IPv6 Operations (v6ops) Working Group X. Xiao
Internet Draft E. Vasilenko
Intended status: Informational Huawei Technologies
Expires: Nov. 2025 E. Metz
KPN
G. Mishra
Verizon Inc.
N. Buraglio
Energy Sciences Network
May 26, 2025
Neighbor Discovery Considerations in IPv6 Deployments
draft-ietf-v6ops-nd-considerations-14
Abstract
The Neighbor Discovery (ND) protocol is a critical component of the
IPv6 architecture. The protocol uses multicast in many messages. It
also assumes a security model where all nodes on a link are trusted.
Such a design might be inefficient in some scenarios (e.g., use of
multicast in wireless networks) or when nodes are not trustworthy
(e.g., public access networks). These security and operational
issues and the associated mitigation solutions are documented in
more than 20 RFCs. There is a need to track these issues and
solutions in a single document.
To that aim, this document summarizes the published ND issues and
then describes how all these issues originate from three causes.
Addressing the issues is made simpler by addressing the causes. This
document also analyzes the mitigation solutions and demonstrates
that isolating hosts into different subnets and links can help to
address the three causes. Guidance is provided for selecting a
suitable isolation method to prevent potential ND issues.
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/.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents
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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 in Nov. 2025.
Copyright Notice
Copyright (c) 2025 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
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents
1. Introduction...................................................3
1.1. Terminology...............................................5
2. Review of Inventoried ND Issues................................6
2.1. Multicast May Cause Performance and Reliability Issues....6
2.2. Trusting-all-hosts May Cause On-link Security Issues......7
2.3. Router-NCE-on-Demand May Cause Forwarding Delay, NCE
Exhaustion, and Address Accountability Issues..................7
2.4. Summary of ND Issues......................................8
3. Review of ND Mitigation Solutions..............................9
3.1. ND Solution in Mobile Broadband IPv6.....................10
3.2. ND Solution in Fixed Broadband IPv6......................11
3.3. Unique IPv6 Prefix per Host (UPPH).......................12
3.4. Wireless ND and Subnet ND................................13
3.5. Scalable Address Resolution Protocol.....................14
3.6. ARP and ND Optimization for TRILL........................14
3.7. Proxy ARP/ND in Ethernet Virtual Private Networks (EVPN).15
3.8. Reducing Router Advertisements...........................15
3.9. Gratuitous Neighbor Discovery (GRAND)....................15
3.10. Source Address Validation Improvement (SAVI) and Router
Advertisement Guard...........................................16
3.11. RFC 6583 Dealing with NCE Exhaustion Attacks............16
3.12. Registering Self-generated IPv6 Addresses using DHCPv6..17
3.13. Enhanced DAD............................................17
3.14. ND Mediation for IP Interworking of Layer 2 VPNs........17
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3.15. ND Solutions Defined before the Latest Versions of ND...17
3.15.1. Secure Neighbor Discovery (SeND)...................18
3.15.2. Cryptographically Generated Addresses (CGA)........18
3.15.3. ND Proxy...........................................18
3.15.4. Optimistic DAD.....................................19
4. Guidelines for Prevention of Potential ND Issues..............19
4.1. Learning Host Isolation from the Existing Solutions......19
4.2. Applicability of Various Isolation Methods...............20
4.2.1. Applicability of L3+L2 Isolation....................20
4.2.2. Applicability of L3 Isolation.......................22
4.2.3. Applicability of Partial L2 Isolation...............22
4.3. Guidelines for Applying Isolation Methods................23
5. Security Considerations.......................................24
6. IANA Considerations...........................................24
7. References....................................................24
7.1. Normative References.....................................24
7.2. Informative References...................................24
8. Acknowledgments...............................................28
1. Introduction
Neighbor Discovery (ND) [RFC4861] specifies the mechanisms that IPv6
nodes (hosts and routers) on the same link use to communicate and
learn about each other. Stateless Address Autoconfiguration (SLAAC)
[RFC4862] builds on those ND mechanisms to let nodes configure their
own IPv6 addresses. When analyzing the issues nodes may encounter
with ND, it helps to view the ND messages they exchange throughout
their life-cycle, taking SLAAC into consideration.
For a host, the overall procedure is as follows:
1. LLA DAD: The host forms a Link-Local Address (LLA) and performs
Duplicate Address Detection (DAD) using multicast Neighbor
Solicitations (NSs).
2. Router Discovery: The host sends multicast Router Solicitations
(RSs) to discover a router on the link. The router responds
with Router Advertisements (RAs), providing subnet prefixes and
other information. The host installs a Neighbor Cache Entry
(NCE) for that router upon receiving the RAs. In contrast, the
router cannot install an NCE for the host at this moment of the
exchange because the host's global IP address is still unknown.
When the router later needs to forward a packet to the host's
global address, it will perform address resolution and install
an NCE for the host.
3. GUA DAD: The host forms a Global Unicast Address (GUA)
[RFC3587] or a Unique Local Address (ULA) [RFC4193] and uses
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multicast NSs for DAD. For simplicity of description, this
document will not further distinguish GUA and ULA.
4. Next-hop determination and address resolution: When the host
needs to send a packet, it will first determine whether the
next-hop is a router or an on-link host (which is the
destination). If the next-hop is a router, the host already has
the NCE for that router. If the next-hop is an on-link host, it
will use multicast NSs to perform address resolution for the
destination host. As a result, the source host installs an NCE
for the destination host.
5. Node Unreachability Detection (NUD): The host uses unicast NSs
to determine whether another node with an NCE is still
reachable.
6. Link-layer address change announcement: If a host's link-layer
address changes, it may use multicast Node Advertisements (NAs)
to announce its new link-layer address to other nodes.
For a router, the procedure is similar except that there is no
Router Discovery. Instead, routers perform a Redirect procedure that
hosts do not have. A router sends a Redirect to inform a node of a
better next-hop for the node's traffic.
ND uses multicast in many messages, trusts messages from all nodes,
and routers may install NCEs for hosts on demand when they are to
forward packets to these hosts. These may lead to issues.
