Mobile IP Working Group F. Adrangi, Ed. Internet-Draft intel Expires: April 4, 2005 H. Levkowetz, Ed. October 4, 2004 Problem Statement: Mobile IPv4 Traversal of VPN Gateways draft-ietf-mip4-vpn-problem-statement-03 Status of this Memo This document is an Internet-Draft and is subject to all provisions of section 3 of RFC 3667. By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she become aware will be disclosed, in accordance with RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 4, 2005. Copyright Notice Copyright (C) The Internet Society (2004). Abstract Deploying Mobile-IP v4 in networks which are connected to the Internet through a VPN (Virtual Private Network) gateway presents some problems which do not currently have well-described solutions. This document aims to describe and illustrate these problems, and propose some guidelines for possible solutions. Adrangi, Ed. & Levkowetz, Ed. Expires April 4, 2005 [Page 1] Internet-Draft MIPv4 VPN Traversal Problem Statement October 2004 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Overview of the Problem . . . . . . . . . . . . . . . . . 3 1.2 Specification of Requirements . . . . . . . . . . . . . . 4 1.3 Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 2. MIP and VPN Deployment Scenarios . . . . . . . . . . . . . . 4 2.1 MIPv4 HA(s) Inside the Intranet behind a VPN Gateway . . . 5 2.2 VPN Gateway and MIPv4 HA(s) on the VPN domain border . . . 6 2.3 Combined VPN Gateway and MIPv4 HA . . . . . . . . . . . . 7 2.4 MIPv4 HA(s) Outside the VPN domain . . . . . . . . . . . . 8 2.5 Combined VPN Gateway and MIPv4 HA(s) on the Local Link . . 9 3. Deployment Scenarios Selection . . . . . . . . . . . . . . . 10 4. Problem statement . . . . . . . . . . . . . . . . . . . . . 10 4.1 Registering in co-located mode . . . . . . . . . . . . . . 11 4.2 Registering via an FA . . . . . . . . . . . . . . . . . . 12 4.3 Summary: MIP Incompatibilities with IPsec-based VPN Gateways . . . . . . . . . . . . . . . . . . . . . . . . . 14 5. Solution Guidelines . . . . . . . . . . . . . . . . . . . . 15 5.1 Preservation of Existing VPN Infrastructure . . . . . . . 15 5.2 Software Upgrades to Existing VPN Client and Gateways . . 15 5.3 IPsec Protocol . . . . . . . . . . . . . . . . . . . . . . 15 5.4 Multi-Vendor Interoperability . . . . . . . . . . . . . . 15 5.5 MIPv4 Protocol . . . . . . . . . . . . . . . . . . . . . . 15 5.6 Handoff Overhead . . . . . . . . . . . . . . . . . . . . . 16 5.7 Scalability, Availability, Reliability, and Performance . 16 5.8 Functional Entities . . . . . . . . . . . . . . . . . . . 16 5.9 Implications of Intervening NAT Gateways . . . . . . . . . 16 5.10 Security Requirements . . . . . . . . . . . . . . . . . 16 6. Security Considerations . . . . . . . . . . . . . . . . . . 16 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 8.1 Normative References . . . . . . . . . . . . . . . . . . . . 17 8.2 Informative References . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 18 Intellectual Property and Copyright Statements . . . . . . . 19 Adrangi, Ed. & Levkowetz, Ed. Expires April 4, 2005 [Page 2] Internet-Draft MIPv4 VPN Traversal Problem Statement October 2004 1. Introduction Mobile IP [RFC3344] agents are being deployed in enterprise networks to enable mobility across wired and wireless LANs while roaming inside the enterprise Intranet. With the growing deployment of IEEE 802.11 access points ("hot spots") in public places such as hotels, airports, and convention centers, and wireless WAN data networks such as General Packet Radio Service (GPRS), the need for enabling mobile users to maintain their transport connections and constant reachability while connecting back to their target "home" networks protected by Virtual Private Network (VPN) technology is increasing. This implies that Mobile IP and VPN technologies have to coexist and function together in order to provide mobility and security to the enterprise mobile users. The goal of this document is to: o Identify and describe practical deployment scenarios for Mobile IP and VPN in enterprise and operator environments. o Identify example usage scenarios for remote users roaming outside the "home" network protected by a VPN gateway. o Articulate the problems resulting from Mobile IP and VPN coexistence. o Specify a set of framework guidelines to evaluate proposed solutions to supporting multi-vendor seamless IPv4 mobility across IPsec-based VPN gateways. 