Network Working Group F. Templin, Ed.
Internet-Draft Boeing Phantom Works
Intended status: Informational October 17, 2008
Expires: April 20, 2009
Virtual Enterprise Traversal (VET)
draft-templin-autoconf-dhcp-18.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.
Routers in enterprise networks must have a way to automatically
provision IP addresses/prefixes and other information, and must also
support post-autoconfiguration operations even for highly-dynamic
networks. This document specifies a Virtual Enterprise Traversal
(VET) abstraction for autoconfiguration and operation of routers in
enterprise networks.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Enterprise Characteristics . . . . . . . . . . . . . . . . . . 7
4. Autoconfiguration . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Enterprise Interior Router (EIR) Autoconfiguration . . . . 8
4.2. Enterprise Border Router (EBR) Autoconfiguration . . . . . 10
4.2.1. VET Interface Autoconfiguration . . . . . . . . . . . 10
4.2.2. Enterprise Border Gateway Discovery and Enterprise
Identification . . . . . . . . . . . . . . . . . . . . 11
4.2.3. Inner IP Address/Prefix Delegation and Maintenance . . 11
4.2.4. Portable Inner IP Addresses/Prefixes . . . . . . . . . 13
4.2.5. Enterprise-edge Interface Autoconfiguration . . . . . 13
4.3. Enterprise Border Gateway (EBG) Autoconfiguration . . . . 13
5. Post-Autoconfiguration Operation . . . . . . . . . . . . . . . 14
5.1. Forwarding Packets to Destinations Outside of the
Enterprise . . . . . . . . . . . . . . . . . . . . . . . . 14
5.2. Enterprise-Local Communications . . . . . . . . . . . . . 15
5.3. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 15
5.4. Service Discovery . . . . . . . . . . . . . . . . . . . . 15
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16
8. Related Work . . . . . . . . . . . . . . . . . . . . . . . . . 16
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 16
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
11.1. Normative References . . . . . . . . . . . . . . . . . . . 17
11.2. Informative References . . . . . . . . . . . . . . . . . . 18
Appendix A. Duplicate Address Detection (DAD) Considerations . . 20
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 20
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 23
Intellectual Property and Copyright Statements . . . . . . . . . . 24
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1. Introduction
Enterprise networks [RFC4852] connect routers over various link types
(see: [RFC4861], Section 2.2). Certain Mobile Ad-hoc Networks
(MANETs) [RFC2501] can 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 runtime operation of enterprise
routers over various interface types, 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][RFC4861] mechanisms is assumed unless
otherwise specified.
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 Architecture
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Figure 1 above depicts the architectural model for an enterprise
router. As shown in the figure, an enterprise router 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.
The VET specification 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.
The VET principles can be either directly or indirectly traced to the
deliberations of the ROAD group in January 1992, and likely also to
still earlier works. [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.
2. Terminology
The mechanisms within this document build upon the fundamental
principles of IP-within-IP encapsulation. The terms "inner" and
"outer" are used throughout this document 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 supports the 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].
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enterprise
the same as defined in [RFC4852].
site
a logical and/or physical grouping of interfaces that connect a
topological area less than or equal to the enterprise in scope. A
site within an enterprise can 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 asymmetric reachability
links (see: [RFC4861], Section 2.2), where a wide variety of
MANETs share common properties with enterprise networks. Further
information on MANETs can be found in [RFC2501].
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 apply equally
to enterprises, sites and MANETs.
enterprise router
an Enterprise Interior Router, Enterprise Border Router, or
Enterprise Border Gateway. For the purose of this specification,
an enterprise router 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.
Enterprise Interior Router (EIR)
a fixed or mobile enterprise router that forwards packets over a
set of enterprise-interior interfaces connected to the same
enterprise.
Enterprise Border Router (EBR)
an EIR 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, i.e.,
an EBR may configure mulitple VET interfaces - one for each
distinct enterprise. All EBRs are also EIRs.
Enterprise Border Gateway (EBG)
an EBR that either directly or indirectly connects the enterprise
to provider networks and can delegate addresses/prefixes to other
EBRs within the enterprise. All EBGs are also EBRs.
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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.
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.
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-interior Interface
a EIR's attachment to a link within an enterprise. An enterprise-
interior interface is "neutral" in its orientation, i.e., it is
inherently neither an enterprise-edge nor provider-edge interface.
In particular, a packet may need to be forwarded over several
enterprise-interior interfaces before it is forwarded via either
an enterprise-edge or provider-edge interface.
