Network Working Group F. Templin, Ed.
Internet-Draft Boeing Research & Technology
Intended status: Informational September 19, 2017
Expires: March 23, 2018
IPv6 Prefix Delegation for End Systems
draft-templin-v6ops-pdhost-09.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 the case when the "requesting router" is
actually an end system which receives a delegated prefix that it can
use for its own sub-delegation and/or multi-addressing purposes.
Status of This Memo
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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 router to a requesting router, 2) a representation
of the prefix in the delegating router's routing table, and 3) a
control messaging service to maintain delegated prefix lifetimes.
Following delegation, the prefix is available for the requesting
router's exclusive use and is not shared with any other nodes. An
example IPv6 PD service is the Dynamic Host Configuration Protocol
for IPv6 (DHCPv6) [RFC3315][RFC3633].
This document considers the case when the "requesting router" is
actually an end system (ES) that can act as a router on behalf of its
downstream networks and/or as a host on behalf of its local
applications. The following paragraphs present possibilities for ES
behavior upon receipt of a delegated prefix.
For ESes that connect downstream-attached (aka "tethered") networks,
a Delegating Router 'D' delegates a prefix 'P' to a Requesting ES
'R'' as shown in Figure 1:
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+---------------------+
|Delegating Router 'D'|
| (Delegate 'P') |
+----------+----------+
|
| Upstream Interface
|
+----------+----------+
| (Receive 'P') |
| Requesting ES 'R' |
+----------+----------+
|
| Downstream Interface
|
X----+-------------+--------+----+---------------+---X
| | | |
+---++-+--+ +---++-+--+ +---++-+--+ +---++-+--+
| |A1| | | |A2| | | |A3| | | |An| |
| +--+ | | +--+ | | +--+ | | +--+ |
| Host H1 | | Host H2 | | Host H3 | ... | Host Hn |
+---------+ +---------+ +---------+ +---------+
<-------------- Tethered Network ------------->
Figure 1: Tethering End System Model
In this figure, when Delegating Router 'D' delegates prefix 'P', it
inserts 'P' into its routing table with Requesting ES 'R' as the next
hop. Meanwhile, 'R' receives 'P' via its upstream interface and sub-
delegates 'P' to its downstream external (physical) and/or internal
(virtual) networks. Hosts 'H(i)' on downstream networks subsequently
assign addresses 'A(i)' taken from 'P' to their interfaces. 'R' then
acts as a router between hosts 'H(i)' and correspondents reachable
via the upstream interface.
This document also considers the case when 'R' does not have any
downstream interfaces, and can use 'P' solely for its own internal
addressing purposes. In that case, 'R' assigns 'P' to a virtual
interface (e.g., a loopback) so that unused portions of the prefix
will be unreachable.
'R' can then function under the weak end system model [RFC1122] by
assigning addresses taken from 'P' to virtual interfaces (e.g., a
loopback) as shown in Figure 2:
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+---------------------+
|Delegating Router 'D'|
| (Delegate 'P') |
+----------+----------+
|
| Upstream Interface
|
+----------+----------+
| (Receive 'P') |
| Requesting ES 'R' |
+---------------------+
| Loopback Interface |
+--+-+--+-+--+-----+--+
|A1| |A2| |A3| ... |An|
+--+-+--+-+--+-----+--+
Figure 2: Weak End System Model
'R' could instead function under the strong end system model
[RFC1122] by assigning IPv6 addresses taken from 'P' to the upstream
interface as shown in Figure 3:
+---------------------+
|Delegating Router 'D'|
| (Delegate 'P') |
+----------+----------+
|
|
|
+----------+----------+
| Upstream Interface |
+--+-+--+-+--+-----+--+
|A1| |A2| |A3| ... |An|
+--+ +--+ +--+ +--+
| (Receive 'P') |
| Requesting ES 'R' |
+---------------------+
Figure 3: Strong End System Model
The major benefit for an ES managing a delegated prefix in either the
weak or strong end system models is multi-addressing. With multi-
addressing, the ES can configure an unlimited supply of addresses to
make them available for local applications without requiring
coordination with any other nodes on the upstream interface.
The following sections present multi-addressing considerations for
ESes 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:
node
a device that observes IPv6 node requirements [RFC6434].
