6lo P. Thubert, Ed.
Internet-Draft cisco
Intended status: Standards Track C. Perkins
Expires: April 25, 2019 Futurewei
October 22, 2018
IPv6 Backbone Router
draft-ietf-6lo-backbone-router-08
Abstract
Backbone Routers running IPv6 Neighbor Discovery can manage multiple
wireless links to form a large MultiLink Subnet, but it is more
efficient if IPv6 Neighbor Discovery packets are not broadcast over
the wireless links. This specification specifies proxy operations
for IPv6 Neighbor Discovery on behalf of devices located on
broadcast-inefficient wireless networks. Backbone Routers placed
along the wireless edge of the backbone handle IPv6 Neighbor
Discovery, and route packets on behalf of registered nodes. Wireless
nodes register, or are registered by proxy, to a Backbone Router to
establish proxy services in a fashion similar to layer-2 association.
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 at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 25, 2019.
Copyright Notice
Copyright (c) 2018 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
(https://trustee.ietf.org/license-info) in effect on the date of
Thubert & Perkins Expires April 25, 2019 [Page 1]
Internet-Draft IPv6 Backbone Router October 2018
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 . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Applicability and Requirements Served . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Backbone Router Routing Operations . . . . . . . . . . . . . 8
5.1. Over the Backbone Link . . . . . . . . . . . . . . . . . 8
5.2. Proxy Operations Over the LLN Interface . . . . . . . . . 9
5.2.1. Routing Proxy Operations . . . . . . . . . . . . . . 10
5.2.2. Bridging Proxy Operations . . . . . . . . . . . . . . 10
6. Backbone Router Proxy Operations . . . . . . . . . . . . . . 11
6.1. Primary and Secondary BBRs . . . . . . . . . . . . . . . 12
6.2. Binding Table . . . . . . . . . . . . . . . . . . . . . . 12
6.3. Registration and Binding Table Entry Creation . . . . . . 13
6.4. Defending Addresses . . . . . . . . . . . . . . . . . . . 14
7. Security Considerations . . . . . . . . . . . . . . . . . . . 15
8. Protocol Constants . . . . . . . . . . . . . . . . . . . . . 16
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
10. Future Work . . . . . . . . . . . . . . . . . . . . . . . . . 16
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
12.1. Normative References . . . . . . . . . . . . . . . . . . 16
12.2. Informative References . . . . . . . . . . . . . . . . . 17
12.3. External Informative References . . . . . . . . . . . . 19
Appendix A. Changes from revision 07 to revision 08 . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction
IEEE STD. 802.1 [IEEEstd8021] Ethernet Bridging provides an efficient
and reliable broadcast service; applications and protocols have been
built that heavily depend on that feature for their core operation.
Unfortunately, many wireless networks do not economically provide the
broadcast capabilities of Ethernet Bridging; protocols designed for
bridged networks that rely on broadcast often exhibit disappointing
behaviours when applied unmodified to a wireless medium (see
[I-D.ietf-mboned-ieee802-mcast-problems]).
WiFi [IEEEstd80211] Access Points (APs) deployed in an Extended
Service Set (ESS) act as bridges. In order to ensure a solid
Thubert & Perkins Expires April 25, 2019 [Page 2]
Internet-Draft IPv6 Backbone Router October 2018
connectivity to the devices and protect the medium against harmful
broadcasts, they refrain from relying on broadcast-intensive
protocols such as Transparent Bridging on the wireless side.
Instead, an association process is used to register the MAC addresses
of the wireless device (STA) to the AP. The APs subsequently proxy
the bridging operation and eliminate the broadcasts.
The IPv6 [RFC8200] Neighbor Discovery [RFC4861] [RFC4862] Protocol
(IPv6 ND) operations are reactive and rely heavily on multicast
transmissions to locate an on-link correspondent and ensure address
uniqueness. Duplicate Address Detection [RFC4862] (DAD) mechanism
was designed as a natural match with the efficient broadcast
operation of Ethernet Bridging. However, since broadcast can be
unreliable over wireless media, DAD often fails to discover
duplications [I-D.yourtchenko-6man-dad-issues]. DAD usually appears
to work on wireless media, not because address duplication is
detected and solved as designed, but because the use of 64-bit
Interface IDs makes duplication into a very rare event.
IPv6 multicast messages are typically broadcast over the wireless
medium. They are processed by most if not all wireless nodes over
the ESS fabric even when very few if any of them are subscribed to
the multicast address. A simple Neighbor Solicitation (NS)
[RFC4861], that is supposedly targeted to a small group of nodes, can
congest the wireless bandwidth
[I-D.ietf-mboned-ieee802-mcast-problems]. The IPv6 ND operation
leads to undesirable power consumption in battery-operated devices.
These problems suggest restricting IPv6 ND broadcasts over wireless
access links, which can be done by dividing up the subnet. Another
way is to take over (proxy) the Layer-3 protocols that rely on
broadcast operation at the boundary of the wired and wireless
domains, emulating the Layer-2 association at layer-3. For instance,
IEEE 802.11 [IEEEstd80211] specifies ARP and ND proxy [RFC4389]
services at the Access Points (APs).
