IPsec Remote Access Working Group Scott Kelly, RedCreek INTERNET-DRAFT Sankar Ramamoorthi, Netscreen draft-ietf-ipsra-reqmts-00.txt March, 2000 Requirements for IPsec Remote Access Scenarios Status of This Memo This document is an Internet Draft and is in full conformance with all provisions of Section 10 of [RFC2026]. Internet Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and 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 document is a submission to the IETF IPsec remote access (IPSRA) working group. Comments on this document should be sent to the IPSRA discussion list (ietf-ipsra@vpnc.org). Abstract IPsec offers much promise as a secure remote access mechanism. However, there are a significant number of remote access scenarios, each having some shared and some unique requirements. A thorough understanding of these requirements is necessary in order to effectively evaluate the suitability of a specific set of mechanisms for any particular remote access scenario. This document enumerates the requirements for a number of common remote access scenarios. Kelly, Ramamoorthi Expires September, 2000 [Page 1]
Internet Draft <draft-ietf-ipsra-reqmts-00.txt> March, 2000 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1 Requirements Terminology . . . . . . . . . . . . . . . . . . . . 4 1.2 Reader Prerequisites . . . . . . . . . . . . . . . . . . . . . . 4 1.3 General Terminology . . . . . . . . . . . . . . . . . . . . . . 4 1.4 Document Organization . . . . . . . . . . . . . . . . . . . . . 5 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1 Endpoint Authentication . . . . . . . . . . . . . . . . . . . . 6 2.1.1 Device (Machine) Authentication . . . . . . . . . . . . . . . 7 2.1.2 User Authentication . . . . . . . . . . . . . . . . . . . . . 7 2.1.3 User/Machine Authentication . . . . . . . . . . . . . . . . . 7 2.1.4 Remote Access Authentication . . . . . . . . . . . . . . . . . 7 2.1.5 Compatibility With Legacy Mechanisms . . . . . . . . . . . . . 8 2.2 Remote Host Configuration . . . . . . . . . . . . . . . . . . . 9 2.3 Security Policy Configuration . . . . . . . . . . . . . . . . . 10 2.4 Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.1 Telecommuters (Dialup/DSL/Cablemodem) . . . . . . . . . . . . . 12 3.1.1 Endpoint Authentication Requirements . . . . . . . . . . . . . 13 3.1.2 Device Configuration Requirements . . . . . . . . . . . . . . 14 3.1.3 Policy Configuration Requirements . . . . . . . . . . . . . . 15 3.1.4 Mobility Requirements . . . . . . . . . . . . . . . . . . . . 16 3.2 Corporate to Remote Extranet . . . . . . . . . . . . . . . . . . 16 3.2.1 Authentication Requirements . . . . . . . . . . . . . . . . . 17 3.2.2 Device Configuration Requirements . . . . . . . . . . . . . . 18 3.2.3 Policy Configuration Requirements . . . . . . . . . . . . . . 18 3.2.4 Mobility Requirements . . . . . . . . . . . . . . . . . . . . 18 3.3 Extranet Laptop to Home Corporate Net . . . . . . . . . . . . . 18 3.3.1 Authentication Requirements . . . . . . . . . . . . . . . . . 19 3.3.2 Device Configuration Requirements . . . . . . . . . . . . . . 20 3.3.3 Policy Configuration Requirements . . . . . . . . . . . . . . 20 3.3.4 Mobility Requirements . . . . . . . . . . . . . . . . . . . . 20 3.4 Extranet Desktop to Home Corporate Net . . . . . . . . . . . . . 21 3.4.1 Authentication Requirements . . . . . . . . . . . . . . . . . 21 3.4.2 Device Configuration Requirements . . . . . . . . . . . . . . 21 3.4.3 Policy Configuration Requirements . . . . . . . . . . . . . . 22 3.4.4 Mobility Requirements . . . . . . . . . . . . . . . . . . . . 22 3.5 Remote Dialup Laptop Access . . . . . . . . . . . . . . . . . . 22 3.6 Road Warrior to Corporate Network . . . . . . . . . . . . . . . 22 3.6.1 Authentication Requirements . . . . . . . . . . . . . . . . . 22 3.6.2 Device Configuration Requirements . . . . . . . . . . . . . . 23 3.6.3 Policy Configuration Requirements . . . . . . . . . . . . . . 23 3.6.4 Mobility Requirements . . . . . . . . . . . . . . . . . . . . 23 4. Scenario Commonalities . . . . . . . . . . . . . . . . . . . . . 23 5. Security Considerations . . . . . . . . . . . . . . . . . . . . . 24 Kelly, Ramamoorthi Expires September, 2000 [Page 2]
Internet Draft <draft-ietf-ipsra-reqmts-00.txt> March, 2000 6. Editors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 25 9. Full Copyright Statement . . . . . . . . . . . . . . . . . . . . 25 Kelly, Ramamoorthi Expires September, 2000 [Page 3]
Internet Draft <draft-ietf-ipsra-reqmts-00.txt> March, 2000 1. Introduction In the recent past, remote access has typically consisted of dial-up users accessing the corporate network via the Public Switched Telephone Network (PSTN), with the dial-up connection terminating at a Network Access Server (NAS) within the corporate domain. The protocols facilitating this have usually been PPP-based, and access control, authorization, and accounting functions have typically been provided using one or more of a number of available mechanisms, including RADIUS [RADIUS], TACACS, and others. With the advent of IPsec, it has become possible to provide secure remote access to corporate resources via the internet, as opposed to via the PSTN alone. This has numerous benefits, financial and otherwise, and presents strong incentives to migrate to an IPsec- based remote access model. However, there are also numerous problems to be solved in order to meet the functional requirements of remote access users. It is the aim of this document to explore and enumerate the requirements of various IPsec remote access scenarios, without suggesting particular solutions for them. 1.1 Requirements Terminology The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this document, are to be interpreted as described in [3]. 1.2 Reader Prerequisites Reader familiarity with RFCs 2401-2412 is a minimum prerequisite to understanding the concepts discussed here. Familiarity with RADIUS, PPP, PPTP, L2F, L2TP, and other remote access support protocols will also be helpful, though not strictly necessary. 1.3 General Terminology o IPsec Remote Access Client (IRAC)- this term is used to refer to the remote access user's system. o IPsec Remote Access Server (IRAS) - this term refers to the device providing access to the corporate network. An alternative term is "Security Gateway". o Security Gateway (SGW) - this refers to the device providing access to the corporate network. An alternative term is IRAS. o Virtual IP Address (VIP) - this term describes an address on the local corporate subnet which is assigned to a remote Kelly, Ramamoorthi Expires September, 2000 [Page 4]
