Network Working Group F. Templin, Ed.
Internet-Draft Boeing Research and Technology
Intended status: Informational February 17, 2009
Expires: August 21, 2009
Virtual Enterprise Traversal (VET)
draft-templin-autoconf-dhcp-34.txt
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Abstract
Enterprise networks connect routers over various link types, and may
also connect to provider networks and/or the global Internet.
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Enterprise network nodes require a means to automatically provision
IP addresses/prefixes and support internetworking operation in a wide
variety of use cases including SOHO networks, Mobile Ad-hoc Networks
(MANETs), multi-organizational corporate networks and the interdomain
core of the global Internet itself. This document specifies a
Virtual Enterprise Traversal (VET) abstraction for autoconfiguration
and operation of nodes in enterprise networks.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Enterprise Characteristics . . . . . . . . . . . . . . . . . . 10
4. Autoconfiguration . . . . . . . . . . . . . . . . . . . . . . 11
4.1. Enterprise Router (ER) Autoconfiguration . . . . . . . . . 11
4.2. Enterprise Border Router (EBR) Autoconfiguration . . . . . 13
4.2.1. VET Interface Autoconfiguration . . . . . . . . . . . 13
4.2.2. Provider-Aggregated (PA) Prefix Autoconfiguration . . 14
4.2.3. Provider-Independent (PI) Prefix Autoconfiguration . . 15
4.3. Enterprise Border Gateway (EBG) Autoconfiguration . . . . 15
4.4. VET Host Autoconfiguration . . . . . . . . . . . . . . . . 16
5. Internetworking Operation . . . . . . . . . . . . . . . . . . 16
5.1. Routing Protocol Participation . . . . . . . . . . . . . . 16
5.2. IPv6 Router Discovery and Prefix Registration . . . . . . 16
5.2.1. IPv6 Default Router Discovery . . . . . . . . . . . . 17
5.2.2. IPv6 PA Prefix Registration . . . . . . . . . . . . . 17
5.2.3. IPv6 PI Prefix Registration . . . . . . . . . . . . . 18
5.2.4. IPv6 Next-Hop EBR Discovery . . . . . . . . . . . . . 19
5.3. IPv4 Router Discovery and Prefix Registration . . . . . . 21
5.4. Forwarding Packets . . . . . . . . . . . . . . . . . . . . 22
5.5. SEAL Encapsulation . . . . . . . . . . . . . . . . . . . . 22
5.6. Generating Errors . . . . . . . . . . . . . . . . . . . . 23
5.7. Processing Errors . . . . . . . . . . . . . . . . . . . . 23
5.8. Mobility and Multihoming Considerations . . . . . . . . . 24
5.9. Enterprise-Local Communications . . . . . . . . . . . . . 25
5.10. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 25
5.11. Service Discovery . . . . . . . . . . . . . . . . . . . . 26
5.12. Enterprise Partitioning . . . . . . . . . . . . . . . . . 27
5.13. EBG Prefix State Recovery . . . . . . . . . . . . . . . . 27
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
7. Security Considerations . . . . . . . . . . . . . . . . . . . 28
8. Related Work . . . . . . . . . . . . . . . . . . . . . . . . . 28
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 29
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 29
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
11.1. Normative References . . . . . . . . . . . . . . . . . . . 29
11.2. Informative References . . . . . . . . . . . . . . . . . . 31
Appendix A. Duplicate Address Detection (DAD) Considerations . . 33
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 34
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 38
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1. Introduction
Enterprise networks [RFC4852] connect routers over various link types
(see: [RFC4861], Section 2.2). The term "enterprise network" in this
context extends to a wide variety of use cases and deployment
scenarios. For example, an "enterprise" can be as small as a SOHO
network, as complex as a multi-organizational corporation, or as
large as the global Internet itself. Certain Mobile Ad-hoc Networks
(MANETs) [RFC2501] can also be considered as a challenging example of
an enterprise network, in that their topologies may change
dynamically over time and that they may employ little/no active
management by a centralized network administrative authority. These
specialized characteristics for MANETs require careful consideration,
but the same principles apply equally to other enterprise network
scenarios.
This document specifies a Virtual Enterprise Traversal (VET)
abstraction for autoconfiguration and internetworking operation,
where addresses of different scopes may be assigned on various types
of interfaces with diverse properties. Both IPv4 [RFC0791] and IPv6
[RFC2460] are discussed within this context. The use of standard
DHCP [RFC2131][RFC3315] and neighbor discovery
[RFC0826][RFC1256][RFC4861] mechanisms is assumed unless otherwise
specified.
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Provider-edge Interfaces
x x x
| | |
+--------------------+---+--------+----------+ E
| | | | | n
| I | | .... | | t
| n +---+---+--------+---+ | e
| t | +--------+ /| | r
| e I x----+ | Host | I /*+------+--< p I
| r n | |Function| n|**| | r n
| n t | +--------+ t|**| | i t
| a e x----+ V e|**+------+--< s e
| l r . | E r|**| . | e r
| f . | T f|**| . | f
| V a . | +--------+ a|**| . | I a
| i c . | | Router | c|**| . | n c
| r e x----+ |Function| e \*+------+--< t e
| t s | +--------+ \| | e s
| u +---+---+--------+---+ | r
| a | | .... | | i
| l | | | | o
+--------------------+---+--------+----------+ r
| | |
x x x
Enterprise-edge Interfaces
Figure 1: Enterprise Router (ER) Architecture
Figure 1 above depicts the architectural model for an Enterprise
Router (ER). As shown in the figure, an ER may have a variety of
interface types including enterprise-edge, enterprise-interior,
provider-edge, internal-virtual, as well as VET interfaces used for
encapsulation of inner IP packets within outer IP headers. The
different types of interfaces are defined, and the autoconfiguration
mechanisms used for each type are specified. This architecture
applies equally for MANET routers, in which enterprise-interior
interfaces correspond to the wireless multihop radio interfaces
typically associated with MANETs. Out of scope for this document is
the autoconfiguration of provider interfaces, which must be
coordinated in a manner specific to the service provider's network.
Enterprise networks must have a means for supporting both Provider-
Independent (PI) and Provider-Aggregated (PA) IP prefixes for global-
scope communications. This is especially true for enterprise
scenarios that involve mobility and multihoming. Also in scope are
ingress filtering for multi-homed sites, adaptation based on
authenticated ICMP feedback from on-path routers, effective tunnel
path MTU mitigations and routing scaling suppression as required in
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many enterprise network scenarios. Recognizing that one size does
not fit all, the VET specification provides adaptable mechanisms that
address these issues and more in a wide variety of enterprise network
use cases.
VET represents a functional superset of 6over4 [RFC2529] and ISATAP
[RFC5214], and further supports additional encapsulations such as
IPsec [RFC4301], SEAL [I-D.templin-seal], etc. As a result, VET
provides a map-and-encaps architecture using IP-in-IP tunneling based
on both IP routing and mapping service resolution (defined herein).
The VET principles can be either directly or indirectly traced to the
deliberations of the ROAD group in January 1992, and also to still
earlier works including NIMROD [RFC1753], the Catenet model for
internetworking [CATENET][IEN48][RFC2775], etc. [RFC1955] captures
the high-level architectural aspects of the ROAD group deliberations
in a "New Scheme for Internet Routing and Addressing [ENCAPS] for
IPNG".
VET is related to the present-day activites of the IETF autoconf,
dhc, ipv6, manet and v6ops working groups, as well as the IRTF rrg
working group.
2. Terminology
The mechanisms within this document build upon the fundamental
principles of IP-within-IP encapsulation. The terms "inner" and
"outer" are used to respectively refer to the innermost IP {address,
protocol, header, packet, etc.} *before* encapsulation, and the
outermost IP {address, protocol, header, packet, etc.} *after*
encapsulation. VET also allows for inclusion of "mid-layer"
encapsulations between the inner and outer layers, including IPSec
[RFC4301], the Subnetwork Encapsulation and Adaptation Layer (SEAL)
[I-D.templin-seal], etc.
The terminology in the normative references apply; the following
terms are defined within the scope of this document:
subnetwork
the same as defined in [RFC3819].
enterprise
the same as defined in [RFC4852]. An enterprise is also
understood to refer to a cooperative networked collective with a
commonality of business, social, political, etc. interests.
Minimally, the only commonality of interest in some enterprise
network scenarios may be the cooperative provisioning of
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connectivity itself.
site
a logical and/or physical grouping of interfaces that connect a
topological area less than or equal to an enterprise in scope. A
site within an enterprise can in some sense be considered as an
enterprise unto itself.