Concretely, various ND issues and mitigation solutions have been
published in more than 20 RFCs, including:
. ND Trust Models and Threats [RFC3756],
. Secure ND [RFC3971],
. Cryptographically Generated Addresses [RFC3972],
. ND Proxy [RFC4389],
. Optimistic ND [RFC4429],
. ND for mobile broadband [RFC6459][RFC7066],
. ND for fixed broadband [TR177],
. ND Mediation [RFC6575],
. Operational ND Problems [RFC6583],
. Wireless ND (WiND) [RFC6775][RFC8505][RFC8928][RFC8929][SND],
. DAD Proxy [RFC6957],
. Source Address Validation Improvement [RFC7039],
. Router Advertisement Guard [RFC6105][RFC7113],
. Enhanced Duplicate Address Detection [RFC7527],
. Scalable ARP [RFC7586],
. Reducing Router Advertisements [RFC7772],
. Unique Prefix Per Host [RFC8273],
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. ND Optimization for Transparent Interconnection of Lots of
Links (TRILL) [RFC8302],
. Gratuitous Neighbor Discovery [RFC9131],
. Proxy ARP/ND for EVPN [RFC9161], and
. Using DHCPv6 Prefix Delegation (DHCPv6-PD) to Allocate Unique
IPv6 Prefixes per Client in Large Broadcast Networks [RFC9663].
This document summarizes these RFCs into a one-stop reference (as of
the time of writing) for easier access. This document also
identifies three causes of the issues and defines three host
isolation methods to address the causes and prevent potential ND
issues.
1.1. Terminology
This document uses the terms defined in [RFC4861]. Additional terms
are defined in this section.
MAC - To avoid confusion with link-local addresses, link-layer
addresses are referred to as MAC addresses in this document.
Host Isolation - separating hosts into different subnets or links.
L3 Isolation - allocating a unique prefix per host
[RFC8273][RFC9663] so that every host is in a different
subnet. Given that a unique prefix can be allocated per host
on shared media, hosts in different subnets may be on the
same link.
L2 Isolation - taking measures to prevent a host from reaching other
hosts directly in Layer 2 (L2) so that every host is in a
different link. Due to the existence of Multi-Link Subnet
[RFC4903], hosts in different links may be in the same
subnet. Therefore, L2 Isolation does not imply L3 Isolation,
and L3 Isolation does not imply L2 Isolation either.
L3+L2 Isolation - applying L3 Isolation and L2 Isolation
simultaneously so that every host is in a different subnet
and on a different link.
Partial L2 Isolation - using an L3 ND proxy [RFC4389] device to
represent the hosts behind it to other hosts in the same
subnet. Within the subnet, ND multicast exchange is
segmented into multiple smaller scopes, each represented by
an ND proxy device.
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2. Review of Inventoried ND Issues
2.1. Multicast May Cause Performance and Reliability Issues
In some cases, ND uses multicast for NSs, NAs, RSs, and RAs. While
multicast can be highly efficient in certain scenarios, e.g., in
wired networks, multicast can also be inefficient in other
scenarios, e.g., in large L2 networks or wireless networks.
Typically, multicast can create a large amount of protocol traffic
in large L2 networks. This can consume network bandwidth, increase
processing overhead, and degrade network performance [RFC7342].
In wireless networks, multicast can be inefficient or even
unreliable due to a higher probability of transmission interference,
lower data rate, and lack of acknowledgements (Section 3.1 of [RFC9119]).
Multicast-related performance issues of the various ND messages are
summarized below:
. Issue 1: LLA DAD Degrading Performance - in an L2 network of N
addresses (which can be much larger than the number of hosts,
as each host can have multiple addresses), there can be N such
multicast messages. This may cause performance issues when N is
large.
. Issue 2: Router's Periodic Unsolicited RAs Draining Hosts'
Battery - multicast RAs are generally limited to one packet
every MIN_DELAY_BETWEEN_RAS (3 seconds), and there are usually
only one or two routers on the link, so it is unlikely to cause
a performance issue. However, for battery-powered hosts, such
messages may wake them up and drain their batteries [RFC7772].
. Issue 3: GUA DAD Degrading Performance - same as in Issue 1.
. Issue 4: Router's Address Resolution for Hosts Degrading
Performance - same as in Issue 1.
. Issue 5: Host's Address Resolution for Hosts Degrading
Performance - same as in Issue 1.
. (For Further Study) Hosts' MAC Address Change NAs Degrading
Performance - with randomized and changing MAC addresses
[MADINAS], there may be many such multicast messages.
In wireless networks, multicast is more likely to cause packet loss.
Because DAD treats no response as no duplicate address detected,
packet loss may cause duplicate addresses to be undetected.
Multicast reliability issues are summarized below:
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. Issue 6: LLA DAD Not Completely Reliable in Wireless Networks.
. Issue 7: GUA DAD Not Completely Reliable in Wireless Networks.
Note: IPv6 address collisions are extremely unlikely. As a result,
these two issues are largely theoretical rather than practical.
2.2. Trusting-all-hosts May Cause On-link Security Issues
In scenarios such as public access networks, some nodes may not be
trustworthy. An attacker on the link can cause the following on-link
security issues [RFC3756][RFC9099]:
. Issue 8: Source IP Address Spoofing - an attacker can use
another node's IP address as the source address of its ND
message to pretend to be that node. The attacker can then
launch various Redirect or Denial-of-Service (DoS) attacks.
. Issue 9: Denial of DAD - an attacker can repeatedly reply to a
victim's DAD messages, causing the victim's address
configuration procedure to fail, resulting in a DoS to the
victim.
. Issue 10: Rogue RAs - an attacker can send RAs to victim hosts
to pretend to be a router. The attacker can then launch various
Redirect or DoS attacks.
. Issue 11: Spoofed Redirects - an attacker can send forged
Redirects to victim hosts to redirect their traffic to the
legitimate router itself.
. Issue 12: Replay Attacks - an attacker can capture valid ND
messages and replay them later.
2.3. Router-NCE-on-Demand May Cause Forwarding Delay, NCE Exhaustion,
and Address Accountability Issues
When a router needs to forward a packet to a node but does not yet
have a Neighbor-Cache Entry (NCE) for that node, it first creates an
NCE in the INCOMPLETE state. The router then multicasts an NS to the
node's solicited-node multicast address. When the destination
replies with an NA containing its MAC address, the router updates
the NCE with that address and changes its state to REACHABLE,
thereby completing the entry. This process is referred to as Router-
NCE-on-Demand in this document.
Router-NCE-on-Demand can cause the following issues:
. Issue 13: NCE Exhaustion - an attacker can send a high volume
of packets targeting non-existent IP addresses, causing the
router to create numerous NCEs in the INCOMPLETE state. The
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resulting resource exhaustion may cause the router to
malfunction. This vulnerability, described as "NCE Exhaustion"
in this document, does not require the attacker to be on-link.