Internet Draft <draft-ietf-ipsra-reqmts-00.txt> March, 2000 client, giving the appearance that the remote client resides locally on the corporate subnet. o Machine-level Authentication - this term describes the case where the identity of a machine is verified by virtue of the machine's possession and application of some combination of authenticators. o User-level Authentication - this term describes the case where the identity of a user (as opposed to that of a machine) is verified by virtue of the user's possession and application of some combination of authenticators. 1.4 Document Organization The balance of this document is organized as follows: First, there is a general overview of the basic requirements categories, including definitions relevant to these categories. Following this is a section devoted to each remote access scenario. Within each of these sections there are subsections detailing requirements specific to that scenario in each of the following areas: endpoint authentication, remote host configuration, policy configuration, and mobility. Following this are sections containing a requirements summary and security considerations. 2. Overview In a very general sense, all remote access scenarios have a similar high-level appearance: target network | | +---+ +-------------+ +-----------+ |---| | |remote access| internet | security | | +---+ | client |=============| gateway |--| | (IRAC) | |(SGW/IRAS) | | +---+ +-------------+ +-----------+ |---| | | +---+ In all cases, a remote client wishes to access resources either behind a SGW or on an IPsec protected host, and/or wishes to provide other (specific) systems with access to the client's own resources. There are numerous details which may differ, depending on the particular scenario. For example, the IRAC may be within another corporate network, or connected to an ISP via dialup, DSL, or CATV media. There may be additional intermediaries between the remote Kelly, Ramamoorthi Expires September, 2000 [Page 5]
Internet Draft <draft-ietf-ipsra-reqmts-00.txt> March, 2000 client and the security gateway, but ultimately, all of these configurations may be viewed somewhat equivalently from a high level. In general, there are several basic categories of requirements relevant to remote access scenarios: endpoint authentication, remote host configuration, and security policy are the most common of these, while some scenarios also pose mobility requirements. Endpoint authentication refers to verification of the identities of the communication partners (e.g. the IRAC and the SGW). Remote host configuration refers to the device configuration parameters of the IRAC system. Security policy configuration refers to IPsec policy configuration of both the security gateway and the remote host, and might also be termed "access control and authorization configuration". Mobility refers to the remote client's ability to acquire a new IP address while maintaining an active session, and may apply to the ability to dynamically migrate between IRAS systems as well. These various categories are treated in more detail below. 2.1 Endpoint Authentication Before discussing endpoint authentication with respect to remote access, it is important to distinguish between data source authentication and end user authentication. Data source authentication in the IPsec context consists in providing assurance that a network packet originates from a specific host (identifiable by its network address). IPsec offers mechanisms for this via AH or ESP. Endpoint authentication within the IPsec context consists in providing assurance that the endpoint is actually who it claims to be. IPsec currently offers mechanisms for this as part of IKE [IKE]. While the two types of authentication differ, they are not unrelated. In fact, data source authentication relies upon endpoint authentication for its effectiveness. This is due to the fact that it is possible to inject packets with a particular IP address into the internet from many arbitrary locations, so that we cannot be certain in many instances that a packet actually originates from a particular host, or even from the network upon which that host resides. To resolve this, one must first authenticate the particular host somehow, and then bind the IP address of this host to the trust relationship established by the endpoint authentication process. In the context of remote access, the authenticated entity may be a machine, a user, or both. The authentication methods currently supported by IPsec range from preshared secrets to various signature and encryption schemes employing private keys and their corresponding public key certificates. These mechanisms may be used to authenticate the end user alone, the device alone, or both the end user and the device. These are each discussed in more detail below. Kelly, Ramamoorthi Expires September, 2000 [Page 6]