Mobile Ad-hoc Network (MANET)
a connected topology of mobile or fixed routers that maintain a
routing structure among themselves over dynamic links, where a
wide variety of MANETs share common properties with enterprise
networks. Characteristics of MANETs are defined in [RFC2501],
Section 3.
enterprise/site/MANET
throughout the remainder of this document, the term "enterprise"
is used to collectively refer to any of enterprise/site/MANET,
i.e., the VET mechanisms and operational principles can be applied
to enterprises, sites and MANETs of any size or shape.
Enterprise Router (ER)
As depicted in Figure 1, an Enterprise Router (ER) is a fixed or
mobile router that comprises a router function, a host function,
one or more enterprise-interior interfaces and zero or more
internal virtual, enterprise-edge, provider-edge and VET
interfaces. At a minimum, an ER forwards packets over one or more
sets of enterprise-interior interfaces, where each set connects to
a distinct enterprise.
Enterprise Border Router (EBR)
an ER that connects edge networks to the enterprise, and/or
connects multiple enterprises together. An EBR configures a
seperate VET interface over each set of enterprise-interior
interfaces that connect the EBR to each distinct enterprise. In
particular, an EBR may configure mulitple VET interfaces - one for
each distinct enterprise. All EBRs are also ERs.
Enterprise Border Gateway (EBG)
an EBR that connects VET interfaces configured over child
enterprises to a provider network - either directly via a
provider-edge interface, or indirectly via another VET interface
configured over a parent enterprise. EBRs may act as EBGs on some
VET interfaces and as ordinary EBRs on other VET interfaces. All
EBGs are also EBRs.
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enterprise-interior interface
a ER's attachment to a link within an enterprise. Packets sent
over enterprise-interior interfaces may be forwarded over multiple
additional enterprise-interior interfaces within the enterprise
before they are forwarded via an enterprise-edge interface,
provider-edge interface or a VET interface configured over a
different enterprise.
enterprise-edge interface
an EBR's attachment to a link (e.g., an ethernet, a wireless
personal area network, etc.) on an arbitrarily-complex edge
network that the EBR connects to an enterprise and/or to provider
networks.
internal-virtual interface
a virtual interface that is a special case of either an
enterprise-edge or an enterprise-interior interface. Internal-
virtual interfaces that are also enterprise-edge interfaces are
often loopback interfaces of some form. Internal-virtual
interfaces that are also enterprise-interior interfaces are often
tunnel interfaces of some form configured over another enterprise-
interior interface.
provider-edge interface
an EBR's attachment to the Internet, or to a provider network
outside of the enterprise via which the Internet can be reached.
Enterprise Local Address (ELA)
an enterprise-scoped IP address (e.g., an IPv6 Unique Local
Address [RFC4193], an IPv4 privacy address [RFC1918], etc.) that
is assigned to an enterprise-interior interface and unique within
the enterprise. ELAs are used as identifiers for operating the
routing protocol and/or locators for packet forwarding within the
scope of the enterprise. ELAs are used as the *outer* IP
addresses during encapsulation, and can also be used as addresses
for enterprise-internal communications that do not require
encapsulation.
Provider-Independent (PI) prefix
an IPv6 or IPv4 prefix (e.g., 2001:DB8::/48, 192.0.2/24, etc.)
that is routable within a limited scope and may also appear in a
global mapping table. PI prefixes that can appear in a global
mapping table are typically delegated to an EBR by a registry, but
are not aggregated by a provider network. Local-use IPv6 and IPv4
prefixes (e.g., FD00::/8, 192.168/16, etc.) are another example of
a PI prefix, but these typically do not appear in a global mapping
table.
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Provider Aggregated (PA) prefix
an IPv6 or IPv4 prefix that is either derived from a PI prefix or
delegated directly to a provider network by a registry.
Virtual Enterprise Traversal (VET)
an abstraction that uses IP-in-IP encapsulation to span a multi-
link enterprise in a single (inner) IP hop.
VET interface
an EBR's Non-Broadcast, Multiple Access (NBMA) interface used for
Virtual Enterprise Traversal. The EBR configures a VET interface
over a set of underlying enterprise-interior interface(s)
belonging to the same enterprise. When there are multiple
distinct enterprises (each with their own distinct set of
enterprise-interior interfaces), the EBR configures a separate VET
interface over each set of enterprise-interior interfaces, i.e.,
the EBR configures multiple VET interfaces.
The VET interface encapsulates each inner IP packet in any mid-
layer headers plus an outer IP header then forwards it on an
underlying enterprise-interior interface such that the TTL/Hop
Limit in the inner header is not decremented as the packet
traverses the enterprise. The VET interface therefore presents an
automatic tunneling abstraction that represents the enterprise as
a single IP hop.
VET host
any node (host or router) that configures a VET interface for host
operation only. Note that a single node may configure some of its
VET interfaces as host interfaces and others as router interfaces.
VET node
any node that configures and uses a VET interface.
The following additional acronyms are used throughout the document:
CGA - Cryptographically Generated Address
DHCP[v4,v6] - the Dynamic Host Configuration Protocol
FIB - Forwarding Information Base
ISATAP - Intra-Site Automatic Tunnel Addressing Protocol
NBMA - Non-Broadcast, Multiple Access
ND - Neighbor Discovery
PA - Provider Aggregated
PI - Provider Independent
PIO - Prefix Information Option
PRL - Potential Router List
PRLNAME - Identifying name for the PRL (default is "isatap")
RIO - Route Information Option
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RS/RA - IPv6 Neighbor Discovery Router Solicitation/Advertisement
SEAL - Subnetwork Encapsulation and Adaptation Layer
SLAAC - IPv6 StateLess Address AutoConfiguation
3. Enterprise Characteristics
Enterprises consist of links that are connected by Enterprise Routers
(ERs) as depicted in Figure 1. ERs typically participate in a
routing protocol over enterprise-interior interfaces to discover
routes that may include multiple Layer-2 or Layer-3 forwarding hops.
Enterprise Border Routers (EBRs) are ERs that connect edge networks
to the enterprise and/or join multiple enterprises together.
Enterprise Border Gateways (EBGs) are EBRs that either directly or
indirectly connect enterprises to provider networks.
An enterprise may be as simple as a small collection of ERs and their
attached edge networks; an enterprise may also contain other
enterprises and/or be a subnetwork of a larger enterprise. An
enterprise may further encompass a set of branch offices and/or
nomadic hosts connected to a home office over one or several service
providers, e.g., through Virtual Private Network (VPN) tunnels.
Enterprises that comprise link types with sufficiently similar
properties (e.g., Layer-2 (L2) address formats, maximum transmission
units (MTUs), etc.) can configure a sub-IP layer routing service such
that IP sees the enterprise as an ordinary shared link the same as
for a (bridged) campus LAN. In that case, a single IP hop is
sufficient to traverse the enterprise without IP layer encapsulation.
Enterprises that comprise link types with diverse properties and/or
configure multiple IP subnets must also provide a routing service
that operates as an IP layer mechanism. In that case, multiple IP
hops may be necessary to traverse the enterprise such that specific
autoconfiguration procedures are necessary to avoid multilink subnet
issues [RFC4903]. In particular, we describe herein the use of IP-
in-IP encapsulation to span the enterprise in a single (inner) IP hop
in order to avoid the multilink subnet issues that arise when
enterprise-interior interfaces are used directly by applications.
Conceptually, an ER embodies both a host function and router
function. The host function supports global-scoped communications
over any of the ER's non-enterprise-interior interfaces according to
the weak end system model [RFC1122] and also supports enterprise-
local-scoped communications over its enterprise-interior interfaces.
The router function engages in the enterprise-interior routing
protocol, connects any of the ER's edge networks to the enterprise
and may also connect the enterprise to provider networks (see:
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Figure 1).
In addition to other interface types, VET nodes configure VET
interfaces that view all other VET nodes in an enterprise as single-
hop neighbors attached to an imaginary Non-Broadcast, Multiple Access
(NBMA) link, where the enterprise can also appear as a single IP hop
within another enterprise. VET nodes configure a separate VET
interface for each distinct enterprise to which they connect, and
discover other EBRs on each VET interface that can be used for
forwarding packets to off-enterprise destinations.
For each distinct enterprise, an enterprise trust basis must be
established and consistently applied. For example, in enterprises in
which EBRs establish symmetric security associations, mechanisms such
as IPsec [RFC4301] can be used to assure authentication and
confidentiality. In other enterprise network scenarios, asymmetric
securing mechanisms such as SEcure Neighbor Discovery (SEND)
[RFC3971] may be necessary to authenticate exchanges based on trust
anchors.