Current devices rely on snooping for detecting association state,
which is failure-prone in lossy and mobile conditions. With
snooping, a state (e.g. a new IPv6 address) may not be discovered, or
a change of state (e.g. a movement) may be missed, leading to
unreliable connectivity.
WPAN devices (i.e., those implementing IEEE STD. 802.15.4
[IEEEstd802154]) can make use of Neighbor Discovery Optimization for
IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)
[RFC6775] which treats the wireless medium as different from
Ethernet. RFC 6775 is updated as [I-D.ietf-6lo-rfc6775-update]; the
update includes changes that are required by this document.
Thubert & Perkins Expires April 25, 2019 [Page 3]
Internet-Draft IPv6 Backbone Router October 2018
2. Applicability and Requirements Served
This specification updates and generalizes 6LoWPAN ND to a broader
range of Low power and Lossy Networks (LLNs) with support for
Duplicate Address Detection (DAD) and address lookup that does not
require broadcasts over the LLNs. The term LLN is used loosely in
this specification to cover multiple types of WLANs and WPANs,
including Low-Power Wi-Fi, BLUETOOTH(R) Low Energy, IEEE STD.
802.11AH and IEEE STD. 802.15.4 wireless meshes, so as to address the
requirements listed in Appendix B.3 of [I-D.ietf-6lo-rfc6775-update]
"Requirements Related to the Variety of Low-Power Link types".
For the TimeSlotted Channel Hopping (TSCH) mode of [IEEEstd802154],
the 6TiSCH architecture [I-D.ietf-6tisch-architecture] describes how
a 6LoWPAN ND host could connect to the Internet via a RPL mesh
Network, but doing so requires extensions to the 6LOWPAN ND protocol
to support mobility and reachability in a secure and manageable
environment. The extensions detailed in this document also work for
the 6TiSCH architecture, serving the requirements listed in
Appendix B.2 of [I-D.ietf-6lo-rfc6775-update] "Requirements Related
to Routing Protocols".
This specification also applies to wireless links such as Low-Power
IEEE STD. 802.11 (Wi-Fi) and IEEE STD. 802.15.1 (Bluetooth)
[IEEEstd802151]. It makes use of extensions to [RFC6775] to enable
proxy operation by the 6BBR, as specified in
[I-D.ietf-6lo-rfc6775-update]. The BBR proxy operations eliminate
the need for wireless nodes to respond synchronously when a lookup is
performed for their addresses. This provides the function of a Sleep
Proxy for ND [I-D.nordmark-6man-dad-approaches].
This draft establishes a Backbone that treats multiple LLNs as a
single IPv6 MultiLink Subnet. Each LLN in the subnet is anchored at
an IPv6 Backbone Router (6BBR). The Backbone Routers interconnect
the LLNs and advertise the addresses of the 6LNs using proxy-ND
operations. This specification extends IPv6 ND over the backbone to
distinguish address movement from duplication and eliminate stale
state in the backbone routers and backbone nodes once a 6LN has
roamed. In this way, mobile nodes may roam rapidly from one 6BBR to
the next and requirements in Appendix B.1 of
[I-D.ietf-6lo-rfc6775-update] "Requirements Related to Mobility" are
met.
This specification enables any 6LN to register its IPv6 addresses and
thereby obtain routing services including proxy-ND operations over
the backbone, providing a solution to the requirements expressed in
Appendix B.4 of [I-D.ietf-6lo-rfc6775-update] "Requirements Related
to Proxy Operations".
Thubert & Perkins Expires April 25, 2019 [Page 4]
Internet-Draft IPv6 Backbone Router October 2018
The Link Layer Address (LLA) that is returned as Target LLA (TLLA) in
Neighbor Advertisements (NA) messages by the 6BBR on behalf of the
Registered Node over the backbone may be that of the Registering
Node. In that case, the 6BBR needs to bridge the unicast packets
(Bridging proxy), or that of the 6BBR on the backbone, in which case
the 6BBRs needs to route the unicast packets (Routing proxy). The
IPv6 ND operation is minimized as the number of 6LNs grows in the
LLN. This meets the requirements in Appendix B.6 of
[I-D.ietf-6lo-rfc6775-update] "Requirements Related to Scalability",
as long has the 6BBRs are dimensioned for the number of registrations
that each needs to support.
In the case of Low-Power IEEE STD. 802.11, a 6BBR may be collocated
with a standalone AP or a CAPWAP [RFC5415] wireless controller. Then
the wireless client (STA) makes use of this specification to register
its IPv6 address(es) to the 6BBR over the wireless medium. In the
case RPL, the RPL root is collocated with a 6LoWPAN Border Router
(6LBR), and either collocated with or connected to the 6BBR over an
IPv6 Link. The 6LBR makes use of this specification to register the
6LNs on their behalf to the 6BBR.
3. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] .