Internet Draft <draft-ietf-ipsra-reqmts-00.txt> March, 2000 2.1.1 Device (Machine) Authentication In the case where no user input is required in order for the subject device to access an authentication credential which is securely stored upon that device, the entity authenticated by any of these various mechanisms will be the device alone. That is, a shared secret or a private key corresponding to a public key certificate may be either stored on the device or contained in another device which is securely accessible by the device (e.g. a smartcard). If a user is not required to somehow "unlock" this credential prior to use, then the knowledge required for its use is entirely contained within the subject device. In this case, the user has not been authenticated by the use of such a credential; rather, the device has. In this case, the IRAS has some level of assurance that a particular machine (the one to which the credential was issued) is the one from which access is being attempted, but no explicit assurance regarding the identity of the user of the system. 2.1.2 User Authentication In some cases, the user may possess an authentication token (preshared key, private key, passphrase, etc.), and may provide this or some derivative of this whenever authentication is required. If this token or derivative is delivered directly to the other endpoint without modification by the IRAC system, then it is the user alone which has been authenticated to some degree. That is, while there is some assurance as to the user's network address, there is no assurance as to the particular machine from which the user is attempting access. This is because no machine/device credential is employed in the authentication process. 2.1.3 User/Machine Authentication In some cases, user input of some sort may be required to either provide the client device with access to an authentication credential, or to somehow modify the credential. That is, the accurate application of the authentication credential requires something which the user possesses or knows in tandem with something which the system controls. For example, a private key may be encrypted and stored either on the device or in a hardware token which the user plugs into the device, and the user must provide a password in order to decrypt it. In this case, assuming the subsequent authentication operation succeeds, then both the user and the user's system have been authenticated. 2.1.4 Remote Access Authentication Kelly, Ramamoorthi Expires September, 2000 [Page 7]
Internet Draft <draft-ietf-ipsra-reqmts-00.txt> March, 2000 In the general case for remote access, authentication requirements are typically asymmetric. From the IRAC's perspective, it is important to ensure that the security gateway at the other end of the connection is indeed the intended SGW, and not some rogue system masquerading as the SGW. That is, the IRAC requires machine authentication for the SGW. This is fairly straightforward, given the authentication mechanisms supported by IKE and IPsec. Further, this sort of authentication tends to persist through time, although the extent of this persistence depends upon the mechanism chosen. While it is difficult to imagine that user-level endpoint authentication for the SGW might ever be required, the situation is quite different for the IRAC. Here, it is often important to know that the individual at the other end of the connection is one who is authorized to access corporate resources, as opposed to someone who happened upon an unoccupied but otherwise authorized system. Authenticating the user is not quite so straightforward as authenticating the user's machine. It typically requires some form of user input, and often requires periodic renewal. In situations where a high level of physical security does not exist, it is common to require a user-input secret as part of authentication, and then to periodically renew the authentication. Choosing a renewal interval which provides an acceptable level of risk, but which does not annoy the user too much, may be challenging. It should be obvious that even this approach offers only limited assurance in many cases. Clearly, there are a number of assurance levels which are obtainable with various endpoint authentication techniques. Also, there is a good deal of variation in authentication requirements for differing remote access scenarios. These are illustrated on a case by case basis below in the detailed scenario descriptions. 2.1.5 Compatibility With Legacy Mechanisms There are a number of currently deployed remote access mechanisms which were installed prior to the deployment of IPsec. Typically, these are dialup systems which rely upon RADIUS for user authentication, but there are other mechanisms as well. An ideal IPsec remote access solution might utilize the underlying remote access framework without modification. Inasmuch as this is possible, this should be a goal. However, there may be cases where this simply cannot be accomplished. In such cases, the IPsec remote access framework should be designed to accommodate migration from these mechanisms as painlessly as is possible. In general, proposed IPsec remote access mechanisms should meet the Kelly, Ramamoorthi Expires September, 2000 [Page 8]
Internet Draft <draft-ietf-ipsra-reqmts-00.txt> March, 2000 following goals: o should provide direct support for legacy user authentication systems such as RADIUS o if legacy support cannot be provided without some sort of migration, the impact of such migration should be minimized o user authentication information must be protected against eavesdropping and replay (including the user identity) o single point of entry should be provided in configurations employing load-balancing and/or redundancy. o must provide migration path to PKI-based mechanisms 2.2 Remote Host Configuration Remote host configuration refers to the network-related device configuration of the client system. This configuration may be fixed or dynamic. It may be completely provided by the administrator of the network upon which the remote user currently resides (e.g. the ISP), or it may be partially provided by that administrator, with the balance provided by an entity on the remote corporate network which the client is accessing. In general, this configuration may include the following: o IP address(es) o Subnet mask(s) o Broadcast address(es) o Host name(s) o Domain name(s) o Time offset o Servers (e.g. SMTP, POP, WWW, DNS/NIS, LPR, syslog, WINS, NTP, etc. ) o Router(s) o Router discovery options o Static routes o MTU o Default TTL o Source routing options o IP Forwarding enable/disable o PMTU options o ARP cache timeout o X Windows options o NIS options o NetBIOS options Kelly, Ramamoorthi Expires September, 2000 [Page 9]
