Network Working Group F. Templin, Ed.
Internet-Draft Boeing Research & Technology
Intended status: Standards Track March 14, 2011
Expires: September 15, 2011
Virtual Enterprise Traversal (VET)
draft-templin-intarea-vet-24.txt
Abstract
Enterprise networks connect hosts and routers over various link
types, and often also connect to provider networks and/or the global
Internet. Enterprise network nodes require a means to automatically
provision addresses/prefixes and support internetworking operation in
a wide variety of use cases including Small Office, Home Office
(SOHO) networks, Mobile Ad hoc Networks (MANETs), ISP networks,
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.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 15, 2011.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
Templin Expires September 15, 2011 [Page 1]
Internet-Draft VET March 2011
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Enterprise Network Characteristics . . . . . . . . . . . . . . 11
4. Autoconfiguration . . . . . . . . . . . . . . . . . . . . . . 13
4.1. Enterprise Router (ER) Autoconfiguration . . . . . . . . . 13
4.2. VET Border Router (VBR) Autoconfiguration . . . . . . . . 15
4.2.1. VET Interface Initialization . . . . . . . . . . . . . 15
4.2.2. Potential Router List (PRL) Discovery . . . . . . . . 15
4.2.3. Provider-Aggregated (PA) EID Prefix
Autoconfiguration . . . . . . . . . . . . . . . . . . 16
4.2.4. Provider-(In)dependent (PI) EID Prefix
Autoconfiguration . . . . . . . . . . . . . . . . . . 18
4.3. VET Border Gateway (VBG) Autoconfiguration . . . . . . . . 18
4.4. VET Host Autoconfiguration . . . . . . . . . . . . . . . . 19
5. Internetworking Operation . . . . . . . . . . . . . . . . . . 20
5.1. Routing Protocol Participation . . . . . . . . . . . . . . 20
5.1.1. PI Prefix Routing Considerations . . . . . . . . . . . 20
5.2. Default Route Configuration and Selection . . . . . . . . 21
5.3. Address Selection . . . . . . . . . . . . . . . . . . . . 21
5.4. Next Hop Determination . . . . . . . . . . . . . . . . . . 22
5.5. VET Interface Encapsulation/Decapsulation . . . . . . . . 23
5.5.1. Inner Network Layer Protocol . . . . . . . . . . . . . 23
5.5.2. Mid-Layer Encapsulation . . . . . . . . . . . . . . . 23
5.5.3. SEAL Encapsulation . . . . . . . . . . . . . . . . . . 23
5.5.4. Outer UDP Header Encapsulation . . . . . . . . . . . . 24
5.5.5. Outer IP Header Encapsulation . . . . . . . . . . . . 25
5.5.6. Decapsulation . . . . . . . . . . . . . . . . . . . . 25
5.6. Mobility and Multihoming Considerations . . . . . . . . . 26
5.7. Neighbor Coordination on VET Interfaces using SEAL . . . . 26
5.7.1. Router Discovery . . . . . . . . . . . . . . . . . . . 28
5.7.2. Neighbor Unreachability Detection . . . . . . . . . . 28
5.7.3. Redirect Function . . . . . . . . . . . . . . . . . . 29
5.8. Neighbor Coordination on VET Interfaces using IPsec . . . 29
5.9. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 30
5.9.1. Multicast over (Non)Multicast Enterprise Networks . . 30
5.9.2. Multicast Over Multicast-Capable Enterprise
Networks . . . . . . . . . . . . . . . . . . . . . . . 30
5.10. Service Discovery . . . . . . . . . . . . . . . . . . . . 31
5.11. VET Link Partitioning . . . . . . . . . . . . . . . . . . 31
Templin Expires September 15, 2011 [Page 2]
Internet-Draft VET March 2011
5.12. VBG Prefix State Recovery . . . . . . . . . . . . . . . . 31
5.13. Legacy ISATAP Services . . . . . . . . . . . . . . . . . . 32
5.14. ISATAP Update . . . . . . . . . . . . . . . . . . . . . . 32
5.14.1. ISATAP Predirection . . . . . . . . . . . . . . . . . 32
5.14.2. Scaling Considerations . . . . . . . . . . . . . . . . 39
5.14.3. Proxy Chaining . . . . . . . . . . . . . . . . . . . . 40
5.14.4. Mobility . . . . . . . . . . . . . . . . . . . . . . . 40
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 41
7. Security Considerations . . . . . . . . . . . . . . . . . . . 41
8. Related Work . . . . . . . . . . . . . . . . . . . . . . . . . 42
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 42
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 43
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 43
11.1. Normative References . . . . . . . . . . . . . . . . . . . 43
11.2. Informative References . . . . . . . . . . . . . . . . . . 44
Appendix A. Duplicate Address Detection (DAD) Considerations . . 49
Appendix B. Anycast Services . . . . . . . . . . . . . . . . . . 50
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 51
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 53
Templin Expires September 15, 2011 [Page 3]
Internet-Draft VET March 2011
1. Introduction
Enterprise networks [RFC4852] connect hosts and 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 Small Office, Home Office (SOHO) network, as complex as a multi-
organizational corporation, or as large as the global Internet
itself. Internet Service Provider (ISP) networks are another example
use case that fits well with the VET enterprise network model.
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/ICMPv4
[RFC0791][RFC0792] and IPv6/ICMPv6 [RFC2460][RFC4443] are discussed
within this context (other network layer protocols are also
considered). The use of standard DHCP [RFC2131] [RFC3315] is assumed
unless otherwise specified.
Templin Expires September 15, 2011 [Page 4]
Internet-Draft VET March 2011
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
encapsulating inner network layer protocol packets for transmission
over outer IPv4 or IPv6 networks. 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 typically correspond to the
wireless multihop radio interfaces 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 require a means for supporting both Provider-
(In)dependent (PI) and Provider-Aggregated (PA) addressing. This is
especially true for enterprise network scenarios that involve
mobility and multihoming. The VET specification provides adaptable
mechanisms that address these and other issues in a wide variety of
enterprise network use cases.
Templin Expires September 15, 2011 [Page 5]
Internet-Draft VET March 2011
The VET framework builds on a Non-Broadcast Multiple Access (NBMA)
[RFC2491] virtual interface model in a manner similar to other
automatic tunneling technologies [RFC2529][RFC5214]. VET interfaces
support the encapsulation of inner network layer protocol packets
over IP networks (i.e., either IPv4 or IPv6). VET is also compatible
with mid-layer encapsulation technologies including IPsec [RFC4301],
and supports both stateful and stateless prefix delegation.
VET and its associated technologies (including the Subnetwork
Encapsulation and Adaptation Layer (SEAL) [I-D.templin-intarea-seal])
are functional building blocks for a new Internetworking architecture
based on the Internet Routing Overlay Network (IRON) [RFC6179] and
Routing and Addressing in Networks with Global Enterprise Recursion
(RANGER) [RFC5720][RFC6139]. Many of the VET principles can be
traced to the deliberations of the ROAD group in January 1992, and
also to still earlier initiatives including NIMROD [RFC1753] and the
Catenet model for internetworking [CATENET] [IEN48] [RFC2775]. The
high-level architectural aspects of the ROAD group deliberations are
captured in a "New Scheme for Internet Routing and Addressing
(ENCAPS) for IPNG" [RFC1955].
VET is related to the present-day activities of the IETF INTAREA,
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 encapsulation. The term "inner" refers to the
innermost {address, protocol, header, packet, etc.} *before*
encapsulation, and the term "outer" refers to the outermost {address,
protocol, header, packet, etc.} *after* encapsulation. VET also
accommodates "mid-layer" encapsulations including the Subnetwork
Encapsulation and Adaptation Layer (SEAL) [I-D.templin-intarea-seal],
IPsec [RFC4301], etc.
The terminology in the normative references apply; the following
terms are defined within the scope of this document:
Virtual Enterprise Traversal (VET)
an abstraction that uses encapsulation to create virtual overlays
for transporting inner network layer packets over outer IPv4 and
IPv6 enterprise networks.
Templin Expires September 15, 2011 [Page 6]
Internet-Draft VET March 2011
enterprise network
the same as defined in [RFC4852]. An enterprise network is
further understood to refer to a cooperative networked collective
of devices within a structured IP routing and addressing plan and
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 connectivity itself.
subnetwork
the same as defined in [RFC3819].
site
a logical and/or physical grouping of interfaces that connect a
topological area less than or equal to an enterprise network in
scope. From a network organizational standpoint, a site within an
enterprise network can be considered as an enterprise network unto
itself.
Mobile Ad hoc Network (MANET)
a connected topology of mobile or fixed routers that maintain a
routing structure among themselves over links that often have
dynamic connectivity properties. The characteristics of MANETs
are described in [RFC2501], Section 3, and a wide variety of
MANETs share common properties with enterprise networks.
enterprise/site/MANET
throughout the remainder of this document, the term "enterprise
network" 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.
VET link
a virtual link that uses automatic tunneling to create an overlay
network that spans an enterprise network routing region. VET
links can be segmented (e.g., by filtering gateways) into multiple
distinct segments that can be joined together by bridges or IP
routers the same as for any link. Bridging would view the
multiple (bridged) segments as a single VET link, whereas IP
routing would view the multiple segments as multiple distinct VET
links. VET links can further be partitioned into multiple logical
areas, where each area is identified by a distinct set of border
nodes.
Templin Expires September 15, 2011 [Page 7]
Internet-Draft VET March 2011
VET links configured over non-multicast enterprise networks
support only Non-Broadcast, Multiple Access (NBMA) services; VET
links configured over enterprise networks that support multicast
can support both NBMA and native multicast services. All nodes
connected to the same VET link appear as neighbors from the
standpoint of the inner network layer.
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 outer IP packets over
one or more sets of enterprise-interior interfaces, where each set
connects to a distinct enterprise network.
VET Border Router (VBR)
an ER that connects edge networks to VET links and/or connects
multiple VET links together. A VBR is a tunnel endpoint router,
and it configures a separate VET interface for each distinct VET
link. All VBRs are also ERs.
VET Border Gateway (VBG)
a VBR that connects VET links to provider networks. A VBG may
alternately act as "half-gateway", and forward the packets it
receives from neighbors on the VET link to another VBG on the same
VET link. All VBGs are also VBRs.
VET host
any node (host or router) that configures a VET interface for
host-operation only. Note that a node may configure some of its
VET interfaces as host interfaces and others as router interfaces.
VET node
any node (host or router) that configures and uses a VET
interface.
enterprise-interior interface
an ER's attachment to a link within an enterprise network.
Packets sent over enterprise-interior interfaces may be forwarded
over multiple additional enterprise-interior interfaces within the
enterprise network before they reach either their final
destination or a border router/gateway. Enterprise-interior
interfaces connect laterally within the IP network hierarchy.
Templin Expires September 15, 2011 [Page 8]
Internet-Draft VET March 2011
enterprise-edge interface
a VBR's attachment to a link (e.g., an Ethernet, a wireless
personal area network, etc.) on an arbitrarily complex edge
network that the VBR connects to a VET link and/or a provider
network. Enterprise-edge interfaces connect to lower levels
within the IP network hierarchy.
provider-edge interface
a VBR's attachment to the Internet or to a provider network via
which the Internet can be reached. Provider-edge interfaces
connect to higher levels within the IP network hierarchy.
internal-virtual interface
an interface that is internal to a VET node and does not in itself
directly attach to a tangible link, e.g., a loopback interface.
