IPv6 Prefix Delegation for Hosts
draft-templin-v6ops-pdhost-05
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draft-templin-v6ops-pdhost-05
Network Working Group F. Templin, Ed.
Internet-Draft Boeing Research & Technology
Intended status: Informational March 27, 2017
Expires: September 28, 2017
IPv6 Prefix Delegation for Hosts
draft-templin-v6ops-pdhost-05.txt
Abstract
IPv6 prefixes are typically delegated to requesting routers which
then use them to number their downstream-attached links and networks.
The requesting router then acts as a router between the downstream-
attached hosts and the upstream Internetwork, and can also act as a
host under the weak end system model. This document considers the
case when the "requesting router" is actually a simple host which
receives a delegated prefix that it can use solely for its own
internal multi-addressing purposes under the strong end system model.
This method can be applied in a wide variety of use cases to allow
ample address availability without impacting link performance.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on September 28, 2017.
Copyright Notice
Copyright (c) 2017 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
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carefully, as they describe your rights and restrictions with respect
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Multi-Addressing Considerations . . . . . . . . . . . . . . . 5
4. Multi-Addressing Alternatives for Delegated Prefixes . . . . 5
5. MLD/DAD Implications . . . . . . . . . . . . . . . . . . . . 6
6. IPv6 Neighbor Discovery Implications . . . . . . . . . . . . 7
7. "Mixed Mode" Implications . . . . . . . . . . . . . . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
9. Security Considerations . . . . . . . . . . . . . . . . . . . 7
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
11.1. Normative References . . . . . . . . . . . . . . . . . . 8
11.2. Informative References . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
IPv6 Prefix Delegation (PD) entails 1) the communication of a prefix
from a delegating authority to a requesting node, 2) a representation
of the prefix in the routing system, and 3) a control messaging
service to maintain delegated prefix lifetimes. Following
delegation, the prefix is available for the requesting node's
exclusive use and is not shared with any other nodes. An example
IPv6 PD service is DHCPv6 PD [RFC3315][RFC3633].
Using services such as DHCPv6 PD, a Delegating Router 'D' delegates a
prefix 'P' to a Requesting Node 'R'' as shown in Figure 1:
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+---------------------+
|Delegating Router 'D'|
| (Delegate 'P') |
+----------+----------+
|
.-(::::::::)
.-(:::: IP ::::)-.
(:: Internetwork ::)
`-(::::::::::::)-'
`-(::::::)-'
| WAN Interface
+----------+----------+
| (Receive 'P') |
| Requesting Node 'R'|
+----------+----------+
| LAN Interface
X----+-------------+--------+----+---------------+---X
| | LAN | |
+---++-+--+ +---++-+--+ +---++-+--+ +---++-+--+
| |A1| | | |A2| | | |A3| | | |An| |
| +--+ | | +--+ | | +--+ | | +--+ |
| Host H1 | | Host H2 | | Host H3 | ... | Host Hn |
+---------+ +---------+ +---------+ +---------+
Figure 1: Prefix Delegation Model
In this figure, when Delegating Router 'D' delegates prefix 'P', the
prefix is injected into the routing system in some fashion to ensure
that IPv6 packets with destination addresses covered by 'P' are
unconditionally forwarded to Requesting Node 'R'. Meanwhile, 'R'
receives 'P' via its "WAN" interface and sub-delegates 'P' to its
downstream-attached links via one or more "LAN" interfaces. Hosts
'Hn' on a LAN interface subsequently receive addresses 'An' taken
from 'P' via an address autoconfiguration service such as IPv6
Stateless Address Autoconfiguration (SLAAC) [RFC4862]. 'R' then acts
as a router between hosts 'Hn' and correspondents reachable via the
WAN interface. 'R' can also (or instead) act as a host under the
weak end system model [RFC1122] if it can assign addresses taken from
'P' to its own internal virtual interfaces (e.g., a loopback).
This document considers the case when 'R' is actually a simple host,
and receives a prefix delegation 'P' as if it were a router. The
host need not have any LAN interfaces, and can use the prefix solely
for its own internal addressing purposes. This could include
assigning IPv6 adddresses taken from prefix 'P' to the WAN interface
and then functioning as a host under the strong end system model
[RFC1122] as shown in Figure 2:
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+---------------------+
|Delegating Router 'D'|
| (Delegate 'P') |
+----------+----------+
|
.-(::::::::)
.-(:::: IP ::::)-.