. Issue 14: Router Forwarding Delay - when a packet arrives at a
router, the router buffers it while attempting to determine the
host's MAC address. This buffering delays forwarding and,
depending on the router's buffer size, may lead to packet loss.
This delay is referred to as "Router-NCE-on-Demand Forwarding
Delay" in this document.
. Issue 15: Lack of Address Accountability - with SLAAC, hosts
generate their IP addresses. The router does not become aware
of a host's IP address until an NCE entry is created. With
DHCPv6 [RFC8415], the router may not know the host's addresses
unless it performs DHCPv6 snooping. In public access networks,
where subscriber management often relies on IP address (or
prefix) identification, this lack of address accountability
poses a challenge [AddrAcc]. Without knowledge of the host's IP
address, network administrators are unable to effectively
manage subscribers, which is particularly problematic in public
access networks. Moreover, once a router has created its NCEs,
ND [RFC4861] provides no mechanism to retrieve them for
management or monitoring, as noted in Section 2.6.1 of [RFC
9099].
2.4. Summary of ND Issues
The ND issues, as discussed in Sections 2.1 to 2.3, are summarized
below. These issues stem from three primary causes: multicast,
Trusting-all-nodes, and Router-NCE-on-Demand. Eliminating any of
these causes would also mitigate the corresponding issues. These
observations provide guidance for addressing and preventing ND-
related issues.
(1) Multicast-related issues:
. Performance issues
o Issue 1: LLA DAD Degrading Performance.
o Issue 2: Unsolicited RA Draining Host Battery Life.
o Issue 3: GUA DAD degrading performance.
o Issue 4: Router Address Resolution for Hosts Degrading
Performance.
o Issue 5: Host Address Resolution for Other Hosts Degrading
Performance.
. Reliability issues
o Issue 6: LLA DAD Not Completely Reliable in Wireless
Networks
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o Issue 7: GUA DAD Not Completely Reliable in Wireless
Networks
(2) Trusting-all-nodes related issues:
o Issue 8: Source IP Address Spoofing
o Issue 9: Denial of DAD
o Issue 10: Rogue RAs
o Issue 11: Spoofed Redirects
o Issue 12: Replay Attacks
(3) Router-NCE-on-Demand related issues:
o Issue 13: NCE Exhaustion
o Issue 14: Router Forwarding Delay
o Issue 15: Lack of Address Accountability
These issues are potential vulnerabilities and may not manifest in
all usage scenarios.
When these issues may occur in a specific deployment, it is
advisable to consider the mitigation solutions available. They are
described in the following section.
3. Review of ND Mitigation Solutions
Table 1 summarizes ND mitigation solutions available for Issues 1-15
described in Section 2.4. Similar solutions are grouped, beginning
with those that address the most issues. Unrelated solutions are
ordered based on the issues (listed in Section 2.4) they address.
Each solution in the table will be explained in a sub-section later,
where abbreviations in the table are described.
In the table, a letter code indicates the RFC category of the
mitigation solution (see BCP 9 [RFC2026] for explanation of these
categories):
S - Standards Track (Proposed Standard, Draft Standard, or
Internet Standard)
E - Experimental
I - Informational
B - Best Current Practice
U - Unknown (not formally defined by the IETF)
+-----+---+-------------------+--------+-------+-------+------+-----+
|ND |RFC| Multicast | Reli- |On-link|NCE |Fwd. |No A.|
|solu-|ty-| performance | ability|securi.|Exhau. |Delay |Acct.|
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|tion |pe |---+---+---+---+---+---+----+-------+-------+------+-----+
| | | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8-12 | 13 | 14 | 15 |
+-----+---+---+---+---+---+---+---+----+-------+-------+------+-----+
|MBBv6| I | All identified issues solved |
+-----+---+---+---+---+---+---+---+----+-------+-------+------+-----+
|FBBv6| U | All identified issues solved |
+-----+---+---+---+---+---+---+---+----+-------+-------+------+-----+
|UPPH | I | | X | | X | X | | X | | X | X | X |
+-----+---+---+---+---+---+---+---+----+-------+-------+------+-----+
|WiND | S |All issues solved for Low-Power and Lossy Networks (LLNs)|
+-----+---+---+---+---+---+---+---+----+-------+-------+------+-----+
|SARP | E | | | | | X | | | | | | |
+-----+---+---+---+---+---+---+---+----+-------+-------+------+-----+
|ND | S | | | | | X | | | | | | |
|TRILL| | | | | | | | | | | | |
+-----+---+---+---+---+---+---+---+----+-------+-------+------+-----+
|ND | S | | | | | X | | | | | | |
|EVPN | | | | | | | | | | | | |
+-----+---+---+---+---+---+---+---+----+-------+-------+------+-----+
|7772 | B | | X | | | | | | | | | |
+-----+---+---+---+---+---+---+---+----+-------+-------+------+-----+
|GRAND| S | | | | X | | | | | | X | |
+-----+---+---+---+---+---+---+---+----+-------+-------+------+-----+
|SAVI/| | | | | | | | | | | | |
|RA | I | | | | | | | | X | | | |
|G/G+ | | | | | | | | | | | | |
+-----+---+---+---+---+---+---+---+----+-------+-------+------+-----+
|6583 | I | | | | | | | | | X | | |
+-----+---+---+---+---+---+---+---+----+-------+-------+------+-----+
|9686 | S | | | | | | | | | | | X |
+-----+---+---+---+---+---+---+---+----+-------+-------+------+-----+
Table 1. Solutions for identified issues
3.1. ND Solution in Mobile Broadband IPv6
The IPv6 solution defined in "IPv6 in 3GPP EPS" [RFC6459], "IPv6 for
3GPP Cellular Hosts" [RFC7066], and "Extending an IPv6 /64 Prefix
from a Third Generation Partnership Project (3GPP) Mobile Interface
to a LAN Link" [RFC7278] is called Mobile Broadband IPv6 (MBBv6) in
this document. They are Informational RFCs. The key points are:
. Putting every host, e.g., the mobile User Equipment (UE), in a
Point-to-Point (P2P) link with the router, e.g., the mobile
gateway. Consequently:
o All multicast is effectively turned into unicast.
o The P2P links do not have a MAC address. Therefore, Router-
NCE-on-Demand is not needed.