VET interface
a VET node's attachment to a VET link. VET nodes configure each
VET interface over a set of underlying enterprise-interior
interfaces that connect to a routing region spanned by a single
VET link. When there are multiple distinct VET links (each with
their own distinct set of underlying interfaces), the VET node
configures a separate VET interface for each link.
The VET interface encapsulates each inner packet in any mid-layer
headers followed by an outer IP header, then forwards the packet
on an underlying interface such that the Time to Live (TTL) - Hop
Limit in the inner header is not decremented as the packet
traverses the link. The VET interface therefore presents an
automatic tunneling abstraction that represents the VET link as a
single hop to the inner network layer.
Provider Aggregated (PA) prefix
a network layer protocol prefix that is delegated to a VET node by
a provider network.
Provider-(In)dependent (PI) address/prefix
a network layer protocol prefix that is delegated to a VET node by
an independent prefix registration authority.
Routing Locator (RLOC)
a public-scope or enterprise-local-scope IP address that can
appear in enterprise-interior and/or interdomain routing tables.
Public-scope RLOCs are delegated to specific enterprise networks
and routable within both the enterprise-interior and interdomain
routing regions. Enterprise-local-scope RLOCs (e.g., IPv6 Unique
Local Addresses [RFC4193], IPv4 privacy addresses [RFC1918], etc.)
are self-generated by individual enterprise networks and routable
Templin Expires September 15, 2011 [Page 9]
Internet-Draft VET March 2011
only within the enterprise-interior routing region.
ERs use RLOCs for operating the enterprise-interior routing
protocol and for next-hop determination in forwarding packets
addressed to other RLOCs. End systems can use RLOCs as addresses
for end-to-end communications between peers within the same
enterprise network. VET interfaces treat RLOCs as *outer* IP
addresses during encapsulation.
Endpoint Interface iDentifier (EID)
a public-scope network layer address that is routable within
enterprise-edge and/or VET overlay networks. In a pure mapping
system, EID prefixes are not routable within the interdomain
routing system. In a hybrid routing/mapping system, EID prefixes
may be represented within the same interdomain routing instances
that distribute RLOC prefixes. In either case, EID prefixes are
separate and distinct from any RLOC prefix space, but they are
mapped to RLOC addresses to support packet forwarding over VET
interfaces.
VBRs participate in any EID-based routing instances and use EID
addresses for next-hop determination. End systems can use EIDs as
addresses for end-to-end communications between peers either
within the same enterprise network or within different enterprise
networks. VET interfaces treat EIDs as *inner* network layer
addresses during encapsulation.
Note that an EID can also be used as an *outer* network layer
address if there are nested encapsulations. In that case, the EID
would appear as an RLOC to the innermost encapsulation.
The following additional acronyms are used throughout the document:
CGA - Cryptographically Generated Address
DHCP(v4, v6) - Dynamic Host Configuration Protocol
ECMP - Equal Cost Multi Path
FIB - Forwarding Information Base
ICMP - either ICMPv4 or ICMPv6
IP - either IPv4 or IPv6
ISATAP - Intra-Site Automatic Tunnel Addressing Protocol
NBMA - Non-Broadcast, Multiple Access
ND - Neighbor Discovery
PIO - Prefix Information Option
PRL - Potential Router List
PRLNAME - Identifying name for the PRL
RIB - Routing Information Base
RIO - Route Information Option
SCMP - SEAL Control Message Protocol
Templin Expires September 15, 2011 [Page 10]
Internet-Draft VET March 2011
SEAL - Subnetwork Encapsulation and Adaptation Layer
SLAAC - IPv6 StateLess Address AutoConfiguration
SNS/SNA - SEAL Neighbor Solicitation/Advertisement
SRS/SRA - SEAL Router Solicitation/Advertisement
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. When used
in lower case (e.g., must, must not, etc.), these words MUST NOT be
interpreted as described in [RFC2119], but are rather interpreted as
they would be in common English.
3. Enterprise Network Characteristics
Enterprise networks 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.
VET Border Routers (VBRs) are ERs that connect edge networks to VET
links that span enterprise networks. VET Border Gateways (VBGs) are
VBRs that connect VET links to provider networks.
Conceptually, an ER embodies both a host function and router
function, and supports communications according to the weak end-
system model [RFC1122]. The router function engages in the
enterprise-interior routing protocol on its enterprise-interior
interfaces, connects any of the ER's edge networks to its VET links,
and may also connect the VET links to provider networks (see
Figure 1). The host function typically supports network management
applications, but may also support diverse applications typically
associated with general-purpose computing platforms.
An enterprise network may be as simple as a small collection of ERs
and their attached edge networks; an enterprise network may also
contain other enterprise networks and/or be a subnetwork of a larger
enterprise network. An enterprise network 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. Finally, an enterprise network may contain
many internal partitions that are logical or physical groupings of
nodes for the purpose of load balancing, organizational separation,
etc. In that case, each internal partition resembles an individual
segment of a bridged LAN.
Enterprise networks that comprise link types with sufficiently
similar properties (e.g., Layer 2 (L2) address formats, maximum
transmission units (MTUs), etc.) can configure a subnetwork routing
Templin Expires September 15, 2011 [Page 11]
Internet-Draft VET March 2011
service such that the inner network layer sees the underlying network
as an ordinary shared link the same as for a (bridged) campus LAN
(this is often the case with large cellular operator networks). In
that case, a single inner network layer hop is sufficient to traverse
the underlying network. Enterprise networks that comprise link types
with diverse properties and/or configure multiple IP subnets must
also provide an enterprise-interior routing service that operates as
an IP layer mechanism. In that case, multiple inner network layer
hops may be necessary to traverse the underlying network such that
care must be taken to avoid multi-link subnet issues [RFC4903].
In addition to other interface types, VET nodes configure VET
interfaces that view all other nodes on the VET link as neighbors on
a virtual NBMA link. VET nodes configure a separate VET interface
for each distinct VET link to which they connect, and discover
neighbors on the link that can be used for forwarding packets to off-
link destinations. VET interface neighbor relationships may be
either unidirectional or bidirectional.
A unidirectional neighbor relationship is typically established and
maintained as a result of network layer control protocol messaging in
a manner that parallels IPv6 neighbor discovery [RFC4861]. A
bidirectional neighbor relationship is typically established and
maintained as result of a short transaction between the neighbors
carried by a reliable transport protocol such as TCP. The protocol
details of the transaction are out of scope for this document, and
indeed need not be standardized as long as both neighbors observe the
same specifications.
For each distinct VET link , a trust basis must be established and
consistently applied. For example, for VET links configured over
enterprise networks in which VBRs establish symmetric security
associations, mechanisms such as IPsec [RFC4301] can be used to
assure authentication and confidentiality. In other enterprise
network scenarios, VET links may require asymmetric securing
mechanisms such as SEcure Neighbor Discovery (SEND) [RFC3971]. VET
links configured over still other enterprise networks may find it
sufficient to employ additional encapsulations (e.g., SEAL
[I-D.templin-intarea-seal]) that include a simple per-packet nonce to
detect off-path attacks.
Finally, for VET links configured over enterprise networks with a
centralized management structure (e.g., a corporate campus network,
an ISP network, etc.), a hybrid routing/mapping service can be
deployed using a synchronized set of VBGs. In that case, the VBGs
can provide a "default mapper" [I-D.jen-apt] service used for short-
term packet forwarding until route-optimized paths can be
established. For VET links configured over enterprise networks with
Templin Expires September 15, 2011 [Page 12]
Internet-Draft VET March 2011
a distributed management structure (e.g., disconnected MANETs), peer-
to-peer coordination between the VET nodes themselves without the
assistance of VBGs may be required. Recognizing that various use
cases will entail a continuum between a fully centralized and fully
distributed approach, the following sections present the mechanisms
of Virtual Enterprise Traversal as they apply to a wide variety of
scenarios.
4. Autoconfiguration
ERs, VBRs, VBGs, 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 any
routing protocols over those interfaces.
When an ER joins an enterprise network, it first configures an IPv6
link-local address on each enterprise-interior interface that
requires an IPv6 link-local capability and configures an IPv4 link-
local address on each enterprise-interior interface that requires an
IPv4 link-local capability. IPv6 link-local address generation
mechanisms include Cryptographically Generated Addresses (CGAs)
[RFC3972], IPv6 Privacy Addresses [RFC4941], StateLess Address
AutoConfiguration (SLAAC) using EUI-64 interface identifiers
[RFC4291] [RFC4862], etc. The mechanisms specified in [RFC3927]
provide an IPv4 link-local address generation capability.
Next, the ER configures one or more RLOCs and engages in any routing
protocols on its enterprise-interior interfaces. The ER can
configure RLOCs via administrative configuration, pseudo-random self-
generation from a suitably large address pool, DHCP
autoconfiguration, or through an alternate autoconfiguration
mechanism.
Pseudo-random self-generation of IPv6 RLOCs can be from a large
public or local-use IPv6 address range (e.g., IPv6 Unique Local
Addresses [RFC4193]). Pseudo-random self-generation of IPv4 RLOCs
can be from a large public or local-use IPv4 address range (e.g.,
[RFC1918]). When self-generation is used alone, the ER continuously
monitors the RLOCs for uniqueness, e.g., by monitoring the
enterprise-interior routing protocol. (Note however that anycast
RLOCs may be assigned to multiple enterprise-interior interfaces;
hence, monitoring for uniqueness applies only to RLOCs that are
provisioned as unicast.)
Templin Expires September 15, 2011 [Page 13]
Internet-Draft VET March 2011
DHCP autoconfiguration of RLOCs uses standard DHCP procedures,
however ERs acting as DHCP clients SHOULD also use DHCP
Authentication [RFC3118] [RFC3315] as discussed further below. In
typical enterprise network scenarios (i.e., those with stable links),
it may be sufficient to configure one or a few DHCP relays on each
link that does not include a DHCP server. In more extreme scenarios
(e.g., MANETs that include links with dynamic connectivity
properties), DHCP operation may require any ERs that have already
configured RLOCs to act as DHCP relays to ensure that client DHCP
requests eventually reach a DHCP server. This may result in
considerable DHCP message relaying until a server is located, but the
DHCP Authentication Replay Detection vector provides relays with a
means for avoiding message duplication.
In all enterprise network scenarios, the amount of DHCP relaying
required can be significantly reduced if each relay has a way of
contacting a DHCP server directly. In particular, if the relay can
discover the unicast addresses for one or more servers (e.g., by
discovering the unicast RLOC addresses of VBGs as described in
Section 4.2.2) it can forward DHCP requests directly to the unicast
address(es) of the server(s). If the relay does not know the unicast
address of a server, it can forward DHCP requests to a site-scoped
DHCP server multicast address if the enterprise network supports
site-scoped multicast services. For DHCPv6, relays can forward
requests to the site-scoped IPv6 multicast group address
'All_DHCP_Servers' [RFC3315]. For DHCPv4, relays can forward
requests to the site-scoped IPv4 multicast group address
'All_DHCPv4_Servers', which SHOULD be set to 239.255.2.1 unless an
alternate multicast group for the enterprise network is known.
DHCPv4 servers that delegate RLOCs SHOULD therefore join the
'All_DHCPv4_Servers' multicast group and service any DHCPv4 messages
received for that group.
A combined approach using both DHCP and self-generation is also
possible when the ER configures 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. The ER first self-generates an RLOC taken from a
temporary addressing range used only for the bootstrapping purpose of
procuring an actual RLOC taken from a delegated addressing range.