Internet Draft <draft-ietf-ipsra-reqmts-00.txt> March, 2000 o (others options) Cases where such configuration is provided by the ISP are, for the most Part, uninteresting for our purposes. It is the cases where specific IRAC configuration occurs as a result of remote access with which we are concerned. For example, in some cases the IRAC may be assigned a "virtual address", giving the appearance that it resides on the (local) corporate network: corporate net +------------------+ | | Remote Access | +--------+ | !~~~~~~~~~~! |+-------+ Client | | | | ! IRAC ! ||virtual| | |security| |---! virtual ! || host | |--------|gateway | | ! presence ! || |<================>| |----| !~~~~~~~~~~! |+-------+ |--------| | | +------------------+ ^ +--------+ | +--------+ | |---| local | IPsec tunnel | | host | with encapsulated | +--------+ traffic inside In this case, the IRAC system begins with an externally routable address. An additional internal corporate address is assigned to the IRAC, and packets containing this assigned address are encapsulated, with the outer headers containing the IRAC's routable address. This provides the IRAC with a virtual presence on the corporate network via an IPsec tunnel. Note that the IRAC now has two active addresses: the ISP-assigned address, and the VIP. Having obtained this virtual presence on the corporate network, the IRAC may now require other sorts of topology-related configuration, e.g. default routers, DNS server(s), etc., just as a dynamically configured host which physically resides upon the corporate network would. It is this sort of configuration with which this requirements category is concerned. 2.3 Security Policy Configuration Security policy configuration refers to IPsec access policies for both the remote access client and the security gateway. It may be desirable to configure access policies on connecting IRAC systems which will protect the corporate network. For example, since a client has access to the internet (via its routable address), other systems on the internet also have some level of access to the client. In some cases, it may be desirable to block this internet access (or force it to pass through the tunnel) while the client has a tunneled Kelly, Ramamoorthi Expires September, 2000 [Page 10]
Internet Draft <draft-ietf-ipsra-reqmts-00.txt> March, 2000 connection to the corporate network. This is a matter of client security policy configuration. For the security gateway, it may also be desirable to dynamically adjust policies based upon the client with which a connection has been established. For example, say there are two remote users, named Alice and Bob. We wish to provide Alice with unrestricted access to the corporate network, while we wish to restrict Bob's access to specific segments. One way to accomplish this would be to statically assign internal corporate "virtual" addresses to each, and then have policies based upon these addresses, but this does not scale well, due in part to the one-to-one mapping of virtual IP addresses. A more scalable solution for remote client access control (or authorization) would be to dynamically assign IP addresses. Such an address could be assigned from a specific pool based upon the authenticated endpoint identity, with access to specific resources controlled by address-based policies in the SGW. Alternatively, an arbitrary address could be assigned, with the security gateway's policy being dynamically updated based upon the identity of the remote client and its assigned virtual address to permit access to particular resources. In either case, the relevant security policy configuration is specific to the security gateway, rather than to the IRAC. It is these sorts of policy configuration which are encompassed by this requirements category. 2.4 Mobility IRAC mobility refers to the client's propensity to change its address while maintaining a connection. For example, this could occur when the DHCP lease for an ISP-assigned address expires, and a new (different) address is allocated to the IRAC. This effectively changes one of the tunnel endpoint addresses. Depending upon how such address changes are handled (i.e is the tunnel dropped and re- established, or maintained?), this capability may impose specific requirements for remote access. 3. Scenarios There are numerous remote access scenarios possible using IPsec. This section contains a brief summary enumeration of these, followed by a section devoted to each which explores the various requirements in terms of the categories defined above. The following scenarios are discussed: o dialup/dsl/cablemodem telecommuters using their own home systems to access corporate resources Kelly, Ramamoorthi Expires September, 2000 [Page 11]
Internet Draft <draft-ietf-ipsra-reqmts-00.txt> March, 2000 o extranet users using their corporate desktop systems to access the remote company network of a business partner o extranet users using their own laptop within another company's network to access their home corporate network o extranet users using another company's system (on that company's network) to access their home corporate network o road warriors using their own laptop systems to access corporate resources via an arbitrary ISP dialup connection o roaming (e.g. wireless) users, using their own laptop systems to access corporate resources o remote users using someone else's system (e.g. an airport kiosk) to access corporate resources o remote user to remote user connections, in which both users have a remote access connection to a common network 3.1 Telecommuters (Dialup/DSL/Cablemodem) The telecommuter scenario is one of the more common remote access scenarios. The