In this document, readers will encounter terms and concepts that are
discussed in the following documents:
o "Neighbor Discovery for IP version 6" [RFC4861],
o "IPv6 Stateless Address Autoconfiguration" [RFC4862],
o "Multi-Link Subnet Issues" [RFC4903],
o "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals" [RFC4919],
o Neighbor Discovery Optimization for Low-power and Lossy Networks
[RFC6775],
o ,"Mobility Support in IPv6" [RFC6275],
o "Neighbor Discovery Proxies (ND Proxy)" [RFC4389]
o "Optimistic Duplicate Address Detection" [RFC4429], and
Thubert & Perkins Expires April 25, 2019 [Page 5]
Internet-Draft IPv6 Backbone Router October 2018
o "Registration Extensions for 6LoWPAN Neighbor Discovery"
[I-D.ietf-6lo-rfc6775-update]
This document also uses terminology from [RFC7102] and
[I-D.ietf-6lo-rfc6775-update], and introduces the following
terminology:
Sleeping Proxy
A 6BBR acts as a Sleeping Proxy if it answers ND Neighbor
Solicitation over the backbone on behalf of the Registered
Node.
Unicasting Proxy
A Unicasting Proxy forwards NS messages to the Registering
Node, transforming Layer-2 multicast into unicast.
Routing proxy
A routing proxy advertises its own MAC address as the TLLA in
the proxied NAs over the backbone, as opposed to that of the
node that performs the registration.
Bridging proxy
A Bridging proxy advertises the MAC address of the node that
performs the registration as the TLLA in the proxied NAs over
the backbone. In that case, the MAC address and the mobility
of 6LN is still visible across the bridged backbone fabric.
Primary BBR
The BBR that will defend a Registered Address for the purpose
of DAD over the backbone.
Secondary BBR
A BBR other than the Primary BBR to which an address is
registered. A Secondary Router MAY advertise the address over
the backbone and proxy for it.
4. Overview
The services specified in this document assist a 6LN to move freely
from an LLN anchored at one 6BBR to an LLN anchored at another 6BBR
on the same backbone and keep any or all of the IPv6 addresses that
the 6LN has formed.
Thubert & Perkins Expires April 25, 2019 [Page 6]
Internet-Draft IPv6 Backbone Router October 2018
|
+-----+
| | Gateway (default) Router
| |
+-----+
|
| Backbone Link
+-------------------------+----------------------+
| | |
+------+ +------+ +------+
| 6BBR | | 6BBR | | 6BBR |
| | | | | |
+------+ +------+ +------+
o o o o o o
o o o o o o o o o o o o o o
o o o o o o o o o o o o o o o
o o o o o o o o o o
o o o o o o o
LLN LLN LLN
Figure 1: Backbone Link and Backbone Routers
Each Backbone Router (6BBR) maintains a Binding Table of its
Registered Nodes. The Binding Tables form a distributed database of
wireless 6LNs that reside on the LLNs or on the backbone, and use an
extension to IPv6 ND to exchange that information across the Backbone
as described below.
The Extended Address Registration Option (EARO) defined in
[I-D.ietf-6lo-rfc6775-update] is used in the ND exchanges over the
backbone between the 6BBRs to enable the registration for routing and
proxy services, as well as distinguish duplication from movement.
Address duplication is detected using the ROVR field in the EARO. In
case of conflicting registrations to multiple 6BBRs from the same
node, the Transaction ID (TID) in the EARO enables 6BBRs to determine
the latest registration for that 6LN.
6BBRs perform ND proxy operations over the backbone, on behalf of
their Registered Nodes. Registration to a proxy service is done via
a NS/NA(EARO) exchange. 6BBR operation resembles that of a Mobile
IPv6 (MIPv6) [RFC6275] Home Agent. This enables mobility support for
6LNs; if they move outside of the network delimited by the Backbone
link, then they make use of a Home Agent. Home Agent functionality
can easily be collocated with a 6BBR on the same backbone interface
of a router.
Thubert & Perkins Expires April 25, 2019 [Page 7]
Internet-Draft IPv6 Backbone Router October 2018
The Optimistic Duplicate Address Detection [RFC4429] (ODAD)
specification details how an address can be used before a Duplicate
Address Detection (DAD) is complete, and mandates that an address
that is TENTATIVE should not be associated to a Source Link-Layer
Address Option in a Neighbor Solicitation message. This
specification makes use of ODAD to create a temporary proxy state in
the 6BBR until DAD is completed over the backbone. This way, the
specification allows proxy state distribution across multiple 6BBR
and co-existence with IPv6 ND over the backbone.