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o Trusting-all-nodes is only relevant to the router. By
applying filtering at the router, e.g., dropping RAs from
the hosts, even malicious hosts cannot cause harm.
. Assigning a unique /64 prefix to each host. Together with the
P2P link, this puts each host on a separate link and subnet.
. Maintaining (prefix, interface) binding at the router for
forwarding purposes.
Since all the three causes of ND issues are addressed, all the
issues discussed in Section 2.4 are addressed.
3.2. ND Solution in Fixed Broadband IPv6
The IPv6 solution defined in "IPv6 in the context of TR-101" [TR177]
is called Fixed Broadband IPv6 (FBBv6) in this document. FBBv6 has
two flavors:
. P2P: Every host, e.g., the Residential Gateway (RG), is in a
P2P link with the router, e.g., the Broadband Network Gateway
(BNG). In this case, the solution is functionally similar to
MBBv6. All ND issues discussed in Section 2.4 are solved.
. Point-to-Multi-Point (P2MP): All hosts, e.g., the RGs,
connected to an access device, e.g., the Optical Line Terminal
(OLT), are in a P2MP link with the router, e.g., the BNG. This
is achieved by placing all hosts in a single VLAN on the router
and configuring the OLT to block any frame from being forwarded
between its access ports; traffic from each host can travel
only up toward the router, not sideways to another host,
thereby preventing direct host-to-host communication.
The following summarizes the two key aspects of the FBBv6-P2MP
architecture as described in [TR177] and the associated benefits:
. Implementing DAD Proxy [RFC6957]:
In a P2MP architecture described above, the normal ND DAD
procedure will breaks down because hosts cannot exchange NSs
with one another. To address this, the router participates in
the DAD process as a DAD Proxy to resolve address duplication.
The benefits are:
o Multicast traffic from all hosts to the router is
effectively converted into unicast, as hosts can only
communicate directly with the router.
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o The Trusting-all-nodes model is limited to the router. By
applying simple filtering, e.g., dropping RAs from hosts,
the router can mitigate security risks, even from
malicious hosts
. Assigning a unique /64 prefix to each host:
Assigning each host a unique /64 prefix results in several
operational improvements:
o The router can proactively install a forwarding entry for
that prefix towards the host, eliminating the need for
Router-NCE-on-Demand.
o Since each host resides in a different subnet, traffic
between hosts is routed through the router, eliminating
the need for hosts to perform address resolution for one
another.
o Without address resolution, router multicast to hosts is
limited to unsolicited RAs. As each host resides in its
own subnet, these RAs are sent as unicast packets to
individual hosts. This follows the approach specified in
[RFC6085], where the host's MAC address replaces the
multicast MAC address in the RA.
Since all three causes of ND issues are addressed, all ND issues
(Section 2.4) are also addressed.
3.3. Unique IPv6 Prefix per Host (UPPH)
UPPH solutions are described in [RFC8273] and [RFC9663]. Both are
Informational RFCs. [RFC8273] relies on SLAAC for unique prefix
allocation while [RFC9663] relies on DHCP-PD. That difference in
allocation mechanism does not change the discussion on ND issues,
because every IPv6 node is still required to run SLAAC, even when it
receives its prefix via DHCP-PD. Therefore, discussing [RFC8273]
alone is sufficient.
[RFC8273] "improves host isolation and enhanced subscriber
management on shared network segments" such as Wi-Fi or Ethernet.
The key points are:
. When a prefix is allocated to the host, the router can
proactively install a forwarding entry for that prefix towards
the host. There is no more Router-NCE-on-Demand.
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. Without address resolution, router multicast to hosts consists
only of unsolicited RAs. They will be sent to hosts one by one
in unicast because the prefix for every host is different.
. Since different hosts are in different subnets, hosts will send
traffic to other hosts via the router. There is no host-to-host
address resolution.
Therefore, ND issues caused by Router-NCE-on-Demand and router
multicast to hosts are prevented.
[RFC8273] indicates that a "network implementing a unique IPv6
prefix per host can simply ensure that devices cannot send packets
to each other except through the first-hop router". But when hosts
are on a shared medium like Ethernet, ensuring "devices cannot send
packets to each other except through the first-hop router" requires
additional measures like Private VLAN [RFC5517]. Without such
additional measures, on a shared medium, hosts can still reach each
other in L2 as they belong to the same Solicited-Node Multicast
Group. Therefore, Trusting-all-nodes and host multicast to routers
may cause issues. Of the host multicast issues (i.e., Issues 1, 3,
5, 6, and 7), Unique Prefix per Host prevents Issues 5 and 7,
because there is no need for address resolution among hosts (Issue
5) and there is no possibility of GUA duplication (Issue 7). But
Issues 1, 3, and 6 may occur.
3.4. Wireless ND and Subnet ND
Wireless ND (WiND) [RFC6775][RFC8505][RFC8928][RFC8929] (Standards
Track) defines a fundamentally different ND solution for Low-Power
and Lossy Networks (LLNs) [RFC7102]. WiND changes host and router
behaviors to use multicast only for router discovery. The key points
are:
. Hosts use unicast to proactively register their addresses at
the routers. Routers use unicast to communicate with hosts and
become an abstract registrar and arbitrator for address
ownership.
. The router also proactively installs NCEs for the hosts. This
avoids the need for address resolution for the hosts.
. The router sets Prefix Information Option (PIO) L-bit to 0.
Each host communicates only with the router (Section 6.3.4 of
[RFC4861]).
. Other functionalities that are relevant only to LLNs.
WiND addresses all ND issues (Section 2.4) in LLNs. However, WiND
support is not mandatory for general-purpose hosts. Therefore, it
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cannot be relied upon as a deployment option without imposing
additional constraints on the participating nodes.
3.5. Scalable Address Resolution Protocol
Scalable Address Resolution Protocol [RFC7586] was an Experimental
solution. That experiment ended in 2017, two years after the RFC was
published. Because the idea has been used in mitigation solutions
for more specific scenarios (described in Sections 3.6 and 3.7), it
is worth describing here. The usage scenario is Data Centers (DCs),
where large L2 domains span across multiple sites. In each site,
multiple hosts are connected to a switch. The hosts can be Virtual
Machines (VMs), so the number can be large. The switches are
interconnected by a native or overlay L2 network.