The ER then engages in the enterprise-interior routing protocol and
performs a DHCP exchange as above using the temporary RLOC as the
address of its relay function. When the DHCP server delegates an
actual RLOC address/prefix, the ER abandons the temporary RLOC and
re-engages in the enterprise-interior routing protocol using an RLOC
taken from the delegation.
Alternatively (or in addition to the above), the ER can request RLOC
Templin Expires September 15, 2011 [Page 14]
Internet-Draft VET March 2011
prefix delegations via an automated prefix delegation exchange over
an enterprise-interior interface and can assign the prefix(es) on
enterprise-edge interfaces. Note that in some cases, the same
enterprise-edge interfaces may assign both RLOC and EID addresses if
there is a means for source address selection. In other cases (e.g.,
for separation of security domains), RLOCs and EIDs are assigned on
separate sets of enterprise-edge interfaces.
In some enterprise network scenarios (e.g., MANETs that include links
with dynamic connectivity properties), assignment of RLOCs on
enterprise-interior interfaces as singleton addresses (i.e., as
addresses with /32 prefix lengths for IPv4, or as addresses with /128
prefix lengths for IPv6) MAY be necessary to avoid multi-link subnet
issues.
4.2. VET Border Router (VBR) Autoconfiguration
VBRs are ERs that configure and use one or more VET interfaces. In
addition to the ER autoconfiguration procedures specified in
Section 4.1, VBRs perform the following autoconfiguration operations.
4.2.1. VET Interface Initialization
VBRs configure a separate VET interface for each VET link, where each
VET link spans a distinct sets of underlying links belonging to the
same enterprise network. All nodes on the VET link appear as single-
hop neighbors from the standpoint of the inner network layer protocol
through the use of encapsulation.
The VBR binds each VET interface to one or more underlying
interfaces, and uses the underlying interface addresses as RLOCs to
serve as the outer source addresses for encapsulated packets. The
VBR then assigns a link-local address to each VET interface if
necessary. When IPv6 and IPv4 are used as the inner/outer protocols
(respectively), the VBR can autoconfigure an IPv6 link-local address
on the VET interface using a modified EUI-64 interface identifier
based on an IPv4 RLOC address (see Section 2.2.1 of [RFC5342]).
Link-local address configuration for other inner/outer protocol
combinations is through administrative configuration, random self-
generation (e.g., [RFC4941], etc.) or through an unspecified
alternate method.
4.2.2. Potential Router List (PRL) Discovery
After initializing the VET interface, the VBR next discovers a
Potential Router List (PRL) for the VET link that includes the RLOC
addresses of VBGs. The PRL can be discovered through administrative
configuration, information conveyed in the enterprise-interior
Templin Expires September 15, 2011 [Page 15]
Internet-Draft VET March 2011
routing protocol, an anycast VBG discovery message exchange, a DHCP
option, etc. In multicast-capable enterprise networks, VBRs can also
listen for advertisements on the 'rasadv' [RASADV] multicast group
address.
When no other information is available, the VBR can resolve an
identifying name for the PRL ('PRLNAME') formed as
'hostname.domainname', where 'hostname' is an enterprise-specific
name string and 'domainname' is an enterprise-specific Domain Name
System (DNS) suffix [RFC1035]. The VBR discovers 'PRLNAME' through
administrative configuration, the DHCP Domain Name option [RFC2132],
'rasadv' protocol advertisements, link-layer information (e.g., an
IEEE 802.11 Service Set Identifier (SSID)), or through some other
means specific to the enterprise network. The VBR can also obtain
'PRLNAME' as part of an arrangement with a private-sector PI prefix
vendor (see: Section 4.2.4).
In the absence of other information, the VBR sets the 'hostname'
component of 'PRLNAME' to "isatapv2" and sets the 'domainname'
component to an enterprise-specific DNS suffix (e.g., "example.com").
Isolated enterprise networks that do not connect to the outside world
may have no enterprise-specific DNS suffix, in which case the
'PRLNAME' consists only of the 'hostname' component. (Note that the
default hostname "isatapv2" is intentionally distinct from the
convention specified in [RFC5214].)
After discovering 'PRLNAME', the VBR resolves the name into a list of
RLOC addresses through a name service lookup. For centrally managed
enterprise networks, the VBR resolves 'PRLNAME' using an enterprise-
local name service (e.g., the DNS). For enterprises with no
centralized management structure, the VBR resolves 'PRLNAME' using
Link-Local Multicast Name Resolution (LLMNR) [RFC4795] over the VET
interface. In that case, all VBGs in the PRL respond to the LLMNR
query, and the VBR accepts the union of all responses.
4.2.3. Provider-Aggregated (PA) EID Prefix Autoconfiguration
VBRs that connect their enterprise networks to a provider network
obtain Provider-Aggregated (PA) EID prefixes through stateful and/or
stateless autoconfiguration mechanisms. The stateful and stateless
approaches are discussed in the following subsections.
4.2.3.1. Stateful Prefix Delegation
For IPv4, VBRs acquire IPv4 PA EID prefixes through administrative
configuration, an automated IPv4 prefix delegation exchange, etc.
For IPv6, VBRs acquire IPv6 PA EID prefixes through administrative
Templin Expires September 15, 2011 [Page 16]
Internet-Draft VET March 2011
configuration or through DHCPv6 Prefix Delegation exchanges with an
VBG acting as a DHCP relay/server. In particular, the VBR (acting as
a requesting router) can use DHCPv6 prefix delegation [RFC3633] over
the VET interface to obtain prefixes from the VBG (acting as a
delegating router). The VBR obtains prefixes using either a
2-message or 4-message DHCPv6 exchange [RFC3315]. When the VBR acts
as a DHCPv6 client, it maps the IPv6
"All_DHCP_Relay_Agents_and_Servers" link- scoped multicast address to
the VBG's outer RLOC address.
To perform the 2-message exchange, the VBR's DHCPv6 client function
can send a Solicit message with an IA_PD option either directly or
via the VBR's own DHCPv6 relay function (see Section 4.1). The VBR's
VET interface then forwards the message using VET encapsulation (see:
Section 5.4) to a VBG which either services the request or relays it
further. The forwarded Solicit message will elicit a Reply message
from the server containing prefix delegations. The VBR can also
propose a specific prefix to the DHCPv6 server per Section 7 of
[RFC3633]. The server will check the proposed prefix for consistency
and uniqueness, then return it in the Reply message if it was able to
perform the delegation.
After the VBR receives IPv4 and/or IPv6 prefix delegations, it can
provision the prefixes on enterprise-edge interfaces as well as on
other VET interfaces configured over child enterprise networks for
which it acts as an VBG. The VBR can also provision the prefixes on
enterprise-interior interfaces to service directly-attached hosts on
the enterprise-interior link.
The prefix delegations remain active as long as the VBR continues to
renew them via the delegating VBG before lease lifetimes expire. The
lease lifetime also keeps the delegation state active even if
communications between the VBR and delegating VBG are disrupted for a
period of time (e.g., due to an enterprise network partition, power
failure, etc.). Note however that if the VBR abandons or otherwise
loses continuity with the prefixes, it may be obliged to perform
network-wide renumbering if it subsequently receives a new and
different set of prefixes.
Stateful prefix delegation for non-IP protocols is out of scope.
4.2.3.2. Stateless Prefix Delegation
When IPv6 and IPv4 are used as the inner and outer protocols,
respectively, a stateless IPv6 PA prefix delegation capability is
available using the mechanisms specified in [RFC5569][RFC5969]. VBRs
can use these mechanisms to statelessly configure IPv6 PA prefixes
that embed one of the VBR's IPv4 RLOCs.
Templin Expires September 15, 2011 [Page 17]
Internet-Draft VET March 2011
Using this stateless prefix delegation, if the IPv4 RLOC changes the
IPv6 prefix also changes and the VBR is obliged to renumber any
interfaces on which sub-prefixes from the delegated prefix are
assigned. This method may therefore be most suitable for enterprise
networks in which IPv4 RLOC assignments rarely change, or in
enterprise networks in which only services that do not depend on a
long-term stable IPv6 prefix (e.g., client-side web browsing) are
used.
Stateless prefix delegation for other protocol combinations is out of
scope.
4.2.4. Provider-(In)dependent (PI) EID Prefix Autoconfiguration
VBRs can acquire Provider (In)dependent (PI) prefixes to facilitate
multihoming, mobility and traffic engineering without requiring site-
wide renumbering events. These PI prefixes are made available to
VBRs through a prefix delegation authority that may or may not be
associated with a specific ISP.
VBRs that connect major enterprise networks (e.g., large
corporations, academic campuses, ISP networks, etc.) to a parent
enterprise network and/or the global Internet can acquire short PI
prefixes (e.g., an IPv6 ::/20, an IPv4 /16, etc.) through a
registration authority such as the Internet Assigned Numbers
Authority (IANA) or a major regional Internet registry. VBRs that
connect small enterprise networks (e.g., SOHO networks, MANETs, etc.)
to a parent enterprise network can acquire longer PI prefixes through
arrangements with a PI prefix delegation vendor.
After a VBR receives PI prefixes, it can sub-delegate portions of the
prefixes on enterprise-edge interfaces, on child VET interfaces for
which it is configured as a VBG and on enterprise-interior interfaces
to service directly-attached hosts on the enterprise-interior link.
The VBR can also sub-delegate portions of its PI prefixes to
requesting routers connected to child enterprise networks. These
requesting routers consider their sub-delegated portions of the PI
prefix as PA, and consider the delegating routers as their points of
connection to a provider network.
4.3. VET Border Gateway (VBG) Autoconfiguration
VBGs are VBRs that connect VET links configured over child enterprise
networks to provider networks via provider-edge interfaces and/or via
VET links configured over parent enterprise networks. A VBG may also
act as a "half-gateway", in that it may need to forward the packets
it receives from neighbors on the VET link via another VBG connected
to the same VET link. This arrangement is seen in the IRON [RFC6179]
Templin Expires September 15, 2011 [Page 18]
Internet-Draft VET March 2011
client/server/relay architecture, in which a server "half-gateway" is
a VBG that forwards packets with off-link destinations via a relay
"half-gateway" VBG that connects the VET link to the provider
network.
VBGs autoconfigure their provider-edge interfaces in a manner that is
specific to the provider connections, and they autoconfigure their
VET interfaces that were configured over parent VET links using the
VBR autoconfiguration procedures specified in Section 4.2. For each
of its VET interfaces connected to child VET links, the VBG
initializes the interface the same as for an ordinary VBR (see
Section 4.2.1). It then arranges to add one or more of its RLOCs
associated with the child VET link to the PRL.
VBGs configure a DHCP relay/server on VET interfaces connected to
child VET links that require DHCP services. VBGs may also engage in
an unspecified anycast VBG discovery message exchange if they are
configured to do so. Finally, VBGs respond to LLMNR queries for
'PRLNAME' on VET interfaces connected to VET links that span child
enterprise networks with a distributed management structure.
4.4. VET Host Autoconfiguration
Nodes that cannot be attached via a VBR'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 on the VET link. Each VET host performs the same
enterprise interior interfaces RLOC configuration procedures as
specified for ERs in Section 4.1. The VET host next performs the
same VET interface initialization and PRL discovery procedures as
specified for VBRs in Section 4.2, except that it configures its VET
interfaces as host interfaces (and not router interfaces). Note also
that a node may be configured as a host on some VET interfaces and as
an VBR/VBG on other VET interfaces.