5. Backbone Router Routing Operations
|
+-----+
| | Gateway (default) Router
| |
+-----+
| /64
| Backbone Link
+-------------------+-------------------+
| /64 | /64 | /64
+------+ +------+ +------+
| 6BBR | | 6BBR | | 6BBR |
| | | | | |
+------+ +------+ +------+
o o o o o o
o o o o o o o o o o o o o o
o o o o o o o o o o o o o o o
o o o o o o o o o o
o o o o o o o
LLN: N*/128 LLN: M*/128 LLN: P*/128
Figure 2: Example Routing Configuration for 3 LLNs in the ML Subnet
5.1. Over the Backbone Link
A 6BBR is a specific kind of Border Router that performs proxy
Neighbor Discovery on its backbone interface on behalf of registered
6LNs on its LLN interfaces.
On the backbone side, the 6BBR advertises the prefixes of the LLNs
for which it serves as a proxy. Some restrictions of the attached
LLNs will apply to the backbone. In particular, the MTU SHOULD be
set to the same value on the backbone and all attached LLNs. The
scalability of the multilink subnet [RFC4903] requires that broadcast
operations are avoided as much as possible on the backbone as well.
Thubert & Perkins Expires April 25, 2019 [Page 8]
Internet-Draft IPv6 Backbone Router October 2018
The 6BBR uses an EARO in the NS-DAD and the multicast NA messages
that it generates over the Backbone Link on behalf of a Registered
Node. The 6BBR places an EARO in its unicast NA messages, if and
only if the NS/NA that stimulates it had an EARO in it and the 'R'
bit set.
The 6BBR SHOULD use unicast or the solicited-node multicast address
(SNMA) [RFC4291] to defend its Registered Addresses in its Binding
Table over the backbone. In particular, the 6BBR MUST join the SNMA
group that corresponds to a Registered Address as soon as it creates
an entry for that address, and maintain its SNMA membership as long
as it maintains that entry.
Optimistic DAD (ODAD) [RFC4429] SHOULD be supported by the 6BBRs in
their proxy activity over the backbone. A 6BBR supporting ODAD MUST
join the SNMA of a Tentative address.
A 6BBR in Routing Proxy mode MAY advertise the Registered IPv6
Address with the 6BBR Link Layer Address, and update Neighbor Cache
Entries (NCE) in correspondent nodes over the backbone, using
gratuitous NA(Override). This method may fail if the multicast
message is not received, and correspondent nodes may maintain an
incorrect neighbor state, which they will eventually discover through
Neighbor Unreachability Detection (NUD). For slow movements, the NUD
procedure defined in [RFC4861] may time out too quickly, and the
support of [RFC7048] is recommended in all 6LNs in the network.
Multicast should be avoided as much as possible even on the backbone
[I-D.ietf-mboned-ieee802-mcast-problems]. Although hosts can
participate using legacy IPv6 ND, all 6LNs connected to the backbone
SHOULD support [I-D.ietf-6man-rs-refresh], which also requires the
support of [RFC7559].
5.2. Proxy Operations Over the LLN Interface
6LNs on the LLN follow [RFC6775] and do not depend on multicast RAs
to discover routers. 6LNs SHOULD accept multicast RAs [RFC7772], but
those are expected to be rare within in the LLN. Nodes SHOULD follow
the Simple Procedures for Detecting Network Attachment in IPv6
[RFC6059] (DNA procedures) to assert movements, and support Packet-
Loss Resiliency for Router Solicitations [RFC7559] to make the
unicast RS more reliable.
A 6LN signals that it requires IPv6 ND proxy services from a 6BBR by
registering the corresponding IPv6 Address with an NS(EARO) message
with the 'R' flag set. The 6LN that performs the registration (the
Registering Node) may be the owner of the IPv6 Address (the
Thubert & Perkins Expires April 25, 2019 [Page 9]
Internet-Draft IPv6 Backbone Router October 2018
Registered Node) or a 6LBR that performs the registration on its
behalf.
5.2.1. Routing Proxy Operations
When operating as a Routing Proxy, the BBR installs host routes
(/128) to the Registered Addresses within the LLN, via the
Registering Node as identified by the Source Address and the SLLA
option in the NS(EARO) messages. In that case, the MAC address of
the 6LN is not visible at Layer-2 over the backbone. The 6BBR
installs a host route towards the Registered Node over the interface
toward the 6LN, and routes unicast packets to the 6LN.
The Routing Proxy 6BBR handles the ND protocol over the backbone on
behalf of the Registered Nodes, using its own MAC address in the TLLA
and SLLA options in proxied NS and NA messages. For each Registered
Address, multiple peer Nodes on the backbone may have resolved the
address with the 6BBR MAC address, maintaining that mapping in their
Neighbor cache.
For each Registered Address, the 6BBR SHOULD maintain a list of the
peers on the backbone which have associated its MAC address with the
Registered Address. If that Registered Address moves to a different
6BBR, the first 6BBR SHOULD unicast a gratuitous NA(Override) to each
such peer, to supply the MAC address of the new 6BBR in the TLLA
option for the Address.
