IPv6 Prefix Delegation for Hosts
draft-templin-v6ops-pdhost-06
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| Author | Fred Templin | ||
| Last updated | 2017-09-05 | ||
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draft-templin-v6ops-pdhost-06
Network Working Group F. Templin, Ed.
Internet-Draft Boeing Research & Technology
Intended status: Informational September 5, 2017
Expires: March 9, 2018
IPv6 Prefix Delegation for Hosts
draft-templin-v6ops-pdhost-06.txt
Abstract
IPv6 prefixes are typically delegated to requesting routers which
then use them to number their downstream-attached links and networks.
This document considers both this traditional case, and the case when
the "requesting router" is actually a simple host which receives a
delegated prefix that it can use for its own internal multi-
addressing purposes. This latter method can be employed 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 March 9, 2018.
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
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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 . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Multi-Addressing Considerations . . . . . . . . . . . . . . . 5
4. Multi-Addressing Alternatives for Delegated Prefixes . . . . 6
5. MLD/DAD Implications . . . . . . . . . . . . . . . . . . . . 6
6. IPv6 Neighbor Discovery Implications . . . . . . . . . . . . 7
7. ICMPv6 Implications . . . . . . . . . . . . . . . . . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
9. Security Considerations . . . . . . . . . . . . . . . . . . . 8
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
11.1. Normative References . . . . . . . . . . . . . . . . . . 8
11.2. Informative References . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10
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 any available prefix delegation service, 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 IP Internetwork 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 'H(i)' on a LAN subsequently receive addresses
'A(i)' taken from 'P' via an address autoconfiguration service such
as IPv6 Stateless Address Autoconfiguration (SLAAC) [RFC4862]. 'R'
then acts as a router between hosts 'H(i)' and correspondents
reachable via the WAN interface.
This document also 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. 'R' can 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) as shown in Figure 2:
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+---------------------+
|Delegating Router 'D'|
| (Delegate 'P') |
+----------+----------+
|
.-(::::::::)
.-(:::: IP ::::)-.
(:: Internetwork ::)
`-(::::::::::::)-'
`-(::::::)-'
| WAN Interface
+----------+----------+
| (Receive 'P') |
| Requesting Node 'R' |
+---------------------+
| Loopback Interface |
+--+-+--+-++-+-----+--+
|A1| |A2| |A3| ... |An|
+--+-+--+-+--+-----+--+
Figure 2: Weak End System Model
'R' could instead function as a host under the strong end system
model [RFC1122] by assigning IPv6 addresses taken from prefix 'P' to
the WAN interface as shown in Figure 3:
+---------------------+
|Delegating Router 'D'|
| (Delegate 'P') |
+----------+----------+
|
.-(::::::::)
.-(:::: IP ::::)-.
(:: Internetwork ::)
`-(::::::::::::)-'
`-(::::::)-'
| WAN Interface
+--+-+--+-++-+-----+--+
|A1| |A2| |A3| ... |An|
+--+ +--+ +--+ +--+
| (Receive 'P') |
| Requesting Node 'R' |
+---------------------+
Figure 3: Strong End System Model
The major benefit for a host managing a delegated prefix in either
the weak or strong end system models is multi-addressing. With
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multi-addressing, the host can configure an unlimited supply of
addresses to make them available for local applications without
requiring coordination with any other nodes.
The following sections present multi-addressing considerations for
hosts that employ prefix delegation mechanisms.
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 multiple access links (e.g.,
multicast-capable, NBMA, shared media, etc.), 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.
[RFC7934] 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/or DHCPv6 address configuration configure
addresses from a shared prefix and assign them to the interface over
which the prefix was received (e.g., in an RA). 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 without invoking MLD/DAD on the WAN
interface, since the prefix has been delegated to the node for its
own exclusive use and is not shared with any other nodes.
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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
when the node receives a prefix delegation in which the prefix is
delegated for its own exclusive use.
When the node receives the prefix, it can distribute the prefix to
downstream-attached networks via its LAN interfaces and configure one
or more addresses for itself on a LAN interface. The node then acts
as a router on behalf of its downstream-attached networks and
configures a default route that points to a router on the WAN link.
This approach is often known as the "tethered" configuration.
The node could instead use the delegated prefix for its own 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.
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.
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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.
6. IPv6 Neighbor Discovery Implications
The node acts as a simple host to send Router Solicitation (RS)
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
[I-D.templin-6man-rio-redirect].
7. ICMPv6 Implications
The Internet Control Message Protocol for IPv6 (ICMPv6) includes a
set of control message types [RFC4443] including Destination
Unreachable (DU). Routers return DU messages with code 0 ("No route
to destination") when a packet arrives for which there is no matching
entry in the routing table, and with code 3 ("Address unreachable")
when the IPv6 destination address cannot be resolved into a link-
layer address. Hosts return DU messages with code 3 to internal
applications when an address cannot be resolved, and with code 4
("Port unreachable") to the sender if the transport protocol has no
listener.
A node that obtains a prefix delegation for "tethering" purposes acts
like a router in all respects and returns DU messages the same as for
any router.
A node that obtains a prefix delegation for its own multi-addressing
purposes (whether weak or strong end system) should act like a host
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and refrain from sending DU messages with code 0 or 3 when it
receives a packet from a sender with an unknown IPv6 destination
address. That is to say that the node should silently drop any IPv6
packets with a destination address that matches the delegated prefix
but does not match any of its configured addresses.
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] and for IPv6 Neighbor Discovery in[RFC4861].
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,
<https://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,
<https://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, <https://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, <https://www.rfc-editor.org/info/rfc3315>.
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[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,
<https://www.rfc-editor.org/info/rfc3633>.
[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>.
[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>.
[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>.
11.2. Informative References
[I-D.templin-6man-rio-redirect]
Templin, F. and j. woodyatt, "Route Information Options in
IPv6 Neighbor Discovery", draft-templin-6man-rio-
redirect-04 (work in progress), August 2017.
[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>.
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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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