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 also used as *outer* IP
addresses during encapsulation.
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 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
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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 presents an automatic
tunneling abstraction that represents the enterprise as a single
IP hop.
The following additional acronyms are used throughout the document:
CGA - Cryptographically Generated Address
DHCP[v4,v6] - the Dynamic Host Configuration Protocol
IP[v4,v6] - the Internet Protocol
ISATAP - Intra-Site Automatic Tunnel Addressing Protocol
ND - Neighbor Discovery
PIO - Prefix Information Option
RIO - Route Information Option
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
as depicted in Figure 1. All enterprise routers are also Enterprise
Interior Routers (EIRs) that 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 EIRs that connect edge networks and/or join
multiple enterprises together, while 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 enterprise routers (and their attached edge
networks); an enterprise may also contain other enterprises/sites
and/or be a subnetwork of a larger enterprise. An enterprise may
further encompass a set of branch offices connected to a home office
over one or several service providers, e.g., through Virtual Private
Network (VPN) tunnels.
Enterprises that comprise homogeneous link types within a single IP
subnet can configure the routing protocol to operate as a sub-IP
layer mechanism 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.
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Enterprises that comprise heterogeneous link types and/or multiple IP
subnets must also provide a routing service that operates as an IP
layer mechanism, e.g., to accommodate media types with dissimilar
Layer-2 address formats and maximum transmission units (MTUs). 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 enterprise router (i.e, an EIR/EBR/EBG) embodies
both a host function and router function. The host function supports
global-scoped communications over any of the enterprise router'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
connects the enterprise router's attached edge networks to the
enterprise and/or connects the enterprise to other networks including
the Internet (see: Figure 1).
In addition to other interface types, EBRs configure VET interfaces
that view all other EBRs in an enterprise as single-hop neighbors,
where the enterprise can also appear as a single IP hop within
another enterprise. EBRs configure a separate VET interface for each
distinct enterprise to which they connect, and discover a list of
EBRs for each VET interface that can be used for forwarding packets
to off-enterprise destinations. The following sections present the
Virtual Enterprise Traversal approach.
4. Autoconfiguration
EIRs configure enterprise-interior interfaces. An EBR is an EIR that
also configures enterprise-edge and VET interfaces. An EBG is an EBR
that also either directly or indirectly connects the enterprise to a
provider network. EIRs, EBRs and EBGs configure themselves for
operation according to the following subsections:
4.1. Enterprise Interior Router (EIR) Autoconfiguration
EIRs configure enterprise-interior interfaces and engage in routing
protocols over those interfaces.
When an EIR 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
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on each enterprise-interior interface that requires an IPv4 link-
local capability. IPv6 link-local address generation mechanisms that
provide sufficient uniqueness include Cryptographically Generated
Addresses (CGAs) [RFC3972], 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 EIR 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 EIR 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.
DHCP configuration of ELAs may require support from relays within the
enterprise that have already autoconfigured an ELA as well as an
enterprise-wide multicast forwarding capability. 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 TBD (see: Section 6).
DHCPv4 servers that delegate ELAs join the TBD 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., [I-D.fuller-240space]. When self-generation is used
alone, the EIR must continuously monitor the ELAs for uniqueness,
e.g., by monitoring the routing protocol, sending beacons, etc.
(This continuous monitoring process is sometimes known as "in-service
duplicate address detection").
A combined approach using both DHCP and self-generation is also
possible. In this combined approach, the EIR first self-generates a
temporary ELA which it will use only for the purpose of procuring an
actual ELA from a DHCP server. Acting as a combined client/relay,
the EIR then assigns the temporary ELA to an enterprise-interior
interface, engages in the routing protocol and performs a relay-
server exchange using the temporary ELA as an address for the relay.
When the DHCP server delegates an actual ELA, the EIR abandons the
temporary ELA, assigns the actual ELA to the enterprise-interior
interface and re-engages in the routing protocol. Note that the
range of ELAs delegated by a DHCP server must be disjoint from the
range of ELAs used by the EIR for self-generation.
