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Auto-Discovery VPN Problem Statement and Requirements

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 7018.
Authors Vishwas Manral , Steve Hanna
Last updated 2018-12-20 (Latest revision 2013-07-15)
Replaces draft-ietf-ipsecme-p2p-vpn-problem
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Informational
Additional resources Mailing list discussion
Stream WG state Submitted to IESG for Publication
Document shepherd Paul E. Hoffman
Shepherd write-up Show Last changed 2013-06-25
IESG IESG state Became RFC 7018 (Informational)
Action Holders
Consensus boilerplate Unknown
Telechat date (None)
Responsible AD Sean Turner
Send notices to (None)
IANA IANA review state Version Changed - Review Needed
IANA action state No IANA Actions
IPsecME Working Group                                          V. Manral
Internet-Draft                                                        HP
Intended status: Informational                                  S. Hanna
Expires: January 17, 2014                                        Juniper
                                                           July 16, 2013

         Auto Discovery VPN Problem Statement and Requirements


   This document describes the problem of enabling a large number of
   systems to communicate directly using IPsec to protect the traffic
   between them.  It then expands on the requirements, for such a

   Manual configuration of all possible tunnels is too cumbersome in
   many such cases.  In other cases the IP address of endpoints change
   or the endpoints may be behind NAT gateways, making static
   configuration impossible.  The Auto Discovery VPN solution will
   address these requirements.

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

   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 January 17, 2014.

Copyright Notice

   Copyright (c) 2013 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
   ( in effect on the date of

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   publication of this document.  Please review these documents
   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Conventions Used in This Document . . . . . . . . . . . .   4
   2.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Endpoint-to-Endpoint VPN Use Case . . . . . . . . . . . .   4
     2.2.  Gateway-to-Gateway VPN Use Case . . . . . . . . . . . . .   5
     2.3.  Endpoint-to-Gateway VPN Use Case  . . . . . . . . . . . .   5
   3.  Inadequacy of Existing Solutions  . . . . . . . . . . . . . .   6
     3.1.  Exhaustive Configuration  . . . . . . . . . . . . . . . .   6
     3.2.  Star Topology . . . . . . . . . . . . . . . . . . . . . .   6
     3.3.  Proprietary Approaches  . . . . . . . . . . . . . . . . .   7
   4.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Gateway and Endpoint Requirements . . . . . . . . . . . .   7
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   IPsec [RFC4301] is used in several different cases, including tunnel-
   mode site-to-site VPNs and Remote Access VPNs.  Both tunneling modes
   for IPsec gateways and host-to-host transport mode are supported in
   this document.

   The subject of this document is the problem presented by large scale
   deployments of IPsec and the requirements on a solution to address
   the problem.  These may be a large collection of VPN gateways
   connecting various sites, a large number of remote endpoints
   connecting to a number of gateways or to each other, or a mix of the
   two.  The gateways and endpoints may belong to a single
   administrative domain or several domains with a trust relationship.

   Section 4.4 of RFC 4301 describes the major IPsec databases needed
   for IPsec processing.  It requires an extensive configuration for
   each tunnel, so manually configuring a system of many gateways and
   endpoints becomes infeasible and inflexible.

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   The difficulty is that a lot of configuration mentioned in RFC 4301
   is required to set up a Security Association.  IKE implementations
   need to know the identity and credentials of all possible peer
   systems, as well as the addresses of hosts and/or networks behind
   them.  A simplified mechanism for dynamically establishing point-to-
   point tunnels is needed.  Section 2 contains several use cases that
   motivate this effort.

1.1.  Terminology

   ADVPN - Auto Discovery Virtual Private Network (ADVPN) is VPN
   solution that enables a large number of systems to communicate
   directly, with minimal configuration and operator intervention using
   IPsec to protect communication between them.

   Endpoint - A device that implements IPsec for its own traffic but
   does not act as a gateway.

   Gateway - A network device that implements IPsec to protect traffic
   flowing through the device.

