop
Options header (HBH) processing implementation is that the node sends
the IPv6 packets with the Hop-by-Hop Options header to the control
plane of the node. The option type of each option carried within the
Hop-by-Hop Options header will not even be examined before the packet
is sent to the control plane. Very often, such processing behavior
is the default configuration or, even worse, is the only behavior of
the ipv6 implementation of the node.
Such default processing behavior of the Hop-by-Hop Options header
could result in various unpleasant effects such as a risk of Denial
of Service (DoS) attack on the router control plane and inconsistent
packet drops due to rate limiting on the interface between the router
control plane and forwarding plane, which will impact the normal end-
to-end IP forwarding of the network services.
This actually introduced a circular problem:
-> An implementation problem caused HBH to become a DoS vector.
-> Because HBH is a DoS vector, network operators deployed ACLs that
discard packets containing HBH.
-> Because network operators deployed ACLs that discard packets
containing HBH, network designers stopped defining new HBH Options.
-> Because network designers stopped defining new HBH Options, the
community was not motivated to fix the implementation problem that
cause HBH to become a DoS vector.
The purpose of this draft is to break the cycle described above,
fixing the problem that caused HBH not actually being utilized in
operators' networks so to allow a better leverage of the HBH
capability.
Driven by the wide deployments of IPv6 and ever-emerging new
services, the Hop-by-Hop Options Header is taken as a valuable
container for carrying the information to facilitate these new
services.
This document suggests the desired processing behavior and the
migration strategies towards it.
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2. Modern Router Architecture
Modern router architecture design maintains a strict separation of
the router control plane and its forwarding plane [RFC6192], as shown
in Figure 1. Either the control plane or the forwarding plane is
composed of both software and hardware, but each plane is responsible
for different functions.
+----------------+
| Router Control |
| Plane |
+------+-+-------+
| |
Interface Z
| |
+------+-+-------+
| Forwarding |
Interface X ==[ Plane ]== Interface Y
+----------------+
Figure 1. Modern Router Architecture
The router control plane supports routing and management functions,
handling packets destined to the device as well as building and
sending packets originated locally on the device, and also drives the
programming of the forwarding plane. The router control plane is
generally realized in software on general-purpose processors, and its
hardware is usually not optimized for high-speed packet handling.
Because of the wide range of functionality, it is more susceptible to
security vulnerabilities and a more likely a target for a DoS attack.
The forwarding plane is typically responsible for receiving a packet
on an incoming interface, performing a lookup to identify the
packet's next hop and determine the outgoing interface towards the
destination, and forwarding the packet out through the appropriate
outgoing interface. Typically, forwarding plane functionality is
realized in high-performance Application Specific Integrated Circuits
(ASICs) or Network Processors (NPs) that are capable of handling very
high packet rates.
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The router control plane interfaces with its forwarding plane through
the Interface Z, as shown in the Figure 1, and the forwarding plane
connects to other network devices via Interfaces such as X and Y.
Since the router control plane is vulnerable to the DoS attack,
usually a traffic filtering mechanism is implemented on Interface Z
in order to block unwanted traffic. In order to protect the router
control plane, a rate-limiting mechanism is always implemented on
this interface. However, such rate limiting mechanism will always
cause inconsistent packet drops, which will impact the normal IP
forwarding.
Semiconductor chip technology has advanced significantly in the last
decade, and as such the widely used network processing and forwarding
process can now not only forward packets at line speed, but also
easily support other feature processing such as QoS for DiffServ/
MPLS, Access Control List (ACL), Firewall, and Deep Packet Inspection
(DPI).
A Network Processing Unit (NPU) is a non-ASIC based Integrated
Circuit (IC) that is programmable through software. It performs all
packet header operations between the physical layer interface and the
switching fabric such as packet parsing and forwarding, modification,
and forwarding. Many equipment vendors implement these functions in
fixed function ASICs rather than using "off-the-shelf" NPUs, because
of proprietary algorithms.