Finally, in enterprises with a centralized management structure
(e.g., a corporate campus network), the enterprise name service and a
synchronized set of EBGs can provide infrastructure support for
virtual enterprise traversal. In that case, the EBGs can provide a
"default mapper" [I-D.jen-apt] service used for short term packet
forwarding until EBR neighbor relationships can be established. In
enterprises with a distributed management structure (e.g., a large
MANET), peer-to-peer coordination between the EBRs themselves may be
required. Recognizing that various use cases will entail a continuum
between a fully-distributed and fully-centralized approach, the
following sections present the mechanisms of Virtual Enterprise
Traversal as they apply to a wide variety of scenarios.
4. Autoconfiguration
ERs, EBRs, EBGs, and VET hosts configure themselves for operation as
specified in the following subsections:
4.1. Enterprise Router (ER) Autoconfiguration
ERs configure enterprise-interior interfaces and engage in routing
protocols over those interfaces.
When an ER joins an enterprise, it first configures a unique IPv6
link-local address on each enterprise-interior interface that
requires an IPv6 link-local capability and an IPv4 link-local address
on each enterprise-interior interface that requires an IPv4 link-
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local capability. IPv6 link-local address generation mechanisms that
provide sufficient uniqueness include Cryptographically Generated
Addresses (CGAs) [RFC3972], IPv6 Privacy Addresses [RFC4941],
StateLess Address AutoConfiguration (SLAAC) using EUI-64 interface
identifiers [RFC4862], etc. The mechanisms specified in [RFC3927]
provide an IPv4 link-local address generation capability.
Next, the ER configures an Enterprise Local Address (ELA) of the
outer IP protocol version on each of its enterprise-interior
interfaces and engages in any routing protocols on those interfaces.
The ER can configure an ELA via explicit management, DHCP
autoconfiguration, pseudo-random self-generation from a suitably
large address pool, or through an alternate autoconfiguration
mechanism. In some enterprise use cases (e.g., highly dynamic
MANETs), assignment of ELAs as singleton addresses (i.e., as /32s for
IPv4 and /128s for IPv6) may be necessary to avoid multilink subnet
issues.
ERs that configure ELAs using DHCP may require relay support from
other ERs within the enterprise; the ER can alternatively configure
both a DHCP client and relay that are connected, e.g., via a pair of
back-to-back connected ethernet interfaces, a tun/tap interface, a
loopback interface, inter-process communication, etc. For DHCPv6,
relays that do not already know the ELA of a server relay requests to
the 'All_DHCP_Servers' site-scoped IPv6 multicast group. For DHCPv4,
relays that do not already know the ELA of a server relay requests to
the site-scoped IPv4 multicast group address 'All_DHCPv4_Servers'
(see: Section 6). DHCPv4 servers that delegate ELAs join the
'All_DHCPv4_Servers' multicast group and service any DHCPv4 messages
received for that group.
Self-generation of ELAs for IPv6 can be from a large IPv6 local-use
address range, e.g., IPv6 Unique Local Addresses [RFC4193]. Self-
generation of ELAs for IPv4 can be from a large IPv4 private address
range (e.g., [RFC1918]). When self-generation is used alone, the ER
must continuously monitor the ELAs for uniqueness, e.g., by
monitoring the routing protocol, but care must be taken in the
interaction of this monitoring with existing mechanisms.
A combined approach using both DHCP and self-generation is also
possible in which the ER first self-generates a temporary ELA used
only for the purpose of procuring an actual ELA taken from a disjoint
addressing range. The ER then assigns the temporary ELA to an
enterprise-interior interface, engages in the routing protocol and
performs a DHCP client/relay exchange using the temporary ELA as the
address of the relay. When the DHCP server delegates an actual ELA,
the ER abandons the temporary ELA, assigns the actual ELA to the
enterprise-interior interface and re-engages in the routing protocol.
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4.2. Enterprise Border Router (EBR) Autoconfiguration
EBRs are ERs that configure VET interfaces over distinct sets of
underlying enterprise-interior interfaces; an EBR can connect to
multiple enterprises, in which case it would configure multiple VET
interfaces. EBRs perform the following autoconfiguration operations:
4.2.1. VET Interface Autoconfiguration
VET interface autoconfiguration entails: 1) interface initialization,
2) EBG discovery and enterprise identification, and 3) IPv6 stateless
address autoconfiguration. These functions are specified in the
following sections:
4.2.1.1. Interface Initialization
EBRs configure a VET interface over a set of underlying enterprise-
interior interfaces belonging to the same enterprise, where the VET
interface presents a Non-Broadcast, Multiple Access (NBMA)
abstraction in which all EBRs in the enterprise appear as single hop
neighbors through the use of IP-in-IP encapsulation.
When IPv6 and IPv4 are used as the inner/outer protocols
(respectively), the EBR autoconfigures an ISATAP link-local address
([RFC5214], Section 6.2) on the VET interface to support packet
forwarding and operation of the IPv6 neighbor discovery protocol.
The ISATAP link-local address embeds an IPv4 ELA assigned to an
underlying enterprise-interior interface, and need not be checked for
uniqueness since the IPv4 ELA itself was already checked (see:
Section 4.1). Link-local address configuration for other inner/outer
IP protocol combinations is through administrative configuration or
through an unspecified alternate method.
After the EBR configures a VET interface, it can communicate with
other VET nodes as single-hop neighbors from the viewpoint of the
inner IP protocol.
4.2.1.2. Enterprise Border Gateway Discovery
The EBR next discovers a list of EBGs for each of its VET interfaces.
The list can be discovered through information conveyed in the
routing protocol and/or through the Potential Router List (PRL)
discovery mechanisms outlined in ([RFC5214], Section 8.3.2). In
multicast-capable enterprises, EBRs can also listen for
advertisements on the 'rasadv' [RASADV] IPv4 multicast group address.
In particular, whether or not routing information is available the
EBR can discover the list of EBGs by resolving an identifying name
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for the PRL ('PRLNAME') formed as 'hostname.domainname', where
'hostname' is an enterprise-specific name string and 'domainname' is
an enterprise-specific DNS suffix. The EBR discovers 'PRLNAME'
through manual configuration, a DHCP option, 'rasadv' protocol
advertisements, link-layer information (e.g., an IEEE 802.11 SSID) or
through some other means specific to the enterprise. In the absence
of other information, the EBR sets the 'hostname' component of
'PRLNAME' to "isatap" and sets the 'domainname' component only if an
enterprise-specifc DNS suffix "example.com" is known (e.g., as
"isatap.example.com").
The global Internet interdomain routing core represents a specific
example of an enterprise network scenario, albeit on an enormous
scale. The 'PRLNAME' assigned to the global Internet interdomain
routing core is "isatap.net".
After discovering 'PRLNAME', the EBR can discover the list of EBGs by
resolving 'PRLNAME' to a list of IPv4 addresses through a name
service lookup. For centrally-managed enterprises, the EBR resolves
'PRLNAME' using an enterprise-local name service (e.g., the
enterprise-local DNS). For enterprises with a distributed management
structure, the EBR resolves 'PRLNAME' using LLMNR [RFC4759] over the
VET interface. In that case, all EBGs in the PRL respond to the
LLMNR query, and the EBR accepts the union of all responses.
4.2.1.3. Enterprise Identification
Each distinct enterprise must have a unique identity that EBRs can
use to discern their enterprise affiliations. 'PRLNAME' as well as
the ELAs of EBGs and the IP prefixes the EBGs aggregate serve as an
identifier for the enterprise.
4.2.2. Provider-Aggregated (PA) Prefix Autoconfiguration
EBRs can acquire Provider-Aggregated (PA) prefixes through
autoconfiguration exchanges with EBGs over VET interfaces, where each
EBG may be configured as either a DHCP relay or DHCP server.
When IPv4 is used as the inner IP protocol, the EBR acquires PA
prefixes via an unspecified automated IPv4 prefix delegation
exchange, explicit management, etc.
When IPv6 is used as the inner IP protocol, the EBR acquires PA
prefixes via IPv6 Neighbor Discovery and DHCPv6 Prefix Delegation
exchanges. In particular, the EBR (acting as a requesting router)
can use DHCPv6 prefix delegation [RFC3633] over the VET interface via
an EBG to obtain PA IPv6 prefixes from the server (acting as a
delegating router).
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The EBR obtains prefixes using either a 2-message or 4-message DHCPv6
exchange [RFC3315]. For example, to perform the 2-message exchange
the EBR's DHCPv6 client forwards a Solicit message with an IA_PD
option to its DHCPv6 relay, i.e., the EBR acts as a combined client/
relay (see: Section 4.1). The relay then forwards the message over
the VET interface to the EBG, which either services the request or
relays it further. The forwarded Solicit message will elicit a reply
from the server containing PA IPv6 prefix delegations.