1.1 Overview of the Problem Access to the Intranet is typically guarded by both a firewall and a VPN device. The Intranet can only be accessed by respecting the security policies in the firewall and the VPN device. When MIP is deployed in a corporate Intranet (also referred to as VPN domain), roaming between the Intranet (i.e., trusted domain) and the internet (i.e., untrusted domain) becomes problematic. It would be desirable to have seamless session mobility between the two domains, because MIP was designed for session mobility regardless of the network point of attachment. Unfortunately, the current MIP standards fall short of this promise for an important customer segment: corporate users (using VPN for remote access) who desire to add mobility support because of a need to have continuous access to Intranet resources while roaming outside the Intranet from one subnet to another, or between the VPN domain and the Internet. From the beginning it was also assumed that VPNs and firewalls were to be taken as more or less granted because they have much wider deployments than MIP at the present. Therefore any solutions would need to minimize impact on existing VPN and firewall deployments, Adrangi, Ed. & Levkowetz, Ed. Expires April 4, 2005 [Page 3] Internet-Draft MIPv4 VPN Traversal Problem Statement October 2004 related standards and "de facto" standards. 1.2 Specification of Requirements In this document, several words are used to signify the requirements of the specification. These words are often capitalized. 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]. 1.3 Terminology MIPv4 Mobile IP for IPv4 [RFC3344] MIPv6 Mobile IP for IPv6 VPN Virtual Private Network GW Gateway VPN Domain An Intranet protected by a VPN gateway. DMZ (Demilitarized Zone) A small network inserted as a "neutral zone" between a company's private network and the outside public network to prevent outside users from getting direct access to the company's private network Home Network A network, possibly virtual, having a network prefix matching that of a mobile node's home address. Home Agent A router on a mobile node's home network which tunnels datagrams for delivery to the mobile node when it is away from home, and maintains current location information for the mobile node. MN Refers to a mobile node that runs both MIP and IPsec-based VPN client software. MIPv4 inside IPsec-ESP tunnel MIPv4 packet is encapsulated in an IPsec-ESP tunnel established between the Mobile Node and the VPN gateway. IPsec-ESP inside MIPv4 tunnel IPsec-ESP packet is encapsulated in an MIPv4 tunnel established between the Mobile Node and the home agent. 2. MIP and VPN Deployment Scenarios This section describes a set of deployment scenarios where MIP agents and VPN gateways have to coexist to provide mobility and security. The intention is to identify practical deployment scenarios for MIP and VPNs where MIP technology might be extended to solve problems resulting from the desire for co-existence. Adrangi, Ed. & Levkowetz, Ed. Expires April 4, 2005 [Page 4] Internet-Draft MIPv4 VPN Traversal Problem Statement October 2004 The network topology in the following diagrams consists of an Intranet connected to the public network (i.e., Internet). Here, the word "Intranet" refers to a private network (where private addresses [RFC1918] are typically used) protected by a VPN gateway and perhaps a layer-3 transparent or non-transparent firewall. When private addresses are used, the non-transparent firewall also functions as a Network Address Translator (NAT) or Network Address Port Translator (NAPT) bridging between the two address realms (i.e., the Intranet and the internet). Firewalls may be placed on either side of the VPN gateway - referred to as inner and outer firewalls. The inner and outer firewalls typically inspect outbound traffic (i.e., from the