IPv6 Operations (v6ops) Working Group X. Xiao
Internet Draft E. Vasilenko
Intended status: Informational Huawei Technologies
Expires: September 2024 E. Metz
KPN
G. Mishra
Verizon Inc.
N. Buraglio
Energy Sciences Network
March 3, 2024
Selectively Isolating Hosts to Prevent Potential Neighbor Discovery
Issues and Simplify IPv6 First-hops
draft-ietf-v6ops-nd-considerations-03
Abstract
Neighbor Discovery (ND) is a key protocol of IPv6 first-hop. ND uses
multicast extensively and trusts all hosts. In some scenarios like
wireless networks, multicast can be inefficient. In other scenarios
like public access networks, hosts may not be trustable.
Consequently, ND has potential issues in various scenarios. The
issues and the solutions for them are documented in more than 30
RFCs. It is difficult to keep track of all these issues and
solutions. Therefore, an overview is useful.
This document firstly summarizes the known ND issues and
optimization solutions into a one-stop reference. Analyzing these
solutions reveals an insight: isolating hosts is effective in
preventing ND issues. Five isolation methods are proposed and their
applicability is discussed. Guidelines are described for selecting a
suitable isolation method based on the deployment scenario. When ND
issues are prevented with a proper isolation method, the solutions
for these issues are not needed. This simplifies the IPv6 first-
hops.
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/.
Xiao Expires September 3, 2024 [Page 1]
Internet-Draft nd-considerations March 2024
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 in Sept. 2024.
Copyright Notice
Copyright (c) 2024 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
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with
respect to this document. Code Components extracted from this
document must include Simplified BSD License text as described in
Section 4.e of the Trust Legal Provisions and are provided without
warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction...................................................3
1.1. Terminology...............................................4
2. Review of ND Issues............................................6
2.1. Multicast Causes Performance and Reliability Issues.......6
2.2. Trusting-all-hosts Causes On-link Security Issues.........7
2.3. Router-NCE-on-Demand Causes Forwarding Delay, NCE Exhaustion
and Lack of Subscriber Management Issues.......................7
2.4. Summary of ND Issue.......................................8
3. Review of ND Solutions.........................................9
3.1. ND Solution in Mobile Broadband IPv6......................9
3.2. ND Solution in Fixed Broadband IPv6......................10
3.3. Unique IPv6 Prefix per Host..............................11
3.4. Wireless ND and Subnet ND................................12
3.5. Scalable Address Resolution Protocol.....................12
3.6. ARP and ND Optimization for Transparent Interconnection of
Lots of Links (TRILL):........................................13
3.7. Proxy ARP/ND in EVPN.....................................13
3.8. Gratuitous Neighbor Discovery............................13
3.9. Reducing Router Advertisements...........................14
3.10. Source Address Validation Improvement and Router
Advertisement Guard...........................................14
Xiao Expires September 3, 2024 [Page 2]
Internet-Draft nd-considerations March 2024
3.11. Dealing with Off-link Attack that May Cause Router NCE
Exhaustion....................................................15
3.12. Enhanced DAD............................................15
3.13. ND Mediation for IP Interworking of Layer 2 VPNs........15
3.14. ND Solutions Defined before the Latest Versions of ND...16
3.14.1. SeND...............................................16
3.14.2. Cryptographically Generated Addresses (CGA)........16
3.14.3. ND Proxy...........................................17
3.14.4. Optimistic DAD.....................................17
3.15. Observations on the Solutions...........................18
4. Selectively Isolating Hosts to Prevent Potential ND Issues and
Simplify IPv6 First-hops.........................................20
4.1. Applicability of Subnet Isolation with P2P Link..........22
4.2. Applicability of Subnet Isolation with P2MP Link.........23
4.3. Applicability of Subnet Isolation with Shared Medium.....23
4.4. Applicability of Proxy Isolation.........................24
4.5. Applicability of GUA Isolation...........................24
4.6. Guidelines for Selecting a Host Isolation Method.........24
4.7. Impact of Host Isolation on Other Protocols in IPv6 First-
hops..........................................................28
5. Security Considerations.......................................29
6. IANA Considerations...........................................29
7. References....................................................29
7.1. Informative References...................................29
8. Acknowledgments...............................................32
1. Introduction
Neighbor Discovery [ND] is specified in RFC 4861. It defines how
hosts and routers in the link interact with each other. ND contains
eight main procedures:
1. Host's LLA DAD: hosts generate Link Local Addresses (LLAs) and
use multicast Neighbor Solicitations (NSs) for Duplicate
Address Detection (DAD).
2. Host's Router Discovery: hosts send multicast Router
Solicitations (RSs) to discover first-hop routers. Routers
respond with unicast Router Advertisements (RAs) with subnet
prefixes for the link and other information. Routers also send
unsolicited multicast RAs from time to time.
3. Host's GUA DAD: hosts form Global Unicast Address (GUA) or
Unique Local Address (ULA) and use multicast NSs for DAD.
4. Router's Neighbor Discovery: When a router is to forward a
packet to an on-link host for the first time, the router uses
multicast NSs to perform address resolution for the host.
Xiao Expires September 3, 2024 [Page 3]
Internet-Draft nd-considerations March 2024
5. Host's Neighbor Discovery: When a host is to send a packet to
another on-link host, the source host uses multicast NSs to
perform address resolution for the destination host.
6. Host/router's NUD: hosts/routers use unicast NS for Node
Unreachability Detection (NUD).
7. Host's link layer address change announcement: hosts may use
multicast NAs to announce link layer address changes.
8. Router's Redirect: Routers send Redirect packets to inform a
host of a better first-hop router or that the destination host
is on-link.
Due to multicast, trusting all hosts, etc., ND has potential issues
in some scenarios. Various ND issues and solutions for them have
been described in more than 30 RFCs. These include: ND Trust Models
and Threats [RFC3756], Secure ND [SeND], Cryptographically Generated
Addresses [CGA], 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 [SAVI], Router
Advertisement Guard [RA-Guard][RA-Guard+], Enhanced Duplicate
Address Detection [RFC7527], Scalable ARP [RFC7586], Reducing Router
Advertisements [RFC7772], Unique Prefix Per Host [RFC8273], ND
Optimization for TRILL [RFC8302], Gratuitous Neighbor Discovery
[GRAND], Proxy ARP/ND for EVPN [RFC9161]. It is difficult to
understand all these issues and solutions, and how they fit
together. If IPv6 deployers are not sufficiently informed before
their deployment, they may encounter problems later. This document
summarizes the potential issues and solutions to provide a clear
picture. It also provides guidelines for preventing the issues as
much as possible.