5.2.2. Bridging Proxy Operations
A Bridging Proxy can be implemented in a Layer-3 switch, or in a
wireless Access Point that acts as an IPv6 Host. In the latter case,
the SLLA option in the proxied NA messages is that of the Registering
Node, and the 6BBR acts as a Layer-2 bridge for unicast packets to
the Registered Address. The MAC address in the S/TLLA is that of the
Registering Node, which is not necessarily the Registered Node. When
a 6LN moves within a LLN mesh, it may attach to a different 6LBR
acting as Registering Node, and the MAC address advertised over the
backbone might change.
If a registration moves from one 6BBR to the next, but the
Registering Node does not change, as indicated by the S/TLLA option
in the ND exchanges, there is no need to update the Neighbor Caches
of the peer's Nodes on the backbone. On the other hand, if the LLA
changes, the 6BBR SHOULD inform all the relevant peers as described
above, to update the affected Neighbor Caches. In the same fashion,
if the Registering Node changes with a new registration, the 6BBR
SHOULD also update the affected Neighbor Caches over the backbone.
Thubert & Perkins Expires April 25, 2019 [Page 10]
Internet-Draft IPv6 Backbone Router October 2018
6. Backbone Router Proxy Operations
The LLNs attached to each 6BBR are considered different Links in a
multi-link subnet. The prefix that is used may still be advertised
as on-link on the backbone to support legacy 6LNs. Multicast ND
messages are link-scoped and not forwarded across the backbone
routers.
By default, a 6BBR operates as a Sleeping Proxy, as follows:
o Create a new entry in a Binding Table for a new Registered Address
and ensure that the address is not a duplicate over the backbone
o Defend a Registered Address over the backbone using NA messages
with the Override bit set on behalf of the sleeping 6LN
o Advertise a Registered Address over the backbone using NA
messages, asynchronously or as a response to a Neighbor
Solicitation messages.
o To deliver packets arriving from the LLN, use Neighbor
Solicitation messages to look up the destination over the
backbone.
o Forward packets between the LLN and the backbone.
o Verify liveliness when needed for a stale registration.
A 6BBR may act as a Sleeping Proxy only for a Registered Address that
is REACHABLE, or TENTATIVE in which case the answer is delayed. In
any other state, the Sleeping Proxy operates as a Unicasting Proxy.
The 6BBR does not act on ND Messages over the backbone unless they
are relevant to a Registered Node on the LLN side, saving wireless
interference. On the LLN side, the prefixes associated to the
MultiLink Subnet are presented as not on-link, so address resolution
for other hosts do not occur.
As a Unicasting Proxy, the 6BBR forwards NS lookup messages to the
Registering Node, transforming Layer-2 multicast into unicast. This
is not possible in UNREACHABLE state, so the NS messages are
multicasted, and rate-limited. Retries are possible, using an
exponential back-off to protect the medium. In other states, the
messages are forwarded to the Registering Node as unicast Layer-2
messages. In TENTATIVE state, the NS message is either held till DAD
completes, or dropped if DAD does not complete.
Thubert & Perkins Expires April 25, 2019 [Page 11]
Internet-Draft IPv6 Backbone Router October 2018
6.1. Primary and Secondary BBRs
A 6BBR MAY be primary or secondary. The primary is the backbone
router that has the highest EUI-64 address of all the 6BBRs that
share a registration for a same Registered Address, with the same
ROVR and same Transaction ID, the EUI-64 address being considered as
an unsigned 64bit integer. A given 6BBR can be primary for a given
address and secondary for another address, regardless of whether or
not the addresses belong to the same 6LN. The primary Backbone
Router is in charge of protecting the address for DAD over the
Backbone. Any of the Primary and Secondary 6BBR may claim the
address over the backbone, since they are all capable to route from
the backbone to the 6LN; the address appears on the backbone as an
anycast address.
6.2. Binding Table
Each 6BBR maintains a Binding Table, using IPv6 ND over the backbone
to detect duplication. Another document
[I-D.ietf-6lo-rfc6775-update] provides details about how the EARO is
used between 6LRs and 6LBRs by way of DAR/DAC messages within the
LLN. Addresses in a LLN that can be reachable from the backbone by
way of a 6BBR MUST be registered to that 6BBR.
A false positive duplicate detection may arise over the backbone, for
instance if a 6LN's Registered Address is registered to more than one
LBR, or if the 6LN has moved. Both situations are handled by the
6BBR transparently to the 6LN. In the former case, one LBR becomes
primary to defend the address over the backbone while the others
become secondary and may still forward packets. In the latter case
the LBR that receives the newest registration becomes primary because
of the TID.
Only one 6LN may register a given Address at a particular 6BBR.
However, that Registered Address may be registered to Multiple 6BBRs
for higher availability.
Over the LLN, Binding Table management is as follows:
De-registrations (newer TID, same ROVR, null Lifetime) are
accepted and acknowledged with a status of 4 (TBD); the entry is
deleted;
Newer registrations (newer TID, same ROVR, non-null Lifetime) are
acknowledged with a status of 0 (success); the binding is updated
with the new TID, the Registration Lifetime and the Registering
Node; in TENTATIVE state the acknowledgement is held and may be
Thubert & Perkins Expires April 25, 2019 [Page 12]
Internet-Draft IPv6 Backbone Router October 2018
overwritten; in other states the Registration-Lifetime timer is
restarted and the entry is placed in REACHABLE state.