The EBR can propose a specific prefix to the DHCPv6 server per
Section 7 of [RFC3633], e.g., if a prefix delegation hint is
available. The server will check the proposed prefix for consistency
and uniqueness, then return it in the reply to the EBR if it was able
to perform the delegation.
After the EBR receives PA prefix delegations, it can provision the
prefixes on its enterprise-edge interfaces as well as on other VET
interfaces for which it is configured as an EBG.
4.2.3. Provider-Independent (PI) Prefix Autoconfiguration
Independent of any PA prefixes, EBRs can acquire and use Provider-
Independent (PI) prefixes that are either self-configured
[RFC4193][I-D.ietf-ipv6-ula-central] or delegated by a registration
authority. When an EBR acquires a PI prefix, it must also obtain
credentials (e.g., from a certification authority) that it can use to
prove prefix ownership when it registers the prefixes with EBGs
within an enterprise (see: Section 5.2 and Section 5.3).
The minimum-sized IPv6 PI prefix that an EBR may acquire is a /56.
The minimum-sized IPv4 PI prefix that an EBR may acquire is a /24.
4.3. Enterprise Border Gateway (EBG) Autoconfiguration
EBGs are EBRs that connect child enterprises to a provider network
via ordinay provider-edge interfaces and/or VET interfaces configured
over parent enterprises. EBGs autoconfigure provider-edge interfaces
in a manner that is specific to their provider connections, and
autoconfigure VET interfaces as specified in Section 4.2.1. EBGs
that support PA prefix delegation also configure a DHCP relay/server.
For each VET interface on which it is configured as an EBG, the EBG
must arrange to add its enterprise-interior interface addresses
(i.e., its ELAs) to the PRL (see: Section 4.2.1.2), and must maintain
these resource records in accordance with ([RFC5214], Section 9). In
particular, for each such VET interface the EBG adds its ELAs to name
service resource records for 'PRLNAME'. To avoid looping, EBGs MUST
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NOT configure a default route over a VET interface on which it is
configured as an EBG.
For enterprises with a distributed management structure, EBGs respond
to LLMNR queries for 'PRLNAME'.
4.4. VET Host Autoconfiguration
Nodes that cannot be attached via an EBR's enterprise-edge interface
(e.g., nomadic laptops that connect to a home office via a Virtual
Private Network (VPN)) can instead be configured for operation as a
simple host connected to the VET interface. Such VET hosts perform
the same VET interface autoconfiguration procedures as specified for
EBRs in Section 4.2.1, but they configure their VET interfaces as
host interfaces (and not router interfaces). VET hosts can then send
packets to other hosts on the VET interface, or to off-enterprise
destinations via a next-hop EBR.
Note that a node may be configured as a host on some VET interfaces
and as an EBR/EBG on other VET interfaces.
5. Internetworking Operation
Following the autoconfiguration procedures specified in Section 4,
ERs, EBRs, EBGs and VET hosts engage in normal internetworking
operations as discussed in the following sections:
5.1. Routing Protocol Participation
Following autoconfiguration, ERs engage in any routing protocols over
their enterprise-interior interfaces and forward outer IP packets
within the enterprise as for any ordinary router.
EBRs can additionally engage in any inner IP routing protocols over
enterprise-edge, provider-edge and VET interfaces, and can use those
interfaces for forwarding inner IP packets to off-enterprise
destinations. Note that these inner IP routing protocols are
separate and distinct from any enterprise-interior routing protocols.
5.2. IPv6 Router Discovery and Prefix Registration
The following sections discuss router and prefix discovery
considerations for the case of IPv6 as the inner IP protocol:
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5.2.1. IPv6 Default Router Discovery
EBGs follow the router and prefix discovery procedures specified in
([RFC5214], Section 8.2). They send solicited RAs over VET
interfaces for which they are configured as gateways with default
router lifetimes, with PIOs that contain PA prefixes for SLAAC, and
with any other required options/parameters. EBGs must set the 'M'
flag in RAs to 0, since the use of DHCPv6 for address configuration
on VET interfaces is undefined. EBGs can also include PIOs with the
'L' bit set to 0 and with a prefix such as '2001:DB8::/48' as a hint
of an aggregated prefix from which it is willing to delegate longer
PA prefixes.
VET nodes follow the router and prefix discovery procedures specified
in ([RFC5214], Section 8.3). They discover EBGs within the
enterprise as specified in Section 4.2.1.2, then perform RS/RA
exchanges with the EBGs to establish and maintain default routes. In
particular the VET node sends unicast RS messages to EBGs over its
VET interface(s) to receive RAs. Depending on the enterprise network
trust basis, VET nodes may be required to use SEND to secure the
RS/RA exchanges.
When the VET node receives an RA, it authenticates the message then
configures a default route based on the Router Lifetime. If the RA
contains Prefix Information Options (PIOs) with the 'A' and 'L' bits
set to 1, the VET node also autoconfigures IPv6 addresses from the
advertised prefixes using SLAAC and assigns them to the VET
interface. Thereafter, the VET node accepts packets that are
fowarded by EBGs for which it has current default routing information
(i.e., ingress filtering is based on the default router trust
relationship rather than a prefix-specific ingress filter entry).
5.2.2. IPv6 PA Prefix Registration
After an EBR discovers default routes, it can use DHCP prefix
delegation to obtain PA prefixes via an EBG as specified in
Section 4.2.2. The DHCP server ensures that the delegations are
unique and that the EBG's router function will forward IP packets
over the VET interface to the correct EBR. In particular, the EBG
must register and track the PA prefixes that are delegated to each
EBR.
The PA prefix registrations remain active in the EBGs as long as the
EBR continues to issue DHCP renewals over the VET interface before
lease lifetimes expire. The lease lifetime also keeps the delegation
state active even if communications between the EBR and DHCP server
are disrupted for a period of time (e.g., due to an enterprise
network partition) before being reestablished (e.g., due to an
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enterprise network merge).
5.2.3. IPv6 PI Prefix Registration
After an EBR discovers default routes, it must register its PI
prefixes by sending RAs to a set of one or more EBGs with Route
information Options (RIOs) [RFC4191] that contain the EBR's PI
prefixes. Each RA must include the ELA of an EBG as the outer IP
destination address and an ISATAP link-local address derived from the
ELA as the inner IP destination address. For enterprises that use
SEND, the RAs also include a CGA link-local inner source address
along with SEND credentials plus any certificates needed to prove
ownership of the PI prefixes. The EBR additionally tracks the set of
EBGs that it sends RAs to so that it can send subsequent RAs to the
same set.
When the EBG receives the RA, it first authenticates the message; if
the authentication fails, the EBG discards the RA. Otherwise, the
EBG installs the PI prefixes with their respective lifetimes in its
Forwarding Information Base (FIB) and configures them for both
ingress filtering [RFC3704] and forwarding purposes. In particular,
the EBG configures the FIB entries as ingress filter rules to accept
packets received on the VET interface that have a source address
taken from the PI prefixes. It also configures the FIB entries to
forward packets received on other interfaces with a destination
address taken from the PI prefixes to the EBR that registered the
prefixes on the VET interface.
The EBG then publishes the PI prefixes in a distributed database
(e.g., in a private instance of a routing protocol in which only EBGs
participate, via an automated name service update mechanism
[RFC3007], etc.). For enterprises that are managed under a
centralized administrative authority, the EBG also publishes the PI
prefixes in the enterprise-local name service (e.g., the enterprise-
local DNS [RFC1035]).
In particular, the EBG publishes each /56 prefix taken from the PI
prefixes as a seperate FQDN that consists of a sequence of 14 nibbles
in reverse order (i.e., the same as in [RFC3596], Section 2.5)
followed by the string 'ip6' followed by the string 'PRLNAME'. For
example, when 'PRLNAME' is "isatap.example.com", the EBG publishes
the prefix '2001:DB8::/56' as:
'0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.isatap.example.com'. The EBG
includes the outer IPv4 source address of the RA (e.g., in a DNS A
resource record) in each prefix publication. For enterprises that
use SEND, the EBG also includes the inner IPv6 CGA source address
(e.g., in a DNS AAAA record) in each prefix publication. If the
prefix was already installed in the distributed database, the EBG
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instead adds the outer IPv4 source address (e.g., in an additional
DNS A records) to the pre-existing publication to support PI prefixes
that are multihomed. For enterprises that use SEND, this latter
provision requires all EBRs of a multihomed site that advertise the
same PI prefixes in RAs to use the same CGA and the same SEND
credentials.
