IPv6 Prefix Delegation for End Systems
draft-templin-v6ops-pdhost-08
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| Author | Fred Templin | ||
| Last updated | 2017-09-18 (Latest revision 2017-09-06) | ||
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draft-templin-v6ops-pdhost-08
Network Working Group F. Templin, Ed.
Internet-Draft Boeing Research & Technology
Intended status: Informational September 18, 2017
Expires: March 22, 2018
IPv6 Prefix Delegation for End Systems
draft-templin-v6ops-pdhost-08.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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This Internet-Draft will expire on March 22, 2018.
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Copyright (c) 2017 IETF Trust and the persons identified as the
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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 DHCPv6 PD [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 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 ("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 |
+---------+ +---------+ +---------+ +---------+
Figure 1: Tethered 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) interfaces. Hosts 'H(i)' on a downstream network
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 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)
an IPv6 node that is capable of acting as a host from the
perspective of local applications and as a router from the
perspective of IPv6 ND and IPv6 prefix delegation. The ES acts as
a host with an embedded gateway function as described in
[RFC1122].
shared prefix
an IPv6 prefix that may be advertised to more than one node on the
same link, e.g., in a multicast 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 a unicast RA message PIO. (However, the node may have no
way of knowing that the prefix is an individual prefix and not a
shared one.)
delegated prefix
a prefix that is exclusively delegated to a requesting ES for
provisioning on its downstream links.
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).
ESes that use SLAAC and/or DHCPv6 address configuration 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) 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
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 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 a downstream interface. 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 use 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 using either SLAAC or
DHCPv6 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 assign 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 are the same as specified for DHCPv6 Prefix
Delegation in [RFC3633] and for IPv6 Neighbor Discovery in[RFC4861].
Additionally, the ES may receive unwanted IPv6 packets via the
upstream interface that match a delegated prefix but do not match one
of the ESes configured addresses. In that case, the ES drops the
packets and follows the procedures in Section 7. The ES may also
receive IPv6 packets via the upstream interface that do not match a
delegated prefix. In that case, the ES drops the packets and follows
the Section 7 procedures, i.e., it does not send the packets to a
default router.
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>.
[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>.
[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>.
[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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