1.1. Terminology
Some important terms are defined in this section.
MAC - To avoid confusion with Link Local Address (LLA), link
layer address is called MAC in this document.
Subnet isolation for hosts - assigning a unique prefix per host so
that each host is in its own subnet [RFC8273].
Xiao Expires September 3, 2024 [Page 4]
Internet-Draft nd-considerations March 2024
P2P link isolation - connecting each host in a P2P link to the
router. The router has a separate interface for each host.
Consequently, any L2 message from a host can only reach the
router, and any L2 message from the router can only reach
one host.
P2MP link isolation - connecting multiple hosts in a P2MP link to
the router. The router has a single interface for all hosts.
Example P2MP links are Private VLAN [PVLAN] and Wi-Fi with
Wireless Isolation [W-Iso]. Consequently, any L2 message
from a host can only reach the router, not other hosts. But
an L2 multicast message from the router can reach multiple
hosts simultaneously.
Proxy isolation - using an ND proxy device to represent the hosts
behind it. There are two kinds of proxies, bridging and
routing. When receiving an address resolution message for a
host, a bridging proxy either passes the message to the host
or directly answer with the host's MAC. In comparison, a
routing proxy [SND] always terminates the address
resolution messages and replies with its own MAC address.
Consequently, a bridging proxy will forward packets to the
destination hosts at L2 based on the destination hosts' MAC
addresses (i.e. bridging), while a routing proxy will
receive packets on its own MAC address and then forward the
packets at L3 to the destination hosts (i.e. routing). From
a host isolation perspective, bridging proxies have no
isolating effect while routing proxies effectively isolate
different groups of hosts behind the proxies into different
broadcast/multicast domains. In this document, proxy
isolation refers to routing proxy isolation.
GUA isolation - setting PIO L-bit=0 so that other hosts appear off-
link [ND]. There will be no GUA address resolution for other
hosts in the link, and all GUA traffic will be sent via the
router. Therefore, hosts appear isolated from a GUA
perspective. This is also applicable to ULA but to be
simple, it is also called GUA Isolation in this document.
Xiao Expires September 3, 2024 [Page 5]
Internet-Draft nd-considerations March 2024
2. Review of ND Issues
2.1. Multicast Causes Performance and Reliability Issues
ND uses multicast for Node Solicitations (NSs), Node Advertisements
(NAs)Router Solicitations (RSs) and Router Advertisements (RAs).
Multicast can be inefficient in some scenarios, e.g. large L2
networks or wireless networks.
In large L2 networks, e.g. DC networks involving many Virtual
Machines (VMs), ND multicast can create a large amount of protocol
traffic. This can consume network bandwidth, create a processing
burden, and reduce network performance [RFC7342].
In wireless networks, multicast messages often require special
processing. For example, to ensure that the multicast messages reach
even the remotest hosts, multicast messages may be sent at the
lowest modulation rate. Alternatively, multicast may be converted
into multiple unicast messages. In addition, many mobile devices
drop substantial percentages of multicast traffic on Wi-Fi by
listening to only one out of multiple Delivery Traffic Indication
Message (DTIM) beacons. Consequently, multicast in wireless networks
reduces not only performance but also reliability [RFC9119]. For
example, ND uses no response as an indication of no duplication in
Duplicate Address Detection (DAD). If the DAD multicast messages are
lost, DAD will not work properly.
ND uses multicast in the following messages. Multicast impact on
performance and reliability is summarized below:
. Hosts' LLA DAD: may cause performance issues in both wired and
wireless networks, and possibly reliability issues in wireless
networks.
. Router's periodic unsolicited RAs: multicast RAs are generally
limited to one packet every 3s, 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 create battery life issues
[RFC7772].
. Hosts' GUA (or ULA) DAD: may cause performance issues in both
wired and wireless networks, and possibly reliability issues in
wireless networks.
. Router's address resolution for hosts: in a large L2 network of
N hosts, there can be N such multicast messages. This may cause
performance issues.
Xiao Expires September 3, 2024 [Page 6]
Internet-Draft nd-considerations March 2024
. Hosts address resolution for hosts: in a large L2 DC network of
N hosts, there can be N-square such multicast messages. This
may cause performance issues.
. Hosts' MAC change NAs: this type of multicast messages is rare
and will not cause a performance issue. It will not be further
discussed.
Multicast originated from hosts and routers will be called host
multicast and router multicast hereafter.
2.2. Trusting-all-hosts Causes On-link Security Issues
ND trusts all hosts. In some scenarios like public access networks,
some hosts may not be trustable. An attacker host in the link can
cause the following security issues [RFC3756][RFC9099]:
. Source IP address spoofing: an attacker can use a victim host's
IP address as the source address of its ND message to pretend
to be the victim. The attacker can then launch Redirect or
Denial of Service (DoS) attacks on the victim.
. DAD denial: an attacker can repeatedly reply to a victim's DAD
messages, causing the victim's address configuration procedure
to fail, and resulting in a denial of service to the victim
host.
. Forged RAs: an attacker can send RAs to other hosts to claim to
be a router and preempt the real router, resulting in a
Redirect attack [RA-Guard].
. Forged Redirects: an attacker can pretend to be the router and
send Redirects to other hosts to redirect their traffic to the
router to itself, resulting in a Redirect attack.
. Replay attacks: an attacker can capture valid ND messages and
replay them later.
2.3. Router-NCE-on-Demand Causes Forwarding Delay, NCE Exhaustion and
Lack of Subscriber Management Issues
In ND, a router does not maintain (IP, MAC) binding (i.e. Neighbor
Cache Entry or NCE) for a host until it is needed. This is called
Router-NCE-on-Demand. When a router is to forward a packet to a
host, it will perform address resolution to find the MAC of the
host. This can cause multiple issues:
. The packet has to be buffered before the router finds out the
MAC of the host. This delays forwarding and depending on the
router's buffer size may also cause packet loss. This is called
"Router-NCE-on-Demand Forwarding Delay" in this document.
Xiao Expires September 3, 2024 [Page 7]
Internet-Draft nd-considerations March 2024
. The way ND performs address resolution is the source node will
create an NCE entry first and set its state to INCOMPLETE, the
node will then multicast NSs to all the nodes and wait for the
destination node to reply with its MAC. This creates a security
vulnerability. If an attacker sends a large number of packets
destined to non-existing IP addresses to a router, the router
will create a large amount of NCEs in INCOMPLETE state while
trying to resolve the MACs. The router may run out of resources
and stop functioning. This is called "NCE Exhaustion" in this
document. Note that in this case, the attacker can be off-link.