After the EBG authenticates the RA and publishes the PI prefixes, it
next acts as a Neighbor Discovery proxy (NDProxy) [RFC4389] on the
VET interfaces configured over any of its parent enterprises and
relays a proxied RA to the EBGs on those interfaces. (For
enterprises that use SEND, the EBG additionally acts as a SEcure
Neighbor Discovery Proxy (SENDProxy) [I-D.ietf-csi-proxy-send].)
EBGs in parent enterprises that receive the proxied RAs in turn act
as NDProxys/SENDProxys to relay the RAs to EBGs on their parent
enterprises, etc. The RA proxying and PI prefix publication recurses
in this fashion and ends when an EBR attached to an interdomain
routing core is reached.
After the initial PI prefix registration, the EBR that owns the
prefix(es) must periodically send additional RAs to its set of EBGs
to refresh prefix lifetimes. Each such EBG tracks the set of EBGs in
parent enterprises that it relays the proxied RAs to, and should
relay subsequent RAs to the same set.
This procedure has a direct analogy in the Teredo method of
maintaining state in network middleboxes through the periodic
transmission of "bubbles" [RFC4380].
5.2.4. IPv6 Next-Hop EBR Discovery
VET nodes discover destination-specific next-hop EBRs within the
enterprise by querying the name service for the /56 IPv6 PI prefix
taken from a packet's destination address, by forwarding packets via
a default route to an EBG, or by some other inner IP to outer IP
address mapping mechansim. For example, for the IPv6 destination
address '2001:DB8:1:2::1' and 'PRLNAME' "isatap.example.com" the VET
node can lookup the domain name:
'0.0.1.0.0.0.8.b.d.0.1.0.0.2.ip6.isatap.example.com'. If the name
service lookup succeeds, it will return IPv4 addresses (e.g., in DNS
A records) that correspond to the ELAs assigned to enterprise
interior interfaces of next-hop EBRs to which the VET node can
forward packets. (In enterprises that use SEND, it will also return
an IPv6 CGA address, e.g., in a DNS AAAA record.)
Name service lookups in enterprises with a centralized management
structure use an infrastructure-based service, e.g., an enterprise-
local DNS. Name service lookups in enterprises with a distributed
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management structure and/or that lack an infrastructure-based name
service instead use LLMNR over the VET interface. When LLMNR is
used, the EBR that performs the lookup sends an LLMNR query (with the
/56 prefix taken from the IP destination address encoded in dotted-
nibble format as shown above) and accepts the union of all replies it
receives from other EBRs on the VET interface. When an EBR receives
an LLMNR query, it responds to the query IFF it aggregates an IP
prefix that covers the prefix in the query.
Alternatively, in enterprises with a stable and highly-available set
of EBGs, the VET node can simply forward an initial packet via a
default route to an EBG. The EBG will forward the packet to a next-
hop EBR on the VET interface and return an ICMPv6 Redirect [RFC4861]
(using SEND, if necessary). If the packet's source address is on-
link on the VET interface, the EBG returns an ordinary "router-to-
host" redirects with the source address of the packet as its
destination. If the packet's source address is not on-link, the EBG
instead returns a "router-to-router" redirect with the link-local
ISATAP address of the previous-hop EBR as its destination. The EBG
also includes in the redirect one or more IPv6 Link-Layer Address
Options (LLAOs) that contain the IPv4 ELAs of potential next-hop EBRs
arranged in order from highest to lowest priority (i.e., the first
LLAO contains the highest priority ELA and the final LLAO option
contains the lowest priority). The LLAOs are formatted using a
modified version of the form specified in ( [RFC2529], Section 5) as
shown in Figure 2:
+-------+-------+-------+-------+-------+-------+-------+-------+
| Type |Length | TTL | IPv4 Address |
+-------+-------+-------+-------+-------+-------+-------+-------+
Figure 2: VET Link-Layer Address Option Format
For each LLAO, the Type is set to 2 (for Target Link-Layer Address
Option), Length is set to 1, and IPv4 Address is set to the IPv4 ELA
of the next-hop EBR. TTL is set to the time in seconds that the
recipient may cache the ELA, where the value 65535 represents
infinity and the value 0 suspends forwarding through this ELA.
When a VET host receives an ordinay "router-to-host" redirect, it
processes the redirect exacly as specified in [RFC4861], Section 8.
When an EBR receives a "router-to-router" redirect, it discovers the
IPv4 ELA addresses of potential next-hop EBRs by examining the LLAOs
included in the redirect. The EBR then installs a FIB entry that
contains the /56 prefix of the destination address encoded in the
redirect and the list of IPv4 ELAs of potential next-hop EBRs. The
EBR then enables the FIB entry for forwarding to next-hop EBRs but
DOES NOT enable it for ingress filtering acceptance of packets from
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next-hop EBRs (i.e., the forwarding determination is unidirectional).
In enterprises in which spoofing is possible, after discovering
potential next-hop EBRs (either through name service lookup or ICMP
redirect) the EBR must send authenticating credentials before
forwarding packets via the next-hops. To do so, the EBR must send
RAs over the VET interface (using SEND, if necessary) to one or more
of the potential next-hop EBRs with a link-local ISATAP address that
embeds a next-hop EBR IPv4 ELA as the destination. The RAs must
include a Route Information Option (RIO) [RFC4191] that contains the
/56 PI prefix of the original packet's source address. After sending
the RAs, the EBR can either enable the new FIB entry for forwarding
immediately or delay until it receives an explicit acknowledgement
that a next-hop EBR received the RA (e.g., using the SEAL explicit
acknowledgement mechanism - see: Section 5.5).
When a next-hop EBR receives the RA, it authenticates the message
then performs a name service lookup on the prefix in the RIO if
further authenticating evidence is required. If the name service
returns resource records that are consistent with the inner and outer
IP addresses of the RA, the next-hop EBR then installs the prefix in
the RIO in its FIB and enables the FIB entry for ingress filtering
but DOES NOT enable it for forwarding purposes. After an EBR sends
initial RAs following a redirect, it should send periodic RAs to
refresh the next-hop EBR's ingress filter prefix lifetimes as long as
traffic is flowing.
EBRs retain the FIB entrys created as result of an ICMP redirect
until all ELA TTLs expire, or until no hints of forward progress
through any of the associated ELAs are received. In this way, ELA
liveness detection exactly parallels IPv6 Neighbor Unreachability
Detection ([RFC4861], Section 3).
5.3. IPv4 Router Discovery and Prefix Registration
When IPv4 is used as the inner IP protocol, router discovery and
prefix registration exactly parallels the mechanisms specified for
IPv6 in Section 5.2. To support this, modifications to the ICMPv4
Router Advertisement [RFC1256] function to include SEND constructs,
and modifications to the ICMPv4 Redirect [RFC0792] function to
support router-to-router redirects will be specified in a future
document. Additionally, publications for IPv4 prefixes will be in
dotted-nibble format in the 'ip4.isatap.example.com' domain. For
example, the IPv4 prefix 192.0.2/24 would be represented as:
'2.0.0.0.0.c.ip4.isatap.example.com'.
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5.4. Forwarding Packets
VET nodes forward packets by consulting the FIB to determine a
specific EBR/EBG as the next-hop router on a VET interface. When
multiple next-hop routers are available, VET nodes can use default
router preferences, routing protocol information, traffic engineering
configurations, etc. to select the best exit router. When there is
no FIB information other than ::/0 available, VET nodes can discover
the next-hop EBR/EBG through the mechanisms specified in Section 5.2.
VET interfaces encapsulate inner IP packets in any mid-layer headers
followed by an outer IP header according to the specific
encapsulation type (e.g., [RFC4301][RFC5214][I-D.templin-seal]); they
next submit the encapsulated packet to the outer IP forwarding engine
for transmission on an underlying enterprise-interior interface.
For forwarding to next-hop addresses over VET interfaces that use
IPv6-in-IPv4 encapsulation, VET nodes determine the outer destination
address (i.e., the IPv4 ELA of the next-hop EBR) through static
extraction of the IPv4 address embedded in the next-hop ISATAP
address. For other IP-in-IP encapsulations, determination of the
outer destination address is through administrative configuration or
through an unspecified alternate method. When there are multiple
candidate destination ELAs available, the VET node should only select
an ELA for which there is current forwarding information in the outer
IP protocol FIB.