   Point-to-Point - Communication between two parties without active
   participation (e.g. encryption or decryption) by any other parties.

   Hub - The central point in a star topology/ dynamic full mesh
   topology, or one of the central points in the full mesh style VPN,
   i.e. gateway where multiple other hubs or spokes connect to.  The
   hubs usually forward traffic coming from encrypted links to other
   encrypted links, i.e. there are no devices connected to it in clear.

   Spoke - The endpoint in a star topology/ dynamic full mesh topology,
   or gateway which forwards traffic from multiple cleartext devices to
   other hubs or spokes, and some of those other devices are connected
   to it in clear (i.e. it encrypts data coming from cleartext devices
   and forwards it to the ADVPN).

   ADVPN Peer - any member of an ADVPN including gateways, endpoints,
   hub or spoke.

   Star topology - This is the topology where there is direct
   connectivity only between the hub and spoke and communication between
   the 2 spokes happens through the hub.

   Allied and Federated Environments - Environments where we have
   multiple different organizations that have close association and need
   to connect to each other.

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   Full Mesh topology - This is the topology where there is a direct
   connectivity between every Spoke to every other Spoke directly,
   without the traffic between the spokes having to be redirected
   through an intermediate hub device.

   Dynamic Full Mesh topology - This is the topology where direct
   connections exist in a hub and spoke manner, but dynamic connections
   are created/ removed between the spokes on a need basis.

   Security Association (SA) - Defined in [RFC4301].

1.2.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

2.  Use Cases

   This section presents the key use cases for large-scale point-to-
   point VPN.

   In all of these use cases, the participants (endpoints and gateways)
   may be from a single organization (administrative domain) or from
   multiple organizations with an established trust relationship.  When
   multiple organizations are involved, products from multiple vendors
   are employed so open standards are needed to provide
   interoperability.  Establishing communications between participants
   with no established trust relationship is out of scope for this

2.1.  Endpoint-to-Endpoint VPN Use Case

   Two endpoints wish to communicate securely via a point-to-point
   Security Association (SA).

   The need for secure endpoint-to-endpoint communications is often
   driven by a need to employ high-bandwidth, low -latency local
   connectivity instead of using slow, expensive links to remote
   gateways.  For example, two users in close proximity may wish to
   place a direct, secure video or voice call without needing to send
   the call through remote gateways, which would add latency to the
   call, consume precious remote bandwidth, and increase overall costs.
   Such a use case also enables connectivity when both users are behind
   NAT gateways.  Such a use case ought to allow for seamless
   connectivity even as endpoints roam, even if they are moving out from
   behind a NAT gateway, from behind one NAT gateway to behind another,
   or from a standalone position to behind a NAT gateway.

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   In a star topology, when two endpoints communicate they need a
   mechanism for authentication, such that they do not expose themselves
   to impersonation by the other spoke endpoint.

2.2.  Gateway-to-Gateway VPN Use Case

   A typical Enterprise traffic model follows a star topology, with the
   gateways connecting to each other using IPsec tunnels.

   However for voice and other rich media traffic that requires a lot of
   bandwidth or is performance sensitive, the traffic tromboning (taking
   a suboptimal path) to the hub can create traffic bottlenecks on the
   hub and can lead to an increase in cost.  A fully meshed solution
   would make best use of the available network capacity and performance
   but the deployment of a fully meshed solution involves considerable
   configuration, especially when a large number of nodes are involved.
   It is for this purpose spoke-to-spoke tunnels are dynamically created
   and torn-down.  For the reasons of cost and manual error reduction,
   it is desired that there be minimal configuration on each gateway.

   The solution ought to work in cases where the endpoints are in
   different administrative domains, albeit, ones that have an existing
   trust relationship (for example two organisations who are
   collaborating on a project, they may wish to join their networks,
   whilst retaining independent control over configuration).  It is
   highly desirable that the solution works for the star, full mesh as
   well as dynamic full mesh topology.

   The solution ought to also address the case where gateways use
   dynamic IP addresses.