Intranet to the Internet) and inbound traffic (i.e., from the Internet to the Intranet) respectively. When a firewall is present, it MUST be configured to allow Mobile IP traffic (both control and tunneled data packets) go through. As our focus here is the relationship between MIP and VPN, we have purposely omitted firewall from the following scenarios in order to keep things simple. It is assumed that encryption is not enforced inside the VPN domain because: 1) the VPN domain (Intranet) is viewed as a trusted network, and users allowed inside the Intranet are also trusted 2) it is a common VPN deployment practice where the VPN is used to guard the Intranet resources from unauthorized users attached to an untrusted network, and to provide a secure communication channel for authorized users to access resources inside the Intranet from outside. The following sub-sections introduce five representative combinations of MIPv4 HA and VPN gateway placement. In order to give a reasonably complete survey of MIPv4 and VPN co-existence scenarios, the ones in Section 2.3 and Section 2.5 are included even though, as covered in more detail below, there are no co-existence problems to be solved in these two cases. 2.1 MIPv4 HA(s) Inside the Intranet behind a VPN Gateway MIPv4 HAs are deployed inside the Intranet protected by a VPN gateway, and are not directly reachable by the MNs outside the Intranet. Adrangi, Ed. & Levkowetz, Ed. Expires April 4, 2005 [Page 5] Internet-Draft MIPv4 VPN Traversal Problem Statement October 2004 ..Foreign Network.. .....VPN Domain..(Intranet)..... . . . . . +----+ +----+ . +----+ +-------+ +-------+ . . |MNs | | FA | . | VPN| | Router| | HA | . . |away| | | .<=========>| | | 1..n | | 1..n | . . +----+ +----+ . | GW | +-------+ +-------+ . . . +----+ . ................... . +-------+ +-------+ . . | CN | | MNs | . . | 1..n | | home | . . +-------+ +-------+ . . . ................................ Figure 1 Direct application of MIPv4 standards [RFC3344] is successfully used to provide mobility for users inside the Intranet. However, mobile users outside the Intranet can only access the Intranet resources (e.g., MIP agents) through the VPN gateway, which will allow only authenticated IPsec traffic inside. This implies that the MIPv4 traffic has to run inside IPsec, which leads to two distinct problems: 1. When the foreign network has an FA deployed (as in e.g. CDMA 2000), MIPv4 registration becomes impossible. This is because the MIPv4 traffic between MN and VPN gateway is encrypted and the FA (which is likely in a different administrative domain) cannot inspect the MIPv4 headers needed for relaying the MIPv4 packets. Please see Section 4.2 for more details. 2. In co-located mode, successful registration is possible but the VPN tunnel has to be re-negotiated every time the MN changes its point of network attachment. These problems are articulated in Section 4. This deployment scenario may not be common yet, but it is practical and becoming important as there is an increasing need for providing corporate remote users with continuous access to the Intranet resources. 2.2 VPN Gateway and MIPv4 HA(s) on the VPN domain border A MIPv4 HA is deployed on the VPN domain border (e.g., in the DMZ) together with the VPN gateway, and it is directly reachable by MNs inside or outside the Intranet. Adrangi, Ed. & Levkowetz, Ed. Expires April 4, 2005 [Page 6] Internet-Draft MIPv4 VPN Traversal Problem Statement October 2004 ..Foreign Network.. .....VPN Domain..(Intranet)..... . . . . . +----+ +----+ . +----+ +-------+ . . |MNs | | FA | . | VPN| | Router| . . |away| | | .<=========>| | | 1..n | . . +----+ +----+ . /\ | GW | +-------+ . . . || +----+ . . . || +----+ +-------+ +-------+ . . . ++====>| HA | | CN | | MNs | . ................... | | | 1..n | | home | . +----+ +-------+ +-------+ . . . ................................ Figure 2 Please note that in deployments where the security policy prohibits direct communication between the MN (roaming outside the Intranet) and outside machines, the HA can be configured to forward only encrypted traffic from/to the MN. The MIPv4 HA has a public interface connected to the Internet, and a private interface attached to the Intranet. Mobile users will most likely have a virtual home network associated with the MIPv4 HA's private interface, so that the mobile users are always away from home and hence registered with the MIPv4 HA. Furthermore, in deployments where the VPN gateway and the HA are placed in a corporate DMZ, this implies that MIPv4 traffic will always be routed through the DMZ (regardless of whether MNs are located outside or inside the Intranet), which may not be acceptable by IT departments in large corporations. This deployment can be used with two different configurations: "MIPv4 inside IPsec-ESP tunnel" and "IPsec-ESP inside MIPv4 tunnel". The "MIPv4 inside IPsec-ESP tunnel" has the same problems as the scenario of Section 2.1 (namely, MIPv4 registration becomes impossible when the registration is to be done via an FA and furthermore in co-located mode, the VPN tunnel has to be re-negotiated every time the MN changes its point of attachment). The "IPsec-ESP inside MIPv4 tunnel" does not have problems described in Section 2.1, however it will require some modifications to the routing logic of the MIPv4 HA or the VPN gateway. 2.3 Combined VPN Gateway and MIPv4 HA This is similar to deployment scenario described in Section 2.2, with the exception that the VPN gateway and MIPv4 HA are running on the same physical machine. Adrangi, Ed. & Levkowetz, Ed. Expires April 4, 2005 [Page 7] Internet-Draft MIPv4 VPN Traversal Problem Statement October 2004 ..Foreign Network.. .....VPN Domain..(Intranet)..... . . . . . +----+ +----+ . +----+ +-------+ . . |MNs | | FA | . | VPN| | Router| . . |away| | | .<==========| GW | | 1..n | . . +----+ +----+ . | + | +-------+ . . . | HA | . ................... +----+ +-------+ +-------+ . . | CN | | MNs | . . | 1..n | | home | . . +-------+ +-------+ . . . ................................ Figure 3 Running MIPv4 HA and VPN on the same machine resolves routing related issues that exist in Section 2.2 when a "IPsec-ESP inside MIPv4 tunnel" configuration is used. However, it does not promote multi-vendor interoperability in environments where MIPv4 HA and VPN technologies must be acquired from different vendors. 2.4 MIPv4 HA(s) Outside the VPN domain In this scenario, MIPv4 HAs are deployed outside the Intranet (e.g., in an operator network), as depicted in Figure 4 below. ..Foreign Network.. .....VPN Domain..(Intranet)..... . . . . . +----+ +----+ . +----+ +-------+ . . |MNs | | FA | . | VPN| | Router| . . |away| | | .<==========| GW | | 1..n | . . +----+ +----+ . /\ | | +-------+ . . . || | | . ................... || | | +-------+ +-------+ . || | | | CN | | MNs | . .....MIPv4 Home.... || | | | 1..n | | home | . . .<===++ | | +-------+ +-------+ . . +------+ . +----+ . . | HAs | . . . . | 1..n | . ................................ . +------+ . ................... Figure 4 The IPsec tunnel end-points will be the MN and the VPN gateway. The 'home network' will most likely be a virtual home network, located at Adrangi, Ed. & Levkowetz, Ed. Expires April 4, 2005 [Page 8] Internet-Draft MIPv4 VPN Traversal Problem Statement October 2004 the HA, through which authorized remote users (i.e., the users have successfully established a connection to the corporate VPN) can reach the Corporate Intranet and maintain their transport session connectivity while roaming outside the Intranet from one subnet to another. Please note that this deployment scenario does not support mobility inside the Intranet. In this case it is most practical to run IPsec-ESP inside a MIPv4 tunnel (i.e., MIPv4 tunnel end-points are the MN and the HA; the IPsec-ESP packet from the MN and to the VPN gateway is encapsulated in the MIPv4 tunnel) as the MNs can register with the HA without establishing an IPsec tunnel to the VPN gateway. This should work without any technical problems. 