5.5. SEAL Encapsulation
VET nodes should use SEAL encapsulation [I-D.templin-seal] in
conjunction with packet forwarding over VET interfaces to accommdate
path MTU diversity, to defeat source address spoofing, and to monitor
next-hop EBR reachability. SEAL encapsulation maintains a
unidirectional and monotonically-incrementing per-packet
identification value known as the 'SEAL_ID'. When a VET node that
uses SEAL encapsulation sends a SEND-protected Router Advertisement
(RA) or Router Solicitation (RS) message to another VET node, both
nodes cache the new SEAL_ID as per-tunnel state used for maintaining
a window of unacknowledged SEAL_IDs.
In terms of security, when a VET node receives an ICMP message, it
can confirm that the packet-in-error within the ICMP message
corresponds to one of its recently-sent packets by examining the
SEAL_ID along with source and destination addresses, etc.
Additionally, a next-hop EBR can track the SEAL_ID in packets
received from EBRs for which there is an ingress filter entry and
discard packets that have SEAL_ID values outside of the current
window.
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In terms of next-hop reachability, an EBR can set the SEAL
"Acknowledgement Requested" bit in messages to receive confirmation
that a next-hop EBR is reachable (see also Section 5.2.4. Setting
the "Acknowledgement Requested" bit is also used as the method for
maintaining the window of outstanding SEAL_ID's.
5.6. Generating Errors
When an EBR receives a packet over a VET interface and there is no
matching ingress filter entry, it drops the packet and returns an
ICMPv6 [RFC4443] "Destination Unreachable; Source address failed
ingress/egress policy" message to the previous hop EBR subject to
rate limiting.
When an EBR receives a packet over a VET interface, and there is no
longest-prefix-match FIB entry for the destination, it returns an
ICMPv6 "Destination Unreachable; No route to destination" message to
the previous hop EBR subject to rate limiting.
When an EBR receives a packet over a VET interface and the longest-
prefix-match FIB entry for the destination is configured over the
same VET interface the packet arrived on, the EBR forwards the packet
then (if the FIB prefix is longer than ::/0) sends a router-to-router
ICMPv6 Redirect message (using SEND, if necessary) to the previous
hop EBR as specified in Section 5.2.4.
Generation of other ICMPv6 messages (e.g., ICMPv6 "Packet Too Big")
is the same as for any IPv6 interface.
5.7. Processing Errors
When an EBR receives an ICMPv6 "Destination Unreachable; Source
address failed ingress/egress policy" message from a next-hop EBR,
and there is a longest-prefix-match FIB entry for the original
packet's destination that is more-specific than ::/0, the EBR
discards the message and marks the FIB entry for the destination as
"forwarding suspended" for the ELA taken from the source address of
the ICMPv6 message. The EBR should then allow subsequent packets to
flow through different ELAs associated with the FIB entry until it
forwards a new RA to the suspended ELA. If the EBR receives
excessive ICMPv6 ingress policy errors through multiple ELAs
associated with the same FIB entry, it should delete the FIB entry
and allow subsequent packets to flow through an EBG if supported in
the specific enterprise scenario.
When a VET node receives an ICMPv6 "Destination Unreachable; No route
to destination" message from a next-hop EBR, it forwards the ICMPv6
message to the source of the original packet as normal. If the EBR
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has longest-prefix-match FIB entry for the original packet's
destination that is more-specific than ::/0, the EBR also deletes the
FIB entry.
When an EBR receives an authentic ICMPv6 Redirect, it processes the
packet as specified in Section 5.2.4.
When an EBG receives new mapping information for a specific
destination prefix, it can propagate the update to other EBRs/EBGs by
sending an ICMPv6 redirect message to the 'All Routers' link-local
multicast address with a LLAO with the TTL for the unreachable LLAO
set to zero, and with a NULL packet in error.
Additionally, a VET node may receive ICMPv4 [RFC0792] "Destination
Unreachable; net / host unreachable" messages from an ER indicating
that the path to a VET neighbor may be failing. The EBR should first
check authenticating information in the message (e.g., the SEAL_ID,
IPsec sequence number, source address of the original packet if
available, etc.) before accepting it, then should mark the longest-
prefix-match FIB entry for the destination as "forwarding suspended"
for the ELA destination address of the ICMPv4 packet-in-error. If
the EBR receives excessive ICMPv4 unreachable errors through multiple
ELAs associated with the same FIB entry, it should delete the FIB
entry and allow subsequent packets to flow through a different route.
5.8. Mobility and Multihoming Considerations
EBRs that travel between distinct enterprise networks must either
abandon their PA prefixes that are relative to the "old" enterprise
and obtain new ones relative to the "new" enterprise, or somehow
coordinate with a "home" enterprise to retain ownership of the
prefixes. In the first instance, the EBR would be required to
coordinate a network renumbering event using the new PA prefixes
[RFC4192]. In the second instance, an ancillary mobilitiy management
mechanism must be used.
EBRs can retain their PI prefixes as they travel between distinct
enterprise networks as long as they register the prefixes with new
EBGs and (preferrably) withdraw the prefixes from old EBGs prior to
departure. Prefix registration with new EBGs is coordinated exactly
as specified in Section 5.2.3; prefix withdrawl from old EBGs is
simply through re-announcing the PI prefixes with zero lifetimes.
Since EBRs can move about independently of one another, stale FIB
entry state may be left in VET nodes when a neighboring EBR departs.
Additionally, EBRs can lose state for various reasons, e.g., power
failure, machine reboot, etc. For this reason, EBRs are advised to
set relatively short PI prefix lifetimes in RIO options, and to send
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additional RAs to refresh lifetimes before they expire. (EBRs should
place conservative limits on the RAs they send to reduce congestion,
however.)
EBRs may register their PI prefixes with multiple EBGs for
multihoming purposes. EBRs should only forward packets via EBGs with
which it has registered its PI prefixes, since other EBGs may drop
the packets and return ICMPv6 "Destination Unreachable; Source
address failed ingress/egress policy" messages.
EBRs can also act as delegating routers to sub-delegate portions of
their PI prefixes to requesting routers on their enterprise edge
interfaces and on VET interfaces for which they are configured as
EBGs. In this sense, the sub-delegations of an EBR's PI prefixes
become the PA prefixes for downstream-dependent nodes. Downstream-
dependent nodes that travel with a mobile provider EBR can continue
to use addresses configured from PA prefixes; downstream-dependent
nodes that move away from their provider EBR must perform address/
prefix renumbering when they assocate with a new provider.
The EBGs of a multi-homed enterprise should participate in a private
inner IP routing protocol instance between themselves (possibly over
an alternate topology) to accommodate enterprise partitions/merges as
well as intra-enterprise mobility events. These peer EBGs should
accept packets from one another without respect to the destination
(i.e., ingress filtering is based on the peering relationship rather
than a prefix-specific ingress filter entry).
5.9. Enterprise-Local Communications
When permitted by policy, end systems that configure the endpoints of
enterprise-local communications can avoid VET interface encapsulation
by directly invoking the outer IP protocol using ELAs assigned to
their enterprise-interior interfaces. For example, when the outer
protocol is IPv4, end systems can use IPv4 ELAs for enterprise-local
communications over their enterprise-interior interfaces without
using encapsulation.
5.10. Multicast
In multicast-capable deployments, ERs provide an enterprise-wide
multicasting service (e.g., Simplified Multicast Forwarding (SMF)
[I-D.ietf-manet-smf], PIM routing, DVMRP routing, etc.) over their
enterprise-interior interfaces such that outer IP multicast messages
of site- or greater scope will be propagated across the enterprise.
For such deployments, VET nodes can also provide an inner IP
multicast/broadcast capability over their VET interfaces through
mapping of the inner IP multicast address space to the outer IP
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multicast address space. In that case, operation of link- or greater
scoped inner IP multicasting services (e.g., a link-scoped neighbor
discovery protocol) over the VET interface is available, but link-
scoped services should be used sparingly to minimize enterprise-wide
flooding.
VET nodes encapsulate inner IP multicast messages sent over the VET
interface in any mid-layer headers (e.g., IPsec, SEAL, etc.) plus an
outer IP header with a site-scoped outer IP multicast address as the
destination. For the case of IPv6 and IPv4 as the inner/outer
protocols (respectively), [RFC2529] provides mappings from the IPv6
multicast address space to a site-scoped IPv4 multicast address space
(for other IP-in-IP encapsulations, mappings are established through
administrative configuration or through an unspecified alternate
static mapping).