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4.2. Enterprise Border Router (EBR) Autoconfiguration
EBRs are EIRs that configure enterprise-edge interfaces, and also
configure a VET interface over a set of underlying enterprise-
interior interfaces belonging to the same enterprise. Note that an
EBR may connect to multiple distinct enterprises, in which case it
would configure multiple VET interfaces over multiple distinct sets
of enterprise-interior interfaces. EBRs perform the following
autoconfiguration operations:
4.2.1. VET Interface Autoconfiguration
EBRs configure a VET interface over a set of underlying enterprise-
interior interfaces belonging to the same enterprise, where the VET
interface presents a virtual view of all EBRs in the enterprise as
single hop neighbors. Inner IP packets forwarded over the VET
interface are encapsulated in any mid-layer headers (e.g., IPsec, the
SEAL header, etc.) followed by an outer IP header, then submitted to
the outer IP forwarding engine for transmission on an underlying
enterprise-interior interface. Further encapsulation details are
specified in Section 5.
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 determined to be
unique. 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 EBRs as single-hop neighbors. It can also confirm reachability
of other EBRs through Neighbor Discovery (ND) and/or DHCP exchanges
over the VET interface, or through other means such as information
conveyed in the routing protocol.
The EBR must be able to detect and recover from the loss of VET
interface neighbors due to e.g., enterprise network partitions, node
failures, etc. Mechanisms specified outside of this document such as
monitoring the routing protocol, ND beaconing/polling, DHCP renewals/
leasequeries, upper layer protocol hints of forward progress,
bidirectional forward detection, detection of network attachment,
etc. can be used according to the particular deployment scenario.
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4.2.2. Enterprise Border Gateway Discovery and Enterprise
Identification
After the EBR configures its VET interfaces, it next discovers a list
of EBGs for each distinct enterprise to which it connects. The list
can be discovered through information conveyed in the routing
protocol or through the discovery mechanisms outlined in [RFC5214],
Section 8.3.2.
In particular, whether or not routing information is available the
EBR can discover the list of EBGs by resolving an identifying name
for the enterprise using an Enterprsie-local name resolution service
(e.g., using LLMNR [RFC4759] over the VET interface). In the absence
of other identifying names, the EBR can resolve either the hostname
"6over4" or the FQDN "6over4.example.com" (i.e., if an enterprise-
specific suffix "example.com" is known) for multicast-capable
enterprises. For non-multicast enterprises, the EBR can instead
resolve the hostname "isatap" or the FQDN "isatap.example.com".
Identifying names along with addresses of EBGs and/or the prefixes
they aggregate serve as an identifier for the enterprise.
4.2.3. Inner IP Address/Prefix Delegation and Maintenance
EBRs acquire inner IP protocol addresses and/or prefix delegations
through autoconfiguration exchanges via EBGs over VET interfaces, as
discussed in the following sections:
4.2.3.1. IPv4 Addresses/Prefix Delegation
When IPv4 is used as the inner IP protocol, the EBR performs DHCPv4 a
prefix delegation exchange [I-D.ietf-dhc-subnet-alloc] via an EBG
over a VET interface to obtain IPv4 prefixes for sub-delegation
and/or assignment on its enterprise-edge interfaces (the EBR may
peform multiple such exchanges via multiple EBGs.)
To perform the DHCPv4 prefix delegation exchange, a DHCPv4 client
associated with the EBR's host function forwards a DHCPDISCOVER
message with a Subnet Allocation option to a DHCPv4 relay associated
with its router function, i.e., the EBR acts as both client and
relay. The relay then forwards the message over the VET interface to
the DHCPv4 server via an EBG that hosts a DHCPv4 relay/server. The
forwarded DHCPDISCOVER will elicit a DHCPOFFER from the server
containing IPv4 prefix delegations, and the EBR completes the
delegation through a DHCPREQUEST/DHCPACK exchange. The EBR can also
obtain /32 prefixes using DHCPv4 prefix delegation the same as for
any IPv4 prefix.
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4.2.3.2. IPv6 Addresses/Prefix Delegation
When IPv6 is used as the inner protocol, the EBR sends unicast IPv6
Router Solicitation (RS) messages to an EBG over a VET interface to
receive Router Advertisements (RAs) with Prefix Information Options
(PIOs) and/or with the M/O flags set to signify whether DHCPv6
autoconfiguration is available; the EBR may also perform RS/RA
exchanges with multiple EBGs. When the EBR receives an RA containing
PIOs with the 'A' and 'L' bits set to 1, it autoconfigures IPv6
addresses from the prefixes using SLAAC and assigns them to the VET
interface. (When IPv4 is used as the outer IP protocol, the
addresses are autoconfigured and assigned as ISATAP addresses the
same as specified in [RFC5214].)