A VET host may receive non-link-local addresses and/or prefixes to
assign to the VET interface via DHCP exchanges and/or through
information conveyed in Router Advertisements (RAs). If prefixes are
provided, however, there must be assurance that either 1) the VET
link will not partition, or 2) that each VET host interface connected
to the VET link will configure a unique set of prefixes. VET hosts
therefore depend on DHCP and/or RA exchanges to provide only
addresses/prefixes that are appropriate for assignment to the VET
interface according to these specific cases, and depend on the VBGs
within the enterprise keeping track of which addresses/prefixes were
assigned to which hosts.
When the VET host solicits a DHCP-assigned EID address/prefix over a
Templin Expires September 15, 2011 [Page 19]
Internet-Draft VET March 2011
(non-multicast) VET interface, it maps the DHCP relay/server
multicast inner destination address to the outer RLOC address of a
VBG that it has selected as a default router. The VET host then
assigns any resulting DHCP-delegated addresses/prefixes to the VET
interface for use as the source address of inner packets. The host
will subsequently send all packets destined to EID correspondents via
a default router on the VET link, and will discover more-specific
routes based on any redirect messages it receives.
5. Internetworking Operation
Following the autoconfiguration procedures specified in Section 4,
ERs, VBRs, VBGs, and VET hosts engage in normal internetworking
operations as discussed in the following sections.
5.1. Routing Protocol Participation
ERs engage in any RLOC-based routing protocols over enterprise-
interior interfaces to exchange routing information for forwarding IP
packets with RLOC addresses. VBRs and VBGs can additionally engage
in any EID-based routing protocols over VET, enterprise-edge and
provider-edge interfaces to exchange routing information for
forwarding inner network layer packets with EID addresses. Note that
any EID-based routing instances are separate and distinct from any
RLOC-based routing instances.
VBR/VBG routing protocol participation on non-multicast VET
interfaces uses the NBMA interface model, e.g., in the same manner as
for OSPF over NBMA interfaces [RFC5340]. (VBR/VBG routing protocol
participation on multicast-capable VET interfaces can alternatively
use the standard multicast interface model, but this may result in
excessive multicast control message overhead.)
VBRs can use the list of VBGs in the PRL (see: Section 4.2.1) as an
initial list of neighbors for EID-based routing protocol
participation. VBRs can alternatively use the list of VBGs as
potential default routers instead of engaging in an EID-based routing
protocol instance. In that case, when the VBR forwards a packet via
a default router it may receive a redirect message indicating a
different VBR as a better next hop.
5.1.1. PI Prefix Routing Considerations
VBRs that connect large enterprise networks to the global Internet
advertise their EID PI prefixes directly into the Internet default-
free RIB via the Border Gateway Protocol (BGP) [RFC4271] the same as
for a major service provider network. VBRs that connect large
Templin Expires September 15, 2011 [Page 20]
Internet-Draft VET March 2011
enterprise networks to provider networks can instead advertise their
EID PI prefixes into the providers' routing system(s) if the provider
networks are configured to accept them.
VBRs that connect small enterprise networks to provider networks
obtain one or more PI prefixes and register the prefixes with a
serving VBG in the PI prefix vendor's network (e.g., through a
vendor-specific short http(s) transaction). The PI prefix vendor
network then acts as a virtual "home" enterprise network that
connects its customer small enterprise networks to the Internet
routing system. The customer small enterprise networks in turn
appear as mobile components of the PI prefix vendor's network, i.e.,
the customer networks are always "away from home".
Further details on routing for PI prefixes is discussed in "The
Internet Routing Overlay Network (IRON)" [RFC6179] and "Fib
Suppression with Virtual Aggregation" [I-D.ietf-grow-va].
5.2. Default Route Configuration and Selection
Configuration of default routes in the presence of VET interfaces
must be carefully coordinated according to the inner and outer
network protocols. If the inner and outer protocols are different
(e.g., IPv6 within IPv4) then default routes of the inner protocol
version can be configured with next-hops corresponding to default
routers on a VET interface while default routes of the outer protocol
version can be configured with next-hops corresponding to default
routers on an underlying interface.
If the inner and outer protocols are the same (e.g., IPv4 within
IPv4), care must be taken in setting the default route to avoid
ambiguity. For example, if default routes are configured on the VET
interface then more-specific routes could be configured on underlying
interfaces to avoid looping. In a preferred method, however,
multiple default routes can be configured with some having next-hops
corresponding to (EID-based) default routers on VET interfaces and
others having next-hops corresponding to (RLOC-based) default routers
on underlying interfaces. In that case, special next-hop
determination rules must be used (see: Section 5.4).
5.3. Address Selection
When permitted by policy and supported by enterprise-interior
routing, VET nodes can avoid encapsulation through communications
that directly invoke the outer IP protocol using RLOC addresses
instead of EID addresses for end-to-end communications. For example,
an enterprise network that provides native IPv4 intra-enterprise
services can provide continued support for native IPv4 communications
Templin Expires September 15, 2011 [Page 21]
Internet-Draft VET March 2011
even when encapsulated IPv6 services are available for inter-
enterprise communications. In other enterprise network scenarios,
the use of EID-based communications (i.e., instead of RLOC-based
communications) may be necessary and/or beneficial to support address
scaling, transparent Network Address Translator (NAT) traversal,
security domain separation, site multihoming, traffic engineering,
etc. .
VET nodes can use source address selection rules (e.g., based on name
service information) to determine whether to use EID-based or RLOC-
based addressing. The remainder of this section discusses
internetworking operation for EID-based communications using the VET
interface abstraction.
5.4. Next Hop Determination
VET nodes perform normal next-hop determination via longest prefix
match, and send packets according to the most-specific matching entry
in the FIB. If the FIB entry has multiple next-hop addresses, the
VBR selects the next-hop with the best metric value. If multiple
next hops have the same metric value, the VET node can use Equal Cost
Multi Path (ECMP) to forward different flows via different next-hop
addresses, where flows are determined, e.g., by computing a hash of
the inner packet's source address, destination address and flow label
fields.
If the VET node has multiple default routes of the same inner and
outer protocol versions, with some corresponding to EID-based default
routers and others corresponding to RLOC-based default routers, it
must perform source address based selection of a default route. In
particular, if the packet's source address is taken from an EID
prefix the VET node selects a default route configured over the VET
interface; otherwise, it selects a default route configured over an
underlying interface.
As a last resort when there is no matching entry in the FIB (i.e.,
not even default), VET nodes can discover neighbors within the
enterprise network through on-demand name service queries for the EID
prefix taken from a packet's destination address (or, by some other
inner address to outer address mapping mechanism). For example, for
the IPv6 destination address '2001:DB8:1:2::1' and 'PRLNAME'
"isatapv2.example.com" the VET node can perform a name service lookup
for the domain name:
'0.0.1.0.0.0.8.b.d.0.1.0.0.2.ip6.isatapv2.example.com'.
Name-service lookups in enterprise networks with a centralized
management structure use an infrastructure-based service, e.g., an
enterprise-local DNS. Name-service lookups in enterprise networks
Templin Expires September 15, 2011 [Page 22]
Internet-Draft VET March 2011
with a distributed management structure and/or that lack an
infrastructure-based name service instead use LLMNR over the VET
interface.
When LLMNR is used, the VBR that performs the lookup sends an LLMNR
query (with the 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 neighbors on the VET interface. When a VET
node receives an LLMNR query, it responds to the query IFF it
aggregates an IP prefix that covers the prefix in the query. If the
name-service lookup succeeds, it will return RLOC addresses (e.g., in
DNS A records) that correspond to neighbors to which the VET node can
forward packets.
5.5. VET Interface Encapsulation/Decapsulation
VET interfaces encapsulate inner network layer packets in any
necessary mid-layer headers and trailers (e.g., IPsec [RFC4301],
etc.) followed by a SEAL header (if necessary) followed by an outer
UDP header (if necessary) followed by an outer IP header. Following
all encapsulations, the VET interface submits the encapsulated packet
to the outer IP forwarding engine for transmission on an underlying
interface. The following sections provide further details on
encapsulation:
5.5.1. Inner Network Layer Protocol
The inner network layer protocol sees the VET interface as an
ordinary network interface, and views the outer network layer
protocol as an ordinary L2 transport. The inner- and outer network
layer protocol types are mutually independent and can be used in any
combination. Inner network layer protocol types include IPv6
[RFC2460] and IPv4 [RFC0791], but they may also include non-IP
protocols such as OSI/CLNP [RFC0994][RFC1070][RFC4548].
5.5.2. Mid-Layer Encapsulation
VET interfaces that use mid-layer encapsulations encapsulate each
inner network layer packet in any mid-layer headers and trailers as
the first step in a potentially multi-layer encapsulation.
5.5.3. SEAL Encapsulation
Following any mid-layer encapsulations, VET interfaces that use SEAL
add a SEAL header as specified in [I-D.templin-intarea-seal].
Inclusion of a SEAL header must be applied uniformly between all
neighbors on the VET link. Note that when a VET interface sends a
SEAL-encapsulated packet to a neighbor that does not use SEAL
Templin Expires September 15, 2011 [Page 23]
Internet-Draft VET March 2011
encapsulation, it may receive an ICMP "port unreachable" or "protocol
unreachable" depending on whether/not an outer UDP header is
included.
SEAL encapsulation is used on VET links that require path MTU
mitigations due to encapsulation overhead and/or mechanisms for VET
interface neighbor coordination. When SEAL encapsulation is used,
the VET interface sets the 'Next Header' value in the SEAL header to
the IP protocol number associated with either the mid-layer
encapsulation or the IP protocol number of the inner network layer
(if no mid-layer encapsulation is used). The VET interface sets the
other fields in the SEAL header as specified in
[I-D.templin-intarea-seal].
5.5.4. Outer UDP Header Encapsulation
Following any mid-layer and/or SEAL encapsulations, VET interfaces
that use UDP encapsulation add an outer UDP header. Inclusion of an
outer UDP header must be applied uniformly between all neighbors on
the VET link. Note that when a VET interface sends a UDP-
encapsulated packet to a neighbor that does not recognize the UDP
port number, it may receive an ICMP "port unreachable" message.
VET interfaces use UDP encapsulation on VET links that may traverse
NATs and/or legacy networking gear (e.g., Equal Cost MultiPath (ECMP)
routers, Link Aggregation Gateways (LAGs), etc.) that only recognize
well-known network layer protocols. When UDP encapsulation is used,
the VET interface encapsulates the mid-layer packet in an outer UDP
header then sets the UDP port numbers as specified for the outermost
mid-layer protocol (e.g., IPsec [RFC3947][RFC3948], etc.).
When SEAL [I-D.templin-intarea-seal] is used as the outermost mid-
layer protocol, the VET interface maintains per-neighbor local and
remote UDP port numbers. For bidirectional neighbors, the interface
sets the local UDP port number to the value reserved for SEAL and
sets the remote UDP port number to the observed UDP source port
number in packets that it receives from the neighbor. In cases in
which one of the bidirectional neighbors is behind a NAT, this
implies that the one behind the NAT initiates the neighbor
relationship. If both neighbors have a way of knowing that there are
no NATs in the path, then they may select and set port numbers as
described for unidirectional neighbors below.
For unidirectional neighbors, the VET interface sets both the local
and remote UDP port numbers to the value reserved for SEAL, and
additionally selects a small set of dynamic port number values for
use as additional local UDP port numbers. The VET interface then
selects one of this set of local port numbers for the UDP source port
Templin Expires September 15, 2011 [Page 24]
Internet-Draft VET March 2011
for each inner packet it sends, where the port number is determined
e.g., by a hash calculated over the inner network layer addresses and
inner transport layer port numbers. The VET interface uses a hash
function of its own choosing when selecting a dynamic port number
value, but it should choose a function that provides uniform
distribution between the set of values, and it shoud be consistent in
the manner in which the hash is applied.