(:: Internetwork ::)
`-(::::::::::::)-'
`-(::::::)-'
| WAN Interface
+--+-+--+-++-+-----+--+
|A1| |A2| |A3| ... |An|
+--+ +--+ +--+ +--+
| (Receive 'P') |
| Requesting Node 'R' |
+---------------------+
Figure 2: Strong End System Model
In the above diagram, Requesting Node 'R' receives prefix 'P' from
Delegating Router 'D' the same as described above. However, when 'R'
receives 'P' it assigns addresses 'An' taken from 'P' to the WAN
interface instead of sub-delegating 'P' to downstream attached LAN
interfaces. The major benefit for a host managing a delegated prefix
in this fashion is multi-addressing. With multi-addressing, the host
can assign an unlimited supply of addresses to make them available
for local applicaitons without requiring coordination with any other
nodes.
This approach is applicable to a wide variety of use cases. For
example, it can be used to coordinate the Virtual Private Network
(VPN) interfaces of mobile devices (e.g., cellphones, tablets, laptop
computers, etc.) that connect into a home enterprise network via
public access networks. In that case, the mobile device can assign
addresses taken from prefix 'P' to the VPN interface so that
applications would work the same as for a simple host connected to a
LAN. The approach can also be applied to aviation applications for
both manned and unmanned aircraft where the aircraft is treated as a
mobile host that needs to maintain stable IPv6 addresses even as it
hands off between available aviation data links across various phases
of flight. The approach further applies to any prefix delegation use
case where the prefix recipient wishes to act as a simple host, for
example a cellular service customer device that receives a prefix
delegation from their service provider.
The following sections present multi-addressing considerations for
hosts that employ prefix delegation mechanisms.
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2. Terminology
The terminology of the normative references apply. The following
terms are defined for the purposes of this document:
shared prefix
an IPv6 prefix that may be advertised to more than one node on the
same link, e.g., in a Prefix Information Option (PIO) included in
a Router Advertisement (RA) message [RFC4861]. The shared prefix
property applies not only on multi-access links (e.g., Ethernet),
but also on point-to-point links where the shared prefix is
visible to both ends of the link.
delegated prefix
a prefix that is delegated to a requesting node solely for its own
use, and is not delegated to any other nodes on the link.
3. Multi-Addressing Considerations
IPv6 allows nodes to assign multiple addresses to a single interface.
[I-D.ietf-v6ops-host-addr-availability] discusses options for multi-
addressing as well as use cases where multi-addressing may be
desirable. Address configuration options for multi-addressing
include SLAAC [RFC4862], stateful DHCPv6 address configuration
[RFC3315] and any other address formation methods (e.g., manual
configuration).
Nodes that use SLAAC and DHCPv6 address configuration configure
addresses from a shared prefix and assign them to the link over which
the prefix was received. When this happens, the node is obliged to
use Multicast Listener Discovery (MLD) 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 that
receives the shared prefix configures a duplicate address.
In contrast, a node that uses address configuration from a delegated
prefix can assign addresses to the interface over which the prefix is
received without invoking MLD/DAD, 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 prefix delegation, it has many alternatives
for the way in which it can provision the prefix. [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
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when the node receives a prefix delegation in which the prefix is
delegated for the exclusive use of the prefix recipient.
When the node receives the prefix (e.g., a /64), it can sub-delegate
the prefix to its LAN interfaces and configure one or more addresses
for itself on a LAN interface. The node also configures a default
route that points to a router on the WAN link. The node can then act
as both a host for its own applications accodring to the weak end
system model and a router for any downstream-attached hosts. This
approach is often known as the "tethered" configuration.
When the node does not have any LAN interfaces, it may still wish to
obtain a prefix for multi-addressing purposes. In a first
alternative, the node can receive the prefix acting as a requesting
node over the WAN interface but then assign the prefix to an internal
virtual interface (e.g., a loopback interface) and assign one or more
addresses taken from the prefix to the virtual interface. In that
case, applications on the node can use the assigned addresses
according to the weak end system model.