When the EBR receives an RA with the M/O flags set to 1, the EBG that
sent the RA also hosts a DHCPv6 relay/server. If the RA also
contains PIOs with the 'L' bit set to 0, the EBR can use them as
hints of prefixes the server is willing to delegate (see:
Section 4.3). Whether or not such hints are available, the EBR
(acting as a requesting router) can use DHCPv6 prefix delegation
[RFC3633] over the VET interface to obtain IPv6 prefixes from the
server (acting as a delegating router). The EBR can then use the
delegated prefixes for sub-delegation and/or assignment on its
enterprise-edge interfaces.
The EBR obtains prefixes using either a 2-message or 4-message DHCPv6
exchange [RFC3315]. For example, to perform the 2-message exchange a
DHCPv6 client associated with the EBR's host function forwards a
Solicit message with an IA_PD option to a DHCPv6 relay associated
with its router function, i.e., the EBR acts as both client and
relay. The relay then forwards the message over the VET interface to
the server via the EBG. The forwarded Solicit message will elicit a
Reply from the server containing IPv6 prefix delegations.
The EBR can also 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. The EBR can use mechanisms such as CGAs
[RFC3972], IPv6 privacy address [RFC4941], etc. to self-generate
addresses in conjunction with prefix delegation.
4.2.3.3. Prefix and Route Maintenance
When DHCP prefix delegation is used, 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 EBR to which the
prefix was delegated. The prefix delegation remains active as long
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as the EBR continues to issue renewals over the VET interface before
the lease lifetime expires. The lease lifetime also keeps the
delegation state active even if communications between the EBR and
DHCP server is disrupted for a period of time (e.g., due to an
enterprise network partition) before being reestablished (e.g., due
to an enterprise network merge). EBRs can also sub-delegate inner IP
prefixes to requesting routers on networks connected on their
enterprise-edge interfaces as well as to EBRs in other enterprises.
Since the DHCP client and relay are co-resident on the same EBR, no
special coordination is necessary for the EBG to maintain routing
information. The EBG simply retains forwarding information base
entries that identify the EBR as the next-hop toward the prefix over
the VET interface, and issues ordinary redirects over the VET
interface when necessary .
4.2.4. Portable Inner IP Addresses/Prefixes
Independent of any inner IP addresses/prefix delegations (see:
Section 4.2.3), an EBR can also use portable IP addresses/prefixes
(e.g., taken from a home network) and/or self-configured IP
addresses/prefixes (e.g., IPv6 Unique Local Addresses (ULAs)
[RFC4193][I-D.ietf-ipv6-ula-central]). The EBR can continue to use
these addresses/prefixes as it travels between visited enterprise
networks as long as it coordinates in some fashion with a mapping
agent, prefix aggregation authority, etc. EBRs can also sub-delegate
portable (and other self-configured) prefixes to requesting routers
on networks connected on their enterprise-edge interfaces as well as
to EBRs in other enterprises.
4.2.5. Enterprise-edge Interface Autoconfiguration
After the EBR receives inner IP address/prefix delegations (see:
Section 4.2.3), it can assign them on enterprise-edge interfaces
only; it does not assign them on provider-edge, VET, or enterprise-
interior interfaces (see: [RFC3633], Section 12.1). Similarly, the
EBR can assign portable and/or self-configured addresses/prefixes
(see: Section 4.2.4) on enterprise-edge interfaces.
4.3. Enterprise Border Gateway (EBG) Autoconfiguration
EBGs are EBRs that connect an enterprise to a service provider either
directly via provider-edge interfaces or indirectly via another
enterprise. EBGs configure provider-edge interfaces in a manner that
is specific to its provider connections.
For IPv6, EBGs send RAs over VET interfaces on enterprises for which
they are gateways with the M/O flags set to indicate whether they
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configure a DHCP relay/server. 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
prefixes.
5. Post-Autoconfiguration Operation
After an EIR has been autoconfigured, it participates in any routing
protocols over enterprise-interior interfaces and forwards 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 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.
The following sections discuss post-autoconfiguration operations:
5.1. Forwarding Packets to Destinations Outside of the Enterprise
EBRs consult the inner IP forwarding table to determine the next hop
address (e.g., the VET interface address of another EBR) for
forwarding packets to destinations outside of the enterprise. When
there is no forwarding information available, the EBR can discover
the next-hop through FQDN or reverse lookup using the same name
resolution services as for EBG discovery (see: Section 4.2.2).
For forwarding to next-hop addresses over VET interfaces that use
IPv6-in-IPv4 encapsulation, EBRs determine the outer destination
address 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.