Finally, for VET links configured over IPv4 enterprise networks, the
VET interface sets the UDP checksum field to zero. For VET links
configured over IPv6 enterprise networks, considerations for setting
the UDP checksum are discussed in [I-D.ietf-6man-udpzero].
5.5.5. Outer IP Header Encapsulation
Following any mid-layer, SEAL and/or UDP encapsulations, the VET
interface adds an outer IP header. Outer IP header construction is
the same as specified for ordinary IP encapsulation (e.g., [RFC2003],
[RFC2473], [RFC4213], etc.) except that the "TTL/Hop Limit", "Type of
Service/Traffic Class" and "Congestion Experienced" values in the
inner network layer header are copied into the corresponding fields
in the outer IP header. The VET interface also sets the IP protocol
number to the appropriate value for the first protocol layer within
the encapsulation (e.g., UDP, SEAL, IPsec, etc.). When IPv6 is used
as the outer IP protocol, the VET interface sets the flow label value
in the outer IPv6 header the same as described in
[I-D.carpenter-flow-ecmp].
5.5.6. Decapsulation
When a VET interface receives an encapsulated packet, it retains the
outer headers and processes the SEAL header as specified in
[I-D.templin-intarea-seal].
Next, if the packet will be forwarded from the receiving VET
interface into a forwarding VET interface, the VET node copies the
"TTL/Hop Limit", "Type of Service/Traffic Class" and "Congestion
Experienced" values in the outer IP header received on the receiving
VET interface into the corresponding fields in the outer IP header to
be sent over the forwarding VET interface (i.e., the values are
transferred between outer headers and *not* copied from the inner
network layer header). This is true even if the packet is forwarded
out the same VET interface that it arrived on, and necessary to
support diagnostic functions (e.g., traceroute) and avoid looping.
During decapsulation, when the next-hop is via a non-VET interface,
the "Congestion Experienced" value in the outer IP header is copied
into the corresponding field in the inner network layer header.
Templin Expires September 15, 2011 [Page 25]
Internet-Draft VET March 2011
5.6. Mobility and Multihoming Considerations
VBRs that travel between distinct enterprise networks must either
abandon their PA prefixes that are relative to the "old" network and
obtain PA prefixes relative to the "new" network, or somehow
coordinate with a "home" network to retain ownership of the prefixes.
In the first instance, the VBR would be required to coordinate a
network renumbering event on its attached networks using the new PA
prefixes [RFC4192][RFC5887]. In the second instance, an adjunct
mobility management mechanism is required.
VBRs can retain their PI prefixes as they travel between distinct
network points of attachment as long as they continue to refresh
their PI prefix to RLOC address mappings with their serving VBG as
described in [RFC6179]. (When the VBR moves far from its serving
VBG, it can also select a new VBG in order to maintain optimal
routing.) In this way, VBRs can update their PI prefix to RLOC
mappings in real time and without requiring an adjunct mobility
management mechanism.
The VBGs of a multihomed enterprise network participate in a private
inner network layer routing protocol instance (e.g., via an interior
BGP instance) to accommodate network partitions/merges as well as
intra-enterprise mobility events.
5.7. Neighbor Coordination on VET Interfaces using SEAL
VET interfaces that use SEAL use the SEAL Control Message Protocol
(SCMP) as specified in Section 4.5 of [I-D.templin-intarea-seal] to
coordinate reachability, routing information, and mappings between
the inner and outer network layer protocols. SCMP directly parallels
the IPv6 Neighbor Discovery (ND) [RFC4191][RFC4861] and ICMPv6
[RFC4443] protocols, but operates from within the tunnel and supports
operation for any combinations of inner and outer network layer
protocols.
VET and SEAL are specifically designed for encapsulation of inner
network layer payloads over outer IPv4 and IPv6 networks as a link
layer. VET interfaces that use SCMP therefore require a new Source/
Target Link-Layer Address Option (S/TLLAO) format that encapsulates
IPv4 addresses as shown in Figure 2 and IPv6 addresses as shown in
Figure 3:
Templin Expires September 15, 2011 [Page 26]
Internet-Draft VET March 2011
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 2 | Length = 1 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 address (bytes 0 thru 3) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: SCMP S/TLLAO Option for IPv4 RLOCs
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 2 | Length = 3 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 address (bytes 0 thru 3) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 address (bytes 4 thru 7) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 address (bytes 8 thru 11) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 address (bytes 12 thru 15) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: SCMP S/TLLAO Option for IPv6 RLOCs
In addition, VET interfaces that use SCMP use a modified version of
the Route Information Option (RIO) (see: [RFC4191]) formatted as
shown in Figure 4:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 24 | Length | Prefix Length | AF |Prf|Resvd|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix (Variable Length) |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: SCMP Route Information Option Format
In this modified format, the VET interface sets the Route Lifetime
and Prefix fields in the RIO option the same as specified in
Templin Expires September 15, 2011 [Page 27]
Internet-Draft VET March 2011
[RFC4191]. It then sets the fields in the header as follows:
o the 'Type', 'Prf', and 'Resvd' fields are set the same as
specified in [RFC4191].
o the 'Length' field is set to 1, 2, or 3 as specified in [RFC4191].
It is instead set to 4 if the 'Prefix Length' is greater than 128
and set to 5 if the 'Prefix Length' is greater than 192 (e.g., in
order to accommodate longer prefixes of non-IP protocols).
o the 'Prefix Length' field ranges from 0 to 255. The 'Prefix'
field is 0, 8, 16, 24 or 32 octets depending on the Length, and
the embedded prefix MAY be up to 255 bits in length.
o bits 24 - 26 are used to contain an 'Address Family (AF)' value
that indicates the embedded prefix protocol type. This document
defines the following values for AF:
* 000 - IPv4
* 001 - IPv6
* 010 - OSI/CLNP NSAP
The following subsections discuss VET interface neighbor coordination
using SCMP:
5.7.1. Router Discovery
VET hosts and VBRs can send SCMP Router Solicitation (SRS) messages
to one or more VBGs in the PRL to receive solicited SCMP Router
Advertisements (SRAs).
When an VBG receives an SRS message on a VET interface, it prepares a
solicited SRA message. The SRA includes Router Lifetimes, Default
Router Preferences, PIOs and any other options/parameters that the
VBG is configured to include. If necessary, the VBG also includes
Route Information Options (RIOs) formatted as specified above.
The VBG finally includes one or more SLLAOs formatted as specified
above that encode the IPv6 and/or IPv4 RLOC unicast addresses of its
own enterprise-interior interfaces or the enterprise-interior
interfaces of other nearby VBGs.
5.7.2. Neighbor Unreachability Detection
VET nodes perform Neighbor Unreachability Detection (NUD) on VET
interface neighbors by monitoring hints of forward progress enabled
Templin Expires September 15, 2011 [Page 28]
Internet-Draft VET March 2011
by SEAL mechanisms as evidence that a neighbor is reachable. First,
when data packets are flowing, the VET node can periodically set the
A bit in the SEAL header of data packets to elicit SCMP responses
from the neighbor. Secondly, when no data packets are flowing, the
VET node can send periodic probes such as SCMP Neighbor Solicitation
(SNS) messages for the same purpose.
Responsiveness to routing changes is directly related to the delay in
detecting that a neighbor has gone unreachable. In order to provide
responsiveness comparable to dynamic routing protocols, a reasonably
short neighbor reachable time (e.g., 5sec) SHOULD be used.
Additionally, a VET node may receive outer IP ICMP "Destination
Unreachable; net / host unreachable" messages from an ER on the path
indicating that the path to a neighbor may be failing. The node
SHOULD first check the packet-in-error to obtain reasonable assurance
that the ICMP message is authentic. If the node receives excessive
ICMP unreachable errors through multiple RLOCs associated with the
same FIB entry, it SHOULD delete the FIB entry and allow subsequent
packets to flow through a different route (e.g., a default route with
a VBG as the next hop).
5.7.3. Redirect Function
[[ UNDER CONSTRUCTION ]]
This section will be updated to reflect the new technique known as
"Predirection" as discussed for ISATAP updates in Section 5.14.
[[ UNDER CONSTRUCTION ]]
5.8. Neighbor Coordination on VET Interfaces using IPsec
VET interfaces that use IPsec encapsulation use the Internet Key
Exchange protocol, version 2 (IKEv2) [RFC4306] to manage security
association setup and maintenance. IKEv2 provides a logical
equivalent of the SCMP in terms of VET interface neighbor
coordinations; for example, IKEv2 also provides mechanisms for
redirection [RFC5685] and mobility [RFC4555].
IPsec additionally provides an extended Identification field and
integrity check vector; these features allow IPsec to utilize outer
IP fragmentation and reassembly with less risk of exposure to data
corruption due to reassembly misassociations. On the other hand,
IPsec entails the use of symmetric security associations and hence
may not be appropriate to all enterprise network use cases.
Templin Expires September 15, 2011 [Page 29]
Internet-Draft VET March 2011
5.9. Multicast
5.9.1. Multicast over (Non)Multicast Enterprise Networks
Whether or not the underlying enterprise network supports a native
multicasting service, the VET node can act as an inner network layer
IGMP/MLD proxy [RFC4605] on behalf of its attached edge networks and
convey its multicast group memberships over the VET interface to a
VBG acting as a multicast router. Its inner network layer multicast
transmissions will therefore be encapsulated in outer headers with
the unicast address of the VBG as the destination.
5.9.2. Multicast Over Multicast-Capable Enterprise Networks
In multicast-capable enterprise networks, ERs provide an enterprise-
wide multicasting service (e.g., Simplified Multicast Forwarding
(SMF) [I-D.ietf-manet-smf], Protocol Independent Multicast (PIM)
routing, Distance Vector Multicast Routing Protocol (DVMRP) routing,
etc.) over their enterprise-interior interfaces such that outer IP
multicast messages of site-scope or greater scope will be propagated
across the enterprise network. For such deployments, VET nodes can
optionally provide a native inner multicast/broadcast capability over
their VET interfaces through mapping of the inner multicast address
space to the outer multicast address space. In that case, operation
of link-or greater-scoped inner multicasting services (e.g., a link-
scoped neighbor discovery protocol) over the VET interface is
available, but SHOULD be used sparingly to minimize enterprise-wide
flooding.
VET nodes encapsulate inner multicast messages sent over the VET
interface in any mid-layer headers (e.g., UDP, SEAL, IPsec, etc.)
followed by 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 encapsulations, mappings are established
through administrative configuration or through an unspecified
alternate static mapping).
Multicast mapping for inner 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 multicast address mapping, the
VET interface acts as a virtual outer IP multicast host connected to
its underlying interfaces. When the VET interface detects that an
inner multicast group joins or leaves, it forwards corresponding
outer IP multicast group membership reports on an underlying
interface over which the VET interface is configured. If the VET
Templin Expires September 15, 2011 [Page 30]
Internet-Draft VET March 2011
node is configured as an outer IP multicast router on the underlying
interfaces, the VET interface forwards locally looped-back group
membership reports to the outer IP multicast routing process. If the
VET node is configured as a simple outer IP multicast host, the VET
interface instead forwards actual group membership reports (e.g.,
IGMP messages) directly over an underlying interface.
