IPv6 Prefix Delegation and Multi-Addressing Models
draft-templin-v6ops-pdhost-25
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draft-templin-v6ops-pdhost-25
Network Working Group F. Templin, Ed.
Internet-Draft Boeing Research & Technology
Intended status: Informational January 1, 2020
Expires: July 4, 2020
IPv6 Prefix Delegation and Multi-Addressing Models
draft-templin-v6ops-pdhost-25
Abstract
Requesting nodes typically acquire IPv6 prefixes from a prefix
delegation service for the network. The requesting node can
provision the prefix according to whether it acts as a router on
behalf of any downstream networks and/or as a host on behalf of its
local applications. In the latter case, the requesting node can use
portions of the delegated prefix for its own multi-addressing
purposes. This document therefore considers prefix delegation models
for both the classic routing and various multi-addressing use cases.
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
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 4, 2020.
Copyright Notice
Copyright (c) 2020 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
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
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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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Multi-Addressing Considerations . . . . . . . . . . . . . . . 6
4. Multi-Addressing Alternatives for Delegated Prefixes . . . . 7
5. Address Autoconfiguration Considerations . . . . . . . . . . 8
6. MLD/DAD Implications . . . . . . . . . . . . . . . . . . . . 8
7. Dynamic Routing Protocol Implications . . . . . . . . . . . . 9
8. IPv6 Neighbor Discovery Implications . . . . . . . . . . . . 9
9. Prefix Delegation Services . . . . . . . . . . . . . . . . . 9
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
11. Security Considerations . . . . . . . . . . . . . . . . . . . 10
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
13.1. Normative References . . . . . . . . . . . . . . . . . . 11
13.2. Informative References . . . . . . . . . . . . . . . . . 12
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
IPv6 Neighbor Discovery (ND) is the process by which nodes on the
link discover each other's presence as well as advertise and receive
configuration information. IPv6 Prefix Delegation (PD) entails 1)
the communication of a prefix from a delegation service to a
requesting node, 2) a representation of the prefix in the network's
Routing Information Base (RIB) and the first-hop router's Forwarding
Information Base (FIB), and 3) a control messaging service to
maintain prefix lifetimes. Following delegation, the prefix is
available for the requesting node's exclusive use and is not shared
with any other nodes. This document considers prefix delegation
models and multiaddressing considerations for requesting nodes that
act as a router on behalf of any downstream networks and/or as a host
on behalf of their local applications.
For nodes that connect downstream-attached networks (e.g., a
cellphone that connects a "tethered" Internet of Things (IoT), a
laptop computer with a complex internal network of virtual machines,
etc.), the classic routing model applies as shown in Figure 1:
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.---------.
,-( )-.
( +----------+ )
( |Server 'S'| )
( +----------+ )
( Network 'N' )
`-(__________)-'
|
+----------+----------+
| first-hop router 'F'|
+----------+----------+
|
upstream link |
|
+----------+----------+
| upstream interface |
+---------------------+
| |
| requesting node 'R' |
| (Prefix 'P') |
| |
+--+-+--+-+--+-----+--+
|A1| |A2| |A3| ... |Aj|
+--+-+--+-+--+-----+--+
|downstream interfaces|
+----------+----------+
|
internal and/or external |
downstream links |
X----+-------------+--------+----+---------------+---X
| | | |
+---++-+--+ +---++-+--+ +---++-+--+ +---++-+--+
| |Ak| | | |Al| | | |Am| | | |A*| |
| +--+ | | +--+ | | +--+ | | +--+ |
| host H1 | | host H2 | | host H3 | ... | host Hn |
+---------+ +---------+ +---------+ +---------+
<-------------- Downstream Network ------------->
Figure 1: Classic Routing Model
In the classic routing model, requesting node 'R' has one or more
upstream interfaces and connects zero or more internal and/or
external downstream networks. When 'R' requests a prefix delegation,
the following sequence of events transpires:
o Server 'S' located in network 'N' delegates prefix 'P' to
requesting node 'R'.
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o 'P' is injected into the RIB for 'N', and first hop router 'F'
configures a FIB entry with 'R' as the next hop.
o R' receives 'P' and assigns zero or more addresses 'A(*)' taken
from 'P' to its downstream interfaces
o 'R' advertises zero or more sub-prefixes taken from 'P' to hosts
'H(i)' on downstream networks.
o 'R' delegates zero or more sub-prefixes taken from 'P' to
requesting nodes in downstream networks.
o 'R' acts as a router for hosts 'H(i)' on downstream networks and
as a host on behalf of its local applications.