EBRs that use IPv6 as the inner protocol can discover default router
preferences and more-specific routes [RFC4191] by sending an RS over
the VET interface to elicit an RA from another EBR. After default
and/or more-specific routes are discovered, the EBR can forward IP
packets via a specific EBR as the next-hop router on the VET
interface. When multiple default routers are available, the EBR can
use default router preferences, routing protocol information, traffic
engineering configurations, etc. to select the best exit router.
Note that the EBR only accepts PIOs, M/O flag settings and default
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router preferences in RAs that are received from EBGs (i.e., it does
not accept them from ordinary EBRs).
5.2. Enterprise-Local Communications
When permitted by policy, pairs of EIRs that configure the endpoints
of a communications session 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, a pair of communicating EIRs can use IPv4 ELAs for
enterprise-local communications over their enterprise-interior
interfaces without using the VET interface.
5.3. Multicast
In multicast-capable deployments, EIRs provide an enterprise-wide
multicasting service such as Simplified Multicast Forwarding (SMF)
[I-D.ietf-manet-smf] 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, EBRs 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 multicast address space.
EBRs 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 the IPv4 multicast address space. For
other IP-in-IP encapsulations, mappings are established through
administrative configuration or through an unspecified alternate
method.
For multicast-capable enterprises, use of the inner IP multicast
service for operating the ND protocol over the VET interface is
available but should be used sparingly to minimize enterprise-wide
flooding. Therefore, EBRs should use unicast ND services over the
VET interface instead of multicast whenever possible.
5.4. Service Discovery
EIRs 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 efficient service
discovery mechanisms are for further study.
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6. IANA Considerations
A Site-Local Scope IPv4 multicast group (TBD) 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.
7. Security Considerations
Security considerations for MANETs are found in [RFC2501].
Security concerns with tunneling along with recommendations that
apply also to VET are found in
[I-D.ietf-v6ops-tunnel-security-concerns] [RFC5214].
8. Related Work
The authors acknowledge the work done by Brian Carpenter and Cyndi
Jung in [RFC2529] that introduced the concept of intra-site automatic
tunneling. This concept was later called: "Virtual Ethernet" and
investigated by Quang Nguyen under the guidance of Dr. Lixia Zhang.
As for this document, these architectural principles also follow from
earlier works articulated by the ROAD group deliberations of 1992.
Telcordia has proposed DHCP-related solutions for the CECOM MOSAIC
program. The Naval Research Lab (NRL) Information Technology
Division uses DHCP in their MANET research testbeds. Various
proposals within the IETF have suggested similar mechanisms.
9. Acknowledgements
The following individuals gave direct and/or indirect input that was
essential to the work: Jari Arkko, Teco Boot, Emmanuel Bacelli, James
Bound, Thomas Clausen, Bob Hinden, Joe Macker, Thomas Narten,
Alexandru Petrescu, John Spence, Jinmei Tatuya, Dave Thaler, Michaela
Vanderveen 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)
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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
[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-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.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
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.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[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.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, November 2005.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
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"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.
11.2. Informative References
[I-D.cheshire-dnsext-multicastdns]
Cheshire, S. and M. Krochmal, "Multicast DNS",
draft-cheshire-dnsext-multicastdns-07 (work in progress),
September 2008.
[I-D.fuller-240space]
Fuller, V., "Reclassifying 240/4 as usable unicast address
space", draft-fuller-240space-02 (work in progress),
March 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-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-07 (work in progress),
February 2008.
[I-D.templin-seal]
Templin, F., "The Subnetwork Encapsulation and Adaptation
Layer (SEAL)", draft-templin-seal-23 (work in progress),
August 2008.
[RFC1122] Braden, R., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, October 1989.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
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[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.
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, February 2001.
[RFC3753] Manner, J. and M. Kojo, "Mobility Related Terminology",
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.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, March 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.
[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.
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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 (such as
specified in [RFC4862]) would require 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, e.g., the soon-
to-be-reclassified 240/4 space [I-D.fuller-240space].
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 EIR'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 -17 to 18:
o adjusted section headings to group autoconf operations under EIR/
EBR/EBG.
o clarified M/O bits
o clarified EBG roles
Changes from -15 to 17:
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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.
Changes from -08 to -09:
o Introduced the term "VET".
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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:
o introduced conceptual "virtual ethernet" model.
o support "raw" and "cooked" modes as equivalent access methods on
the virutal ethernet.
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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
Author's Address
Fred L. Templin (editor)
Boeing Phantom Works
P.O. Box 3707 MC 7L-49
Seattle, WA 98124
USA
Email: fltemplin@acm.org
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