So, this is different from the on-link security issues.
o To prevent this NCE Exhaustion problem, some
implementations limit the maximal number of NCEs a router
will maintain for each host. When a host uses more IPv6
addresses than the limit, irregular packet drops may
result at the router because the router does not maintain
NCEs for all those IPv6 addresses [DHCP-PD]. This can be
considered as a special flavor of NCE Exhaustion issue.
. With SLAAC, a host forms its own IP address. A router does not
know the host's IP address until an NCE entry is installed. In
a service provider network, subscribers are generally managed
by their IP addresses. Consequently, if the router does not
know a host's IP address, the service provider cannot manage
the subscriber. This is an issue for public access networks.
2.4. Summary of ND Issue
The ND issues discussed in Sections 2.1 to 2.3 are summarized below.
It is worth noting that these issues originate from three causes:
multicast, trusting all hosts and Router-NCE-on-Demand. If a cause
can be eliminated, the corresponding issues will also be eliminated.
This points out the directions for ND optimization.
. Performance issues caused by multicast
o LLA DAD degrading performance
o Unsolicited RA draining hosts' battery
o GUA/ULA DAD degrading performance
o Router address resolution for hosts degrading performance
o Host Address resolution for other hosts degrading
performance
o Host MAC change announcement degrading performance (minor
issue, no further discussion)
. Reliability issues caused by multicast
o LLA DAD not reliable for wireless networks
o GUA/ULA DAD not reliable for wireless networks
. On-link security issues caused by trusting all hosts
Xiao Expires September 3, 2024 [Page 8]
Internet-Draft nd-considerations March 2024
o Source IP address spoofing
o DAD denial
o Forged RAs
o Forged Redirects
o Replay attacks
. Off-link attack and other issues caused by Router-NCE-on-Demand
o Router NCE exhaustion
o Router forwarding delay
o Lack of subscriber management with SLAAC
It is worth noting that these are just potential issues. Depending
on the usage scenarios, they may not actually happen. More
specifically:
. Performance issues caused by multicast only happens in large L2
networks. If one's usage scenario is not a large L2 network,
one needs not be concerned.
. Reliability issues caused by multicast only happens in wireless
networks.
. On-link security issues caused by trusting all hosts are non-
issues if hosts can be trusted.
. Off-link attack and other issues caused by Router-NCE-on-Demand
will not happen if one already deployed an optimized ND
solution such as [RFC8273] or [DHCP-PD].
When the above issues can happen, it is advisable to be aware of the
solutions available for them, as described in the next section.
3. Review of ND Solutions
This section reviews the ND optimization solutions developed over
the years so that network administrators can get an idea of what
solutions are available for which issues. The solutions are reviewed
in an order that helps to reveal a theme: isolating hosts can help
to prevent ND issues.
3.1. ND Solution in Mobile Broadband IPv6
Mobile Broadband IPv6 (MBBv6) is 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]. The solution key
points are:
. Putting every host, i.e. the mobile User Equipment (UE), in a
P2P link with the router, i.e. the mobile gateway. MBBv6 also
Xiao Expires September 3, 2024 [Page 9]
Internet-Draft nd-considerations March 2024
simplifies ND to take advantage of this P2P architecture. As a
result:
o All multicast is effectively turned into unicast
o The P2P links in MBB do not have link layer address.
Therefore, Router-NCE-on-Demand is not needed.
o Trusting-all-host is only relevant to the router. By
applying some filtering at the router, e.g. dropping RAs
from the host, even malicious hosts cannot cause security
harm.
. Assigning a unique /64 prefix to each host. Together with the
P2P link, this puts each host in a separate link and subnet.
. Maintaining (prefix, interface) binding at the router for
forwarding purpose.
Since all the three causes of ND issues are addressed, MBBv6 solves
all ND issues.
3.2. ND Solution in Fixed Broadband IPv6
FBBv6 is defined in "IPv6 in the context of TR-101" [TR177]. FBBv6
has two flavors:
. P2P: every host, i.e. the Residential Gateway (RG), is in a P2P
link with the router, i.e. the Broadband Network Gateway (BNG).
In this case, the solution is essentially the same as MBBv6.
All ND issues are solved.
. P2MP: all hosts on an access device, e.g. the Optical Line
Terminal (OLT), are in a P2MP link with the router. This is
implemented by aggregating all hosts into a single VLAN at the
router and implementing Split Horizon at the access device to
prevent direct host communication.
The solution key points of FBBv6-P2MP [TR177] are:
. Putting all hosts in a P2MP link with the router, and
implementing DAD Proxy. P2MP architecture with Split Horizon
breaks normal ND's DAD procedure. Because all hosts are in the
same interface from the router's perspective, the router must
ensure that the hosts have different LLAs and GUAs. Otherwise,
the router will not be able to distinguish them. But because
hosts cannot reach each other, normal DAD will not work.
Therefore, the router must participate in the hosts' DAD
process and help hosts resolve duplication. This is called DAD
Proxy [RFC6957]. With P2MP link and DAD Proxy:
o All host multicast to the router is effectively turned into
unicast, as every host can only reach the router.
Xiao Expires September 3, 2024 [Page 10]
Internet-Draft nd-considerations March 2024
o Trusting-all-host is only relevant to the router. By
applying some simple filtering at the router, e.g.
dropping RAs from the host, even malicious hosts cannot
cause security harm.
. Assigning a unique /64 prefix to each host. As a result:
o When a prefix is assigned to the host, the router can
proactively create (IP prefix, MAC) binding and use it for
forwarding. There is no Router-NCE-on-Demand.
o Since different hosts are in different subnets, hosts will
send traffic to other hosts via the router. There is no
address resolution for other hosts.
o Without address resolution, router multicast to hosts
consists only of unsolicited RAs. Because every host is in
its own subnet, unsolicited RAs will be sent individually
to each host with the "host's MAC replacing the multicast
MAC" approach specified in [RFC6085]. Therefore, router
multicast is turned into unicast.
Since all the three causes of ND issues are addressed, FBBv6-P2MP
addresses all ND issues.