This document also considers the case when 'R' uses portions of 'P'
for its own internal multi-addressing purposes. [RFC7934] provides
Best Current Practice (BCP) motivations for the benefits of multi-
addressing, while an operational means for providing nodes with
multiple addresses is given in [RFC8273]. The following multi-
addressing alternatives for delegated prefixes compliment this
framework.
In a first alternative, when requesting node 'R' receives prefix 'P',
it can assign addresses taken from 'P' to downstream virtual
interfaces (e.g., a loopback) as shown in Figure 2:
x
|
upstream link |
|
+----------+----------+
| upstream interface |
+---------------------+
| |
| requesting node 'R' |
| |
+--+-+--+-+--+-----+--+
|A1| |A2| |A3| ... |An|
+--+-+--+-+--+-----+--+
| virtual interfaces |
+---------------------+
Figure 2: Address Assignment to Downstream Virtual Interfaces
In a second alternative, 'R' could assign IPv6 addresses taken from
'P' to the upstream interface over which the prefix was received as
shown in Figure 3:
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x
|
upstream link |
|
+----------+----------+
| upstream interface |
+--+-+--+-+--+-----+--+
|A1| |A2| |A3| ... |An|
+--+-+--+-+--+-----+--+
| |
| requesting node 'R' |
| |
+---------------------+
Figure 3: Upstream Interface Address Assignment
In a third alternative, 'R' could assign IPv6 addresses taken from
'P' to its local applications which appear as "psuedo" virtual
interfaces as shown in Figure 4:
x
|
upstream link |
|
+----------+----------+
| upstream interface |
+---------------------+
| |
| requesting node 'R' |
| |
+--+-+--+-+--+-----+--+
|A1| |A2| |A3| ... |An|
+--+-+--+-+--+-----+--+
| Applications |
+---------------------+
Figure 4: Application Addresssing Model
With these IPv6 PD-based multi-addressing considerations, the node
can configure an unlimited supply of addresses to make them available
for local applications without requiring coordination with other
nodes on upstream interfaces. The following sections present
considerations for nodes that employ IPv6 PD mechanisms.
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2. Terminology
The terms "node", "host" and "router" are the same as defined in
[RFC8200]. The terms Router Solicitation (RS), Router Advertisement
(RA), Neighbor Solicitation (NS), Neighbor Advertisment (NA),
Redirect and Prefix Information Option (PIO) are the same as defined
in [RFC4861]. All other terminology in the normative references
applies, while the following terms are defined within the context of
this document:
shared prefix
an IPv6 prefix that may be advertised to more than one node on the
link. The router that advertises the prefix must consider the
prefix as on-link so that the IPv6 ND address resolution function
will identify the correct neighbor for each packet.
individual prefix
an IPv6 prefix that is advertised to exactly one node on the link,
where the node may be unaware that the prefix is individual and
may not participate in prefix maintenance procedures. The router
that advertises the prefix can consider the prefix as on-link or
not on-link. In the former case, the router performs address
resolution and only forwards those packets that match one of the
node's configured addresses so that the node will not receive
unwanted packets. In the latter case, the router can simply
forward all packets matching the prefix to the node which must
then drop any packets that do not match one of its configured
addresses. An example individual prefix service is documented in
[RFC8273].
delegated prefix
an IPv6 prefix that is explicitly conveyed to a node for its own
exclusive use, where the node is an active participant in prefix
delegation and maintenance procedures. The first-hop router
simply forwards all packets matching the prefix to the requesting
node. The requesting node associates the prefix with downstream
and/or internal virtual interfaces (i.e., and not the upstream
interface).
3. Multi-Addressing Considerations
IPv6 allows nodes to assign multiple addresses to a single interface.
[RFC7934] discusses options for multi-addressing as well as use cases
where multi-addressing may be desirable. Address configuration
options for multi-addressing include StateLess Address
AutoConfiguration (SLAAC) [RFC4862], Dynamic Host Configuration
Protocol for IPv6 (DHCPv6) address configuration [RFC8415], manual
configuration, etc.
