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Internet Engineering Task Force (IETF)                         V. ManralRequest for Comments: 7018                                            HPCategory: Informational                                         S. HannaISSN: 2070-1721                                                  Juniper                                                          September 2013Auto-Discovery VPN Problem Statement and RequirementsAbstract   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   solution.   Manual configuration of all possible tunnels is too cumbersome in   many such cases.  In other cases, the IP addresses 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 document is not an Internet Standards Track specification; it is   published for informational purposes.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Not all documents   approved by the IESG are a candidate for any level of Internet   Standard; seeSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7018.Manral & Hanna                Informational                     [Page 1]

RFC 7018                   Auto-Discovery VPN             September 2013Copyright Notice   Copyright (c) 2013 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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   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 Contents1. Introduction ....................................................21.1. Terminology ................................................31.2. Conventions Used in This Document ..........................42. Use Cases .......................................................42.1. Use Case 1: Endpoint-to-Endpoint VPN .......................42.2. Use Case 2: Gateway-to-Gateway VPN .........................52.3. Use Case 3: Endpoint-to-Gateway VPN ........................63. Inadequacy of Existing Solutions ................................63.1. Exhaustive Configuration ...................................63.2. Star Topology ..............................................63.3. Proprietary Approaches .....................................74. Requirements ....................................................74.1. Gateway and Endpoint Requirements ..........................75. Security Considerations ........................................116. Acknowledgements ...............................................117. Normative References ...........................................121.  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.Manral & Hanna                Informational                     [Page 2]

RFC 7018                   Auto-Discovery VPN             September 2013Section 4.4 of RFC 4301 describes the major IPsec databases needed   for IPsec processing.  It requires extensive configuration for each   tunnel, so manually configuring a system of many gateways and   endpoints becomes infeasible and inflexible.   The difficulty is that a lot of configuration mentioned inRFC 4301   is required to set up a Security Association.  The Internet Key   Exchange Protocol (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   Auto-Discovery Virtual Private Network (ADVPN) -  A 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., a gateway to which multiple other hubs or spokes connect.      The hubs usually forward traffic coming from encrypted links to      other encrypted links, i.e., there are no devices connected to      them in the clear.   Spoke -  The endpoint in a star topology/dynamic full-mesh topology      or gateway that forwards traffic from multiple cleartext devices      to other hubs or spokes, and some of those other devices are      connected to it in the 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,      hubs, or spokes.Manral & Hanna                Informational                     [Page 3]

RFC 7018                   Auto-Discovery VPN             September 2013   Star Topology -  Topology in which there is direct connectivity only      between the hub and spoke, and where communication between the 2      spokes happens through the hub.   Allied and Federated Environments -  Environments where we have      multiple different organizations that have close associations and      need to connect to each other.   Full-Mesh Topology -  Topology in which there is direct connectivity      between every spoke to every other spoke, without the traffic      between the spokes having to be redirected through an intermediate      hub device.   Dynamic Full-Mesh Topology -  Topology in which direct connections      exist in a hub-and-spoke manner but dynamic connections are      created/removed between the spokes on an as-needed basis.   Security Association (SA) -  Defined in [RFC4301].1.2.  Conventions Used in This Document   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].2.  Use Cases   This section presents the key use cases for large-scale   point-to-point VPNs.   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   effort.2.1.  Use Case 1: Endpoint-to-Endpoint VPN   Two endpoints wish to communicate securely via a point-to-point 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 sendManral & Hanna                Informational                     [Page 4]

RFC 7018                   Auto-Discovery VPN             September 2013   the call through remote gateways, as the remote gateways 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 and 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.   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.  Use Case 2: Gateway-to-Gateway VPN   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 require 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 that 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 that have an existing trust   relationship (for example, two organizations that are collaborating   on a project may wish to join their networks while retaining   independent control over configuration).  It is highly desirable that   the solution works for the star, full-mesh, and dynamic full-mesh   topologies.   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.Manral & Hanna                Informational                     [Page 5]