3.3. Unique IPv6 Prefix per Host
Unique IPv6 Prefix per Host is specified in [RFC8273]. The purpose
is to "improve host isolation and enhanced subscriber management on
shared network segments" such as Wi-Fi or Ethernet. The solution key
points are:
. Assigning a unique prefix to each host with SLAAC. As a result:
o When a prefix is assigned to the host, the router can
proactively create (Prefix, MAC) binding and use it for
forwarding. There is no more Router-NCE-on-Demand.
o 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.
o Without address resolution, downstream multicast to hosts
consists only of unsolicited RAs. They will be sent host
by host in unicast because the prefix for every host is
different.
Therefore, ND issues caused by NCE-on-Demand and router multicast
are avoided.
RFC 8273 believes 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 this may not be true
Xiao Expires September 3, 2024 [Page 11]
Internet-Draft nd-considerations March 2024
when hosts are on a shared medium like Ethernet. In this case, hosts
may still reach each other in L2 with their LLAs via upstream
multicast. So, issues caused by host multicast and Trusting-all-
hosts may happen.
3.4. Wireless ND and Subnet ND
Wireless ND (WiND) is specified in a series of RFCs
[RFC6775][RFC8505][RFC8928][RFC8929]. WiND 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 solution 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 Neighbor Cache Entries
(NCEs) for the hosts. This avoids the need for address
resolution for the hosts.
. The router sets PIO L-bit to 0. Each host communicates only
with the router.
. Other functionalities that are relevant only to LLNs.
WiND addresses all ND issues in LLNs. If it is used outside LLNs, it
avoids ND issues caused by NCE-on-Demand and router multicast.
Subnet Neighbor Discovery [SND] generalizes the solutions defined in
WiND and defines a new protocol named Subnet Gateway Protocol (SGP).
It is being discussed in the IPv6 Maintenance (6man) WG.
3.5. Scalable Address Resolution Protocol
Scalable Address Resolution Protocol (SARP) is an Experimental
solution specified in [RFC7586]. The usage scenario is Data Centers
(DCs) where large L2 domains spanned 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) 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. This way,
all hosts in a site will appear to have a single MAC to other sites.
Therefore, a switch only needs to build a MAC table for the local
hosts and the remote switches, not for all the hosts in the L2
Xiao Expires September 3, 2024 [Page 12]
Internet-Draft nd-considerations March 2024
domain. The MAC table size of the switches is therefore
significantly reduced. A switch will also add the (IP, MAC) replies
from remote switches to its proxy ND table so that it can reply to
future address resolution requests for such IPs directly. This
greatly reduces the number of address resolution multicast in the
network.
Unlike MBBv6, FBBv6 and RFC 8372 which try to address all ND issues,
SARP focuses on reducing address resolution multicast to improve
performance and scalability of large L2 domains in DCs.
3.6. ARP and ND Optimization for Transparent Interconnection of Lots of
Links (TRILL):
ARP and ND Optimization for TRILL is specified in [RFC8302]. The
solution is very similar to SARP discussed in Section 3.5. It can
be considered as an application of SARP in the TRILL environment.
Like SARP, ARP and ND Optimization for TRILL focuses on reducing
address resolution multicast.
3.7. Proxy ARP/ND in EVPN
Proxy ARP/ND in EVPN is specified in [RFC9161]. The usage scenario
is Data Centers (DCs) where large L2 domains spanned across multiple
sites. In each site, multiple hosts are connected to a Provider Edge
(PE) router acting as a switch. The PEs are interconnected by an
overlay network.
PE of each site snoops the local address resolution NAs to build
(IP, MAC) Proxy ND table entries. PEs then propagate such Proxy ND
entries to other PEs via BGP EVPN. Each PE also snoops address
resolution NSs from its hosts. If an entry exists in its Proxy ND
table for the specified destination IP address, 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. Gratuitous Neighbor Discovery
Gratuitous Neighbor Discovery is specified in [GRAND]. GRAND changes
ND in the following ways:
Xiao Expires September 3, 2024 [Page 13]
Internet-Draft nd-considerations March 2024
. A node sends unsolicited NAs upon assigning a new IPv6 address
to its interface.
. A router creates a new NCE for the host and set its state to
STALE.
Later, when the router receives traffic to the host, the existence
of the NCE entry in STALE state will cause the router to send
unicast NS to the host to verify its reachability rather than
sending multicast NS to resolve its MAC. This can shorten the time
the host's NCE entry reaches REACHABLE state and improve forwarding
performance. Therefore, GRAND provides an improvement but does not
fully solve the Router-NCE-on-Demand issues. For example, NCE
exhaustion can still happen.
3.9. Reducing Router Advertisements
[RFC7772] specifies a solution for reducing RAs. The key points are:
. The router should respond to RS with unicast RA if the host's
source IP address is not unspecified (i.e. the RS is not the
first RS before GUA DAD) and the host's MAC is valid.
. The router should reduce multicast RA frequency.
. Sleeping hosts that process unicast packets while asleep must
also process multicast RAs while asleep.
. Sleeping hosts that do not intend to maintain IPv6 connectivity
while asleep should either disconnect from the network and
clear all IPv6 configuration, or perform Detecting Network
Attachment in IPv6 (DNAv6) procedures [RFC6059] when waking up.
By reducing RAs, RFC 7772 reduces energy consumption of battery-
powered hosts that can be waken up by RAs.
3.10. Source Address Validation Improvement and Router Advertisement
Guard
Source Address Validation Improvement is specified in [SAVI]. Router
Advertisement Guard is specified in [RA-Guard][RA-Guard+]. SAVI
binds an address to a port and rejects claims from other ports for
that address. Therefore, a node cannot spoof the IP address of
another node. RA-Guard and RA-Guard+ only allow RAs from a port
that a router is connected to. Therefore, nodes on other ports
cannot pretend to be a router.
SAVI, RA-Guard and RA-Guard+ address the on-link security issues.
Xiao Expires September 3, 2024 [Page 14]
Internet-Draft nd-considerations March 2024
3.11. Dealing with Off-link Attack that May Cause Router NCE Exhaustion
Router NCE Exhaustion handling is described in [RFC6583]. This is to
deal with the off-link attack issue discussed in Section 2.3. The
solution key points are:
. For operators:
o Filtering of unused address space so that messages to such
addresses can be dropped rather than triggering NCE
creation;
o Minimizing subnet size so that there are fewer potential
NCEs to create;
o Rate-limiting the NDP queue to avoid CPU/memory overflow.
. For vendors:
o Prioritizing NDP processing for existing NCEs over creating
new NCEs
RFC 6583 acknowledges that "some of these options are 'kludges',
and can be operationally difficult to manage". RFC 6583 partially
addresses the Router NCE Exhaustion issue.