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Nodes configure addresses from a shared or individual prefix and
assign them to the upstream interface over which the prefix was
received. When the node assigns the addresses, it is required to use
Multicast Listener Discovery (MLD) [RFC3810] to join the appropriate
solicited-node multicast group(s) and to use the Duplicate Address
Detection (DAD) algorithm [RFC4862] to ensure that no other node
configures a duplicate address.
In contrast, a node that configures addresses from a delegated prefix
can assign them without invoking MLD/DAD on an upstream interface,
since the prefix has been delegated to the node for its own exclusive
use and is not shared with any other nodes.
4. Multi-Addressing Alternatives for Delegated Prefixes
When a node receives a delegated prefix, it has many alternatives for
provisioning the prefix to its local interfaces and/or downstream
networks. [RFC7278] discusses alternatives for provisioning a prefix
obtained by a User Equipment (UE) device under the 3rd Generation
Partnership Program (3GPP) service model. This document considers
the more general case when the node receives a delegated prefix
explicitly provided for its own exclusive use.
When the node receives the prefix, it can distribute the prefix to
internal (virtual) or external (physical) downstream networks and
optionally configure addresses for itself on downstream interfaces.
The node then acts as a router on behalf of its downstream networks.
The node could instead (or in addition) use portions of the delegated
prefix for its own multi-addressing purposes. In a first
alternative, the node can assign as many addresses as it wants from
the prefix to downstream virtual interfaces.
In a second alternative, the node can assign as many addresses as it
wants from the prefix to the upstream interface over which the prefix
was received, but in normal practice does not assign the prefix
itself (or subnets from the prefix) to the upstream interface. If
the node assigned the prefix to the upstream interface, any neighbors
on the upstream link receiving an RA could configure addresses from
the prefix and a default route with the node as the next hop. This
could create a loop where upstream link neighbors send packets to the
node which in turn forwards them to another upstream link neighbor.
Still, there may be cases where the node provides services for
dependent neighbors on the upstream link that have no other means of
connecting to the network. ([RFC8415] chose to remain silent on this
subject since it is operational rather than functional in nature.)
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In a third alternative, the node can assign addresses taken from the
delegated prefix to its local applications. The applications
themselves then serve as virtual interfaces. (Note that, in the
future, the practice of assigning unique non-link-local IPv6
addresses to applications could obviate the need for transport
protocol port numbers.)
In these multi-addressing cases, the node normally assigns the prefix
itself to a virtual interface such as a loopback so that unused
portions of the prefix are correctly identified as unreachable. The
node then acts as a host on behalf of its local applications even
though neighbors on the upstream link consider it as a router.
5. Address Autoconfiguration Considerations
Nodes autoconfigure addresses according to Section 6 of IPv6 Node
Requirements [RFC8504].
Nodes that connect to a network that spans more than just a single
LAN configure at least one non-link-local adddress, i.e., for network
management and error reporting purposes.
Nodes recognize the Subnet Router Anycast address [RFC4291] for each
delegated prefix. Therefore, the node's use of the Subnet Router
Anycast address must be indistinguishable from the behavior of an
ordinary router when viewed from the outside world.
6. MLD/DAD Implications
When a node configures addresses for itself from a shared or
individual prefix (and when the interface variable
'DupAddrDetectTransmits' is non-zero [RFC4862]), the node performs
MLD/DAD by sending multicast messages over the upstream interface to
test whether there is another node on the link that configures a
duplicate address. When there are many such addresses and/or many
such nodes, this could result in substantial multicast traffic that
affects all nodes on the link.
When a node configures addresses for itself from a delegated prefix
and assigns them on downstream interfaces, it can configure as many
addresses as it wants without performing MLD/DAD for any of the
addresses over the upstream interface.
When a node configures addresses for itself from a delegated prefix
and assigns them on the upstream interface over which the prefix was
received, the node honors MLD/DAD procedures according the the
interface's 'DupAddrDetectTransmits' variable.
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7. Dynamic Routing Protocol Implications
Nodes that receive delegated prefixes can be configured to either
participate or not participate in a dynamic routing protocol over the
upstream interface. When there are many nodes on the upstream link,
dynamic routing protocol participation might be impractical due to
scaling limitations, and may also be exacerbated by factors such as
node mobility.
Unless it participates in a dynamic routing protocol, the node
initially has only a default route pointing to a neighbor via an
upstream interface. This means that packets sent by the node over an
upstream interface will initially go through a default router even if
there is a better first-hop node on the link. The node may
subsequently receive Redirect messages from the default router that
identify a better first-hop.