RFC 7018                   Auto-Discovery VPN             September 2013   There is also the case where 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.  Use Case 3: Endpoint-to-Gateway VPN   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 that,   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 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 gateway.Manral & Hanna                Informational                     [Page 6]

RFC 7018                   Auto-Discovery VPN             September 2013   This solution, however, is complicated by the case where 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   and the hub.  This load impacts both processing power and 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, given that a more   optimal direct path exists.   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   away from 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   based.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 hubs other than where the spoke was        connected and SHOULD NOT require configuration changes to the        hub to which the spoke was connected.  The changes also MUST NOT        require configuration changes in other spokes.Manral & Hanna                Informational                     [Page 7]

RFC 7018                   Auto-Discovery VPN             September 2013        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,        in addition to the amount of static configuration required.        This requirement is driven by use cases 1 and 2 and by the        scaling limitations pointed out inSection 3.1.   2.   ADVPN Peers MUST allow IPsec tunnels to be set up 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 Security Policy Database (SPD) entries or        other configuration based on a 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 topologies, 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 1 and 2 and by the        limitations of a star topology as pointed out inSection 3.2.   5.   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 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.Manral & Hanna                Informational                     [Page 8]

RFC 7018                   Auto-Discovery VPN             September 2013   6.   Gateways SHOULD allow for seamless handoff of sessions in cases        where 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        firewalls and NAT boxes that will be part of the overall        solution when ADVPN is deployed will not be considered part of        this solution.        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 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 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.  When 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 1 and 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.Manral & Hanna                Informational                     [Page 9]

RFC 7018                   Auto-Discovery VPN             September 2013   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.  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.        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 partial full-mesh        topology, based on which tunnels are allowed to be set up.        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        traffic.        This requirement is driven by use case 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 with        troubleshooting such environments.        This requirement is driven by demand for all the use cases in        federated and allied environments.   14.  There is also the case where L3VPNs operate over IPsec tunnels,        for example, Provider-Edge-based VPNs.  An ADVPN MUST support        L3VPNs as applications protected by the IPsec tunnels.        This requirement is driven by demand for all the use cases in        federated and allied environments.   15.  The ADVPN solution SHOULD allow the enforcement of per-peer QoS        in both the star and full-mesh topologies.        This requirement is driven by demand for all the use cases in        federated and allied environments.Manral & Hanna                Informational                    [Page 10]

RFC 7018                   Auto-Discovery VPN             September 2013   16.  The ADVPN solution SHOULD take care of not letting the hub 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 requirements document for the   ADVPN solution and in itself does not introduce any new security   concerns.  The solution to the problems presented in this document   may involve dynamic updates to databases defined byRFC 4301,   such as the Security Policy Database (SPD) or the Peer Authorization   Database (PAD).RFC 4301 is silent about the way these databases are populated, and   it is implied that these databases are static and preconfigured 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 www.example.com is 192.0.2.10.   If we add an entry to an IPsec endpoint's SPD that says that traffic   to 192.0.2.10 is protected through peer Gw-Mallory, then this allows   Gw-Mallory to either pretend to be www.example.com or proxy and read   all traffic to that site.  Updates to this database require a clear   trust model.   Hubs can be a single point of failure that can cause loss of   connectivity of the entire system; this can be a big security issue.   Any ADVPN solution design should take care of these concerns.6.  Acknowledgements   Many people have contributed to the development of this problem   statement.  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 specification was based.  Geoffrey Huang, Toby Mao, Suresh   Melam, Praveen Sathyanarayan, Andreas Steffen, Brian Weis, Lou   Berger, and Tero Kivinen provided essential input.Manral & Hanna                Informational                    [Page 11]

RFC 7018                   Auto-Discovery VPN             September 20137.  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   Vishwas Manral   Hewlett-Packard Co.   3000 Hanover St.   Palo Alto, CA  94304   USA   EMail: vishwas.manral@hp.com   Steve Hanna   Juniper Networks, Inc.   1194 N. Mathilda Ave.   Sunnyvale, CA  94089   USA   EMail: shanna@juniper.netManral & Hanna                Informational                    [Page 12]