End System (ES)
a node with an embedded gateway function [RFC1122] that acts as a
host on behalf of its local applications and/or as a router on
behalf of any nodes on its tethered downstream interface(s). The
ES further behaves as a router from the standpoint of prefix
delegation and neighbor discovery over the upstream interface.
shared prefix
an IPv6 prefix that may be advertised to more than one node on the
link, e.g., in a Router Advertisement (RA) message Prefix
Information Option (PIO) [RFC4861].
individual prefix
an IPv6 prefix that is advertised to exactly one node on the link
(e.g., in an PIO); however, the node may have no way of knowing
that the prefix is an individual prefix and not a shared one.
delegated prefix
an IPv6 prefix that is conveyed to an ES for its own exclusive
use, where the ES is an active participant in the prefix
delegation procedure.
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], stateful DHCPv6 address
configuration [RFC3315], manual configuration, etc.
ESes configure addresses from a shared or individual prefix and
assign them to the upstream interface. When it assigns the
addresses, the ES 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.
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In contrast, an ES that uses address configuration from a delegated
prefix can assign addresses without invoking MLD/DAD on the upstream
interface, since the prefix has been delegated to the ES for its own
exclusive use and is not shared with any other nodes.
4. Multi-Addressing Alternatives for Delegated Prefixes
When an ES receives a prefix delegation, it has many alternatives for
provisioning 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 ES receives a
prefix delegation in which the prefix is delegated for its own
exclusive use.
When the ES receives the prefix, it can distribute the prefix to
downstream interfaces and configure one or more addresses for itself
on downstream interfaces. The ES then acts as a router on behalf of
its downstream-attached networks and configures a default route that
points to a router via the upstream interface.
The ES could instead (or in addition) use portions of the delegated
prefix for its own multi-addressing purposes. In a first
alternative, the ES can assign the prefix to a virtual interface
(e.g., a loopback) and assign one or more addresses taken from the
prefix to virtual interfaces. In that case, applications on the ES
can use the assigned addresses according to the weak end system
model.
In a second alternative, the ES can assign the prefix to a virtual
interface and assign one or more addresses taken from the prefix to
the upstream interface. In that case, applications on the ES can use
the assigned addresses according to the strong end system model.
In both of these latter two cases, the ES acts as a host internally
even though it behaves as a router from the standpoint of prefix
delegation and neighbor discovery over the upstream interface. The
ES can configure as many addresses for itself as it wants.
5. MLD/DAD Implications
When an ES configures addresses for itself from a shared or
individual prefix, the ES 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.
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When an ES configures addresses for itself from a delegated prefix,
the ES can configure as many addresses as it wants but does not
perform MLD/DAD for any of the addresses over the upstream interface.
This means that the ES can configure arbitrarily many addresses
without causing any multicast messaging over the upstream interface
that could disturb other nodes.
6. IPv6 Neighbor Discovery Implications
The ES acts as a simple host to send Router Solicitation (RS)
messages over the upstream interface (i.e., the same as described in
Section 4.2 of [RFC7084]) but also 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 ES initially has only a default route pointing to a router via
the upstream interface. This means that packets sent over the ES's
upstream 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 ES'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).
According to [RFC4443], routers SHOULD return DU messages (subject to
rate limiting) 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.
According to [RFC4443], hosts SHOULD return DU messages (subject to
rate limiting) with code 3 to internal applications when the IPv6
destination address cannot be resolved, and with code 4 ("Port
unreachable") if the IPv6 destination address is one of its own
addresses but the transport protocol has no listener.
An ES that obtains and manages a prefix delegation per this document
follows the same procedures as described for both routers and hosts
above.
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8. IANA Considerations
This document introduces no IANA considerations.
9. Security Considerations
Security considerations for IPv6 Neighbor Discovery [RFC4861] and any
applicable prefix delegation mechanisms apply to this document.
Additionally, the ES may receive unwanted IPv6 packets via the
upstream interface that match a delegated prefix but do not match a
configured IPv6 address. In that case, the ES drops the packets and
follows the "Address unreachable" procedures in Section 7.
The ES may also receive IPv6 packets via the upstream interface that
do not match any of the ES's delegated prefixes. In that case, the
ES drops the packets and follows the "No route to destination"
procedures in Section 7, i.e., even if it has a matching route in its
routing table with a neighbor on the upstream link as the next hop.
This is necessary to avoid reflection attacks over the upstream
interface.
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, Naveen Lakshman and Ole Troan provided
useful comments that have greatly improved the document.
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>.
[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>.
[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>.
[RFC6434] Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node
Requirements", RFC 6434, DOI 10.17487/RFC6434, December
2011, <https://www.rfc-editor.org/info/rfc6434>.
[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>.
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.
[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>.
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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