Classification Co-processor is a specialized processor that can be
used to lighten the processing load on an NPU by handling the parsing
and classification of incoming packets such as IPv6 extended header
HBH options processing. This advancement enables network processors
to do the general process to handle simple control messages for
traffic management, such as signaling for hardware programming,
congestion state report, OAM, etc. Industry trend is for intelligent
multi-core CPU hardware using modern NPUs for forwarding packets at
line rate while still being able to perform other complex tasks such
as HBH forwarding options processing without having to punt to the
control plane.
Many of the packet-processing devices employed in modern switch and
router designs are fixed-function ASICs to handle proprietary
functions. While these devices can be very efficient for the set of
functions they are designed for, they can be very inflexible. There
is a tradeoff of price, performance and flexibility when vendors make
a choice to use a fixed function ASIC as opposed to NPU. Due to the
inflexibility of the fixed function ASIC, tasks that require
additional processing such as IPv6 HBH header processing must be
punted to the control plane. This problem is still a challenge today
and is the reason why operators to protect against control plane DOS
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attack vector must drop or ignore HBH options. As industry shifts to
Merchant Silicon based NPU evolution from fixed function ASIC, the
gap will continue to close increasing the viability ubiquitous HBH
use cases due to now processing in the forwarding plane.
Most modern routers maintain a strict separation between forwarding
plane and control plane hardware. Forwarding plane bandwidth and
resources are plentiful, while control plane bandwidth and resources
are constrained. In order to protect scarce control plane resources,
routers enforce policies that restrict access from the forwarding
plane to the control plane. Effective policies address packets
containing the HBH Options Extension header, because HBH control
options require access from the forwarding plane to the control
plane. Many network operators perceive HBH Options to be a breach of
the separation between the forwarding and control planes. In this
case HBH control options would be required to be punted to control
plane by fixed function ASICs as well as NPUs.
The maximum length of an HBH Options header is 2,048 bytes. A source
node can encode hundreds of options in 2,048 bytes. With today's
technology it would be cost prohibitive to be able to process
hundreds of options with either NPU or proprietary fixed function
ASIC.
While [RFC8200] required that all nodes must examine and process the
Hop-by-Hop Options header, it is now expected that nodes along a
packet's delivery path only examine and process the Hop-by-Hop
Options header if explicitly configured to do so. This can be
beneficial in cases where transit nodes are legacy hardware and the
destination endpoint PE is newer NPU based hardware that can process
HBH in the forwarding plane.
IPv6 Extended Header limitations that need to be addressed to make
HBH processing more efficient and viable in the forwarding plane:
[RFC8504] defines the IPv6 node requirements and how to protect a
node from excessive header chain and excessive header options with
various limitations that can be defined on a node. [RFC8883] defines
ICMPv6 Errors for discarding packets due to processing limits. Per
[RFC8200] HBH options must be processed serially. However, an
implementation of options processing can be made to be done with more
parallelism in serial processing grouping of similar options to be
processed in parallel.
The IPv6 standard does not currently limit the header chain length or
number of options that can be encoded.
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Each Option is encoded in a TLV and so processing of a long list of
TLVs is expensive. Zero data length encoded options TLVs are a valid
option. A DOS vector could be easily generated by encoding 1000 HBH
options (Zero data length) in a standard 1500 MTU packet. So now
imagine if you have a Christmas tree long header chain to parse each
with many options.
3. Specification of RFC 8200
[RFC8200] defines several IPv6 extension header types, including the
Hop-by-Hop (HBH) Options header. As specified in [RFC8200], the Hop-
by-Hop (HBH) Options header is used to carry optional information
that will be examined and processed by every node along a packet's
delivery path, and it is identified by a Next Header value of zero in
the IPv6 header.
The Hop-by-Hop (HBH) Options header contains the following fields:
-- Next Header: 8-bit selector, identifies the type of header
immediately following the Hop-by-Hop Options header.
-- Hdr Ext Len: 8-bit unsigned integer, the length of the Hop-by-Hop
Options header in 8-octet units, not including the first 8 octets.
-- Options: Variable-length field, of length such that the complete
Hop-by-Hop Options header is an integer multiple of 8 octets long.
The Hop-by-Hop (HBH) Options header carries a variable number of
"options" that are encoded in the format of type-length-value (TLV).