Identical registrations (same TID, same ROVR) from a same
Registering Node are acknowledged with a status of 0 (success).
If they are not identical, an error SHOULD be logged. In
TENTATIVE state, the response is held and may be overwritten, but
it MUST be eventually produced and it carries the result of the
DAD process;
Older registrations (older TID, same ROVR) from a Registering Node
are ignored;
Identical and older registrations (not-newer TID, same ROVR) from
a different Registering Node are acknowledged with a status of 3
(moved); this may be rate limited to protect the medium;
Any registration for a different Registered Node (different ROVR)
are acknowledged with a status of 1 (duplicate).
6.3. Registration and Binding Table Entry Creation
Upon receiving a registration for a new address with an NS(EARO) with
the 'R' bit set, the 6BBR performs DAD over the backbone, placing the
new address as target in the NS-DAD message. The EARO from the
registration MUST be placed unchanged in the NS-DAD message, and an
Neighbor Cache entry created in TENTATIVE state for a duration of
TENTATIVE_DURATION. The NS-DAD message is sent multicast over the
backbone to the SNMA associated with the registered address, unless
that operation is known to be costly, and the 6BBR has an indication
from another source (such as a Neighbor Cache entry) that the
Registered Address was known on the backbone; in the latter case, an
NS-DAD message may be sent as a Layer-2 unicast to the MAC Address
that was associated with the Registered Address.
In TENTATIVE state after EARO with 'R' bit set:
1. The entry is removed if an NA is received over the backbone for
the Registered Address with no EARO, or containing an EARO with a
status of 1 (duplicate) that indicates an existing registration
for another 6LN. The ROVR and TID fields in the EARO received
over the backbone are ignored. A status of 1 is returned in the
EARO of the NA back to the Registering Node;
2. The entry is also removed if an NA with an ARO option with a
status of 3 (moved), or a NS with an ARO option that indicates a
newer registration for the same Registered Node, is received over
Thubert & Perkins Expires April 25, 2019 [Page 13]
Internet-Draft IPv6 Backbone Router October 2018
the backbone for the Registered Address. A status of 3 is
returned in the NA(EARO) back to the Registering Node;
3. When a registration is updated but not deleted, e.g. from a newer
registration, the DAD process on the backbone continues and the
running timers are not restarted;
4. Other NS (including DAD with no EARO) and NA from the backbone
are not acknowledged in TENTATIVE state. To cover legacy 6LNs
that do not support ODAD, the list of their origins MAY be stored
and then, if the TENTATIVE_DURATION timer elapses, the 6BBR MAY
send each such legacy 6LN a unicast NA.
5. When the TENTATIVE_DURATION timer elapses, a status 0 (success)
is returned in a NA(EARO) back to the Registering Node(s), and
the entry goes to REACHABLE state for the Registration Lifetime.
The 6BBR MUST send a multicast NA(EARO) to the SNMA associated to
the Registered Address over the backbone with the Override bit
set so as to take over the binding from other 6BBRs.
6.4. Defending Addresses
If a 6BBR has an entry in REACHABLE state for a Registered Address:
o If the 6BBR is primary, or does not support the function of
primary, it MUST defend that address over the backbone upon
receiving NS, either if the NS does not carry an EARO, or if an
EARO is present that indicates a different Registering Node
(different ROVR). The 6BBR sends a NA message with the Override
bit set and the NA carries an EARO if and only if the NS-DAD did
so. When present, the EARO in the NA(Override) that is sent in
response to the NS(EARO) carries a status of 1 (duplicate), and
the ROVR and TID fields in the EARO are obfuscated with null or
random values to avoid network scanning and impersonation attacks.
o If the 6BBR receives an NS(EARO) for a newer registration, the
6BBR updates the entry and the routing state to forward packets to
the new 6BBR, but keeps the entry REACHABLE. Afterwards, the 6BBR
MAY use REDIRECT messages to reroute traffic for the Registered
Address to the new 6BBR.
o If the 6BBR receives an NA(EARO) for a newer registration, the
6BBR removes its entry and sends a NA(EARO) with a status of 3
(MOVED) to the Registering Node, if the Registering Node is
different from the Registered Node. The 6BBR cleans up existing
Neighbor Cache entries in peer nodes as discussed in Section 5.1,
by unicasting to each such peer, or one broadcast NA(Override).
Thubert & Perkins Expires April 25, 2019 [Page 14]
Internet-Draft IPv6 Backbone Router October 2018
o If the 6BBR receives a NS(LOOKUP) for a Registered Address, it
answers immediately with an NA on behalf of the Registered Node,
without polling it. There is no need of an EARO in that exchange.
o When the Registration-Lifetime timer elapses, the entry goes to
STALE state for a duration of STABLE_STALE_DURATION in LLNs that
keep stable addresses such as LWPANs, and UNSTABLE_STALE_DURATION
in LLNs where addresses are renewed rapidly, e.g. for privacy
reasons.