3.12. Enhanced DAD
Enhanced DAD is specified in [RFC7527]. Enhanced DAD addresses a DAD
failure issue in a specific situation: 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 (defined in [SeND]) 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 of the ND issues discussed in
Section 2. It extends ND to work in a new scenario: looped back
interface. It is reviewed here for completeness but will not be
further discussed.
3.13. ND Mediation for IP Interworking of Layer 2 VPNs
ND mediation is specified in [RFC6575]. When two Attachment Circuits
(ACs) are interconnected by a Virtual Private Wired Service (VPWS),
and the two ACs are of different medium (e.g. one is Ethernet while
the other is Frame Relay), the two Provider Edges (PEs) must
interwork to provide mediation service so that a Customer Edge (CE)
can resolve the link layer address of the remote end. RFC 6575
specifies such a solution.
Xiao Expires September 3, 2024 [Page 15]
Internet-Draft nd-considerations March 2024
ND Mediation does not address any of the ND issues discussed in
Section 2. It extends ND to work in a new scenario: two ACs of
different media interconnected by a VPWS. It is reviewed here for
completeness but will not be further discussed.
3.14. ND Solutions Defined before the Latest Versions of ND
The latest versions of [ND] and [SLAAC] are specified in RFCs 4861
and 4862. Several ND optimization solutions are based on the older
version of ND and SLAAC. They are reviewed in this section for
completeness but will not be further discussed.
3.14.1. SeND
Secure Neighbor Discovery [SeND] is specified in RFC 3971. The
purpose is to ensure that hosts and routers are trustable. SeND
defined three new ND options (i.e. Cryptographically Generated
Addresses [CGA], RSA public-key cryptosystem, Timestamp/Nonce), an
authorization delegation discovery process, an address ownership
proof mechanism, and requirements for the use of these components in
NDP.
SeND addresses the Trusting-all-hosts issues. But it has high
requirements on the hosts and routers, especially to maintain the
keys. SeND is rarely deployed and will not be further discussed.
3.14.2. Cryptographically Generated Addresses (CGA)
Cryptographically Generated Addresses [CGA] is specified in RFC
3972. The purpose is to associate a cryptographic public key with an
IPv6 address in [SeND]. The solution key point is to generate the
Interface Identifier (IID) of the 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 uses the fact that a legitimate host does not care about the bit
combination of IID that would be created as a result of 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 that is a strong mathematical challenge.
CGA is part of SeND. It is rarely deployed and will not be further
discussed.
Xiao Expires September 3, 2024 [Page 16]
Internet-Draft nd-considerations March 2024
3.14.3. ND Proxy
ND Proxy is specified in [RFC4389]. It is an Experimental solution.
The purpose is to enable multiple links joined by an ND-Proxy device
to work as a single link. The ND-Proxy acts like a bridge. The
solution key points are:
. When it receives an ND request from a host in a link, it will
"proxy" the message out from the "best" outgoing interface. How
to determine the "best" interface is explained later. 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 to
the ND-Proxy's outgoing interface's IP and MAC, 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 to 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
future ND requests. The ND-Proxy then "proxy" the ND message
back to the requesting host.
ND Proxy does not solve any of the ND issues discussed in Section 2.
It extends ND to work in a new scenario: multiple links joined by a
device that is not a bridge but acting like a bridge.
The idea of ND Proxy is widely used in SARP, ND Optimization for
TRILL and Proxy ARP/ND in EVPN which are discussed in Sections 3.4
to 3.6.
3.14.4. Optimistic DAD
Optimistic DAD is specified in [RFC4429]. The purpose is 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 actually completes, assuming that DAD will
succeed anyway. If the address turns out to be a duplicate,
Optimistic DAD provides a set of mechanisms to minimize the impact.
Optimistic DAD modified the original ND (RFC 2461) and SLAAC (RFC
2462) but the solution was not incorporated into the latest
specification of [ND] and [SLAAC].
Optimistic DAD does not solve any of the ND issues discussed in
Section 2. It is reviewed here for completeness.
Xiao Expires September 3, 2024 [Page 17]
Internet-Draft nd-considerations March 2024
3.15. Observations on the Solutions
Which ND solution solving which ND issue is tabulated below, for the
fifteen issues summarized in Section 2.4:
. Performance issues caused by multicast
o I1: LLA DAD multicast degrading performance
o I2: Unsolicited RA multicast draining hosts' battery
o I3: GUA/ULA DAD multicast degrading performance
o I4: Router address resolution multicast degrading
performance
o I5: Host Address resolution multicast degrading performance
. Reliability issues caused by multicast
o I6: LLA DAD not reliable for wireless networks
o I7: GUA/ULA DAD not reliable for wireless networks
. On-link security issues caused by trusting all hosts
o I8: Source IP address spoofing
o I9: DAD denial
o I10: Fake RAs
o I11: Fake Redirect
o I12: Replay attacks
. Off-link attack and other issues caused by Router-NCE-on-Demand
o I13: Router NCE exhaustion
o I14: Router forwarding delay
o I15: Lack of subscriber management with SLAAC
+-----+-------------------+--------+--------+--------+------+-----+
| | Multicast | Reli- |On-link |R NCE |R Fwd.|Sub |
| | performance | ability|security|Exhaust.|Delay |Mgmt.|
+-----+---+---+---+---+---+---+----+--------+--------+------+-----+
|Issue| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8-12 | 13 | 14 | 15 |
+-----+---+---+---+---+---+---+----+--------+--------+------+-----+
|MBBv6| All issues solved |
+-----+---+---+---+---+---+---+----+--------+--------+------+-----+
|FBBv6| All issues solved |
+-----+---+---+---+---+---+---+----+--------+--------+------+-----+
Xiao Expires September 3, 2024 [Page 18]
Internet-Draft nd-considerations March 2024
|8273 | | X | X | X | X | | X | | X | X | X |
+-----+---+---+---+---+---+---+----+--------+--------+------+-----+
|WiND | All issues solved for LLNs |
+-----+---+---+---+---+---+---+----+--------+--------+------+-----+
|SARP | | | | | X | | | | | | |
+-----+---+---+---+---+---+---+----+--------+--------+------+-----+
|ND | | | | | X | | | | | | |
|TRILL| | | | | | | | | | | |
+-----+---+---+---+---+---+---+----+--------+--------+------+-----+
|ND | | | | | X | | | | | | |
|EVPN | | | | | | | | | | | |
+-----+---+---+---+---+---+---+----+--------+--------+------+-----+
|7772 | | X | | | | | | | | | |
+-----+---+---+---+---+---+---+----+--------+--------+------+-----+
|GRAND| | | | X | | | | | |Partly| |
+-----+---+---+---+---+---+---+----+--------+--------+------+-----+
|SAVI/| | | | | | | | | | | |
|RAG | | | | | | | | X | | | |
|G+ | | | | | | | | | | | |
+-----+---+---+---+---+---+---+----+--------+--------+------+-----+
|6583 | | | | | | | | | X | | |
+-----+---+---+---+---+---+---+----+--------+--------+------+-----+
Table 1. Which solution solves which issue(s)
Xiao Expires September 3, 2024 [Page 19]
Internet-Draft nd-considerations March 2024
Although the various ND solutions look unrelated, dividing them into
three groups will help to reveal a theme: isolating hosts can
prevent issues.