The highest-order two bits (i.e., the ACT bits) of the Option Type
specify the action that must be taken if the processing IPv6 node
does not recognize the Option Type. The third-highest-order bit
(i.e., the CHG bit) of the Option Type specifies whether or not the
Option Data of that option can change en route to the packet's final
destination.
While [RFC2460] required that all nodes must examine and process the
Hop-by-Hop Options header, with [RFC8200] it is expected that nodes
along a packet's delivery path only examine and process the Hop-by-
Hop Options header if explicitly configured to do so. It means that
the HBH processing behavior in a node depends on its configuration.
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However, in the current [RFC8200], there is no explicit specification
of the possible configurations. Therefore, the nodes may be
configured to ignore the Hop-by-Hop Options header, drop packets
containing a Hop-by-Hop Options header, or assign packets containing
a Hop-by-Hop Options header to the control plane [RFC8200]. Because
of these likely uncertain processing behaviors, new hop-by-hop
options are not recommended.
4. Common Implementations
In the current common implementations, once an IPv6 packet, with its
Next Header field set to 0, arrives at a node, it will be directly
sent to the control plane of the node. With such implementations,
the value of the Next Header field in the IPv6 header is the only
trigger for the default processing behavior. The option type of each
option carried within the Hop-by-Hop Options header will not even be
examined before the packet is sent to the control plane.
Very often, such processing behavior is the default configuration on
the node, which is embedded in the implementation and cannot be
changed or reconfigured.
Another critical component of IPv6 HBH processing, in some cases
overlooked, is the operator core network which can be designed to use
the global Internet routing table for internet traffic and in other
cases use an overlay MPLS VPN to carry Internet traffic.
In the global Internet routing table scenario where only an underlay
global routing table exists, and no VPN overlay carrying customer
Internet traffic, the IPv6 HBH options can be used as a DOS attack
vector for both the operator nodes, adjacent inter-as peer nodes as
well as customer nodes along a path.
In a case where the Internet routing table is carried in a MPLS VPN
overlay payload, the HBH options header does not impact the operator
underlay framework and only impacts the VPN overlay payload and thus
the operator underlay topmost label global table routing FEC LSP
instantiation is not impacted as the operator underlay is within the
operators closed domain.
However, HBH options DOS attack vector in the VPN overlay can still
impact the customer CE destination end nodes as well as other
adjacent inter-as operators that only use underlay global Internet
routing table. In an operator closed domain where MPLS VPN overlay
is utilized to carry internet traffic, the operator has full control
of the underlay and IPv6 Extended header chain length as well as the
number of HBH options encoded.
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In the global routing table scenario for Internet traffic there is no
way to control the IPv6 Extended header chain lenghth as well as the
number of HBH options encoded.
4.1. Historical Reasons
When IPv6 was first implemented on high-speed routers, HBH options
were not yet well-understood and ASICs were not as capable as they
are today. So, early IPv6 implementations dispatched all packets
that contain HBH options to their control plane.
4.2. Consequences
Such implementation introduces a risk of a DoS attack on the control
plane of the node, and a large flow of IPv6 packets could congest the
control plane, causing other critical functions (including routing
and network management) that are executed on the control plane to
fail. Rate limiting mechanisms will cause inconsistent packet drops
and impact the normal end-to-end IP forwarding of the network
services.
5. Operators' Typical Processing
To mitigate this DoS vulnerability, many operators deployed Access
Control Lists (ACLs) that discard all packets containing HBH Options.
[RFC6564] shows the Reports from the field indicating that some IP
routers deployed within the global Internet are configured either to
ignore or to drop packets having a hop-by-hop header. As stated in
[RFC7872], many network operators perceive HBH Options to be a breach
of the separation between the forwarding and control planes.
Therefore, several network operators configured their nodes so as to
discard all packets containing the HBH Options Extension Header,
while others configured nodes to forward the packet but to ignore the
HBH Options. [RFC7045] also states that hop-by-hop options are not
handled by many high-speed routers or are processed only on a control
plane.