The switch will snoop and install (IP, MAC address) proxy table for
the local hosts. The switch will also reply to address resolution
requests from other sites to its hosts with its own MAC address. In
doing so, all hosts within a site will appear to have a single MAC
address to other sites. As such, a switch only needs to build a MAC
address table for the local hosts and the remote switches, not for
all the hosts in the L2 domain. Consequently, the MAC address table
size of the switches is significantly reduced. A switch will also
add the (IP, MAC address) replies from remote switches to its proxy
ND table so that it can reply to future address resolution requests
from local hosts for such IPs directly. This greatly reduces the
number of address resolution multicast in the network.
Unlike MBBv6, FBBv6, and UPPH, which try to address all ND issues
discussed in Section 2.4, SARP focuses on reducing address
resolution multicast to improve the performance and scalability of
large L2 domains in DCs.
3.6. ARP and ND Optimization for TRILL
ARP and ND Optimization for TRILL [RFC8302] (Standards Track) is
similar to SARP (Section 3.5). It can be considered an application
of SARP in the TRILL environment.
Like SARP, ARP, and ND Optimization for TRILL focuses on reducing
multicast address resolution. That is, it addresses Issue 5 (Section
2.1).
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3.7. Proxy ARP/ND in Ethernet Virtual Private Networks (EVPN)
Proxy ARP/ND in EVPN is specified in [RFC9161] (Standards Track).
The usage scenario is DCs where large L2 domains span across
multiple sites. In each site, multiple hosts are connected to a
Provider Edge (PE) router. The PEs are interconnected by EVPN
tunnels.
PE of each site snoops the local address resolution NAs to build
(IP, MAC address) Proxy ND table entries. PEs then propagate such
Proxy ND entries to other PEs via the Border Gateway Protocol (BGP).
Each PE also snoops local hosts' address resolution NSs for remote
hosts. If an entry exists in its Proxy ND table for the remote
hosts, the PE will reply directly. Consequently, the number of
multicast address resolution messages is significantly reduced.
Like SARP, Proxy ARP/ND in EVPN also focuses on reducing address
resolution multicast.
3.8. Reducing Router Advertisements
Maintaining IPv6 connectivity requires that hosts be able to receive
periodic multicast RAs [RFC4861]. Hosts that process unicast
packets while they are asleep must also process multicast RAs while
they are asleep. An excessive number of RAs can significantly reduce
the battery life of mobile hosts. [RFC7772] (Best Current Practice)
specifies a solution to reduce RAs:
. The router should respond to RS with unicast RA (rather than
the normal multicast RA) if the host's source IP address is
specified and the host's MAC address is valid. This way, other
hosts will not receive this RA.
. The router should reduce the multicast RA frequency
[RFC7772] addresses Issue 2 (Section 2.1).
3.9. Gratuitous Neighbor Discovery (GRAND)
GRAND [RFC9131] (Standards Track) changes ND in the following ways:
. A node sends unsolicited NAs upon assigning a new IPv6 address
to its interface.
. A router creates a new NCE for the node and sets its state to
STALE.
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When a packet for the host later arrives, the router can use the
existing STALE NCE to forward it immediately ([RFC4861] Section
7.2.2). It then verifies reachability by sending a unicast NS rather
than a multicast one for address resolution. In this way, GRAND
eliminates the Router Forwarding Delay. But it does not solve other
Router-NCE-on-Demand issues. For example, NCE Exhaustion can still
happen.
3.10. Source Address Validation Improvement (SAVI) and Router
Advertisement Guard
SAVI [RFC7039] (Informational) binds an address to a port on an L2
switch and rejects claims from other ports for that address.
Therefore, a node cannot spoof the IP address of another node.
Router Advertisement Guard (RA-Guard) [RFC6105][RFC7113]
(Informational) only allows RAs from a port that a router is
connected to. Therefore, nodes on other ports cannot pretend to be a
router.
SAVI and RA-Guard address the on-link security issues.
3.11. RFC 6583 Dealing with NCE Exhaustion Attacks
[RFC6583] (Informational) deals with the NCE Exhaustion attack issue
(Section 2.3). It recommends that:
. Operators should
o Filter unused address space so that messages to such
addresses can be dropped rather than triggering NCE
creation.
o Implement rate-limiting mechanisms for ND message
processing to prevent CPU and memory resources from being
overwhelmed.
. Vendors should
o Prioritizing NDP processing for existing NCEs over creating
new NCEs
[RFC6583] acknowledges that "some of these options are 'kludges',
and can be operationally difficult to manage". [RFC6583] partially
addresses the Router NCE Exhaustion issue. In practice, router
vendors cap the number of NCEs per interface to prevent cache
exhaustion. If the link has more addresses than that cap, the router
cannot keep an entry for every address, and packets destined for
addresses without an NCE are simply dropped [RFC9663].
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3.12. Registering Self-generated IPv6 Addresses using DHCPv6
In IPv4, network administrators can retrieve a host's IP address
from the DHCP server and use it for subscriber management. In IPv6
and SLAAC, this is not possible (Section 2.3).
[RFC9686] (Standards Track) defines a method for informing a DHCPv6
server that a host has one or more self-generated or statically
configured addresses. This enables network administrators to
retrieve the IPv6 addresses for each host from the DHCPv6 server.
[RFC9686] provides a solution for Issue 15 (Section 2.3).
3.13. Enhanced DAD
Enhanced DAD [RFC7527] (Standards Track) addresses a DAD failure
issue in a specific situation: a looped back interface. DAD will
fail in a looped-back interface because the sending host will
receive the DAD message back and will interpret it as another host
is trying to use the same address. The solution is to include a
Nonce option [RFC3971] in each DAD message so that the sending host
can detect that the looped-back DAD message is sent by itself.
Enhanced DAD does not solve any ND issue. It extends ND to work in a
new scenario: looped-back interface. It is reviewed here only for
completeness.
3.14. ND Mediation for IP Interworking of Layer 2 VPNs
ND mediation is specified in [RFC6575] (Standards Track). When two
Attachment Circuits (ACs) are interconnected by a Virtual Private
Wired Service (VPWS), and the two ACs are of different media (e.g.,
one is Ethernet while the other is Frame Relay), the two PEs must
interwork to provide mediation service so that a Customer Edge (CE)
can resolve the MAC address of the remote end. [RFC6575] specifies
such a solution.
ND Mediation does not address any ND issue. It extends ND to work in
a new scenario: two ACs of different media interconnected by a VPWS.
It is reviewed here only for completeness.