Since inner multicast groups are mapped to site-scoped outer IP
multicast groups, the VET node MUST ensure that the site-scoped outer
IP multicast messages received on the underlying interfaces for one
VET interface do not "leak out" to the underlying interfaces of
another VET interface. This is accommodated through normal site-
scoped outer IP multicast group filtering at enterprise network
boundaries.
5.10. Service Discovery
VET nodes can perform enterprise-wide service discovery using a
suitable name-to-address resolution service. Examples of flooding-
based services include the use of LLMNR [RFC4795] over the VET
interface or multicast DNS (mDNS) [I-D.cheshire-dnsext-multicastdns]
over an underlying interface. More scalable and efficient service
discovery mechanisms (e.g., anycast) are for further study.
5.11. VET Link Partitioning
A VET link can be partitioned into multiple distinct logical
groupings. In that case, each partition configures its own distinct
'PRLNAME' (e.g., 'isatapv2.zone1.example.com',
'isatapv2.zone2.example.com', etc.).
VBGs can further create multiple IP subnets within a partition, e.g.,
by sending SRAs with PIOs containing different IP prefixes to
different groups of VET hosts. VBGs can identify subnets, e.g., by
examining RLOC prefixes, observing the enterprise-interior interfaces
over which SRSs are received, etc.
In the limiting case, VBGs can advertise a unique set of IP prefixes
to each VET host such that each host belongs to a different subnet
(or set of subnets) on the VET interface.
5.12. VBG Prefix State Recovery
VBGs retain explicit state that tracks the inner network layer
prefixes delegated to VBRs connected to the VET link, e.g., so that
packets are delivered to the correct VBRs. When a VBG loses some or
all of its state (e.g., due to a power failure), client VBRs must
refresh the VBG's state so that packets can be forwarded over correct
Templin Expires September 15, 2011 [Page 31]
Internet-Draft VET March 2011
routes.
5.13. Legacy ISATAP Services
VBGs can support legacy ISATAP services according to the
specifications in [RFC5214]. In particular, VBGs can configure
legacy ISATAP interfaces and VET interfaces over the same sets of
underlying interfaces as long as the PRLs and IPv6 prefixes
associated with the ISATAP/VET interfaces are distinct.
Legacy ISATAP hosts acquire addresses and/or prefixes in the same
manner and using the same mechanisms as described for VET hosts in
Section 4.4 above.
In order to support dynamic on-demand routing on ISATAP interfaces, a
new (and backwards-compatible) approach called "ISATAP Predirection"
is specified in the following sections:
5.14. ISATAP Update
In order to support dynamic on-demand routing on ISATAP interfaces, a
new (and backwards-compatible) approach called "ISATAP Predirection"
is specified in the following sections. This section updates
[RFC5214].
5.14.1. ISATAP Predirection
Figure 5 depicts a reference ISATAP network topology. The scenario
shows an advertising ISATAP router ('A'), two non-advertising ISATAP
routers ('B', 'D') and two ordinary IPv6 hosts ('C', 'E') in a
typical deployment configuration:
Templin Expires September 15, 2011 [Page 32]
Internet-Draft VET March 2011
.-(::::::::)
.-(::: IPv6 :::)-.
(:::: Internet ::::)
`-(::::::::::::)-'
`-(::::::)-'
,-.
,-----+-/-+--' \+------.
/ ,~~~~~~~~~~~~~~~~~, :
/ |companion gateway| |.
,-' '~~~~~~~~~~~~~~~~~' `.
; +--------------+ )
: | Router A | /
: | (isatap) | ;
+- +--------------+ -+
; fe80::5efe:192.0.2.1 :
| ;
: IPv4 Provider Network -+-'
`-. (PRL: 192.0.2.1) .)
\ _)
`-----+--------)----+'----'
fe80::5efe:192.0.2.2 fe80::5efe:192.0.2.3 .-.
+--------------+ +--------------+ ,-( _)-.
| (isatap) | | (isatap) | .-(_ IPv6 )-.
| Router B | | Router D |--(__Edge Network )
+--------------+ +--------------+ `-(______)-'
2001:db8::/48 2001:db8:1::/48 |
| 2001:db8:1::1
.-. +-------------+
,-( _)-. 2001:db8::1 | IPv6 Host E |
.-(_ IPv6 )-. +-------------+ +-------------+
(__Edge Network )--| IPv6 Host C |
`-(______)-' +-------------+
Figure 5: Reference ISATAP Network Topology
With reference to Figure 5, when router 'A' receives an IPv6 packet
on an advertising ISATAP interface that it will forward back out the
same interface, 'A' must arrange to redirect the originating ISATAP
node 'B' to a better next hop ISATAP node 'D' that is closer to the
final destination 'E'. First, however, 'A' must direct 'D' to
establish a forwarding table entry so that it will have a means to
determine that 'B' is authorized to produce packets using a given
source address. This process is accommodated via a unidirectional
reliable exchange in which 'A' first informs 'D', then 'D' informs
'B' via 'A' as a trusted intermediary. 'B' therefore knows that 'D'
will accept the packets it sends as long as 'D' retains the
forwarding table entry. We call this process "predirection", which
stands in contrast to ordinary IPv6 redirection.
Templin Expires September 15, 2011 [Page 33]
Internet-Draft VET March 2011
Consider the alternative in which 'A' informs both 'B' and 'D'
separately via independent IPv6 Redirect messages (see: [RFC4861]).
In that case, several conditions can occur that could result in
communications failures. First, if 'B' receives the Redirect message
but 'D' does not, subsequent packets sent by 'B' would disappear into
a black hole since 'D' would not have a forwarding table entry to
verify their source addresses. Second, if 'D' receives the Redirect
message but 'B' does not, subsequent packets sent in the reverse
direction by 'D' would be lost. Finally, timing issues surrounding
the establishment and garbage collection of forwarding table entries
at 'B' and 'D' could yield unpredictable behavior. For example,
unless the timing were carefully coordinated through some form of
synchronization loop, there would invariably be instances in which
one node has the correct forwarding table state and the other node
does not resulting in non-deterministic packet loss.
The following subsections discuss the predirection steps that support
the reference operational scenario:
5.14.1.1. 'A' Sends Predirect Forward To 'D'
When 'A' forwards an original IPv6 packet sent by 'B' out the same
ISATAP interface that it arrived on, it sends a "Predirect" message
forward toward 'D' instead of sending a Redirect message back to 'B'.
The Predirect message is simply an ISATAP-specific version of an
ordinary IPv6 Redirect message as depicted in Section 4.5 of
[RFC4861], and is identified by two new backward-compatible bits
taken from the Reserved field as shown in Figure 6:
Templin Expires September 15, 2011 [Page 34]
Internet-Draft VET March 2011
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (=137) | Code (=0) | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|I|P| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Target Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Destination Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
Figure 6: ISATAP-Specific IPv6 Redirect Message Format
Where the new bits are defined as:
I (1) the "ISATAP" bit. Set to 1 to indicate an ISATAP-specific
Redirect message, and set to 0 to indicate an ordinary IPv6
Redirect message.
P (1) the "Predirect" bit. Set to 1 to indicate a Predirect
message, and set to 0 to indicate a Redirect response to a
Predirect message. (This bit is valid only when the I bit is set
to 1.)
Using this new Predirect message format, 'A' prepares the message in
a similar fashion as for an ordinary ISATAP-encapsulated IPv6
Redirect message as follows:
o the outer IPv4 source address is set to 'A's IPv4 address.
o the outer IPv4 destination address is set to 'D's IPv4 address.
Templin Expires September 15, 2011 [Page 35]
Internet-Draft VET March 2011
o the inner IPv6 source address is set to 'A's ISATAP link-local
address.
o the inner IPv6 destination address is set to 'D's ISATAP link-
local address.
o the Predirect Target and Destination Addresses are both set to
'B's ISATAP link-local address.
o the Predirect message includes Route Information Options (RIOs)
[RFC4191] that encode an IPv6 prefix taken from 'B's address/
prefix delegations that covers the IPv6 source address of the
originating IPv6 packet.
o the Predirect message includes a Redirected Header Option (RHO)
that contains at least the header of the originating IPv6 packet.
o the I and P bits in the Predirect message header are both set to
1.
'A' then sends the Predirect message forward to 'D'.
5.14.1.2. 'D' Processes the Predirect and Sends Redirect Back To 'A'
When 'D' receives the Predirect message, it decapsulates the message
according to Section 7.3 of [RFC5214] since the outer IPv4 source
address is a member of the PRL.
'D' then uses the message validation checks specified in Section 8.1
of [RFC4861], except that instead of verifying that the "IP source
address of the Redirect is the same as the current first-hop router
for the specified ICMP Destination Address" (i.e., the 6th
verification check), it accepts the message if the "outer IP source
address of the Predirect is the same as the current first-hop router
for the destination address of the originating IPv6 packet
encapsulated in the RHO". (Note that this represents an ISATAP-
specific adaptation of the verification checks.) Finally, 'D' only
accepts the message if the destination address of the originating
IPv6 packet encapsulated in the RHO is covered by one of its CURRENT
delegated addresses/prefixes (see Section 5.14.4).
'D' then either creates or updates an IPv6 forwarding table entry
with the prefix encoded in the RIO option as the target prefix, and
the IPv6 Target Address of the Predirect message (i.e., 'B's ISATAP
link-local address) as the next hop. 'D' places the entry in the
FILTERING state, then sets/resets a filtering expiration timer value
of 40 seconds. If the filtering timer expires, the node clears the
FILTERING state and deletes the forwarding table entry if it is not
Templin Expires September 15, 2011 [Page 36]
Internet-Draft VET March 2011
in the FORWARDING state. This suggests that 'D's ISATAP interface
should maintain a private forwarding table separate from the common
IPv6 forwarding table, since the entry must be managed by the ISATAP
interface itself.
After processing the Predirect message and establishing the
forwarding table entry, 'D' prepares an ISATAP Redirect message in
response to the Predirect as follows:
o the outer IPv4 source address is set to 'D's IPv4 address.
o the outer IPv4 destination address is set to 'A's IPv4 address.
o the inner IPv6 source address, is set to 'D's ISATAP link-local
address.
o the inner IPv6 destination address is set to 'A's ISATAP link-
local address.
o the Redirect Target and the Redirect Destination Addresses are
both set to 'D's ISATAP link-local address.
o the Redirect message includes RIOs that encode IPv6 prefixes taken
from 'D's address/prefix delegations that covers the IPv6
destination address of the originating IPv6 packet encapsulated in
the Redirected Header option of the Predirect.
o the Redirect message includes an RHO copied from the corresponding
Predirect message.
o the (I, P) bits in the Redirect message header are set to (1, 0).
'D' then sends the Redirect message to 'A'.
5.14.1.3. 'A' Processes the Redirect then Proxies it Back To 'B'
When 'A' receives the Redirect message, it decapsulates the message
according to Section 7.3 of [RFC5214] since the inner IPv6 source
address embeds the outer IPv4 source address.
'A' next accepts the message only if it satisfies the same message
validation checks specified for Predirects in Section 3.2.4.6.2.
'A' then locates a forwarding table entry that covers the IPv6 source
address of the packet segment in the RHO (i.e., a forwarding table
entry with next hop 'B'), then proxies the Redirect message back
toward 'B'. Without decrementing the IPv6 hop limit in the Redirect
message, 'A' next changes the IPv4 source address of the Redirect
Templin Expires September 15, 2011 [Page 37]
Internet-Draft VET March 2011
message to its own IPv4 address, changes the IPv4 destination address
to 'B's IPv4 address, changes the IPv6 source address to its own IPv6
link-local address, and changes the IPv6 destination address to 'B's
IPv6 link-local address. 'A' then sends the proxied Redirect message
to 'B'.