2.5 Combined VPN Gateway and MIPv4 HA(s) on the Local Link This is similar to the deployment scenario described in Section 2.3, with the difference that the VPN gateway/HA is sitting on the local link. In this case the VPN gateway and HA would most naturally be co-located in the same box, although this is in no way a requirement. The VPN/HA is assumed to be reachable from the external network, i.e. it is assumed to have a public IP address, and the firewall is assumed to be configured to allow direct access to the VPN/HA from the external network. ..Foreign Network.. .....VPN Domain..(Intranet)..... . . . . . +----+ +----+ . +------+ +-------+ +-------+ . . |MNs | | FA | . | Fire | | Router| | VPN/HA| . . |away| | | .<=======>| wall | | 1..n | | 1..n | . . +----+ +----+ . | | +-------+ +-------+ . . . | NAT | . ................... +------+ +-------+ +-------+ . . | CN | | MNs | . . | 1..n | | home | . . +-------+ +-------+ . . . ................................ Figure 5 This deployment works today without any technical problems with IPsec-ESP running inside a MIPv4 tunnel. If you were to run MIPv inside the IPsec-ESP tunnel it would have the same problems as in Section 2.1, so it is deployed with the IPsec-ESP running inside the MIPv4 tunnel. This deployment is not practical for large deployments Adrangi, Ed. & Levkowetz, Ed. Expires April 4, 2005 [Page 9] Internet-Draft MIPv4 VPN Traversal Problem Statement October 2004 (on the order of thousands of users) because of the large and distributed security perimeter. 3. Deployment Scenarios Selection The deployment scenarios described in Section 2 were evaluated to identify the ones most in need of solving. The evaluation was done based on two main criteria: 1) Is the deployment scenario common and practical? and 2) Does the deployment scenario reveal any problems resulting from MIPv4 and VPN coexistence? The authors believe that the scenario in Section 2.1 is the most important and practical one because of rising needs to provide corporate remote users with continuous access to their Intranet resources. After analyzing each scenario one realizes that problems occurring in scenarios in Section 2.2 and Section 2.4 are either the same as or a subset of those in the scenario in Section 2.1. Therefore, solving the scenario in Section 2.1 will also solve the scenarios in Section 2.2 and Section 2.4. The scenarios in Section 2.3 and Section 2.5 do not introduce functional problems resulting from MIPv4 and VPN co-existence, hence there is no need to seek a solution. A solution for the deployment scenario in Section 2.1 is therefore seen as essential, and this in turn can also be applied to solve problems in other scenarios. In subsequent sections, we will articulate the roaming scenarios, the problems, and the solution guidelines relevant to the scenario in Section 2.1. 4. Problem statement This section describes roaming scenarios corresponding to the deployment scenario in Section 2.1 where an MN needs to have continuous access to the Intranet resources regardless of whether it is roaming inside or outside the Intranet, and their associated problems. The scenarios are constructed based on a multi-subnetted, MIPv4-enabled Intranet (hereafter, referred to as Intranet or VPN domain) protected by an IPsec-based VPN gateway as depicted in Figure 6. Adrangi, Ed. & Levkowetz, Ed. Expires April 4, 2005 [Page 10] Internet-Draft MIPv4 VPN Traversal Problem Statement October 2004 ....Internet....... .....VPN Domain..(Intranet)..... . . . . . +----+ . +----+ +-------+ +-------+ . . |MNs | . | VPN| | Router| | VPN/HA| . . |away| .<=========>| | | 1..n | | 1..n | . . +----+ . | GW | +-------+ +-------+ . . . +----+ . ................... . +-------+ +-------+ . . | CN | | MNs | . . | 1..n | | home | . . +-------+ +-------+ . . . ................................ Figure 6: Intranet protected by a VPN Gateway The Intranet, depicted in Figure 6, may include both wired (IEEE 802.3) and IEEE 802.11 wireless LAN deployments. However, it is also possible to see IEEE 802.11 deployments outside the Intranet due to the perceived lack of current 802.11 security, as depicted in Figure 7. ....Internet....... .....VPN Domain..(Intranet)..... . . . . . +----+ . +----+ +-------+ +-------+ . . |MNs | . | VPN| | Router| | VPN/HA| . . |away| .