3.15. ND Solutions Defined before the Latest Versions of ND
The latest versions of ND and SLAAC are specified in [RFC4861] and
[RFC4862]. Several ND mitigation solutions were published before
[RFC4861]. They are reviewed in this section only for completeness.
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3.15.1. Secure Neighbor Discovery (SeND)
The purpose of SeND [RFC3971] (Standards Track) is to ensure that
hosts and routers are trustworthy. SeND defined three new ND
options, i.e., Cryptographically Generated Addresses (CGA) [RFC3972]
(Standards Track), RSA public-key cryptosystem, and Timestamp/Nonce,
an authorization delegation discovery process, an address ownership
proof mechanism, and requirements for the use of these components in
the ND protocol.
3.15.2. Cryptographically Generated Addresses (CGA)
The purpose of CGA is to associate a cryptographic public key with
an IPv6 address in the SeND protocol. The key point is to generate
the Interface Identifier (IID) of an IPv6 address by computing a
cryptographic hash of the public key. The resulting IPv6 address is
called a CGA. The corresponding private key can then be used to
sign messages sent from the address.
CGA assumes that a legitimate host does not care about the bit
combination of the IID that would be created by some hash procedure.
The attacker needs an exact IID to impersonate the legitimate hosts,
but then the attacker is challenged to do a reverse hash calculation
which is a strong mathematical challenge.
CGA is part of SeND. There is no reported deployment.
3.15.3. ND Proxy
ND Proxy [RFC4389] (Experimental) aims to enable multiple links
joined by an ND Proxy device to work as a single link.
. When an ND Proxy receives an ND request from a host on a link,
it will proxy the message out the "best" (defined in the next
paragraph) outgoing interface. If there is no best interface,
the ND Proxy will proxy the message to all other links. Here,
proxy means acting as if the ND message originates from the ND
Proxy itself. That is, the ND Proxy will change the ND
message's source IP and source MAC address to the ND Proxy's
outgoing interface's IP and MAC address, and create an NCE
entry at the outgoing interface accordingly.
. When ND Proxy receives an ND reply, it will act as if the ND
message is destined for itself, and update the NCE entry state
at the receiving interface. Based on such state information,
the ND Proxy can determine the "best" outgoing interface for
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future ND requests. The ND Proxy then proxies the ND message
back to the requesting host.
ND Proxy is widely used in SARP (Sections 3.5), ND Optimization for
TRILL (Sections 3.6), and Proxy ARP/ND in EVPN (Sections 3.7).
3.15.4. Optimistic DAD
Optimistic DAD [RFC4429] (Standards Track) seeks to minimize address
configuration delays in the successful case and to reduce disruption
as far as possible in the failure case. That is, Optimistic DAD lets
hosts immediately use the newly formed address to communicate before
DAD completes, assuming that DAD will succeed anyway. If the address
turns out to be duplicate, Optimistic DAD provides a set of
mechanisms to minimize the impact. Optimistic DAD modified the
original ND [RFC2461] and SLAAC [RFC2462], but the solution was not
incorporated into the latest specifications of [RFC4861] and
[RFC4862]. However, implementations of Optimistic DAD exist.
Optimistic DAD does not solve any ND issue (Section 2). It is
reviewed here only for completeness.
4. Guidelines for Prevention of Potential ND Issues
By knowing the potential ND issues and associated mitigation
solutions, network administrators of existing IPv6 deployments can
assess whether these issues may occur in their networks and, if so,
whether to deploy the mitigation solutions proactively. Deploying
these solutions may take time and additional resources. Therefore,
it is advisable to plan.
Network administrators planning to start their IPv6 deployments can
use the issue-solution information to help plan their deployments.
Moreover, they can take proactive action to prevent potential ND
issues.
4.1. Learning Host Isolation from the Existing Solutions
While various ND solutions may initially appear unrelated,
categorizing them into four distinct groups highlights an important
observation: "host isolation" is an effective strategy for
mitigating ND-related issues.
Group 1: L3 and L2 Isolation
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This group includes MBBv6 and FBBv6, which isolate hosts at both L3
and L2 by placing each host within its subnet and link. This
prevents ND issues caused by multicast and Trusting-all-nodes, as
each host operates within its isolated domain. Furthermore, since
routers can route packets to a host based on its unique prefix, the
need for Router-NCE-on-Demand is also eliminated. Therefore, L3 and
L2 Isolation prevent all ND issues.
Group 2: L3 Isolation
This group includes UPPH solutions like [RFC8273] and [RFC9663],
which isolate hosts into separate subnets while potentially leaving
them on the same shared medium. This approach mitigates ND issues
caused by router multicast to hosts and eliminates the need for
"Router-NCE-on-Demand", as detailed in Section 3.3.
Group 3: Partial L2 Isolation
This group encompasses solutions such as WiND, SARP, ND Optimization
for TRILL, and Proxy ND in EVPN. These solutions use a proxy device
to represent the hosts behind it, effectively isolating those hosts
into distinct multicast domains. While hosts are still located
within the same subnet, their separation into different multicast
domains reduces the scope of ND issues related to multicast-based
address resolution.
Group 4: Non-Isolating Solutions
The final group includes remaining solutions that do not implement
host isolation. These solutions do not prevent ND issues but instead
focus on addressing specific ND problems.
The analysis demonstrates that the stronger the isolation of hosts,
the more ND issues can be mitigated. This correlation is intuitive,
as isolating hosts reduces the multicast scope, minimizes the number
of nodes that must be trusted, and may eliminate the need for
"Router-NCE-on-Demand", the three primary causes of ND issues.
This understanding can be used to prevent ND issues.
4.2. Applicability of Various Isolation Methods
4.2.1. Applicability of L3+L2 Isolation
Benefits:
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o All ND issues (Section 2.4) can be effectively mitigated.
Constraints:
1. L2 Isolation:
Actions must be taken to isolate hosts in L2. The required effort
varies by the chosen method and deployment context. For example, the
P2P method [RFC7066] is heavy-weight, while the Private VLAN method
[RFC5517] is more manageable.
2. Unique Prefix Allocation:
A large number of prefixes will be required, with one prefix
assigned per host. This is generally not a limitation for IPv6. For
instance, members of a Regional Internet Registry (RIR) can obtain a
/29 prefix allocation [RIPE738], which provides 32 billion /64
prefixes - sufficient for any foreseeable deployment scenarios.