Multicast mapping for inner IP multicast groups over outer IP
multicast groups can be accommodated, e.g. through VET interface
snooping of inner multicast group membership and routing protocol
control messages. To support inner-to-outer IP multicast mappinging,
the VET interface acts as a virtual outer IP multicast host connected
to its underlying enterprise-interior interfaces. When the VET
interface detects inner IP multicast group joins or leaves, it
forwards corresponding outer IP multicast group membership reports
for each enterprise-interior interface over which the VET interface
is configured. If the VET node is configured as an outer IP
multicast router on the underlying enterprise-interior interfaces,
the VET interface forwards locally looped-back group membership
reports to the outer IP multicast routing process. If the VET node
is configued as a simple outer IP multicast host, the VET interface
instead fowards actual group membership reports (e.g., IGMP messages)
directly over each of the underlying enterprise-interior interfaces.
Since inner IP multicast groups are mapped to site-scoped outer IP
multicast groups, the VET node must ensure that the site-scope outer
IP multicast messages received on the enterprise-interior interfaces
for one VET interface do not "leak out" to the enterprise-interior
interfaces of another VET interface. This is accomodated through
normal site-scoped outer IP multicast group filtering at enterprise-
interior interface boundaries.
5.11. Service Discovery
VET nodes can peform enterprise-wide service discovery using a
suitable name-to-address resolution service. Examples of flooding-
based services include the use of LLMNR [RFC4759] over the VET
interface or mDNS [I-D.cheshire-dnsext-multicastdns] over an
underlying enterprise-interior interface. More scalable and
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efficient service discovery mechanisms are for further study.
5.12. Enterprise Partitioning
EBGs can physically partition an enterprise by configuring multiple
VET interfaces over multiple distinct sets of underlying interfaces.
In that case, each partition (i.e., each VET interface) must
configure its own distinct 'PRLNAME' (e.g.,
'isatap.zone1.example.com', 'isatap.zone2.example.com', etc.).
EBGs can logically partition an enterprise using a single VET
interface by sending RAs with PIOs containing different IPv6 PA
prefixes to group nodes into different logical partitions. EBGs can
identify partitions, e.g., by examining IPv4 ELA prefixes, observing
the interfaces over which RSs are received, etc. In that case, a
single 'PRLNAME' can cover all partitions.
5.13. EBG Prefix State Recovery
EBGs must retain explicit state that tracks the inner IP prefixes
owned by EBRs within the enterprise, e.g., so that packets are
delivered to the correct EBRs and not incorrectly "leaked out" of the
enterprise via a default route. For PA prefixes the state is
maintained via an EBR's DHCP prefix delegation lease renewals, while
for PI prefixes the state is maintained via an EBR's periodic prefix
registration RAs.
When an EBG loses some or all of its state (e.g., due to a power
failure), it must recover the state before allowing packets to flow
over incorrect routes. If the EBG aggregates PA prefixes from which
the IP prefixes of all EBRs in the enterprise are sub-delegated, then
the EBG can recover state through DHCP prefix delegation lease
renewals, through bulk lease queries, or through on-demand name
service lookups based due to IP packet forwarding. If the EBG serves
as an anchor for PI prefixes, however, care must be taken to avoid
looping while state is recovered through prefix registration RAs from
EBRs. In that case, when the EBG that is recovering state forwards
an IP packet for which it has no explicit route other than ::/0, it
must first perform an on-demand name service lookup to refresh state.
6. IANA Considerations
A Site-Local Scope IPv4 multicast group ('All_DHCPv4_Servers') for
DHCPv4 server discovery is requested. The allocation should be taken
from the 239.255.000.000-239.255.255.255 Site-Local Scope range in
the IANA 'multicast-addresses' registry.
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7. Security Considerations
Security considerations for MANETs are found in [RFC2501].
Security considerations with tunneling that apply also to VET are
found in [RFC2529][RFC5214]. In particular, VET nodes must verify
that the outer IP source address of a packet received on a VET
interface is correct for the inner IP source address using the
procedures specified in ([RFC5214], Section 7.3) in conjunction with
the ingress filtering mechanisms specified in this document.
SEND [RFC3971], IPsec [RFC4301] and SEAL Section 5.5 provide
additional securing mitigations to detect source address spoofing and
bogus RA messages sent by rogue routers.
Rogue routers can send bogus RA messages with spoofed ELA source
addresses that can consume network resources and cause EBGs to
perform extra work. Nonetheless, EBGs should not "blacklist" such
ELAs, as that may result in a denial of service to the ELAs'
legitimate owners.
8. Related Work
Brian Carpenter and Cyndi Jung introduced the concept of intra-site
automatic tunneling in [RFC2529]; this concept was later called:
"Virtual Ethernet" and investigated by Quang Nguyen under the
guidance of Dr. Lixia Zhang. Subsequent works by these authors and
their colleagues have motivated a number of foundational concepts on
which this work is based.
Telcordia has proposed DHCP-related solutions for MANETs through the
CECOM MOSAIC program.
The Naval Research Lab (NRL) Information Technology Division uses
DHCP in their MANET research testbeds.
[I-D.ietf-v6ops-tunnel-security-concerns] discusses security concerns
pertaining to tunneling mechanisms.
An automated IPv4 prefix delegation mechanism is proposed in
[I-D.ietf-dhc-subnet-alloc].
MANET link types are discussed in [I-D.clausen-manet-linktype].
Various proposals within the IETF have suggested similar mechanisms.
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9. Acknowledgements
The following individuals gave direct and/or indirect input that was
essential to the work: Jari Arkko, Teco Boot, Emmanuel Bacelli, Scott
Brim, Brian Carpenter, James Bound, Thomas Clausen, Claudiu Danilov,
Dino Farinacci, Vince Fuller, Thomas Goff, Joel Halpern, Bob Hinden,
Sapumal Jayatissa, Dan Jen, Darrel Lewis, Tony Li, Joe Macker, David
Meyer, Thomas Narten, Pekka Nikander, Dave Oran, Alexandru Petrescu,
John Spence, Jinmei Tatuya, Dave Thaler, Ole Troan, Michaela
Vanderveen, Lixia Zhang and others in the IETF AUTOCONF and MANET
working groups. Many others have provided guidance over the course
of many years.
10. Contributors
The following individuals have contributed to this document:
Eric Fleischman (eric.fleischman@boeing.com)
Thomas Henderson (thomas.r.henderson@boeing.com)
Steven Russert (steven.w.russert@boeing.com)
Seung Yi (seung.yi@boeing.com)
Ian Chakeres (ian.chakeres@gmail.com) contributed to earlier versions
of the document.
11. References
11.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, September 1981.
[RFC0826] Plummer, D., "Ethernet Address Resolution Protocol: Or
converting network protocol addresses to 48.bit Ethernet
address for transmission on Ethernet hardware", STD 37,
RFC 826, November 1982.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997.
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[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC3007] Wellington, B., "Secure Domain Name System (DNS) Dynamic
Update", RFC 3007, November 2000.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
"DNS Extensions to Support IP Version 6", RFC 3596,
October 2003.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, March 2005.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, November 2005.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control
Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification", RFC 4443, March 2006.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
[RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
March 2008.
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11.2. Informative References
[CATENET] Pouzin, L., "A Proposal for Interconnecting Packet
Switching Networks", May 1974.
[I-D.cheshire-dnsext-multicastdns]
Cheshire, S. and M. Krochmal, "Multicast DNS",
draft-cheshire-dnsext-multicastdns-07 (work in progress),
September 2008.
[I-D.clausen-manet-linktype]
Clausen, T., "The MANET Link Type",
draft-clausen-manet-linktype-00 (work in progress),
October 2008.
[I-D.ietf-autoconf-manetarch]
Chakeres, I., Macker, J., and T. Clausen, "Mobile Ad hoc
Network Architecture", draft-ietf-autoconf-manetarch-07
(work in progress), November 2007.
[I-D.ietf-csi-proxy-send]
Krishnan, S., Laganier, J., and M. Bonola, "Secure Proxy
ND Support for SEND", draft-ietf-csi-proxy-send-00 (work
in progress), November 2008.
[I-D.ietf-dhc-subnet-alloc]
Johnson, R., "Subnet Allocation Option",
draft-ietf-dhc-subnet-alloc-07 (work in progress),
July 2008.
[I-D.ietf-ipv6-ula-central]
Hinden, R., "Centrally Assigned Unique Local IPv6 Unicast
Addresses", draft-ietf-ipv6-ula-central-02 (work in
progress), June 2007.
[I-D.ietf-manet-smf]
Macker, J. and S. Team, "Simplified Multicast Forwarding
for MANET", draft-ietf-manet-smf-08 (work in progress),
November 2008.
[I-D.ietf-v6ops-tunnel-security-concerns]
Hoagland, J., Krishnan, S., and D. Thaler, "Security
Concerns With IP Tunneling",
draft-ietf-v6ops-tunnel-security-concerns-01 (work in
progress), October 2008.