The first group contains MBBv6, FBBv6, and Unique Prefix Per Host.
These solutions isolate hosts in L3 and possibly L2, and they
prevent all or most ND issues.
The second group contains WiND, SARP, ND Optimization for TRILL, and
Proxy ND in EVPN. They use a proxy device to represent the hosts
behind it, and effectively isolate such hosts into different
multicast/broadcast domains from other hosts. These solutions
alleviate address resolution and in the case of WiND other issues.
The third group contains the remaining solutions. They do not try to
isolate hosts. They focus on solving a specific ND issue.
This theme reveals that, the stronger hosts are isolated, the more
ND issues can be prevented. This is natural because isolating hosts
reduces multicast and hosts to trust, two of the causes of ND
issues.
This understanding can be used to formulate guidelines to prevent ND
issues and simplify IPv6 first-hops where ND plays a key role.
4. Selectively Isolating Hosts to Prevent Potential ND Issues and
Simplify IPv6 First-hops
This section describes how to isolate hosts, and the advantages and
disadvantages of doing so. It also provides guidelines on how to
select a suitable isolation method based on the deployment scenario.
The solution review in Section 3 reveals four different host
isolation mechanisms:
. L3/Subnet isolation (i.e. Unique Prefix Per Host), used in
MBBv6, FBBv6 and RFC 8273.
. L2/Link isolation, with two flavors:
o P2P link isolation, used in MBBv6 and FBBv6-PPPoE;
o P2MP link isolation, used in FBBv6-IPoE.
. Proxy isolation, used in WiND/SND, SARP, ND Optimization for
TRILL, Proxy ND in EVPN. This effectively divides a subnet into
multiple multicast domains and can be considered as a L2 host
isolation method.
. GUA isolation (i.e. setting PIO L-bit=0), which is a native ND
mechanism used in many solutions.
Xiao Expires September 3, 2024 [Page 20]
Internet-Draft nd-considerations March 2024
o GUA isolation is different from link isolation in that
there can be multiple hosts in the link. It is just that
each host treats other hosts as off-link and does not
perform address resolution for other hosts' GUA. The host
will send messages with GUA via the router instead. But
all messages with LLA can still reach other hosts in the
same broadcast domain. In link isolation, there is only
one host in each link. A host cannot send messages with
LLAs to other hosts.
These isolation mechanisms are not completely independent:
First, [RFC4291] stated that "IPv6 continues the IPv4 model in that
a subnet prefix is associated with one link". Therefore, link
isolation and subnet isolation are better used together, otherwise,
some ND issues may appear:
. L2 isolation without subnet isolation, which creates a Multi-
Link SubNet (MLSN), can cause GUA DAD not to work unless the
router provides DAD Proxy [RFC6957] or address registration and
arbitration [SND]. [RFC4903] documented the concerns about
MLSN.
. Subnet isolation without L2 isolation, when used for multiple
hosts on a shared medium, can have on-link security issues if
the hosts cannot be trusted. For example, LLA DAD denial may
happen if attacker hosts exist.
However, link isolation depends on the physical media and may not
always be possible, while subnet isolation requires a prefix for
each host and may not always be possible either. Therefore,
solutions using subnet isolation or link isolation separately exist.
Second, Proxy Isolation divides hosts in the same subnet into
different broadcast domains. Hosts are isolated in different groups
but not necessarily individually. This is effectively "L2 (Group)
Isolation without L3 Isolation".
Third, GUA isolation is only meaningful for hosts in the same subnet
and broadcast domain. Otherwise, setting PIO L-bit to 0 or 1 makes
no difference.
Therefore, these different isolation mechanisms produce six
meaningful combinations:
. Subnet Isolation with P2P Link
. Subnet Isolation with P2MP Link
Xiao Expires September 3, 2024 [Page 21]
Internet-Draft nd-considerations March 2024
. Subnet Isolation with Shared Medium. A shared medium is a
broadcast domain. So, this is "Subnet Isolation without L2
Isolation"
. Proxy Isolation, i.e. "L2 Isolation without Subnet Isolation"
. GUA Isolation, i.e. "No L2 or L3 Isolation but GUA Isolation"
. No isolation whatsoever
There is a logic in arranging the six isolation methods this way:
the first three are L3 isolation with decreasing degree of L2
isolation, i.e. from P2P Link to P2MP Link to Shared Medium. The
fourth is "L2 isolation without L3 isolation". Here the L2-isolated
entity is usually a group of hosts but it can also be a single host.
The fifth isolates hosts in the same subnet and broadcast domain
from a GUA perspective. The sixth is no isolation at all. They go
from the strongest degree to the weakest degree, and cover all
possible isolation scenarios.
Their applicability is discussed below.
4.1. Applicability of Subnet Isolation with P2P Link
The advantages are:
o All ND issues are prevented.
The disadvantages are:
o The hosts must be able to set up P2P links with the router.
o Many prefixes will be needed, one per host.
o This is unlikely to be an issue for IPv6. Today, any member
of a Regional Internet Registry (RIR) can get a /29
[RIPE738]. This contains 32 billion /64 prefixes and should
be sufficient for any scenarios. The fact that MBBv6 assigns
a /64 to billions of mobile UEs [RFC6459], and FBBv6 assigns
a /56 to millions of routed RGs [TR177] is evidence.
o Each host is easily identifiable by its unique prefix. This
reduces privacy.
o The router must support a "Subnet Isolation with P2P Link"
solution, e.g. MBBv6.
o Many interfaces will be needed at the router, one per host.