<=========>| | | 1..n | | 1..n | . . +----+ . | GW | +-------+ +-------+ . . . | | . ................... | | +-------+ +-------+ . | | | CN | | MNs | . ..802.11 Wireless.. <====>| | | 1..n | | home | . . Network . +----+ +-------+ +-------+ . . . . . ................... ................................ Figure 7: IEEE 802.11 Wireless deployment outside the home network 4.1 Registering in co-located mode In co-located mode, the IPsec tunnel endpoints would be at the MN and the VPN gateway, which (supposing we have the scenario described in Section 2.1) results in the mobile-ip tunnel from MN to HA being encapsulated inside the IPsec tunnel. See Figure 8 below. This scenario is still possible, but has some major drawbacks. Adrangi, Ed. & Levkowetz, Ed. Expires April 4, 2005 [Page 11] Internet-Draft MIPv4 VPN Traversal Problem Statement October 2004 ....Internet....... .....VPN Domain..(Intranet)..... . . . . . +----+ . +----+ +-------+ +-------+ . . |MNs | . | VPN| | Router| | VPN/HA| . . |away|<###################>| |-----| 1..n |->| 1..n | . . +----+ . \ | GW | +-------+ +-------+ . . . \ +----+ . ................... mip . +-------+ +-------+ . inside . | CN | | MNs | . IPsec . | 1..n | | home | . . +-------+ +-------+ . . . ................................ Figure 8 The MN obtains an address at its point of attachment (via DHCP [RFC2131] or some other means), and then first sets up an IPsec tunnel to the VPN gateway, after which it can successfully register with its HA through the IPsec tunnel. The IPsec tunnel SA (Security Association) is identified by a triplet consisting of SPI (Security Parameter Index), MN's IP destination address (i.e., the address obtained at the point of attachment), and Security Protocol (AH or ESP) Identifier as described in [RFC2401]. This means that as the MN's IP destination address changes on each IP subnet handoff, the IPsec tunnel needs to be re-established. This could have noticeable performance implications on real-time applications and in resource-constrained wireless networks. In effect, we don't have mobility support for the tunnel endpoint changes associated with MN movements. 4.2 Registering via an FA In the case where a mobile node is in a network where mobility support is provided through the use of an FA, and no DHCP allocated address and co-located mode is possible, we run into severe trouble. This is illustrated in Figure 9 and explained below: Adrangi, Ed. & Levkowetz, Ed. Expires April 4, 2005 [Page 12] Internet-Draft MIPv4 VPN Traversal Problem Statement October 2004 ..Foreign Network.. .....VPN Domain..(Intranet)..... . . . . . +----+ +----+ . +----+ +-------+ +-------+ . . |MNs | | FA | . | VPN| | Router| | VPN/HA| . . |away|| |-----| 1..n |->| 1..n | . . +----+ \ +----+ . \ | GW | +-------+ +-------+ . . \ . \ +----+ . ...........\....... mip . +-------+ +-------+ . \ inside . | CN | | MNs | . MN expects IPsec . | 1..n | | home | . IPsec traffic . +-------+ +-------+ . . . ................................ Figure 9 The MN, when arriving at the visited network on the left in this figure, has to reach the FA with registration requests in order to have the FA send them on to the HA. However, the MN in all likelihood cannot register with the FA because the registration requests will be sent encrypted, and the FA will not be able to decrypt them. Now, if the MN would have a policy which allowed split tunneling, so that it could reach the FA with clear text messages, the FA would still not be able to get through the VPN gateway unless the HA is reachable from outside and the Intranet security policy allows MIP registration packets bypass the VPN gateway. Even if the HA is reachable and the MIP registration succeeds, the FA (which is likely in a different administrative domain) will not be able to relay packets between the MN and the VPN gateway. Packets from the MN will be encapsulated by the FA with IP-in-IP (RFC 2003) which the VPN gateway will drop, and packets from the VPN gateway will have ESP payloads (with IP-in-IP inside) which the FA will drop (as it expects IP-in-IP encapsulated traffic to the MN). The use of a 'trusted FA' has also been suggested in this scenario; meaning an FA which is actually a combined VPN GW and FA. The scenario will work fine in this case as the tunnel end-points are at the FA and the VPN gateway as shown in Figure 10 below. However, we cannot expect the FA in access networks (e.g., wireless hot-spots or CDMA 2000 networks) will have security associations with any given corporate network, so this is not particularly realistic in the general mobility case. Adrangi, Ed. & Levkowetz, Ed. Expires April 4, 2005 [Page 13] Internet-Draft MIPv4 VPN Traversal Problem Statement October 2004 ..Foreign Network.. .....VPN Domain..