convenience and wide availability of internet access makes this an attractive option under many circumstances. Users may access the internet from the comfort of their homes (or hotel rooms), and using this internet connection, access the resources of a corporate network. In some cases, dialup accounts are used to provide the initial internet access, while in others some type of "always-on" connection such as a DSL or CATV modem is used. The dialup and always-on cases are very similar, with two significant differences: address assignment mechanism, and connection duration. In most dialup cases, the IRAC's IP address is dynamically assigned as part of connection setup, and with fairly high likelihood, it is different each time the IRAC connects. DSL/CATV users, on the other hand, often have static IP addresses assigned to them. As for connection duration, dialup remote access connections are typically short-lived, while always-on connections may maintain remote access connections for significantly longer periods of time. The general configuration in either case looks like this: corporate net | +----+ +-----+ +-----+ /---/ internet +---+ |--| | Kelly, Ramamoorthi Expires September, 2000 [Page 12]
Internet Draft <draft-ietf-ipsra-reqmts-00.txt> March, 2000 |IRAC |---|modem|------|ISP|==========|SGW|--| +----+ +-----+ +-----+ /---/ +---+ | | An alternative to this configuration entails placing a security gateway between the IRAC and the modem. This is currently most common in cases where DSL/CATV connections are used. 3.1.1 Endpoint Authentication Requirements The authentication requirements of this scenario depend in part upon the general security requirements of the network to which access is to be provided. Assuming that the corporate SGW is physically secure, machine authentication for the SGW is sufficient. If the assumption regarding physical security is incorrect, it is not clear that stronger authentication for the SGW could be guaranteed, and derivation of an effective mechanism for this is beyond the scope of this document. For the IRAC, the question arises as to whether machine authentication may be acceptable under some circumstances, or whether user authentication, either alone or in concert with machine authentication, is required instead. In general, a system within a user's home may be considered to be reasonably secure for purposes of a typical short-lived remote access session. That is, under normal circumstances, it is reasonable to believe that there are no potential intruders lurking about, waiting for the user to leave the PC momentarily unprotected. Likewise, it may be reasonable to believe that insufficient incentive exists for someone to covertly enter the user's home and compromise the user's credential. On the other hand, and especially in the case of an always-on connection, there is some likelihood that someone other than the intended user may acquire access to the corporate network by virtue of the fact that an active remote access session exists, and the authorized user is not currently using it. This someone might be the user's spouse, children, childrens' friend(s), housekeeper, or any of a number of others. This tends to suggest that authentication should be at the user level, and that it should be renewed relatively frequently during active sessions. To summarize, the following are the authentication requirements for the IRAS and IRAC: IRAS ---- o machine authentication MUST be provided. Kelly, Ramamoorthi Expires September, 2000 [Page 13]
Internet Draft <draft-ietf-ipsra-reqmts-00.txt> March, 2000 IRAC ---- o support for either user or machine authentication MUST be provided o support for machine authentication MAY be provided o support for user authentication SHOULD be provided o support for a combination of user and machine authentication MAY be provided o if user authentication is provided for short-lived dialup connections, periodic renewal MAY occur o if user authentication is provided for always-on connections, periodic renewal SHOULD occur 3.1.2 Device Configuration Requirements There are 2 possibilities for device configuration in the telecommuter scenario: either access to the corporate network is permitted for the native ISP-assigned address of the telecommuter's system, or the telecommuter's system is assigned a virtual address from within the corporate address space. In the first case, there are no device configuration requirements which are not already satisfied by the ISP. However, this case is the exception, rather than the rule. The second case is far more common, due to the numerous benefits derived by providing the IRAC with a virtual presence on the corporate network. For example, the virtual presence allows the client to receive subnet broadcasts, which permits it to use WINS on the corporate network. In addition, if the IRAC tunnels all traffic to the corporate network, then the corporate policy can be applied to internet traffic to/from the IRAC. In this case, the IRAC requires, at minimum, assignment of a corporate IP address. Typically, the IRAC requires anywhere from several more to many more bits of configuration information, depending upon the corporate network's level of topological complexity. For a fairly complete list, see section 2.2. To summarize, the following are the device configuration requirements for the IRAC: o support for a virtual address MAY be provided o if VIP support is provided, support for all device-related parameters listed in section 2.2 above SHOULD be provided o support for address assignment based upon authenticated identity SHOULD be supported Kelly, Ramamoorthi Expires September, 2000 [Page 14]