Due to such behaviors observed and described in these specifications,
new hop-by-hop options are not recommended in [RFC8200] hence the
usability of HBH options is severely limited.
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6. New Services
As IPv6 is being rapidly and widely deployed worldwide, more and more
applications and network services are migrating to or directly
adopting IPv6. More and more new services that require HBH are
emerging and the HBH Options header is going to be utilized by the
new services in various scenarios.
In-situ OAM (IOAM) with IPv6 encapsulation
[I-D.ietf-ippm-ioam-ipv6-options] is one of the examples. IOAM in
IPv6 is used to enhance diagnostics of IPv6 networks and complements
other mechanisms, such as the IPv6 Performance and Diagnostic Metrics
Destination Option described in [RFC8250]. The IOAM data fields are
encapsulated in "option data" fields of the Hop-by-Hop Options header
if Pre-allocated Tracing Option, Incremental Tracing Option, or Proof
of Transit Option are carried [I-D.ietf-ippm-ioam-data], that is, the
IOAM performs per hop.
Alternate Marking Method can be used as the passive performance
measurement tool in an IPv6 domain. The AltMark Option is defined as
a new IPv6 extension header option to encode alternate marking
technique and Hop-by-Hop Options Header is considered
[I-D.ietf-6man-ipv6-alt-mark].
The Minimum Path MTU Hop-by-Hop Option is defined in
[I-D.ietf-6man-mtu-option] to record the minimum Path MTU along the
forward path between a source host to a destination host. This Hop-
by-Hop option is intended to be used in environments like Data
Centers and on paths between Data Centers as well as other
environments including the general Internet. It provides a useful
tool for allowing to better take advantage of paths able to support a
large Path MTU.
As more services start utilizing the HBH Options header, more packets
containing HBH Options are going to be injected into the networks.
According to the current common configuration in most network
deployments, all the packets of the new services are going to be sent
to the control plane of the nodes, with the possible consequence of
causing a DoS on the control plane. The packets will be dropped and
the normal IP forwarding may be severely impacted. The deployment of
new network services involving multi-vendor interoperability will
become impossible.
7. Requirements
* The HBH options header MUST NOT become a possible DDoS Vector.
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* HBH options SHOULD be designed so that they don't reduce the
probability of packet delivery. For example, an intermediate node
may discard a packet because it contains more HBH options than the
node can process.
* HBH processing MUST be efficient. That is, it MUST be possible to
produce implementations that perform well at a reasonable cost.
* The Router Alert Option MUST NOT impact the processing of other
HBH options that should be processed more quickly.
* HBH Options MAY influence how a packet is forwarded. However,
with the exception of the Router Alert Option, an HBH Option MUST
NOT cause control plane state to be created, modified or destroyed
on the processing node. As per [RFC6398], protocol developers
SHOULD avoid future use of the Router Alert Option.
* More requirements are to be added.
8. Migration Strategies
In order to achieve the desired processing behavior of the HBH
options header and facilitate the ever-emerging new services to be
deployed in operators' networks across multiple vendors' devices, the
migration can happen in three parts as described below:
1. The source of the HBH options header encapsulation.
The information to be carried in the HBH options header needs to be
first categorized and encapsulated into either control options or
forwarding options, and then encapsulated in different packets.
2. The nodes within the network.
The nodes within the network are updated to the proposed behavior
introduced in the previous section.
3. The edge nodes of the network.
The edge nodes should check whether the packet contains an HBH header
with control or forwarding option. Packets with a control option may
still be filtered and dropped while packets with forwarding option
SHOULD be allowed by the ACL.
If it is certain that there is no harm that can be introduced by the
HBH control options to the nodes and the services, they can also be
allowed.
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Note: During the migration stage, the nodes that are not yet updated
will stay with their existing configurations.
9. Security Considerations
The same as the Security Considerations apply as in [RFC8200] for the
part related with the HBH Options header.
10. IANA Considerations
This document does not include an IANA request.
11. Acknowledgements
The authors would like to acknowledge Ron Bonica, Fred Baker, Bob
Hinden, Stefano Previdi, and Donald Eastlake for their valuable
review and comments.