8. IPv6 Neighbor Discovery Implications
According to [RFC4861], when a node receives a shared or individual
prefix with "L=1" and has a packet to send to an IPv6 destination
within the prefix, it is required to use the IPv6 ND address
resolution function to resolve the link-layer address of a neighbor
on the link that configures the address.
Also according to [RFC4861], when a node receives a shared or
individual prefix with "L=0" and has a packet to send to an IPv6
destination within the prefix, it sends the packet to a default
router since "L=0" makes no statement about on-link or off-link
properties of the prefix.
When a node requires a delegated prefix, it acts as a simple host by
sending RS messages over the upstream interface in the manner
described in Section 4.2 of [RFC7084] and invokes prefix delegation
services as discussed in Section 9. The node considers the upstream
interface as a non-advertising interface [RFC4861], i.e., it does not
send RA messages over the upstream interface. The node further does
not perform the IPv6 ND address resolution function over the upstream
interface, since the delegated prefix is by definition not associated
with the upstream interface.
9. Prefix Delegation Services
Selection of prefix delegation services must be considered according
to specific use cases. An example service is that offered by
standard DHCPv6 Prefix Delegation [RFC8415]. Alternative services
based on IPv6 ND messaging have also been proposed
[I-D.templin-6man-dhcpv6-ndopt][I-D.naveen-slaac-prefix-management].
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Other, non-router, mechanisms may exist, such as proprietary IPAMs,
[I-D.ietf-anima-prefix-management] and
[I-D.li-opsawg-address-pool-management-arch]. Requirements for
extending an IPv6 /64 Prefix from a Third Generation Partnership
Project (3GPP) Mobile Interface to a LAN Link are discussed in
[RFC7278].
10. IANA Considerations
This document introduces no IANA considerations.
11. Security Considerations
Security considerations for IPv6 Neighbor Discovery [RFC4861] and any
applicable PD mechanisms apply to this document. Nodes that manage
their delegated prefixes such that MLD/DAD procedures are not needed
on the upstream interface can avoid introducing multicast messaging
congestion on the upstream link. Also, routers that delegate
prefixes keep only a single neighbor cache entry for each prefix
delegation recipient, meaning that the router's neighbor cache cannot
be subject to address resolution-based resource exhaustion attacks.
For shared and individual prefixes, if the advertising router
considers the prefix as on-link the IPv6 ND address resolution
function will prevent unwanted IPv6 packets from reaching the node.
For delegated prefixes and individual prefixes that are not
considered on-link, the router delivers all packets that match the
prefix to the node. In that case, the node may receive unwanted IPv6
packets via an upstream interface for which it has no matching
configured address. The node then drops the packets and observes the
ICMPv6 "Destination Unreachable - Address/Port unreachable"
procedures discussed in [RFC4443].
The node may also receive IPv6 packets via an upstream interface that
do not match any of the node's delegated prefixes. In that case, the
node drops the packets and observes the ICMPv6 "Destination
Unreachable - No route to destination" procedures discussed in
[RFC4443]. Dropping the packets is necessary to avoid a reflection
attack that would cause the node to forward packets received from an
upstream interface via the same or a different upstream interface.
12. Acknowledgements
This work was motivated by discussions on the v6ops list. Mark
Smith, Ricardo Pelaez-Negro, Edwin Cordeiro, Fred Baker, Ron Bonica,
Naveen Lakshman, Ole Troan, Bob Hinden, Brian Carpenter, Joel
Halpern, Albert Manfredi, Dusan Mudric, Paul Marks, Joe Touch, Alex
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Petrescu, Lorenzo Colitti, Tatuya Jinmei and Naveen Kottapalli
provided useful comments that have greatly improved the document.
This work is aligned with the NASA Safe Autonomous Systems Operation
(SASO) program under NASA contract number NNA16BD84C.
This work is aligned with the FAA as per the SE2025 contract number
DTFAWA-15-D-00030.
This work is aligned with the Boeing Commercial Airplanes (BCA)
Internet of Things (IoT) and autonomy programs.
This work is aligned with the Boeing Information Technology (BIT)
MobileNet program.
13. References
13.1. Normative References
[RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
DOI 10.17487/RFC3810, June 2004,
<https://www.rfc-editor.org/info/rfc3810>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
[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>.