Internet Draft <draft-ietf-ipsra-reqmts-00.txt> March, 2000 o if authenticated address assignment is not supported, an identity-based dynamic policy update mechanism such as is described in [ARCH] MUST be supported. 3.1.3 Policy Configuration Requirements In terms of IRAC policy configuration, the most important issue pertains to whether the IRAC has direct internet access enabled (for browsing, etc.) while a connection to the corporate network exists. This is important since the fact that the IRAC has access to sites on the internet implies that those sites have some level of reciprocal access to the IRAC. It may be desirable to completely eliminate this type of access while a tunnel is active. Alternatively, the risks may be mitigated by forcing all non-corporate packets leaving the IRAC to first traverse the tunnel to the corporate network, where they may be subjected to corporate policy. A second approach which carries a bit less overhead entails modifying the IRAC's policy configuration to reflect that of the corporation during the time the IRAC is connected to the corporate network. In this case, traffic is not forced to loop through the corporate site prior to exiting to the internet or entering the IRAC. This requires some sort of policy download capability as part of the SA establishment process. In terms of IRAS configuration, it may be necessary to dynamically update the security policy database (SPD) when the remote user connects. This is because transit selectors must be based upon network address parameters, but these cannot always be known a priori in the remote access case. As is noted above, this may be avoided by provision of a mechanism which permits address assignment based upon authenticated identity. To summarize, the following are the authentication requirements for the IRAS and IRAC: IRAS ---- o dynamic policy update mechanism based upon identity and assigned address MAY be supported. o if address assignment-based policy update mechanism is not supported, address assignment based upon authenticated identity MUST be supported. Kelly, Ramamoorthi Expires September, 2000 [Page 15]
Internet Draft <draft-ietf-ipsra-reqmts-00.txt> March, 2000 IRAC ---- o support for IRAS update of IRAC policy SHOULD be provided. o if IRAS update of IRAC policy is not supported, IRAC MUST support IRAS directives to "tunnel-all" and "block-all" for non-tunneled traffic. 3.1.4 Mobility Requirements It is possible, in the case where the IRAC's address is dynamically provided by the ISP, that this address will change during a remote access session. If this occurs, one of two things must also occur: either the session must be dropped and re-established, or mechanisms must exist for communicating the new address to the SGW, and for modifying the SGW's outbound SA to reflect the new address. 3.2 Corporate to Remote Extranet Extranets are becoming increasingly common, especially as IPsec becomes more widely deployed. In this scenario, a user from one corporation uses a local corporate system to access resources on another corporation's network. Typically, these corporations are cooperating on some level, but not to the degree that unbridled access between the two networks would be acceptable. Hence, this scenario is characterized by limited access. The general topological appearance is similar to this: CORP A CORP B | | +----+ | | +-----+ |USER|---| |--| S1 | +----+ | +------++ ++------+ | +-----+ |---|SGW/FW||===internet===||SGW/FW|---| | +------++ ++------+ | +-----+ | SGW-A SGW-B |--| S2 | | | +-----+ This is purposely simplified in order to illustrate some basic characteristics without getting bogged down in details. At the edge of each network is a combination security gateway and firewall device. These are labeled "SGW-A" and "SGW-B". In this diagram, corporation B wishes to provide a user from corporation A with access to servers S1 and/or S2. This may be accomplished in one of several different ways: 1) an end-to-end SA is formed from USER to S1 or S2 Kelly, Ramamoorthi Expires September, 2000 [Page 16]
Internet Draft <draft-ietf-ipsra-reqmts-00.txt> March, 2000 2) a tunnel-mode SA is formed between SGW-A and SGW-B which only permits traffic between S1/S2 and USER. 3) a tunnel-mode SA is formed between USER and SGW-B which only permits traffic between S1/S2 and USER. These various cases are individually discussed with respect to each requirements category below. 3.2.1 Authentication Requirements For the corporate extranet scenario, the authentication requirements vary slightly depending upon the manner in which the connection is accomplished. If only a particular user is permitted to access S1/S2, then user-level authentication is required. If connection types (1) or (3) are used, this may be accomplished in the same manner as it would be for a telecommuter. If connection type (2) is used, then SGW-A must provide some local mechanism for authenticating USER, and further, SGW-B must trust this mechanism. If access is permitted for anyone within corporation A, then machine authentication might suffice. However, this is highly unlikely. A slightly more likely situation might be one in which access is permitted to anyone within a particular organizational unit in corporation A. This case is very similar the single user access case discussed above, and essentially has the same requirements in terms of the mechanism required for SGW-A, although machine authentication might suffice if the organizational unit which is permitted access has a sufficient level of physical security. Again, this requires that corporation B trust corporation A in this regard. To summarize, the following are the authentication requirements for the IRAS and IRAC: IRAS ---- o machine authentication MUST be provided. IRAC ---- o support for either user or machine authentication MAY be provided o support for machine authentication MAY be provided o support for user authentication MUST be provided o support for a combination of user and machine authentication Kelly, Ramamoorthi Expires September, 2000 [Page 17]