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <https://www.rfc-editor.org/info/rfc2460>.
[RFC6192] Dugal, D., Pignataro, C., and R. Dunn, "Protecting the
Router Control Plane", RFC 6192, DOI 10.17487/RFC6192,
March 2011, <https://www.rfc-editor.org/info/rfc6192>.
[RFC6398] Le Faucheur, F., Ed., "IP Router Alert Considerations and
Usage", BCP 168, RFC 6398, DOI 10.17487/RFC6398, October
2011, <https://www.rfc-editor.org/info/rfc6398>.
[RFC7045] Carpenter, B. and S. Jiang, "Transmission and Processing
of IPv6 Extension Headers", RFC 7045,
DOI 10.17487/RFC7045, December 2013,
<https://www.rfc-editor.org/info/rfc7045>.
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[RFC7872] Gont, F., Linkova, J., Chown, T., and W. Liu,
"Observations on the Dropping of Packets with IPv6
Extension Headers in the Real World", RFC 7872,
DOI 10.17487/RFC7872, June 2016,
<https://www.rfc-editor.org/info/rfc7872>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
12.2. Informative References
[I-D.ietf-6man-ipv6-alt-mark]
Fioccola, G., Zhou, T., Cociglio, M., Qin, F., and R.
Pang, "IPv6 Application of the Alternate Marking Method",
Work in Progress, Internet-Draft, draft-ietf-6man-ipv6-
alt-mark-08, 26 July 2021,
<https://www.ietf.org/archive/id/draft-ietf-6man-ipv6-alt-
mark-08.txt>.
[I-D.ietf-6man-mtu-option]
Hinden, R. M. and G. Fairhurst, "IPv6 Minimum Path MTU
Hop-by-Hop Option", Work in Progress, Internet-Draft,
draft-ietf-6man-mtu-option-06, 7 August 2021,
<https://www.ietf.org/archive/id/draft-ietf-6man-mtu-
option-06.txt>.
[I-D.ietf-ippm-ioam-data]
Brockners, F., Bhandari, S., and T. Mizrahi, "Data Fields
for In-situ OAM", Work in Progress, Internet-Draft, draft-
ietf-ippm-ioam-data-14, 24 June 2021,
<https://www.ietf.org/archive/id/draft-ietf-ippm-ioam-
data-14.txt>.
[I-D.ietf-ippm-ioam-ipv6-options]
Bhandari, S. and F. Brockners, "In-situ OAM IPv6 Options",
Work in Progress, Internet-Draft, draft-ietf-ippm-ioam-
ipv6-options-06, 31 July 2021,
<https://www.ietf.org/archive/id/draft-ietf-ippm-ioam-
ipv6-options-06.txt>.
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[RFC2711] Partridge, C. and A. Jackson, "IPv6 Router Alert Option",
RFC 2711, DOI 10.17487/RFC2711, October 1999,
<https://www.rfc-editor.org/info/rfc2711>.
[RFC8250] Elkins, N., Hamilton, R., and M. Ackermann, "IPv6
Performance and Diagnostic Metrics (PDM) Destination
Option", RFC 8250, DOI 10.17487/RFC8250, September 2017,
<https://www.rfc-editor.org/info/rfc8250>.
[RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node
Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504,
January 2019, <https://www.rfc-editor.org/info/rfc8504>.
[RFC8883] Herbert, T., "ICMPv6 Errors for Discarding Packets Due to
Processing Limits", RFC 8883, DOI 10.17487/RFC8883,
September 2020, <https://www.rfc-editor.org/info/rfc8883>.
Authors' Addresses
Shuping Peng
Huawei Technologies
Beijing
China
Email: pengshuping@huawei.com
Zhenbin Li
Huawei Technologies
Beijing
China
Email: lizhenbin@huawei.com
Chongfeng Xie
China Telecom
China
Email: xiechf@chinatelecom.cn
Zhuangzhuang Qin
China Unicom
Beijing
China
Email: qinzhuangzhuang@chinaunicom.cn
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Gyan Mishra
Verizon Inc.
United States of America
Email: gyan.s.mishra@verizon.com
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