[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>.
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[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/info/rfc8415>.
13.2. Informative References
[I-D.ietf-anima-prefix-management]
Jiang, S., Du, Z., Carpenter, B., and Q. Sun, "Autonomic
IPv6 Edge Prefix Management in Large-scale Networks",
draft-ietf-anima-prefix-management-07 (work in progress),
December 2017.
[I-D.li-opsawg-address-pool-management-arch]
Li, C., Xie, C., Kumar, R., Fioccola, G., Xu, W., LIU, W.,
Ma, D., and J. Bi, "Coordinated Address Space Management
architecture", draft-li-opsawg-address-pool-management-
arch-01 (work in progress), July 2018.
[I-D.naveen-slaac-prefix-management]
Kottapalli, N., "IPv6 Stateless Prefix Management", draft-
naveen-slaac-prefix-management-00 (work in progress),
November 2018.
[I-D.templin-6man-dhcpv6-ndopt]
Templin, F., "A Unified Stateful/Stateless Configuration
Service for IPv6", draft-templin-6man-dhcpv6-ndopt-08
(work in progress), June 2019.
[I-D.templin-6man-rio-redirect]
Templin, F. and j. woodyatt, "Route Information Options in
IPv6 Neighbor Discovery", draft-templin-6man-rio-
redirect-08 (work in progress), June 2019.
[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>.
[RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic
Requirements for IPv6 Customer Edge Routers", RFC 7084,
DOI 10.17487/RFC7084, November 2013,
<https://www.rfc-editor.org/info/rfc7084>.
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[RFC7278] Byrne, C., Drown, D., and A. Vizdal, "Extending an IPv6
/64 Prefix from a Third Generation Partnership Project
(3GPP) Mobile Interface to a LAN Link", RFC 7278,
DOI 10.17487/RFC7278, June 2014,
<https://www.rfc-editor.org/info/rfc7278>.
[RFC7934] Colitti, L., Cerf, V., Cheshire, S., and D. Schinazi,
"Host Address Availability Recommendations", BCP 204,
RFC 7934, DOI 10.17487/RFC7934, July 2016,
<https://www.rfc-editor.org/info/rfc7934>.
[RFC8273] Brzozowski, J. and G. Van de Velde, "Unique IPv6 Prefix
per Host", RFC 8273, DOI 10.17487/RFC8273, December 2017,
<https://www.rfc-editor.org/info/rfc8273>.
[RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node
Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504,
January 2019, <https://www.rfc-editor.org/info/rfc8504>.
Appendix A. Change Log
<< RFC Editor - remove prior to publication >>
Changes from -24 to -25:
o Version and reference update
Changes from -23 to -24:
o Version and reference update
Changes from -22 to -23:
o Changed DHCPv6 references to RFC8415. Deprecate RFC3315 and
RFC3633.
o New text on assignment of addresses and prefixes on the upstream
interface.
Changes from -21 to -22:
o Changes to address list comments contributed by Lorenzo Colitti,
Tatuya Jinmei, Brian Carpenter and Fred Baker.
o Deleted section on ICMPv6 - now defer to normative reference
[RFC4443].
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o Discuss 'DupAddrDetectTransmits' variable implications under MLD/
DAD considerations.
Changes from -20 to -21:
o Re-worked classic routing model section
o Included multi-addressing case where addresses may be assigned to
applications
o Removed strong/weak end system discussions
Changes from -19 to -20:
o figure 1 updates to show Server as being somewhere in the network
o Introductory material to show relation to other RFCs on multi-
addressing
Changes from -18 to -19:
o added new section on Prefix Delegation Services
Changes from -17 to -18:
o re-worked discussion on the prefix delegation service in Section 1
o updated figures in Section 1
Changes from -16 to -17:
o added supporting text in the introduction to discuss the
Delegating Router's relationship with the Requesting Router and
with supporting intrastructure in the operator's network
o updated figures in introduction to include representation of
operator's network
o added new section on Address Autoconfiguration Considerations
Author's Address
Templin Expires July 4, 2020 [Page 14]
Internet-DrafIPv6 Prefix Delegation and Multi-Addressing Mo January 2020
Fred L. Templin (editor)
Boeing Research & Technology
P.O. Box 3707
Seattle, WA 98124
USA
Email: fltemplin@acm.org
Templin Expires July 4, 2020 [Page 15]