Practical implementations, such as MBBv6 assigning /64 prefixes to
billions of mobile UEs [RFC6459] and FBBv6 assigning /56 prefixes to
hundreds of millions of routed RGs [TR177], demonstrate the
feasibility of this approach.
3. Privacy Issue from Unique Prefix Identifiability:
Assigning a unique prefix to each host may theoretically reduce
privacy, as hosts can be directly identified by their assigned
prefix. However, alternative host identification methods, such as
cookies, are commonly used. Therefore, unique prefix identifiability
may not make much difference. The actual impact on privacy is
therefore likely to be limited.
4. Router Support for L3 Isolation:
The router must support an L3 Isolation solution, e.g., [RFC8273] or
[RFC9663].
5. A Large Number of Router Interfaces May be Needed:
If the P2P method is used, the router must instantiate a separate
logical interface for every attached host. In this case, a large
number of interfaces will be needed at the router.
6. Router as a Bottleneck:
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Since all communication between hosts is routed through the router,
the router may become a performance bottleneck in high-traffic
scenarios.
7. Incompatibility with Host-Based Multicast Services:
Services that rely on multicast communication among hosts, such as
Multicast Domain Name System [RFC6762], will be disrupted.
4.2.2. Applicability of L3 Isolation
Benefits:
. All ND issues (Section 2.4) are mitigated, with the exception
of:
o LLA DAD multicast degrading performance,
o LLA DAD not reliable in wireless networks, and
o On-link security
These remaining issues depend on the characteristics of the
shared medium:
o If the shared medium is Ethernet, the issues related to LLA
DAD multicast are negligible.
o If nodes can be trusted, such as in private networks, on-
link security concerns are not significant.
. No need for L2 Isolation. Consequently, this method can be
applied in a wide range of scenarios, making it possibly the
most practical host isolation method.
Constraints, as discussed in Section 4.2.1:
1. Unique Prefix Allocation
2. Router Support for L3 Isolation
3. Router as a Bottleneck
4. Privacy Issue from Unique Prefix Identifiability.
4.2.3. Applicability of Partial L2 Isolation
Benefits:
. Reduced Multicast Traffic:
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This method reduces multicast traffic, particularly for address
resolution, by dividing the subnet into multiple multicast
domains.
Constraint:
. Router Support for Partial L2 Isolation:
The router must implement a Partial L2 Isolation solution such as
WiND, SARP, ND Optimization for TRILL, and Proxy ND in EVPN to
support this method.
4.3. Guidelines for Applying Isolation Methods
Based on the applicability analysis provided in the preceding
sections, network administrators can determine whether to implement
an isolation method and, if so, which method is most appropriate for
their specific deployment.
A simple guideline is to consider the isolation methods in the order
listed in the preceding sections, progressing from the strongest
isolation to the weakest:
. Stronger isolation methods can prevent more ND issues, but may
also impose higher entry requirements.
. Weaker isolation methods have fewer entry requirements but may
leave some ND issues unmitigated.
The choice between L3+L2 Isolation and L3 Isolation often depends on
the cost of implementing L2 Isolation:
. If the cost is acceptable, L3+L2 Isolation is preferable
because it eliminates every ND issue listed in Section 2.4.
. Otherwise, L3 Isolation addresses most of those issues while
keeping the implementation effort reasonable.
Selecting an isolation method that is either too strong or too weak
does not result in serious consequences:
. Choosing an overly strong isolation method may require the
network administrator to meet higher entry requirements
initially, such as measures for L2 Isolation, additional
prefixes, or additional router capabilities.
. Choosing a "weaker isolation method" may necessitate deploying
supplemental ND mitigation techniques to address any unresolved
ND issues.
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In either case, the resulting solution can be functional and
effective.
5. Security Considerations
This document is a review of known ND issues and solutions,
including security. It does not introduce any new solutions.
Therefore, it does not introduce new security issues.
6. IANA Considerations
This document has no request to IANA.
7. References
7.1. Normative References
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862.
7.2. Informative References
[AddrAcc] T. Chown, C. Cummings, D.Carder, "IPv6 Address
Accountability Considerations", Internet draft, Oct. 2024.
[MADINAS] J. Henry, Y. Lee, "Randomized and Changing MAC Address:
Context, Network Impacts, and Use Cases", draft-ietf-
madinas-use-cases-19.
[RFC2026] S. Bradner, "The Internet Standards Process -- Revision
3", RFC 2026.
[RFC2461] T. Narten, E. Nordmark, W. Simpson, "Neighbor Discovery
for IP Version 6 (IPv6)", RFC 2461, obsoleted by RFC 4861.
[RFC2462] S. Thomson, T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, obsoleted by RFC 4862.
[RFC3587] R. Hinden, S. Deering, E. Nordmark, "IPv6 Global Unicast
Address Format", RFC 3587.
[RFC3756] P. Nikander, J. Kempf, E. Nordmark, "IPv6 Neighbor
Discovery (ND) Trust Models and Threats", RFC 3756.
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[RFC3971] J. Arkko, J. Kempf, B. Zill, P. Nikander, "SEcure Neighbor
Discovery (SEND)", RFC3971.
[RFC3972] T. Aura, "Cryptographically Generated Addresses (CGA)",
RFC3972.
[RFC4193] R. Hinden, B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193.
[RFC4389] D. Thaler, M. Talwar, C. Patel, "Neighbor Discovery
Proxies (ND Proxy)", RFC 4389.
[RFC4429] N. Moore, "Optimistic Duplicate Address Detection (DAD)
for IPv6", RFC 4429.
[RFC4903] D. Thaler, "Multi-Link Subnet Issues", RFC 4903.
[RFC5517] S. HomChaudhuri, M. Foschiano, "Cisco Systems' Private
VLANs: Scalable Security in a Multi-Client Environment",
RFC 5517.
[RFC6085] S. Gundavelli, M. Townsley, O. Troan, W. Dec, "Address
Mapping of IPv6 Multicast Packets on Ethernet", RFC 6085.
[RFC6105] E. Levy-Abegnoli, G. Van de Velde, C. Popoviciu, J.
Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105.
[RFC6459] J. Korhonen, J. Soininen, B. Patil, T. Savolainen, G.
Bajko, K. Iisakkila, "IPv6 in 3rd Generation Partnership
Project (3GPP) Evolved Packet System (EPS)", RFC 6459.
[RFC6575] H. Shah, E. Rosen, G. Heron, V. Kompella, "Address
Resolution Protocol (ARP) Mediation for IP Interworking of
Layer 2 VPNs", RFC 6575.