Internet Draft <draft-ietf-ipsra-reqmts-00.txt> March, 2000 MAY be provided o if user authentication is used, periodic renewal SHOULD occur 3.2.2 Device Configuration Requirements It is possible that corporation B would want to assign a virtual address to USER for the duration of the connection. The only way this could be accomplished would be if USER were a tunnel endpoint (e.g. in cases (1) and (3)). It is not clear what benefits, if any, this would offer. To summarize, the following are the device configuration requirements for the IRAC: o support for a virtual address MAY be provided o if VIP support is provided, support for all device-related parameters listed in section 2.2 above SHOULD be supported o support for address assignment based upon authenticated identity SHOULD be supported o if authenticated address assignment is not supported, an identity-based dynamic policy update mechanism such as is described in [ARCH] MUST be supported. 3.2.3 Policy Configuration Requirements Any of the cases discussed above would present some static policy configuration requirements. Case (1) would require that SGW-A and SGW-B permit IPsec traffic to pass between USER and S1/S2. Case (3) would have similar requirements, except that the IPsec traffic would be between USER and SGW-B. Case (3) would require that the appropriate transit traffic be secured between USER and S1/S2. None of these cases require dynamic policy configuration. 3.2.4 Mobility Requirements None. 3.3 Extranet Laptop to Home Corporate Net The use of a laptop while visiting another corporation presents another increasingly common extranet scenario. In this case, a user works temporarily within another corporation, perhaps as part of a service agreement of some sort. The user brings along a CORP-A laptop which is assigned a CORP-B address either statically or dynamically, and the user wishes to securely access resources on CORP-A's network Kelly, Ramamoorthi Expires September, 2000 [Page 18]
Internet Draft <draft-ietf-ipsra-reqmts-00.txt> March, 2000 using this laptop. This scenario has the following appearance: CORP A CORP B | | +----+ | | +--------+ |POP |---| |--| CORP-A | +----+ | +------++ ++------+ | | laptop | |---|SGW/FW||===internet===||SGW/FW|---| +--------+ | +------++ ++------+ | +----+ | SGW-A SGW-B | |FTP |---| | +----+ | | This is very similar to the telecommuter scenario, but it differs in at least two important ways. First, in this case there is often a SGW and/or firewall at the edge of CORP-B's site. Second, there may be a significantly increased risk that a long-lived connection could become accessible to someone other than the intended user. 3.3.1 Authentication Requirements In most cases, the only acceptable connections from CORP-A's perspective are between the laptop and either SGW-A or the CORP-A servers the laptop wishes to access. Since the laptop is in an environment where unauthorized users might easily gain access, user- level authentication is required. As an added precaution, a combination of user-level and machine-level authentication may be warranted in some cases. Further, in either case this authentication should be renewed frequently. To summarize, the following are the authentication requirements for the IRAS and IRAC: IRAS ---- o machine authentication MUST be provided. IRAC ---- o support for machine authentication SHOULD be provided o support for user authentication MUST be provided o support for a combination of user and machine authentication SHOULD be provided o periodic renewal of user authentication MUST be supported Kelly, Ramamoorthi Expires September, 2000 [Page 19]
Internet Draft <draft-ietf-ipsra-reqmts-00.txt> March, 2000 3.3.2 Device Configuration Requirements The device configuration requirements in this scenario are the same as for the telecommuter, i.e. the laptop may be assigned a virtual presence on the corporate network, and if so, will require full infrastructure configuration. To summarize, the following are the device configuration requirements for the IRAC: o support for a virtual address MAY be provided o if VIP support is provided, support for all device-related parameters listed in section 2.2 above SHOULD be supported o support for address assignment based upon authenticated identity SHOULD be supported o if authenticated address assignment is not supported, an identity-based dynamic policy update mechanism such as is described in [ARCH] MUST be supported. 3.3.3 Policy Configuration Requirements The policy configuration requirements in this scenario differ from those of the telecommuter, in that the laptop cannot be assigned a policy which requires all traffic to be forwarded to CORP-A via the tunnel. This is due to the fact that the laptop has a CORP-B address, and as such, may have traffic destined to CORP-B. If this traffic were tunneled to CORP-A, there might be no return path to CORP-B except via the laptop. On the other hand, internet-bound traffic could be subjected to this restriction if desired, and/or all traffic other than that between CORP-A and the laptop could be blocked for the duration of the connection. IRAC ---- o support for IRAS update of IRAC policy SHOULD be provided. o if IRAS update of IRAC policy is not supported, IRAC MUST support IRAS directives to "block-all" for non-tunneled traffic. 3.3.4 Mobility Requirements The mobility requirements in this scenario are the same as for the telecommuter scenario, i.e. if the laptop has a dynamically assigned CORP-B address which changes during the session with CORP- A, the session must either be re-established, or a mechanism for Kelly, Ramamoorthi Expires September, 2000 [Page 20]