(Intranet)..... . . . . . +----+ +----+ . +----+ +-------+ +-------+ . . | FA | | VPN| . | VPN| | Router| | VPN/HA| . . | |<--| GW |<###########>| |-----| 1..n |->| 1..n | . . +----+ +----+ . \ | GW | +-------+ +-------+ . . | . \ +----+ . . +----+ . mip . +-------+ +-------+ . . |MNs | . inside . | CN | | MNs | . . |away| . IPsec . | 1..n | | home | . . +----+ . . +-------+ +-------+ . ................... . . ................................ Figure 10 Furthermore, this solution would leave the traffic between FA and MN unprotected, and as this link in particular may be a wireless link, this is clearly undesirable. 4.3 Summary: MIP Incompatibilities with IPsec-based VPN Gateways An MN roaming outside the Intranet has to establish an IPsec tunnel to its home VPN gateway first, in order to be able to register with its home agent. This is because the MN cannot reach its HA (inside the private protected network) directly from the outside. This implies that the MIPv4 traffic from the MN to a node inside the Intranet is forced to run inside an IPsec tunnel, and hence will not be in the clear. This in turn leads to two distinct problems depending on whether the MN uses co-located or non co-located modes to register with its HA. In co-located mode, the IPsec tunnel needs to be re-established on each IP subnet handoff which will have performance implications on real-time applications and resource-constrained wireless networks. In non co-located mode (i.e., using an FA care-of address), the problem becomes severe as the MN may be unable to register with its HA through the FA, because the FA cannot understand MIPv4 registration requests if they are encrypted in the IPsec tunnel (i.e., split tunneling is not supported). Even if the MN could reach the FA with non-encrypted registration requests (i.e., split tunneling is supported), and the requests going from the FA to the HA can pass through the VPN gateway, there will still be a problem with routing of data packets between the Intranet and the internet. This is because the VPN will not allow IP-in-IP encapsulated packets from the FA go through. And furthermore, ESP encapsulated packets from the VPN gateway to the MN will be dropped by the FA as it expects Adrangi, Ed. & Levkowetz, Ed. Expires April 4, 2005 [Page 14] Internet-Draft MIPv4 VPN Traversal Problem Statement October 2004 IP-in-IP encapsulated traffic to the MN. 5. Solution Guidelines This section describes guidelines for a solution to MIPv4 traversal across VPN gateways. 5.1 Preservation of Existing VPN Infrastructure o The solution MUST work with currently deployed VPN gateways. This is the whole raison d'etre of this investigation: Finding a way to deploy Mobile-IP in cases where a VPN solution is already in place. 5.2 Software Upgrades to Existing VPN Client and Gateways o The solution SHOULD minimize changes to existing VPN client/ gateway software. 5.3 IPsec Protocol o The solution SHOULD NOT require any changes to existing IPsec or key exchange standard protocols implemented by VPN gateways. o The solution SHOULD NOT require that the VPN gateway or the VPN client implement any new protocols in addition to the existing standard protocols. 