5.14.1.4. 'B' Processes The Redirect Message
When 'B' receives the Redirect message, it decapsulates the message
according to Section 7.3 of [RFC5214] since the outer IPv4 source
address is a member of the PRL.
'B' next accepts the message only if it satisfies the same message
validation checks specified for Predirects in Section 3.2.4.6.2.
'B' then either creates or updates an IPv6 forwarding table entry
with the prefix encoded in the RIO option as the target prefix, and
the IPv6 Target Address of the Redirect message (i.e., 'D's ISATAP
link-local address) as the next hop. 'B' places the entry in the
FORWARDING state, then sets/resets a forwarding expiration timer
value of 30 seconds. If the forwarding timer expires, the node
clears the FORWARDING state and deletes the forwarding table entry if
it is not in the FILTERING state. Again, this suggests that 'B's
ISATAP interface should maintain a private forwarding table separate
from the common IPv6 forwarding table, since the entry must be
managed by the ISATAP interface itself.
Now, 'B' has a forwarding table entry in the FORWARDING state, and
'D' has a forwarding table entry in the FILTERING state. Therefore,
'B' may send ordinary IPv6 data packets with destination addresses
covered by 'D's prefix directly to 'D' without involving 'A'. 'D'
will in turn accept the packets since it has a forwarding table entry
authorizing 'B' to source packets from its claimed IPv6 address.
To enable packet forwarding from 'D' directly to 'B', a reverse-
predirection operation is required which is the mirror-image of the
forward-predirection operation described above. Following the
reverse predirection, both 'B' and 'D' will have forwarding table
entries in the "(FORWARDING | FILTERING)" state, and IPv6 packets can
be exchanged bidirectionally without involving 'A'.
5.14.1.5. 'B' Sends Periodic Predirect Messages Forward to 'A'
In order to keep forwarding table entries alive while data packets
are actively flowing, 'B' can periodically send additional Predirect
messages via 'A' to solicit Redirect messages from 'D'. When 'B'
forwards an IPv6 packet via 'D', and the corresponding forwarding
table entry FORWARDING state timer is nearing expiration, 'B' sends
Templin Expires September 15, 2011 [Page 38]
Internet-Draft VET March 2011
Predirect messages (subject to rate limiting) prepared as follows:
o the outer IPv4 source address is set to 'B's IPv4 address.
o the outer IPv4 destination address is set to 'A's IPv4 address.
o the inner IPv6 source address is set to 'B's ISATAP link-local
address.
o the inner IPv6 destination address is set to 'A's ISATAP link-
local address.
o the Predirect Target and Destination Addresses are both set to
'B's ISATAP link-local address.
o the Predirect message includes RIOs that encode IPv6 prefixes
taken from 'B's address/prefix delegations that cover the IPv6
source address of the originating IPv6 packet.
o the Predirect message includes an RHO that contains at least the
header of the originating IPv6 packet.
o the I and P bits in the Predirect message header are both set to
1.
When 'A' receives the Predirect message, it decapsulates the message
according to Section 7.3 of [RFC5214] since the inner IPv6 source
address embeds the outer IPv4 source address.
'A' next accepts the message only if it satisfies the same message
validation checks specified for Predirects in Section 3.2.4.6.2.
'A' then locates a forwarding table entry that covers the IPv6
destination address of the packet segment in the RHO (in this case, a
forwarding table entry with next hop 'D'). Without decrementing the
IPv6 hop limit in the Redirect message, 'A' next changes the IPv4
source address of the Predirect message to its own IPv4 address,
changes the IPv4 destination address to 'D's IPv4 address, changes
the IPv6 source address to its own IPv6 link-local address, and
changes the IPv6 destination address to 'D's IPv6 link-local address.
'A' then sends the proxied Predirect message to 'D'. When 'D'
receives the proxied message, it processes the message the same as if
it had originated from 'A' as described in Section 3.2.4.6.2.
5.14.2. Scaling Considerations
Figure 5 depicts an ISATAP network topology with only a single
advertising ISATAP router within the provider network. In order to
Templin Expires September 15, 2011 [Page 39]
Internet-Draft VET March 2011
support larger numbers of non-advertising ISATAP routers and ISATAP
hosts, the provider network can deploy more advertising ISATAP
routers to support load balancing and generally shortest-path
routing.
Such an arrangement requires that the advertising ISATAP routers
participate in an IPv6 routing protocol instance so that IPv6
address/prefix delegations can be mapped to the correct router. The
routing protocol instance can be configured as either a full mesh
topology involving all advertising ISATAP routers, or as a partial
mesh topology with each ISATAP router associating with one or more
companion gateways and a full mesh between companion gateways.
5.14.3. Proxy Chaining
In large ISATAP deployments, there may be many advertising ISATAP
routers, each serving many ISATAP clients (i.e., both non-advertising
routers and simple hosts). The advertising ISATAP routers then
either require full topology knowledge, or a default route to a
companion gateway that does have full topology knowledge. For
example, if Client 'A' connects to advertising ISATAP router 'B', and
Client 'E' connects to advertising ISATAP router 'D', then 'B' and
'D' must either have full topology knowledge or have a default route
to a companion gateway (e.g., 'C') that does.
In that case, when 'A' sends an initial packet to 'E', 'B' generates
a Predirect message toward 'C', which proxies the message toward 'D'
which finally proxies the message toward 'E'.
In the reverse direction, when 'E' sends a Redirect response message
to 'A', it first sends the message to 'D', which proxies the message
toward 'C', which proxies the message toward 'B', which finally
proxies the message toward 'A'.
5.14.4. Mobility
An ISATAP router 'A' can configure both a non-advertising ISATAP
interface on a provider network and an advertising ISATAP interface
on an edge network. In that case, 'A' can service ISATAP clients
(i.e. both non-advertising routers and simple hosts) within the edge
network by acting as a DHCPv6 relay. When a client 'B' in the edge
network that has obtained IPv6 addresses/prefixes moves to a
different edge network, however, 'B' can release its address/prefix
delegations via 'A' and re-establish them via a different ISATAP
router 'C' in the new edge network.
When 'B' releases its address/prefix delegations via 'A', 'A' marks
the IPv6 forwarding table entries that cover the addresses/prefixes
Templin Expires September 15, 2011 [Page 40]
Internet-Draft VET March 2011
as DEPARTED (i.e., it clears the CURRENT state). 'A' therefore
ceases to respond to Predirect messages correlated with the DEPARTED
entries, and also schedules a garbage-collection timer of 60 seconds,
after which it deletes the DEPARTED entries.
When 'A' receives IPv6 packets destined to an address covered by the
DEPARTED IPv6 forwarding table entries, it forwards them to the last-
known edge network link-layer address of 'B' as a means for avoiding
mobility-related packet loss during routing changes. Eventually,
correspondents will receive new Redirect messages from the network to
discover that 'B' is now associated with 'C'.
Note that this mobility management method works the same way when the
edge networks comprise native IPv6 links (i.e., and not just for
ISATAP links), however any IPv6 packets forwarded by 'A' via an IPv6
forwarding table entry in the DEPARTED state may be lost if the
mobile node moves off-link with respect to its previous edge network
point of attachment. This should not be a problem for large links
(e.g., large cellular network deployments, large ISP networks, etc.)
in which all/most mobility events are intra-link.
6. IANA Considerations
There are no IANA considerations for this document.
7. Security Considerations
Security considerations for MANETs are found in [RFC2501].
The security considerations found in
[RFC2529][RFC5214][I-D.nakibly-v6ops-tunnel-loops] also apply to VET.
SEND [RFC3971] and/or IPsec [RFC4301] can be used in environments
where attacks on the neighbor coordination protocol are possible.
SEAL [I-D.templin-intarea-seal] provides a per-packet identification
that can be used to detect source address spoofing.
Rogue neighbor coordination messages with spoofed RLOC source
addresses can consume network resources and cause VET nodes to
perform extra work. Nonetheless, VET nodes SHOULD NOT "blacklist"
such RLOCs, as that may result in a denial of service to the RLOCs'
legitimate owners.
VBRs and VBGs observe the recommendations for network ingress
filtering [RFC2827].
Templin Expires September 15, 2011 [Page 41]
Internet-Draft VET March 2011
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.
Security concerns pertaining to tunneling mechanisms are discussed in
[I-D.ietf-v6ops-tunnel-security-concerns].
Default router and prefix information options for DHCPv6 are
discussed in [I-D.droms-dhc-dhcpv6-default-router].
An automated IPv4 prefix delegation mechanism is proposed in
[I-D.ietf-dhc-subnet-alloc].
RLOC prefix delegation for enterprise-edge interfaces is discussed in
[I-D.clausen-manet-autoconf-recommendations].
MANET link types are discussed in [I-D.clausen-manet-linktype].
The LISP proposal [I-D.ietf-lisp] examines encapsulation/
decapsulation issues and other aspects of tunneling.
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, Fred
Baker, James Bound, Scott Brim, Brian Carpenter, Thomas Clausen,
Claudiu Danilov, Chris Dearlove, Remi Despres, Gert Doering, Ralph
Droms, Washam Fan, Dino Farinacci, Vince Fuller, Thomas Goff, David
Green, Joel Halpern, Bob Hinden, Sascha Hlusiak, Sapumal Jayatissa,
Dan Jen, Darrel Lewis, Tony Li, Joe Macker, David Meyer, Gabi
Nakibly, Thomas Narten, Pekka Nikander, Dave Oran, Alexandru
Petrescu, Mark Smith, John Spence, Jinmei Tatuya, Dave Thaler, Mark
Townsley, Ole Troan, Michaela Vanderveen, Robin Whittle, James
Woodyatt, Lixia Zhang, and others in the IETF AUTOCONF and MANET
Templin Expires September 15, 2011 [Page 42]
Internet-Draft VET March 2011
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.
Jim Bound's foundational work on enterprise networks provided
significant guidance for this effort. We mourn his loss and honor
his contributions.
11. References
11.1. Normative References
[I-D.templin-intarea-seal]
Templin, F., "The Subnetwork Encapsulation and Adaptation
Layer (SEAL)", draft-templin-intarea-seal-28 (work in
progress), February 2011.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, September 1981.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, May 2000.
Templin Expires September 15, 2011 [Page 43]
Internet-Draft VET March 2011
[RFC3118] Droms, R. and W. Arbaugh, "Authentication for DHCP
Messages", RFC 3118, June 2001.
[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.
[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.
[RFC5342] Eastlake, D., "IANA Considerations and IETF Protocol Usage
for IEEE 802 Parameters", BCP 141, RFC 5342,
September 2008.
11.2. Informative References
[CATENET] Pouzin, L., "A Proposal for Interconnecting Packet
Switching Networks", May 1974.
[I-D.carpenter-flow-ecmp]
Carpenter, B. and S. Amante, "Using the IPv6 flow label
for equal cost multipath routing and link aggregation in
tunnels", draft-carpenter-flow-ecmp-03 (work in progress),
October 2010.
Templin Expires September 15, 2011 [Page 44]
Internet-Draft VET March 2011
[I-D.cheshire-dnsext-multicastdns]
Cheshire, S. and M. Krochmal, "Multicast DNS",
draft-cheshire-dnsext-multicastdns-14 (work in progress),
February 2011.
