Internet DRAFT - draft-ietf-ipsecme-ad-vpn-problem
draft-ietf-ipsecme-ad-vpn-problem
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
draft-ietf-ipsecme-ad-vpn-problem-09
Abstract
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 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.
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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
(http://trustee.ietf.org/license-info) in effect on the date of
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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",
"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 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
effort.
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
gateway.
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
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 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
spokes.
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
traffic.
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
environments.
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
(PAD).
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 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 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
USA
Email: vishwas.manral@hp.com
Steve Hanna
Juniper Networks, Inc.
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
USA
Email: shanna@juniper.net
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