[RFC6583] I. Gashinsky, J. Jaeggli, W. Kumari, "Operational Neighbor
Discovery Problems", RFC 6583.
[RFC6762] S. Cheshire, M. Krochmal, "Multicast DNS", RFC 6762.
[RFC6775] Z. Shelby, S. Chakrabarti, E. Nordmark, C. Bormann,
"Neighbor Discovery Optimization for IPv6 over Low-Power
Wireless Personal Area Networks (6LoWPANs)", RFC 6775.
[RFC6957] F. Costa, J-M. Combes, X. Pougnard, H. Li, "Duplicate
Address Detection Proxy", RFC 6957
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[RFC7039] J. Wu, J. Bi, M. Bagnulo, F. Baker, C. Vogt, "Source
Address Validation Improvement (SAVI) Framework", RFC
7039.
[RFC7066] J. Korhonen, J. Arkko, T. Savolainen, S. Krishnan, "IPv6
for Third Generation Partnership Project (3GPP) Cellular
Hosts", RFC 7066.
[RFC7102] JP. Vasseur, "Terms Used in Routing for Low-Power and
Lossy Networks", RFC 7102.
[RFC7113] F. Gont, "Implementation Advice for IPv6 Router
Advertisement Guard (RA-Guard)", RFC 7113.
[RFC7278] Extending an IPv6 /64 Prefix from a Third Generation
Partnership Project (3GPP) Mobile Interface to a LAN
Link", RFC7278.
[RFC7342] L. Dunbar, W. Kumari, I. Gashinsky, "Practices for Scaling
ARP and Neighbor Discovery (ND) in Large Data Centers",
RFC 7342.
[RFC7527] R. Asati, H. Singh, W. Beebee, C. Pignataro, E. Dart, W.
George, "Enhanced Duplicate Address Detection", RFC 7527.
[RFC7586] Y. Nachum, L. Dunbar, I. Yerushalmi, T. Mizrahi, "The
Scalable Address Resolution Protocol (SARP) for Large Data
Centers", RFC7586.
[RFC7772] A. Yourtchenko, L. Colitti, "Reducing Energy Consumption
of Router Advertisements", RFC 7772.
[RFC8273] J. Brzozowski, G. Van de Velde, "Unique IPv6 Prefix per
Host", RFC 8273.
[RFC8302] Y. Li, D. Eastlake 3rd, L. Dunbar, R. Perlman, M. Umair,
"Transparent Interconnection of Lots of Links (TRILL): ARP
and Neighbor Discovery (ND) Optimization", RFC 8302.
[RFC8415] T. Mrugalski, M. Siodelski, A. Yourtchenko, M. Richardson,
S. Jiang, T. Lemon, T. Winters, "Dynamic Host
Configuration Protocol for IPv6 (DHCPv6)", RFC 8415.
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[RFC8505] P. Thubert, E. Nordmark, S. Chakrabarti, C. Perkins,
"Registration Extensions for IPv6 over Low-Power Wireless
Personal Area Network (6LoWPAN) Neighbor Discovery", RFC
8505.
[RFC8928] P. Thubert, B. Sarikaya, M. Sethi, R. Struik, "Address-
Protected Neighbor Discovery for Low-Power and Lossy
Networks", RFC 8928.
[RFC8929] P. Thubert, C.E. Perkins, E. Levy-Abegnoli, "IPv6 Backbone
Router", RFC 8929.
[RFC9099] E. Vyncke, K. Chittimaneni, M. Kaeo, E. Rey, "Operational
Security Considerations for IPv6 Networks", RFC 9099.
[RFC9119] C. Perkins, M. McBride, D. Stanley, W. Kumari, JC. Zuniga,
"Multicast Considerations over IEEE 802 Wireless Media",
RFC 9119.
[RFC9131] J. Linkova, "Gratuitous Neighbor Discovery: Creating
Neighbor Cache Entries on First-Hop Routers", RFC 9131.
[RFC9161] J. Rabadan, S. Sathappan, K. Nagaraj, G. Hankins, T. King,
"Operational Aspects of Proxy ARP/ND in Ethernet Virtual
Private Networks", RFC 9161.
[RFC9663] L. Colitti, J. Linkova, X. Ma, "Using DHCP-PD to Allocate
Unique IPv6 Prefix per Client in Large Broadcast
Networks", RFC 9663.
[RFC9686] W. Kumari, S. Krishnan, R. Asati, L. Colitti, J. Linkova,
S. Jiang, "Registering Self-generated IPv6 Addresses using
DHCPv6", RFC 9686.
[RIPE738] IPv6 Address Allocation and Assignment Policy,
https://www.ripe.net/publications/docs/ripe-738
[SND] P. Thubert, M. Richardson, "Architecture and Framework for
IPv6 over Non-Broadcast Access", Internet draft, June
2023.
[TR177] S. Ooghe, B. Varga, W. Dec, D. Allan, "IPv6 in the context
of TR-101", Broadband Forum, TR-177.
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8. Acknowledgments
The authors would like to thank Eric Vyncke, Gunter Van de Velde,
Lorenzo Colitti, Erik Kline, Warren Kumari, Mohamed Boucadair, Gorry
Fairhurst, Pascal Thubert, Jen Linkova, Brian Carpenter, Mike
Ackermann, Nalini Elkins, Ed Horley, Ole Troan, David Thaler,
Chongfeng Xie, Chris Cummings, Dale Carder, Tim Chown, Priyanka
Sinha, Aijun Wang, Ines Robles, Magnus Westerlund, Barry Leiba, Deb
Cooley and Paul Wouters for their reviews and comments. The authors
would also like to thank Tim Winters for being the document
shepherd.
Authors' Addresses
XiPeng Xiao
Huawei Technologies Dusseldorf
Hansaallee 205, 40549 Dusseldorf, Germany
Email: xipengxiao@huawei.com
Eduard Vasilenko
Huawei Technologies
17/4 Krylatskaya st, Moscow, Russia 121614
Email: vasilenko.eduard@huawei.com
Eduard Metz
KPN N.V.
Email: eduard.metz@kpn.com
Gyan Mishra
Verizon Inc.
Email: gyan.s.mishra@verizon.com
Nick Buraglio
Energy Sciences Network
Email: buraglio@es.net
Xiao Expires Nov. 26, 2025 [Page 28]