[I-D.clausen-manet-autoconf-recommendations]
Clausen, T. and U. Herberg, "MANET Router Configuration
Recommendations",
draft-clausen-manet-autoconf-recommendations-00 (work in
progress), February 2009.
[I-D.clausen-manet-linktype]
Clausen, T., "The MANET Link Type",
draft-clausen-manet-linktype-00 (work in progress),
October 2008.
[I-D.droms-dhc-dhcpv6-default-router]
Droms, R. and T. Narten, "Default Router and Prefix
Advertisement Options for DHCPv6",
draft-droms-dhc-dhcpv6-default-router-00 (work in
progress), March 2009.
[I-D.ietf-6man-udpzero]
Fairhurst, G. and M. Westerlund, "IPv6 UDP Checksum
Considerations", draft-ietf-6man-udpzero-02 (work in
progress), October 2010.
[I-D.ietf-dhc-subnet-alloc]
Johnson, R., Kumarasamy, J., Kinnear, K., and M. Stapp,
"Subnet Allocation Option", draft-ietf-dhc-subnet-alloc-11
(work in progress), May 2010.
[I-D.ietf-grow-va]
Francis, P., Xu, X., Ballani, H., Jen, D., Raszuk, R., and
L. Zhang, "FIB Suppression with Virtual Aggregation",
draft-ietf-grow-va-04 (work in progress), February 2011.
[I-D.ietf-lisp]
Farinacci, D., Fuller, V., Meyer, D., and D. Lewis,
"Locator/ID Separation Protocol (LISP)",
draft-ietf-lisp-10 (work in progress), March 2011.
[I-D.ietf-manet-smf]
Macker, J. and S. Team, "Simplified Multicast Forwarding",
draft-ietf-manet-smf-11 (work in progress), March 2011.
[I-D.ietf-v6ops-tunnel-security-concerns]
Krishnan, S., Thaler, D., and J. Hoagland, "Security
Templin Expires September 15, 2011 [Page 45]
Internet-Draft VET March 2011
Concerns With IP Tunneling",
draft-ietf-v6ops-tunnel-security-concerns-04 (work in
progress), October 2010.
[I-D.jen-apt]
Jen, D., Meisel, M., Massey, D., Wang, L., Zhang, B., and
L. Zhang, "APT: A Practical Transit Mapping Service",
draft-jen-apt-01 (work in progress), November 2007.
[I-D.nakibly-v6ops-tunnel-loops]
Nakibly, G. and F. Templin, "Routing Loop Attack using
IPv6 Automatic Tunnels: Problem Statement and Proposed
Mitigations", draft-nakibly-v6ops-tunnel-loops-03 (work in
progress), August 2010.
[IEN48] Cerf, V., "The Catenet Model for Internetworking",
July 1978.
[RASADV] Microsoft, "Remote Access Server Advertisement (RASADV)
Protocol Specification", October 2008.
[RFC0994] International Organization for Standardization (ISO) and
American National Standards Institute (ANSI), "Final text
of DIS 8473, Protocol for Providing the Connectionless-
mode Network Service", RFC 994, March 1986.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC1070] Hagens, R., Hall, N., and M. Rose, "Use of the Internet as
a subnetwork for experimentation with the OSI network
layer", RFC 1070, February 1989.
[RFC1122] Braden, R., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, October 1989.
[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.
[RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003,
Templin Expires September 15, 2011 [Page 46]
Internet-Draft VET March 2011
October 1996.
[RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997.
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, December 1998.
[RFC2491] Armitage, G., Schulter, P., Jork, M., and G. Harter, "IPv6
over Non-Broadcast Multiple Access (NBMA) networks",
RFC 2491, January 1999.
[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.
[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.
[RFC3947] Kivinen, T., Swander, B., Huttunen, A., and V. Volpe,
"Negotiation of NAT-Traversal in the IKE", RFC 3947,
January 2005.
[RFC3948] Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M.
Stenberg, "UDP Encapsulation of IPsec ESP Packets",
RFC 3948, January 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.
[RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
for IPv6 Hosts and Routers", RFC 4213, October 2005.
Templin Expires September 15, 2011 [Page 47]
Internet-Draft VET March 2011
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
RFC 4306, December 2005.
[RFC4548] Gray, E., Rutemiller, J., and G. Swallow, "Internet Code
Point (ICP) Assignments for NSAP Addresses", RFC 4548,
May 2006.
[RFC4555] Eronen, P., "IKEv2 Mobility and Multihoming Protocol
(MOBIKE)", RFC 4555, June 2006.
[RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick,
"Internet Group Management Protocol (IGMP) / Multicast
Listener Discovery (MLD)-Based Multicast Forwarding
("IGMP/MLD Proxying")", RFC 4605, August 2006.
[RFC4795] Aboba, B., Thaler, D., and L. Esibov, "Link-local
Multicast Name Resolution (LLMNR)", RFC 4795,
January 2007.
[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.
[RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
March 2008.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, July 2008.
[RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4
Infrastructures (6rd)", RFC 5569, January 2010.
[RFC5685] Devarapalli, V. and K. Weniger, "Redirect Mechanism for
the Internet Key Exchange Protocol Version 2 (IKEv2)",
Templin Expires September 15, 2011 [Page 48]
Internet-Draft VET March 2011
RFC 5685, November 2009.
[RFC5720] Templin, F., "Routing and Addressing in Networks with
Global Enterprise Recursion (RANGER)", RFC 5720,
February 2010.
[RFC5887] Carpenter, B., Atkinson, R., and H. Flinck, "Renumbering
Still Needs Work", RFC 5887, May 2010.
[RFC5969] Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4
Infrastructures (6rd) -- Protocol Specification",
RFC 5969, August 2010.
[RFC6139] Russert, S., Fleischman, E., and F. Templin, "Routing and
Addressing in Networks with Global Enterprise Recursion
(RANGER) Scenarios", RFC 6139, February 2011.
[RFC6179] Templin, F., "The Internet Routing Overlay Network
(IRON)", RFC 6179, March 2011.
Appendix A. Duplicate Address Detection (DAD) Considerations
A priori uniqueness determination (also known as "pre-service DAD")
for an RLOC assigned on an enterprise-interior interface would
require either flooding the entire enterprise network or somehow
discovering a link in the network 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 RLOCs 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 RLOCs can be generated with mechanisms such as
CGAs, IPv6 privacy addresses, etc. with very small probability of
collision. Pseudo-random IPv4 RLOCs can be generated through random
assignment from a suitably large IPv4 prefix space.
Consistent operational practices can assure uniqueness for VBG-
aggregated addresses/prefixes, while statistical properties for
pseudo-random address self-generation can assure uniqueness for the
RLOCs assigned on an ER's enterprise-interior interfaces. Still, an
RLOC delegation authority should be used when available, while a
passive in-service DAD mechanism should be used to detect RLOC
duplications when there is no RLOC delegation authority.
Templin Expires September 15, 2011 [Page 49]
Internet-Draft VET March 2011
Appendix B. Anycast Services
Some of the IPv4 addresses that appear in the Potential Router List
may be anycast addresses, i.e., they may be configured on the VET
interfaces of multiple VBRs/VBGs. In that case, each VET router
interface that configures the same anycast address must exhibit
equivalent outward behavior.
Use of an anycast address as the IP destination address of tunneled
packets can have subtle interactions with tunnel path MTU and
neighbor discovery. For example, if the initial fragments of a
fragmented tunneled packet with an anycast IP destination address are
routed to different egress tunnel endpoints than the remaining
fragments, the multiple endpoints will be left with incomplete
reassembly buffers. This issue can be mitigated by ensuring that
each egress tunnel endpoint implements a proactive reassembly buffer
garbage collection strategy. Additionally, ingress tunnel endpoints
that send packets with an anycast IP destination address must use the
minimum path MTU for all egress tunnel endpoints that configure the
same anycast address as the tunnel MTU. Finally, ingress tunnel
endpoints should treat ICMP unreachable messages from a router within
the tunnel as at most a weak indication of neighbor unreachability,
since the failures may only be transient and a different path to an
alternate anycast router quickly selected through reconvergence of
the underlying routing protocol.
Use of an anycast address as the IP source address of tunneled
packets can lead to more serious issues. For example, when the IP
source address of a tunneled packet is anycast, ICMP messages
produced by routers within the tunnel might be delivered to different
ingress tunnel endpoints than the ones that produced the packets. In
that case, functions such as path MTU discovery and neighbor
unreachability detection may experience non-deterministic behavior
that can lead to communications failures. Additionally, the
fragments of multiple tunneled packets produced by multiple ingress
tunnel endpoints may be delivered to the same reassembly buffer at a
single egress tunnel endpoint. In that case, data corruption may
result due to fragment misassociation during reassembly.
In view of these considerations, VBGs that configure an anycast
address should also configure one or more unicast addresses from the
Potential Router List; they should further accept tunneled packets
destined to any of their anycast or unicast addresses, but should
send tunneled packets using a unicast address as the source address.
Templin Expires September 15, 2011 [Page 50]
Internet-Draft VET March 2011
Appendix C. Change Log
(Note to RFC editor - this section to be removed before publication
as an RFC.)
Changes from -14 to -15:
o new insights into default route configuration and next-hop
determination
Changes from -13 to -14:
o fixed Idnits
Changes from -12 to -13:
o Changed "VGL" *back* to "PRL"
o More changes for multi-protocol support
o Changes to Redirect function
Changes from -11 to -12:
o Major section rearrangement
o Changed "PRL" to "VGL"
o Brought back text that was lost in the -10 to -11 transition
Changes from -10 to -11:
o Major changes with significant simplifications
o Now support stateless PD using 6rd mechanisms
o SEAL Control Message Protocol (SCMP) used instead of ICMPv6
o Multi-protocol support including IPv6, IPv4, OSI/CLNP, etc.
Changes from -09 to -10:
o Changed "enterprise" to "enterprise network" throughout
o dropped "inner IP", since inner layer may be non-IP
o TODO - convert "IPv6 ND" to SEAL SCMP messages so that control
messages remain *within* the tunnel interface instead of being
Templin Expires September 15, 2011 [Page 51]
Internet-Draft VET March 2011
exposed to the inner network layer protocol engine.
Changes from -08 to -09:
o Expanded discussion of encapsulation/decapsulation procedures
o cited IRON
Changes from -07 to -08:
o Specified the approach to global mapping using virtual aggregation
and BGP
Changes from -06 to -07:
o reworked redirect function
o created new section on VET interface encapsulation
o clarifications on nexthop selection
o fixed several bugs
Changed from -05 to -06:
o reworked VET interface ND
o anycast clarifications
Changes from -03 to -04:
o security consideration clarifications
Changes from -02 to -03:
o security consideration clarifications
o new PRLNAME for VET is "isatav2.example.com"
o VET now uses SEAL natively
o EBGs can support both legacy ISATAP and VET over the same
underlying interfaces.
Changes from -01 to -02:
Templin Expires September 15, 2011 [Page 52]
Internet-Draft VET March 2011
o Defined CGA and privacy address configuration on VET interfaces
o Interface identifiers added to routing protocol control messages
for link-layer multiplexing
Changes from -00 to -01:
o Section 4.1 clarifications on link-local assignment and RLOC
autoconfiguration.
o Appendix B clarifications on Weak End System Model
Changes from RFC5558 to -00:
o New appendix on RLOC configuration on VET interfaces.
Author's Address
Fred L. Templin (editor)
Boeing Research & Technology
P.O. Box 3707 MC 7L-49
Seattle, WA 98124
USA
Email: fltemplin@acm.org
Templin Expires September 15, 2011 [Page 53]