Xiao Expires September 3, 2024 [Page 22]
Internet-Draft nd-considerations March 2024
o All hosts will communicate through the router, and the router may
become a bottleneck.
o Services relying on multicast communication among hosts, e.g.
mDNS, will not work.
4.2. Applicability of Subnet Isolation with P2MP Link
The advantages and disadvantages of Subnet Isolation with P2MP Link
are same as the P2P method, except that:
o Hosts do not need the capability to set up P2P links with the
router. The L2 medium must support P2MP Link, e.g. with [PVLAN]
or Wireless Isolation [W-Iso].
o The router must support a "Subnet Isolation with P2MP Link"
solution, including DAD Proxy.
o Only one interface is needed at the router
4.3. Applicability of Subnet Isolation with Shared Medium
The advantages are:
o All ND issues are prevented except "LLA DAD multicast degrading
performance", "LLA DAD not reliable for wireless networks", and
"On-link security" issues. Depending on the shared medium, these
remaining issues may not actually happen. For example, if the
shared medium is Ethernet, "LLA DAD multicast degrading
performance" and "LLA DAD not reliable for wireless networks" are
non-issues. If the hosts can be trusted, e.g. in a private
network, "On-link security" is also a non-issue.
o There is no new requirement on the hosts. Therefore, this method
can be applied in many scenarios. It is likely the most usable
host isolation method.
The disadvantages are:
o Many prefixes will be needed, one per host. But as explained
above, this may not be an issue for organizations that can obtain
sufficient IPv6 addresses from RIRs.
o The router must support a Subnet Isolation solution, e.g.
[RFC8273] or [DHCP-PD].
Xiao Expires September 3, 2024 [Page 23]
Internet-Draft nd-considerations March 2024
o All host-to-host communication with GUA will go through the
router, and the router may become a bottleneck.
o Each host is identifiable by its unique prefix. This can be a
privacy issue.
4.4. Applicability of Proxy Isolation
The advantages of Proxy Isolation are:
o Reduced multicast especially for address resolution, as the
subnet is divided into multiple multicast domains.
o For solutions that proactively install NCEs on the router, e.g.
WiND, all Router-NCE-On-Demand issues are prevented.
The disadvantages are:
o The router must support Proxy Isolation.
o Except WiND, other Proxy Isolation solutions are mainly to reduce
address resolution. Other multicast, Trusting-all-hosts and
Router-NCE-on-Demand issues will remain.
4.5. Applicability of GUA Isolation
The advantages of GUA Isolation are:
o No address resolution for GUA among hosts.
o This is normal ND behavior. No additional ND optimization
solution is needed.
The disadvantages are:
o Only multicast address resolution for GUA among hosts is
eliminated. All other ND issues may still happen.
o All host communication with GUA will go through the router, and
the router may become a bottleneck.
4.6. Guidelines for Selecting a Host Isolation Method
Given the applicability analysis above, network administrators can
decide where to apply which isolation method.
Xiao Expires September 3, 2024 [Page 24]
Internet-Draft nd-considerations March 2024
The guidelines below start from the strongest isolation method. This
prevents the largest number of ND issues, and therefore, requires
fewest additional solutions for the remaining issues. But the
strongest isolation also has the highest entry requirements and the
fewest applicable scenarios. If the strongest isolation is not
possible, the next level of isolation is probed, all the way to no
isolation at the end. Therefore, network administrators can likely
find the most suitable isolation method for their deployment
scenarios.
It is worth noting that, if a network administrator picks an
isolation method that is too strong or too weak, there is no serious
consequence. Picking a too-strong isolation method means that the
network administrator needs to do more work in meeting the higher
entry requirement, while picking a too-weak isolation method means
that the network administrator may need to deploy more ND
optimization solutions to deal with potential issues. Either way,
the overall solution can still work.
1. If Subnet Isolation with P2P Link is feasible:
a) Applicable scenarios:
1) The medium is P2P.
2) Direct host to host communication without going through
the router is not needed.
3) Multicast is not desirable (implying mDNS is not
needed).
4) Hosts may not be trustable.
5) Subscriber management is needed.
6) Privacy of hosts are not a major concern.
Examples are public access networks such as MBBv6 or FBBv6
with PPPoE.
b) Entry requirements:
1) Hosts must be able to set up P2P links with the router.
2) There are sufficient IPv6 addresses to provide Unique
Prefix Per Host.
Xiao Expires September 3, 2024 [Page 25]
Internet-Draft nd-considerations March 2024
3) The router must support a "Subnet Isolation with P2P
Link" solution, e.g. MBBv6.
c) Remaining ND issues and solutions:
1) None.
2. Otherwise, if Subnet Isolation with P2MP Link is feasible
a) Applicable scenarios:
1) Same as the P2P scenarios except that the medium is
P2MP.
Examples are FBBv6 with IPoE or public Wi-Fi access.
b) Entry requirements:
1) There are sufficient IPv6 addresses to provide Unique
Prefix Per Host.
2) The router must support a "Subnet Isolation with P2MP
Link" solution, including DAD Proxy, e.g. FBBv6-P2MP.
c) Remaining ND issues and solutions
1) None
3. Otherwise, if Subnet Isolation with Shared Medium is feasible
a) Applicable scenarios:
1) The medium is a shared medium.
2) Direct host to host communication is not needed.
3) Privacy of hosts is not a major concern.
b) Entry requirements:
1) There are sufficient IPv6 addresses to provide Unique
Prefix Per Host.
2) The router must support Unique Prefix Per Host, e.g.
[RFC8273] or [DHCP-PD].
Xiao Expires September 3, 2024 [Page 26]
Internet-Draft nd-considerations March 2024
c) Remaining ND issues and solutions
1) "LLA DAD multicast degrading performance", "LLA DAD not
reliable for wireless networks", and "On-link security"
issues can theoretically happen. Depending on the shared
medium, these remaining issues may not actually happen.
For example, if the shared medium is Ethernet, "LLA DAD
multicast degrading performance" and "LLA DAD not
reliable for wireless networks" are non-issues. If the
link is not a public access link, "On-link security" may
also be non-issues. It is advisable to use this method
where these remain issues are not a big concern. If they
are a concern, Subnet Isolation with P2P or P2MP Link
may be more suitable.