   Additionally, the routing implications of gateway-to-gateway
   communication need to be addressed.  In the simple case, selectors
   provide sufficient information for a gateway to forward traffic
   appropriately.  In other cases, additional tunneling (e.g., Generic
   Routing Encapsulation - GRE) and routing (e.g., Open Shortest Path
   First - OSPF) protocols are run over IPsec tunnels, and the
   configuration impact on those protocols needs to be considered.
   There is also the case when Layer-3 Virtual Private Networks (L3VPNs)
   operate over IPsec Tunnels.

   When two gateways communicate, they need to use a mechanism for
   authentication, such that they do not expose themselves to the risk
   of impersonation by the other entities.

2.3.  Endpoint-to-Gateway VPN Use Case

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   A mobile endpoint ought to be able to use the most efficient gateway
   as it roams in the internet.

   A mobile user roaming on the Internet may connect to a gateway, which
   because of roaming is no longer the most efficient gateway to use
   (reasons could be cost/ efficiency/ latency or some other factor).
   The mobile user ought to be able to discover and then connect to the
   current most efficient gateway in a seamless way without having to
   bring down the connection.

3.  Inadequacy of Existing Solutions

   Several solutions exist for the problems described above.  However,
   none of these solutions is adequate, as described here.

3.1.  Exhaustive Configuration

   One simple solution is to configure all gateways and endpoints in
   advance with all the information needed to determine which gateway or
   endpoint is optimal and to establish an SA with that gateway or
   endpoint.  However, this solution does not scale in a large network
   with hundreds of thousands of gateways and endpoints, especially when
   multiple administrative domains are involved and things are rapidly
   changing (e.g. mobile endpoints).  Such a solution is also limited by
   the smallest endpoint/ gateway, as the same exhaustive configuration
   is to be applied on all endpoints/ gateways.  A more dynamic, secure
   and scalable system for establishing SAs between gateways is needed.

3.2.  Star Topology

   The most common way to address a part of this this problem today is
   to use what has been termed a "star topology".  In this case one or a
   few gateways are defined as "hub gateways", while the rest of the
   systems (whether endpoints or gateways) are defined as "spokes".  The
   spokes never connect to other spokes.  They only open tunnels with
   the hub gateways.  Also for a large number of gateways in one
   administrative domain, one gateway may be defined as the hub, and the
   rest of the gateways and remote access clients connect only to that

   This solution however is complicated by the case when the spokes use
   dynamic IP addresses and DNS with dynamic updates needs to be used.
   It is also desired that there is minimal to no configuration on the
   hub as the number of spokes increases and new spokes are added and
   deleted randomly.

   Another problem with the star topology is that it creates a high load
   on the hub gateways as well as on the connection between the spokes

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   and the hub.  This load is both in processing power and in network
   bandwidth.  A single packet in the hub-and-spoke scenario can be
   encrypted and decrypted multiple times.  It would be much preferable
   if these gateways and clients could initiate tunnels between them,
   bypassing the hub gateways.  Additionally, the path bandwidth to
   these hub gateways may be lower than that of the path between the
   spokes.  For example, two remote access users may be in the same
   building with high-speed wifi (for example, at an IETF meeting).
   Channeling their conversation through the hub gateways of their
   respective employers seems extremely wasteful, as well as having
   lower bandwidth.

   The challenge is to build large scale, IPsec-protected networks that
   can dynamically change with minimal administrative overhead.

3.3.  Proprietary Approaches

   Several vendors offer proprietary solutions to these problems.
   However, these solutions offer no interoperability between equipment
   from one vendor and another.  This means that they are generally
   restricted to use within one organization, and it is harder to move
   off such solutions as the features are not standardized.  Besides
   multiple organizations cannot be expected to all choose the same
   equipment vendor.