The STALE state enables tracking of the backbone peers that have a
Neighbor Cache entry pointing to this 6BBR in case the Registered
Address shows up later. If the Registered Address is claimed by
another 6LN on the backbone, with an NS-DAD or an NA, the 6BBR does
not defend the address. In STALE state:
o If STALE_DURATION elapses, the 6BBR removes the entry.
o Upon receiving an NA(Override) the 6BBR removes its entry and
sends a NA(EARO) with a status of 4 (removed) to the Registering
Node.
o If the 6BBR receives a NS(LOOKUP) for a Registered Address, the
6BBR MUST send an NS(NUD) following rules in [RFC7048] to the
Registering Node targeting the Registered Address prior to
answering. If the NUD succeeds, the operation in REACHABLE state
applies. If the NUD fails, the 6BBR refrains from answering the
lookup. The NUD SHOULD be used by the Registering Node to
indicate liveness of the Registered Node, if they are different
nodes.
7. Security Considerations
This specification applies to LLNS in which the link layer is
protected, either by means of physical or IP security for the
Backbone Link or MAC sublayer cryptography. In particular, the LLN
MAC is required to provide secure unicast to/from the Backbone Router
and secure Broadcast from the Backbone Router in a way that prevents
tampering with or replaying the RA messages.
The use of EUI-64 for forming the Interface ID in the link local
address prevents the usage of Secure ND ([RFC3971] and [RFC3972]) and
address privacy techniques. Additional protection against address
theft is provided by [I-D.ietf-6lo-ap-nd], which guarantees the
ownership of the ROVR.
Thubert & Perkins Expires April 25, 2019 [Page 15]
Internet-Draft IPv6 Backbone Router October 2018
When the ownership of the ROVR cannot be assessed, this specification
limits the cases where the ROVR and the TID are multicasted, and
obfuscates them in responses to attempts to take over an address.
8. Protocol Constants
This Specification uses the following constants:
TENTATIVE_DURATION: 800 milliseconds
STABLE_STALE_DURATION: 24 hours
UNSTABLE_STALE_DURATION: 5 minutes
DEFAULT_NS_POLLING: 3 times
9. IANA Considerations
This document has no request to IANA.
10. Future Work
Future documents may extend this specification by allowing the 6BBR
to redistribute host routes in routing protocols that would operate
over the backbone, or in MIPv6, or FMIP, or the Locator/ID Separation
Protocol (LISP) [RFC6830] to support mobility on behalf of the 6LNs,
etc...
11. Acknowledgments
Kudos to Eric Levy-Abegnoli who designed the First Hop Security
infrastructure at Cisco.
12. References
12.1. Normative References
[I-D.ietf-6lo-rfc6775-update]
Thubert, P., Nordmark, E., Chakrabarti, S., and C.
Perkins, "Registration Extensions for 6LoWPAN Neighbor
Discovery", draft-ietf-6lo-rfc6775-update-21 (work in
progress), June 2018.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
Thubert & Perkins Expires April 25, 2019 [Page 16]
Internet-Draft IPv6 Backbone Router October 2018
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD)
for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006,
<https://www.rfc-editor.org/info/rfc4429>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<https://www.rfc-editor.org/info/rfc4862>.
[RFC6059] Krishnan, S. and G. Daley, "Simple Procedures for
Detecting Network Attachment in IPv6", RFC 6059,
DOI 10.17487/RFC6059, November 2010,
<https://www.rfc-editor.org/info/rfc6059>.
[RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
Bormann, "Neighbor Discovery Optimization for IPv6 over
Low-Power Wireless Personal Area Networks (6LoWPANs)",
RFC 6775, DOI 10.17487/RFC6775, November 2012,
<https://www.rfc-editor.org/info/rfc6775>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
12.2. Informative References
[I-D.ietf-6lo-ap-nd]
Thubert, P., Sarikaya, B., Sethi, M., and R. Struik,
"Address Protected Neighbor Discovery for Low-power and
Lossy Networks", draft-ietf-6lo-ap-nd-08 (work in
progress), October 2018.
[I-D.ietf-6man-rs-refresh]
Nordmark, E., Yourtchenko, A., and S. Krishnan, "IPv6
Neighbor Discovery Optional RS/RA Refresh", draft-ietf-
6man-rs-refresh-02 (work in progress), October 2016.
Thubert & Perkins Expires April 25, 2019 [Page 17]
Internet-Draft IPv6 Backbone Router October 2018
[I-D.ietf-6tisch-architecture]
Thubert, P., "An Architecture for IPv6 over the TSCH mode
of IEEE 802.15.4", draft-ietf-6tisch-architecture-15 (work
in progress), October 2018.
[I-D.ietf-mboned-ieee802-mcast-problems]
Perkins, C., McBride, M., Stanley, D., Kumari, W., and J.
Zuniga, "Multicast Considerations over IEEE 802 Wireless
Media", draft-ietf-mboned-ieee802-mcast-problems-02 (work
in progress), August 2018.