In a second alternative, the node can receive the prefix as a
requesting node over the WAN interface but then assign one or more
addresses taken from the prefix to the WAN interface. In that case,
applications on the node can use the assigned addresses according to
the strong end system model as shown in Figure 2.
In both of these latter two cases, the node acts as a host internally
even though it behaves as a router from the standpoint of prefix
delegation and neighbor discovery over the WAN interface. The host
can configure as many addresses for itself as it wants.
5. MLD/DAD Implications
When a node configures addresses for itself using either SLAAC or
DHCPv6 from a shared prefix, the node performs MLD/DAD by sending
multicast messages to test whether there is another node on the link
that configures a duplicate address from the shared prefix. 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 using a delegated prefix,
the node can configure as many addresses as it wants but does not
perform MLD/DAD for any of the addresses over the WAN interface.
This means that arbitrarily many addresses can be assigned without
causing any multicast messaging over the WAN link that could disturb
other nodes. Note however that nodes that assign addresses directly
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to the WAN interface must be capable of disabling MLD/DAD on the WAN
interface, i.e., by setting DupAddrDetectTransmits to zero [RFC4862].
6. IPv6 Neighbor Discovery Implications
The node acts as a simple host to send Router Solicitation messages
over the WAN interface the same as described in Section 4.2 of
[RFC7084].
In order to maintain the appearance of a router (i.e., even though it
is acting as a simple host), the node sets the "Router" flag to TRUE
in any Neighbor Advertisement messages it sends. This ensures that
the "isRouter" flag in the neighbor cache entries of any neighbors
remains TRUE.
The node initially has only a default route pointing to a router on
the WAN link. This means that packets sent over the node's WAN
interface will initially go through a default router even if there is
a better first-hop node on the link. In that case,a Redirect message
can update the node's neighbor cache, and future packets can take the
more direct route without disturbing the default router. The
Redirect can apply either to a singleton destination address, or to
an entire destination prefix as described in AERO
[I-D.templin-aerolink].
7. "Mixed Mode" Implications
In some instances, a node may receive both delegated and shared
prefixes. In that case, the node could avoid MLD/DAD for addresses
configured from the delegated prefixes and employ MLD/DAD for
addresses configured from he shared prefixes. Note however that
since DupAddrDetectTransmits applies on a per-interface (and not a
per-prefix) basis any such considerations are out of scope since this
document does not update any standards-track specifications.
8. IANA Considerations
This document introduces no IANA considerations.
9. Security Considerations
Security considerations are the same as specified for DHCPv6 Prefix
Delegation in [RFC3633].
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10. Acknowledgements
This work was motivated by recent discussions on the v6ops list.
Mark Smith pointed out the need to consider MLD as well as DAD for
the assignment of addresses to interfaces. Ricardo Pelaez-Negro,
Edwin Cordeiro, Fred Baker and Naveen Lakshman provided useful
comments that have greatly improved the draft.
11. References
11.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<http://www.rfc-editor.org/info/rfc791>.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989,
<http://www.rfc-editor.org/info/rfc1122>.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <http://www.rfc-editor.org/info/rfc2460>.
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
2003, <http://www.rfc-editor.org/info/rfc3315>.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
DOI 10.17487/RFC3633, December 2003,
<http://www.rfc-editor.org/info/rfc3633>.
[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,
<http://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,
<http://www.rfc-editor.org/info/rfc4862>.
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[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,
<http://www.rfc-editor.org/info/rfc7084>.
[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,
<http://www.rfc-editor.org/info/rfc7278>.
11.2. Informative References
[I-D.ietf-v6ops-host-addr-availability]
Colitti, L., Cerf, D., Cheshire, S., and d.
dschinazi@apple.com, "Host address availability
recommendations", draft-ietf-v6ops-host-addr-
availability-07 (work in progress), May 2016.
[I-D.templin-aerolink]
Templin, F., "Asymmetric Extended Route Optimization
(AERO)", draft-templin-aerolink-74 (work in progress),
November 2016.
Author's Address
Fred L. Templin (editor)
Boeing Research & Technology
P.O. Box 3707
Seattle, WA 98124
USA
Email: fltemplin@acm.org
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