4. Otherwise, if Proxy Isolation is feasible
a) Applicable scenarios:
1) The hosts are in a subnet, but it is possible to
separate them into different broadcast/multicast
domains, e.g. in a multi-link subnet, or a large DC
involving a large number of VMs spanning across multiple
sites interconnected by PEs supporting SARP.
b) Entry requirements:
1) The PEs must support a Proxy Isolation solution like
WiND, SARP, or Proxy ND in EVPN.
c) Remaining ND issues and solutions:
1) WiND/SND solves all ND issues but they are fundamentally
different ND solutions that require both router and host
changes. Other proxy isolation solutions only reduce
multicast address resolution for GUA among hosts while
other ND issues may happen. Depending on the deployment
scenarios, solutions in Table 1 can be selected for the
issues that will actually happen.
5. If there are still multiple hosts in a same subnet and broadcast
domain, if GUA Isolation (i.e. setting PIO L-bit=0) is feasible
a) Applicable scenarios:
Xiao Expires September 3, 2024 [Page 27]
Internet-Draft nd-considerations March 2024
1) It is desirable to avoid host address resolution for
other hosts in the same broadcast domain.
b) Entry requirements:
1) None as this is a native ND mechanism.
c) Remaining ND issues and solutions:
1) Only multicast GUA address resolution is eliminated. All
other ND issues may happen. Depending on the deployment
scenarios, solutions in Table 1 can be selected for the
issues that will actually happen.
6. Otherwise, no isolation to apply
a) Applicable scenarios:
1) ND issues are not a concern. That is, multicast is not a
problem, hosts can be trusted, and Router-NCE-on-demand
is not an issue.
2) Some ND issues are a concern, but it is preferable to
deploy the corresponding ND optimization solutions than
to isolate hosts.
b) Entry requirements:
1) None.
c) Remaining issues and solutions
1) All ND issues can happen theoretically. Depending on
what are of concern practically, the corresponding ND
optimization solutions tabulated in Table 1 can be
applied.
4.7. Impact of Host Isolation on Other Protocols in IPv6 First-hops
The impact (i.e. the disadvantages) of various isolation methods to
the IPv6 first-hop has been discussed in the applicability sections.
The guidelines have taken such applicability into consideration and
given network administrators the option not to apply any isolation.
Therefore, if an isolation method is indeed selected, its advantages
likely outweigh its disadvantages.
Xiao Expires September 3, 2024 [Page 28]
Internet-Draft nd-considerations March 2024
5. Security Considerations
This document provides guidelines on how to select a suitable
isolation method depending on the deployment scenarios. When an
isolation method is selected, the security considerations of the
used solutions which are defined in the corresponding RFCs apply.
These security considerations are discussed in Section 4. In
particular, using Unique Prefix Per Host makes a host identifiable
by the prefix and reduces privacy. It is incompatible with using
temporary addresses to increase privacy [RFC8981]. This document
itself 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. Informative References
[CGA] T. Aura, "Cryptographically Generated Addresses (CGA)",
RFC3972
[DHCP-PD] L. Colitti, J. Linkova, X. Ma, "Using DHCP-PD to
Allocate Unique IPv6 Prefix per Host in Broadcast
Networks", draft-ietf-v6ops-dhcp-pd-per-device-07.
[GRAND] J. Linkova, "Gratuitous Neighbor Discovery: Creating
Neighbor Cache Entries on First-Hop Routers", RFC 9131
[mDNS] S. Cheshire, M. Krochmal, "Multicast DNS", RFC 6762.
[ND] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007, RFC 4861.
[PVLAN] https://en.wikipedia.org/wiki/Private_VLAN
[RA-Guard]E. Levy-Abegnoli, G. Van de Velde, C. Popoviciu, J.
Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105, DOI
10.17487/RFC6105, February 2011, RFC 6105.
[RA-Guard+] F. Gont, "Implementation Advice for IPv6 Router
Advertisement Guard (RA-Guard)", RFC 7113, DOI
10.17487/RFC7113, February 2014, RFC 7113.
Xiao Expires September 3, 2024 [Page 29]
Internet-Draft nd-considerations March 2024
[RFC3756] P. Nikander, J. Kempf, E. Nordmark, "IPv6 Neighbor
Discovery (ND) Trust Models and Threats", RFC 3756.
[RFC4291] R. Hinden, S.Deering, "IP Version 6 Addressing
Architecture", RFC 4291.
[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.
[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.
[RFC6059] S. Krishnan, G. Daley, "Simple Procedures for Detecting
Network Attachment in IPv6", RFC 6059.
[RFC6085] S. Gundavelli, M. Townsley, O. Troan, W. Dec, "Address
Mapping of IPv6 Multicast Packets on Ethernet", RFC 6085.
[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.
[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
[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.
Xiao Expires September 3, 2024 [Page 30]
Internet-Draft nd-considerations March 2024
[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.
[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.
[RFC8981] F. Gont, S.Krishnan, T.Narten, R. Draves, "Temporary
Address Extensions for Stateless Address Autoconfiguration
in IPv6", RFC 8981.
[RFC9099] E. Vyncke, K. Chittimaneni, M. Kaeo, E. Rey, "Operational
Security Considerations for IPv6 Networks", RFC 9099.
Xiao Expires September 3, 2024 [Page 31]
Internet-Draft nd-considerations March 2024
[RFC9119] C. Perkins, M. McBride, D. Stanley, W. Kumari, JC. Zuniga,
"Multicast Considerations over IEEE 802 Wireless Media",
RFC 9119.
[RFC9161] J. Rabadan, S. Sathappan, K. Nagaraj, G. Hankins, T. King,
"Operational Aspects of Proxy ARP/ND in Ethernet Virtual
Private Networks", RFC 9161.
[RIPE738] IPv6 Address Allocation and Assignment Policy,
https://www.ripe.net/publications/docs/ripe-738
[SAVI] J. Wu, J. Bi, M. Bagnulo, F. Baker, C. Vogt, "Source
Address Validation Improvement (SAVI) Framework", RFC
7039.
[SeND] J. Arkko, J. Kempf, B. Zill, P. Nikander, "SEcure Neighbor
Discovery (SEND)", RFC3971.
[SLAAC] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862.
[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.
[W-Iso] Wireless Isolation, https://www.quora.com/What-is-
wireless-isolation
8. Acknowledgments
The authors would like to thank Lorenzo Colitti, Pascal Thubert, Jen
Linkova, Brian Carpenter, Mike Ackermann, Nalini Elkins, Ed Horley,
Ole Troan, David Thaler, Eric Vyncke for their reviews and comments.
Xiao Expires September 3, 2024 [Page 32]
Internet-Draft nd-considerations March 2024
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.
Maanplein 55, 2516CK The Hague, The Netherlands
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 September 3, 2024 [Page 33]