4.  Requirements

   This section defines the requirements, on which the solution will be

4.1.  Gateway and Endpoint Requirements

   1.  For any network topology (star, full mesh and dynamic full mesh),
   when a new gateway or endpoint is added, removed, or changed,
   configuration changes are minimized as follows.  Adding or removing a
   spoke in the topology MUST NOT require configuration changes to the
   hubs other than where the spoke was connected to and SHOULD NOT
   require configuration changes to the hub the spoke was connected to.
   The changes also MUST NOT require configuration changes in other

   Specifically, when evaluating potential proposals, we will compare
   them by looking at how many endpoints or gateways must be
   reconfigured when a new gateway or endpoint is added, removed, or
   changed and how substantial this reconfiguration is, besides the
   amount of static configuration required.

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   This requirement is driven by use cases 2.1 and 2.2 and by the
   scaling limitations pointed out in section 3.1.

   2.  ADVPN peers MUST allow IPsec Tunnels to be setup with other
   members of the ADVPN without any configuration changes, even when
   peer addresses get updated every time the device comes up.  This
   implies that SPD entries or other configuration based on peer IP
   address will need to be automatically updated, avoided, or handled in
   some manner to avoid a need to manually update policy whenever an
   address changes.

   3.  In many cases additional tunneling protocols (e.g. GRE) or
   Routing protocols (e.g. OSPF) are run over the IPsec tunnels.
   Gateways MUST allow for the operation of tunneling and Routing
   protocols operating over spoke-to-spoke IPsec Tunnels with minimal or
   no, configuration impact.  The ADVPN solution SHOULD NOT increase the
   amount of information required to configure protocols running over
   IPsec tunnels.

   4.  In the full mesh and dynamic full mesh topology, Spokes MUST
   allow for direct communication with other spoke gateways and
   endpoints.  In the star topology mode, direct communication between
   spokes MUST be disallowed.

   This requirement is driven by use cases 2.1 and 2.2 and by the
   limitations of a star topology pointed out in section 3.2.

   5.  Any of the ADVPN Peers MUST NOT have a way to get the long term
   authentication credentials for any other ADVPN Peers.  The compromise
   of an Endpoint MUST NOT affect the security of communications between
   other ADVPN Peers.  The compromise of a Gateway SHOULD NOT affect the
   security of the communications between ADVPN Peers not associated
   with that Gateway.

   This requirement is driven by use case 2.1.  ADVPN Peers (especially
   Spokes) become compromised fairly often.  The compromise of one ADVPN
   Peer SHOULD NOT affect the security of other unrelated ADVPN Peers.

   6.  Gateways SHOULD allow for seamless handoff of sessions in case
   endpoints are roaming, even if they cross policy boundaries.  This
   would mean the data traffic is minimally affected even as the handoff
   happens.  External factors like firewall, NAT boxes that will be part
   of the overall solution when DVPN is deployed will not be considered
   part of this solution.

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   Such endpoint roaming may affect not only the endpoint-to-endpoint SA
   but also the relationship between the endpoints and gateways (such as
   when an endpoint roams to a new network that is handled by a
   different gateway).

   This requirement is driven by use case 2.1.  Today's endpoints are
   mobile and transition often between different networks (from 4G to
   WiFi and among various WiFi networks).

   7.  Gateways SHOULD allow for easy handoff of a session to another
   gateway, to optimize latency, bandwidth, load balancing,
   availability, or other factors, based on policy.

   This ability to migrate traffic from one gateway to another applies
   regardless of whether the gateways in question are hubs or spokes.
   It even applies in the case where a gateway (hub or spoke) moves in
   the network, as may happen with a vehicle-based network.

   This requirement is driven by use case 2.3.

   8.  Gateways and endpoints MUST have the capability to participate in
   an ADVPN even when they are located behind NAT boxes.  However, in
   some cases they may be deployed in such a way that they will not be
   fully reachable behind a NAT box.  It is especially difficult to
   handle cases where the Hub is behind a NAT box.  Where the two
   endpoints are both behind separate NATs, communication between these
   spokes SHOULD be supported using workarounds such as port forwarding
   by the NAT or detecting when two spokes are behind uncooperative NATs
   and using a hub in that case.