Internet Draft <draft-ietf-ipsra-reqmts-00.txt> March, 2000 changing the associated session address must exist. 3.4 Extranet Desktop to Home Corporate Net This is very similar to the extranet laptop scenario discussed above, except that a higher degree of trust for CORP-B is required by CORP- A. This scenario has the following appearance: CORP A CORP B | | +----+ | | +--------+ |POP |---| |--| CORP-B | +----+ | +------++ ++------+ | |desktop | |---|SGW/FW||===internet===||SGW/FW|---| +--------+ | +------++ ++------+ | +----+ | SGW-A SGW-B | |FTP |---| | +----+ | | 3.4.1 Authentication Requirements The authentication requirements for the desktop extranet scenario are very similar to those of the extranet laptop scenario discussed above. The primary difference lies in the authentication type which may be used, i.e. in the laptop case, CORP-A can verify that the connection is coming from one of CORP-A's systems by placing an encrypted CORP-A credential on the laptop which requires a passphrase to "unlock". In the desktop case this is not possible. To summarize, the following are the authentication requirements, for the IRAS and IRAC: IRAS ---- o machine authentication MUST be provided. IRAC ---- o support for machine authentication MAY be provided o support for user authentication MUST be provided o support for a combination of user and machine authentication MAY be provided o periodic renewal of user authentication MUST occur 3.4.2 Device Configuration Requirements Kelly, Ramamoorthi Expires September, 2000 [Page 21]
Internet Draft <draft-ietf-ipsra-reqmts-00.txt> March, 2000 The device configuration requirements in this scenario are the same as for the laptop extranet scenario, i.e. the desktop system may be assigned a virtual presence on the corporate network, and if so, will require full infrastructure configuration. However, this seems less likely than in the laptop scenario, given CORP-A's lack of control over the software configuration of CORP-B's desktop system. 3.4.3 Policy Configuration Requirements The policy configuration requirements are quite similar to those of the extranet laptop, except that in this scenario there is even less control over CORP-B's desktop than there would be over the laptop. This means it may not be possible to restrict traffic in any way at the desktop system. 3.4.4 Mobility Requirements None, unless the desktop has a dynamically assigned address which changes. If so, the requirements are the same as for the extranet laptop. 3.5 Remote Dialup Laptop Access This is a very common remote access scenario, and is virtually indistinguishable from the telecommuter scenario, except that the connections are typically dialup only, and hence, short-lived. Refer to section 3.1.1 for details. 3.6 Road Warrior to Corporate Network This scenario entails a traveling user connecting back to the corporate network using a system owned by someone else. A commonly cited example is an airport kiosk. This looks very similar to the extranet desktop scenario, except that in the extranet scenario, CORP-A might have a trust relationship with CORP-B, whereas in this scenario, CORP-A cannot trust a publically accessible system. This being the case, it seems likely that access from such a terminal would often be severely restricted, perhaps only permitting access to a mail server. 3.6.1 Authentication Requirements Given that a publically accessible machine cannot be trusted, machine authentication of the remote system is out of the question. Since such a system could easily capture and re-use a long-lived passphrase, use of these would be ill advised. It seems that the Kelly, Ramamoorthi Expires September, 2000 [Page 22]
Internet Draft <draft-ietf-ipsra-reqmts-00.txt> March, 2000 most secure remaining authentication mechanisms in this circumstance would be to use either a smartcard, or a one-time password. IRAS ---- o machine authentication MUST be provided. IRAC ---- o support for user authentication using one-time password or hardware token SHOULD be provided o if a passphrase is used, frequent renewal of user authentication MUST occur to insure that an active session is not in use by someone other than the intial user 3.6.2 Device Configuration Requirements None. 3.6.3 Policy Configuration Requirements None. 3.6.4 Mobility Requirements None. 4. Scenario Commonalities As we examine the various remote access scenarios, a general set of common requirements emerge. Following is a summary: o Support for user authentication is required in almost all scenarios o Machine authentication for the IRAC is required in all scenarios o A mechanism for providing device configuration for the IRAC is useful in most scenarios. Such a mechanism must be extensible. o Machine authentication for the IRAS is generally only useful when combined with user authentication, and such dual authentication Kelly, Ramamoorthi Expires September, 2000 [Page 23]
Internet Draft <draft-ietf-ipsra-reqmts-00.txt> March, 2000 is useful in some scenarios. o Dynamic IRAS policy configuration is required in several scenarios. 5. Security Considerations [TBD] 6. Editors' Addresses Scott Kelly RedCreek Communications 3900 Newpark Mall Road Newark, CA 94560 USA email: skelly@redcreek.com Telephone: +1 (510) 745-3969 Sankar Ramamoorthi Netscreen 2860 San Tomas Expwy Santa Clara, CA 95051 E-mail: sramamoorthi@netscreen.com Telephone: +1 (408) 330-7800 The IPSRA working group can be contacted via the IPSRA working group's mailing list (ietf-ipsra@vpnc.org) or through its chairs: Sara Bitan sarab@radguard.com Radguard Paul Hoffman paul.hoffman@vpnc.org VPN Consortium 7. References [ARCH] Kent, S., and R. Atkinson, "Security Architecture for the Internet Protocol", RFC 2401, November 1998. [KEYWORDS] Bradner, S., "Key Words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. Kelly, Ramamoorthi Expires September, 2000 [Page 24]
Internet Draft <draft-ietf-ipsra-reqmts-00.txt> March, 2000 [RADIUS] C. Rigney, A. Rubens, W. Simpson, S. Willens, "Remote Authentication Dial In User Service (RADIUS)", RFC2138 [SASL] Myers, J., "Simple Authentication and Security Layer (SASL)", RFC 2222, October 1997. [IKE] Harkins, D., and D. Carrel, "The Internet Key Exchange (IKE)", RFC 2409, November 1998. 8. Acknowledgements The authors would like to acknowledge the many helpful comments of Sara Bitan. 9. Full Copyright Statement Copyright (C) The Internet Society (1998). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS 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. Kelly, Ramamoorthi Expires September, 2000 [Page 25]