5.4 Multi-Vendor Interoperability o The solution MUST provide multi-vendor interoperability, where MIPv4 mobility agents, mobility clients (MN), VPN server, and VPN client solutions may come from four different vendors. This is typical for medium and large enterprises which purchase and deploy best-of-breed multi-vendor solutions for IP routing, VPNs, firewalls etc. 5.5 MIPv4 Protocol o The solution MUST adhere to MIPv4 protocol [RFC3344]. That is, the solution MUST NOT impose any changes that violates MIPv4 protocol. o The solution MAY introduce new extensions to MIPv4 nodes per guidelines specified in the MIPv4 protocol [RFC3344]. However, it is highly desirable to avoid any changes to MIPv4 mobility agents such as the FA and HA in order to overcome barriers to deployment. o The solution MAY require more than one instance of MIPv4 running in parallel (multiple encapsulation). Adrangi, Ed. & Levkowetz, Ed. Expires April 4, 2005 [Page 15] Internet-Draft MIPv4 VPN Traversal Problem Statement October 2004 5.6 Handoff Overhead o It is imperative to keep the key management overhead down to a minimum, in order to support fast handoffs across IP subnets. Hence, the solution MUST propose a mechanism to avoid or minimize IPsec tunnel SA renegotiation and IKE renegotiation as the MN changes its current point of network attachment. 5.7 Scalability, Availability, Reliability, and Performance o The solution complexity MUST increase at most linearly with the number of MNs registered and accessing resources inside the Intranet. o The solution MAY introduce additional header or tunnelling overhead if needed. 5.8 Functional Entities o The solution MAY introduce new MIPv4 compliant functional entities. 5.9 Implications of Intervening NAT Gateways o The solution MUST be able to work with the existing MIPv4 and IPsec NAT traversal solutions [RFC3519][RFC3715][IKE-NAT]. 5.10 Security Requirements o The solution MUST provide security which is not inferior to what is already provided to existing "nomadic computing" remote access users, i.e. for confidentiality, authentication, message integrity, protection against replay attacks and related security services. 6. Security Considerations This document describes an existing problem and proposes guidelines for possible solutions; as such its security implications are indirect, through the guidelines it proposes for the solutions. Section 5.10 gives the relevant security requirements. 7. Acknowledgements The authors who contributed text to this document were in no particular order: Farid Adrangi, Milind Kulkarni, Gopal Dommety, Eli Gelasco, Qiang Zhang, Sami Vaarala, Dorothy Gellert, Nitsan Baider and Henrik Levkowetz. Adrangi, Ed. & Levkowetz, Ed. Expires April 4, 2005 [Page 16] Internet-Draft MIPv4 VPN Traversal Problem Statement October 2004 The authors would like to thank other contributors, especially Prakash Iyer, Mike Andrews, Ranjit Narjala, Joe Lau, Kent Leung, Alpesh Patel, Phil Roberts, Hans Sjostrand, Serge Tessier, Antti Nuopponen, Alan O'neill, Gaetan Feige, Brijesh Kumar for their continuous feedback and helping us improve this draft. 8. References 8.1 Normative References [RFC3344] Perkins, C., "IP Mobility Support for IPv4", RFC 3344, August 2002. 8.2 Informative References [RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G. and E. Lear, "Address Allocation for Private Internets", BCP 5, RFC 1918, February 1996. [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. [RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the Internet Protocol", RFC 2401, November 1998. [RFC3519] Levkowetz, H. and S. Vaarala, "Mobile IP Traversal of Network Address Translation (NAT) Devices", RFC 3519, May 2003. [RFC3715] Aboba, B. and W. Dixon, "IPsec-Network Address Translation (NAT) Compatibility Requirements", RFC 3715, March 2004. [IKE-NAT] Kivinen, T., "Negotiation of NAT-Traversal in the IKE", draft-ietf-ipsec-nat-t-ike-08 (work in progress), February 2004. Adrangi, Ed. & Levkowetz, Ed. Expires April 4, 2005 [Page 17] Internet-Draft MIPv4 VPN Traversal Problem Statement October 2004 Authors' Addresses Farid Adrangi Intel Corporation 2111 N.E. 25th Avenue Hillsboro OR USA Phone: +1 503-712-1791 EMail: farid.adrangi@intel.com Henrik Levkowetz Torsgatan 71 Stockholm S-113 37 SWEDEN Phone: +46 7 08 32 16 08 EMail: henrik@levkowetz.com Adrangi, Ed. & Levkowetz, Ed. Expires April 4, 2005 [Page 18] Internet-Draft MIPv4 VPN Traversal Problem Statement October 2004 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2004). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Adrangi, Ed. & Levkowetz, Ed. Expires April 4, 2005 [Page 19]