   This requirement is driven by use cases 2.1 and 2.2.  Endpoints are
   often behind NATs and gateways sometimes are.  IPsec SHOULD continue
   to work seamlessly regardless, using ADVPN techniques whenever
   possible and providing graceful fallback to hub and spoke techniques
   as needed.

   9.  Changes such as establishing a new IPsec SA SHOULD be reportable
   and manageable.  However, creating a MIB or other management
   technique is not within scope for this effort.

   This requirement is driven by manageability concerns for all the use
   cases, especially use case 2.2.  As IPsec networks become more
   dynamic, management tools become more essential.

   10.  To support allied and federated environments, endpoints and
   gateways from different organizations SHOULD be able to connect to
   each other.

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   This requirement is driven by demand for all the use cases in
   federated and allied environments.

   11.  The administrator of the ADVPN SHOULD allow for the
   configuration of a Star, Full mesh or a partial full mesh topology,
   based on which tunnels are allowed to be setup.

   This requirement is driven by demand for all the use cases in
   federated and allied environments.

   12.  The ADVPN solution SHOULD be able to scale for multicast

   This requirement is driven by the use case 2.2, where the amount of
   rich media multicast traffic is increasing.

   13.  The ADVPN solution SHOULD allow for easy monitoring, logging and
   reporting of the dynamic changes, to help for trouble shooting such

   This requirement is driven by demand for all the use cases in
   federated and allied environments.

   14.  There is also the case when L3VPNs operate over IPsec Tunnels,
   for example Provider Edge (PE) based VPN's. An ADVPN MUST support
   L3VPN as an application protected by the IPsec Tunnels.

   This requirement is driven by demand for all the use cases in
   federated and allied environments.

   15.  There ADVPN solution SHOULD allow the enforcement of per peer
   QoS in both the Star as well as the Full Mesh topology.

   This requirement is driven by demand for all the use cases in
   federated and allied environments.

   16.  There ADVPN solution SHOULD take care of not letting the Hub to
   be a single point of failure.

   This requirement is driven by demand for all the use cases in
   federated and allied environments.

5.  Security Considerations

   This is a Problem statement and requirement document for the ADVPN
   solution, and in itself does not introduce any new security concerns.
   The solution to the problems presented in this draft may involve
   dynamic updates to databases defined by RFC 4301, such as the

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   Security Policy Database (SPD) or the Peer Authorization Database

   RFC 4301 is silent about the way these databases are populated, and
   it is implied that these databases are static and pre-configured by a
   human.  Allowing dynamic updates to these databases must be thought
   out carefully, because it allows the protocol to alter the security
   policy that the IPsec endpoints implement.

   One obvious attack to watch out for is stealing traffic to a
   particular site.  The IP address for is
   If we add an entry to an IPsec endpoint's SPD that says that traffic
   to is protected through peer Gw-Mallory, then this allows
   Gw-Mallory to either pretend to be or to proxy and
   read all traffic to that site.  Updates to this database requires a
   clear trust model.

   Hubs can be a single point of failure which can cause loss of
   connectivity of the entire system, that can be a big security issue.
   Any ADVPN solution design should take care of these concerns.

6.  IANA Considerations

   No actions are required from IANA for this informational document.

7.  Acknowledgements

   Many people have contributed to the development of this problem
   statement and many more will probably do so before we are done with
   it.  While we cannot thank all contributors, some have played an
   especially prominent role.  Yoav Nir, Yaron Sheffer, Jorge Coronel
   Mendoza, Chris Ulliott, and John Veizades wrote the document upon
   which this draft was based.  Geoffrey Huang, Toby Mao, Suresh Melam,
   Praveen Sathyanarayan, Andreas Steffen, Brian Weis, and Lou Berger
   provided essential input.

8.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

Authors' Addresses

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   Vishwas Manral
   Hewlett-Packard Co.
   19111 Pruneridge Ave.
   Cupertino, CA  95113


   Steve Hanna
   Juniper Networks, Inc.
   1194 N. Mathilda Ave.
   Sunnyvale, CA  94089


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