[I-D.nordmark-6man-dad-approaches]
Nordmark, E., "Possible approaches to make DAD more robust
and/or efficient", draft-nordmark-6man-dad-approaches-02
(work in progress), October 2015.
[I-D.yourtchenko-6man-dad-issues]
Yourtchenko, A. and E. Nordmark, "A survey of issues
related to IPv6 Duplicate Address Detection", draft-
yourtchenko-6man-dad-issues-01 (work in progress), March
2015.
[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971,
DOI 10.17487/RFC3971, March 2005,
<https://www.rfc-editor.org/info/rfc3971>.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, DOI 10.17487/RFC3972, March 2005,
<https://www.rfc-editor.org/info/rfc3972>.
[RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April
2006, <https://www.rfc-editor.org/info/rfc4389>.
[RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903,
DOI 10.17487/RFC4903, June 2007,
<https://www.rfc-editor.org/info/rfc4903>.
[RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6
over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals",
RFC 4919, DOI 10.17487/RFC4919, August 2007,
<https://www.rfc-editor.org/info/rfc4919>.
Thubert & Perkins Expires April 25, 2019 [Page 18]
Internet-Draft IPv6 Backbone Router October 2018
[RFC5415] Calhoun, P., Ed., Montemurro, M., Ed., and D. Stanley,
Ed., "Control And Provisioning of Wireless Access Points
(CAPWAP) Protocol Specification", RFC 5415,
DOI 10.17487/RFC5415, March 2009,
<https://www.rfc-editor.org/info/rfc5415>.
[RFC6275] Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility
Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July
2011, <https://www.rfc-editor.org/info/rfc6275>.
[RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
Locator/ID Separation Protocol (LISP)", RFC 6830,
DOI 10.17487/RFC6830, January 2013,
<https://www.rfc-editor.org/info/rfc6830>.
[RFC7048] Nordmark, E. and I. Gashinsky, "Neighbor Unreachability
Detection Is Too Impatient", RFC 7048,
DOI 10.17487/RFC7048, January 2014,
<https://www.rfc-editor.org/info/rfc7048>.
[RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and
Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January
2014, <https://www.rfc-editor.org/info/rfc7102>.
[RFC7559] Krishnan, S., Anipko, D., and D. Thaler, "Packet-Loss
Resiliency for Router Solicitations", RFC 7559,
DOI 10.17487/RFC7559, May 2015,
<https://www.rfc-editor.org/info/rfc7559>.
[RFC7772] Yourtchenko, A. and L. Colitti, "Reducing Energy
Consumption of Router Advertisements", BCP 202, RFC 7772,
DOI 10.17487/RFC7772, February 2016,
<https://www.rfc-editor.org/info/rfc7772>.
12.3. External Informative References
[IEEEstd8021]
IEEE standard for Information Technology, "IEEE Standard
for Information technology -- Telecommunications and
information exchange between systems Local and
metropolitan area networks Part 1: Bridging and
Architecture".
Thubert & Perkins Expires April 25, 2019 [Page 19]
Internet-Draft IPv6 Backbone Router October 2018
[IEEEstd80211]
IEEE standard for Information Technology, "IEEE Standard
for Information technology -- Telecommunications and
information exchange between systems Local and
metropolitan area networks-- Specific requirements Part
11: Wireless LAN Medium Access Control (MAC) and Physical
Layer (PHY) Specifications".
[IEEEstd802151]
IEEE standard for Information Technology, "IEEE Standard
for Information Technology - Telecommunications and
Information Exchange Between Systems - Local and
Metropolitan Area Networks - Specific Requirements. - Part
15.1: Wireless Medium Access Control (MAC) and Physical
Layer (PHY) Specifications for Wireless Personal Area
Networks (WPANs)".
[IEEEstd802154]
IEEE standard for Information Technology, "IEEE Standard
for Local and metropolitan area networks -- Part 15.4:
Low-Rate Wireless Personal Area Networks (LR-WPANs)".
Appendix A. Changes from revision 07 to revision 08
This section lists the changes between draft-ietf-6lo-backbone-router
revisions ...-07.txt and ...-08.txt.
o Reorganized the order of presentation of some sections so that
related material is closer together.
o Added "Future Work" section.
o Added this section detailing recent changes.
o Used '6LN' when LLN node is meant.
o Updated bibliographic citations.
Authors' Addresses
Thubert & Perkins Expires April 25, 2019 [Page 20]
Internet-Draft IPv6 Backbone Router October 2018
Pascal Thubert (editor)
Cisco Systems, Inc
Building D
45 Allee des Ormes - BP1200
MOUGINS - Sophia Antipolis 06254
FRANCE
Phone: +33 497 23 26 34
Email: pthubert@cisco.com
Charles E. Perkins
Futurewei
2330 Central Expressway
Santa Clara 95050
United States of America
Email: charliep@computer.org
Thubert & Perkins Expires April 25, 2019 [Page 21]