[I-D.jen-apt]
Jen, D., Meisel, M., Massey, D., Wang, L., Zhang, B., and
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L. Zhang, "APT: A Practical Transit Mapping Service",
draft-jen-apt-01 (work in progress), November 2007.
[I-D.templin-seal]
Templin, F., "The Subnetwork Encapsulation and Adaptation
Layer (SEAL)", draft-templin-seal-23 (work in progress),
August 2008.
[IEN48] Cerf, V., "The Catenet Model for Internetworking",
July 1978.
[RASADV] Microsoft, "Remote Access Server Advertisement (RASADV)
Protocol Specification", October 2008.
[RFC1122] Braden, R., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, October 1989.
[RFC1256] Deering, S., "ICMP Router Discovery Messages", RFC 1256,
September 1991.
[RFC1753] Chiappa, J., "IPng Technical Requirements Of the Nimrod
Routing and Addressing Architecture", RFC 1753,
December 1994.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC1955] Hinden, R., "New Scheme for Internet Routing and
Addressing (ENCAPS) for IPNG", RFC 1955, June 1996.
[RFC2501] Corson, M. and J. Macker, "Mobile Ad hoc Networking
(MANET): Routing Protocol Performance Issues and
Evaluation Considerations", RFC 2501, January 1999.
[RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4
Domains without Explicit Tunnels", RFC 2529, March 1999.
[RFC2775] Carpenter, B., "Internet Transparency", RFC 2775,
February 2000.
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, February 2001.
[RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed
Networks", BCP 84, RFC 3704, March 2004.
[RFC3753] Manner, J. and M. Kojo, "Mobility Related Terminology",
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RFC 3753, June 2004.
[RFC3819] Karn, P., Bormann, C., Fairhurst, G., Grossman, D.,
Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L.
Wood, "Advice for Internet Subnetwork Designers", BCP 89,
RFC 3819, July 2004.
[RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
Configuration of IPv4 Link-Local Addresses", RFC 3927,
May 2005.
[RFC4192] Baker, F., Lear, E., and R. Droms, "Procedures for
Renumbering an IPv6 Network without a Flag Day", RFC 4192,
September 2005.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through
Network Address Translations (NATs)", RFC 4380,
February 2006.
[RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
Proxies (ND Proxy)", RFC 4389, April 2006.
[RFC4759] Stastny, R., Shockey, R., and L. Conroy, "The ENUM Dip
Indicator Parameter for the "tel" URI", RFC 4759,
December 2006.
[RFC4852] Bound, J., Pouffary, Y., Klynsma, S., Chown, T., and D.
Green, "IPv6 Enterprise Network Analysis - IP Layer 3
Focus", RFC 4852, April 2007.
[RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903,
June 2007.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, September 2007.
Appendix A. Duplicate Address Detection (DAD) Considerations
A-priori uniqueness determination (also known as "pre-service DAD")
for an ELA assigned on an enterprise-interior interface would require
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either flooding the entire enterprise or somehow discovering a link
in the enterprise on which a node that configures a duplicate address
is attached and performing a localized DAD exchange on that link.
But, the control message overhead for such an enterprise-wide DAD
would be substantial and prone to false-negatives due to packet loss
and intermittent connectivity. An alternative to pre-service DAD is
to autoconfigure pseudo-random ELAs on enterprise-interior interfaces
and employ a passive in-service DAD (e.g., one that monitors routing
protocol messages for duplicate assignments).
Pseudo-random IPv6 ELAs can be generated with mechanisms such as
CGAs, IPv6 privacy addresses, etc. with very small probability of
collision. Pseudo-random IPv4 ELAs can be generated through random
assignment from a suitably large IPv4 prefix space.
Consistent operational practices can assure uniqueness for EBG-
aggregated addresses/prefixes, while statistical properties for
pseudo-random address self-generation can assure uniqueness for the
ELAs assigned on an ER's enterprise-interior interfaces. Still, an
ELA delegation authority should be used when available, while a
passive in-service DAD mechanism should be used to detect ELA
duplications when there is no ELA delegation authority.
Appendix B. Change Log
(Note to RFC editor - this section to be removed before publication
as an RFC.)
Changes from -33 to 34:
o Enterprise management models described
o Enterprise security models described
o Clarification of mechanisms based on enterprise management/
security models
Changes from -32 to 33::
o Secure Neighbor Discovery Proxy
Changes from -28 to 29:
o Updates on processing/receiving errors.
Changes from -27 to 28:
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o Introduced concept of a default mapper.
Changes from -26 to 27:
o Introduced new model for PI prefix management.
o Teredo mechanisms used in conjunction with ISATAP ("teratap"?
"isado"?)
Changes from -25 to 26:
o Clarifications on Router Discovery and Ingress FIltering.
o Mechanisms for detecting locator liveness
o Mechanisms for avoiding state synchonization requirements.
Changes from -23 to 24:
o Clarifications on router discovery.
Changes from -22 to 23:
o Clarifications on prefix mapping.
Changes from -21 to 22:
o Using SEAL to secure VET
Changes from -20 to 21:
o Enterprise partitioning.
o Mapping and name service management.
Changes from -18 to 20:
o Added support for simple hosts.
o Added EBG name service maintenace procedures
o Added router and prefix maintenace procedures
Changes from -17 to 18:
o adjusted section headings to group autoconf operations under EIR/
EBR/EBG.
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o clarified M/O bits
o clarified EBG roles
Changes from -15 to 17:
o title change to "Virtual Enterprise Traversal (VET)".
o changed document focus from MANET-centric to the much-broader
Enterprise-centric, where "Enterprise" is understood to also cover
a wide range of MANET types.
Changes from -14 to 15:
o title change to "Virtual Enterprise Traversal (VET) for MANETs".
o Address review comments
Changes from -12 to 14:
o title change to "The MANET Virtual Ethernet Abstraction".
o Minor section rearrangement.
o Clartifications on portable and self-configured prefixes.
o Clarifications on DHCPv6 prefix delegation procedures.
Changes from -11 to 12:
o title change to "MANET Autoconfiguration using Virtual Ethernet".
o DHCP prefix delegation for both IPv4 and IPv6 as primary address
delegation mechanism.
o IPv6 SLAAC for address autoconfiguration on the VET interface.
o fixed editorials based on comments received.
Changes from -10 to 11:
o removed the transparent/opaque VET portal abstractions.
o removed routing header as an option for MANET exit router
selection.
o included IPv6 SLAAC as an endorsed address configuration mechanism
for the VET interface.
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Changes from -08 to -09:
o Introduced the term "VET".
o Changed address delegation language to speak of "MNBR-aggregated"
instead of global/local.
o Updated figures 1-3.
o Explained why a MANET interface is "neutral".
o Removed DHCPv4 "MLA Address option". Now, MNBRs can only be
DHCPv4 servers; not relays.
Changes from -07 to -08:
o changed terms "unenhanced" and "enhanced" to "transparent" and
"opaque".
o revised MANET Router diagram.
o introduced RFC3753 terminology for Mobile Router; ingress/egress
interface.
o changed abbreviations to "MNR" and "MNBR".
o added text on ULAs and ULA-Cs to "Self-Generated Addresses".
o rearranged Section 3.1.
o various minor text cleanups
Changes from -06 to -07:
o added MANET Router diagram.
o added new references
o various minor text cleanups
Changed from -05 to -06:
o Changed terms "raw" and "cooked" to "unenhanced" and "enhanced".
o minor changes to preserve generality
Changed from -04 to -05:
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o introduced conceptual "virtual ethernet" model.
o support "raw" and "cooked" modes as equivalent access methods on
the virutal ethernet.
Changed from -03 to -04:
o introduced conceptual "imaginary shared link" as a representation
for a MANET.
o discussion of autonomous system and site abstractions for MANETs
o discussion of autoconfiguration of CGAs
o new appendix on IPv6 StateLess Address AutoConfiguration
Changes from -02 to -03:
o updated terminology based on RFC2461 "asymmetric reachability"
link type; IETF67 MANET Autoconf wg discussions.
o added new appendix on IPv6 Neighbor Discovery and Duplicate
Address Detection
o relaxed DHCP server deployment considerations allow DHCP servers
within the MANET itself
Changes from -01 to -02:
o minor updates for consistency with recent developments
Changes from -00 to -01:
o new text on DHCPv6 prefix delegation and multilink subnet
considerations.
o various editorial changes
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Author's Address
Fred L. Templin (editor)
Boeing Research and Technology
P.O. Box 3707 MC 7L-49
Seattle, WA 98124
USA
Email: fltemplin@acm.org
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