Internet Engineering Task Force Brian Weis (Cisco) INTERNET-DRAFT George Gross (IdentAware) draft-ietf-msec-ipsec-extensions-00.txt Dragan Ignjatic (Polycom) Expires: December, 2005 June, 2005 Multicast Extensions to the Security Architecture for the Internet Protocol Status of this Memo 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 becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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. Abstract The Security Architecture for the Internet Protocol [RFC2401BIS] describes security services for traffic at the IP layer. That architecture primarily defines services for Internet Protocol (IP) unicast packets, as well as manually configured IP multicast packets. This document further defines the security services for IP multicast packets within that Security Architecture. Weis Expires December, 2005 [Page 1]
The Use of RSA Signatures with ESP and AH June, 2005 Table of Contents 1.0 Introduction.......................................................2 1.1 Scope...........................................................3 1.2 Terminology......................................................3 2.0 Overview of IP Multicast Operation.................................4 3.0 Security Association Modes.........................................4 4.0 Security Association...............................................5 4.1 Major IPsec Databases............................................5 4.1.1 SPD..........................................................5 4.1.2 SAD..........................................................6 4.1.3 PAD..........................................................6 4.1.4 GSA..........................................................8 4.2 Data Origin Authentication.......................................9 4.3 Group SA and Key Management.....................................10 4.3.1 Co-Existence of Multiple Key Management Protocols...........10 5.0 IP Traffic Processing.............................................10 5.1 Outbound IP Multicast Traffic Processing........................10 5.2 Inbound IP Multicast Traffic Processing.........................11 5.0 Networking Issues.................................................11 5.1 Network Address Translation.....................................11 5.1.1 SPD Losses Synchronization with Internet Layer's State......11 5.1.2 Secondary Problems Created by NAT Traversal.................12 5.1.3 Avoidance of NAT Using an IP-v6 Over IP-v4 Network..........14 5.1.4 GKMP/IPsec Multi-Realm IP-v4 NAT Architecture...............14 6.0 Security Considerations...........................................20 7.0 Acknowledgements..................................................20 8.0 Appendix A - Multicast Application Service Models.................20 8.1 Unidirectional Multicast Applications...........................21 8.2 Bi-directional Reliable Multicast Applications..................21 8.3 Any-To-Any Multicast Applications...............................22 9.0 References........................................................22 9.1 Normative References............................................22 9.2 Informative References..........................................22 Author's Address......................................................24 Full Copyright Statement..............................................24 Intellectual Property.................................................24 1.0 Introduction The Security Architecture for the Internet Protocol [RFC2401BIS] provides security services for traffic at the IP layer. It describes a base architecture for IPsec compliant systems, and a set of security services for the IP layer. These security services primarily describe services and semantics for IP packets that carry a unicast address in the IP destination field. Those security services can also be used to tunnel IP multicast packets, where the tunnel is a Weis Expires December, 2005 [Page 2]
The Use of RSA Signatures with ESP and AH June, 2005 pairwise tunnel between two IPsec devices. Some support for IP packets with a multicast address in the IP destination field is supported, but only with manual keying. This document describes extensions to [RFC2401BIS] that further define the IPsec security architecture for packets with a multicast address in the IP destination field to remain IP multicast packets. [NOTE TO THE READER: The scope of the extensions proposed has not been finalized. For example, there are varying opinions as to the extent that this document must accommodate interoperability between different group key management and policy systems, which may occur in very large groups. Comments regarding matters of scope are solicited.] 1.1 Scope The IPsec extensions described in this document support for IPsec Security Associations used with both Any-Source Multicast (ASM) and Source-Specific Multicast (SSM) [RFC3569, RFC3376] groups. They extensions also support Security Associations with IPv4 Broadcast addresses, and Anycast addresses [RFC2526], since there are be multiple receivers defined for a packet sent to those addresses. The IPsec Architecture does not make requirements upon entities not participating in IPsec (e.g., network devices between IPsec endpoints). As such, these multicast extensions do not require multicast routing protocols (e.g., PIM-SM [RFC2362]) or multicast admission protocols (e.g., IGMP [RFC3376] to participate in IPsec. All implementation models of IPsec (e.g., "bump-in-the-stack", "bump- in-the-wire") are supported. 1.2 Terminology The following key terms are used throughout this document. Any-Source Multicast (ASM) The Internet Protocol (IP) multicast service model as defined in RFC 1112 [RFC1112]. In this model one or more senders source packets to a single IP multicast address. When receivers join the group, they receive all packets sent to that IP multicast address. This is known as a (*,G) group. Source-Specific Multicast (SSM) The Internet Protocol (IP) multicast service model as defined in RFC 3569 [RFC3569]. In this model each combination of a sender and an IP multicast address is considered a group. This is known as an (S,G) group. Weis Expires December, 2005 [Page 3]
The Use of RSA Signatures with ESP and AH June, 2005 2.0 Overview of IP Multicast Operation IP multicasting is a means of sending a single packet to a "host group", a set of zero or more hosts identified by a single IP destination address. IP multicast packets are UDP data packets delivered with either a "best-effort" reliability to all members of the group [RFC1112], or reliably (e.g., NORM) [RFC3940]. A sender to an IP multicast group sets the destination of the packet to an IP address allocated to be used for IP multicast. Allocated IP multicast addresses are defined in RFC 3171 [RFC3171]. Potential receivers of the packet "join" the IP multicast group by registering with a network routing device, signaling its intent to receive packets sent to a particular IP multicast group. Network routing devices configured to pass IP multicast packets participate in multicast routing protocols (e.g., PIM-SM) [RFC2362]. Multicast routing protocols maintain state regarding which devices have registered to receive packets for a particular IP multicast group. When a router receives an IP multicast packet, it forwards a copy of the packet out each interface for which there are known receivers. 3.0 Security Association Modes IPsec supports two modes of use: transport mode and tunnel mode. In transport mode, AH and ESP provide protection primarily for next layer protocols; in tunnel mode, AH and ESP are applied to tunneled IP packets. A host implementation of IPsec using the multicast extensions MAY support both modes to encapsulate an IP multicast packet. These processing rules are identical to the rules described in [RFC2401BIS, Section 4.1]. However, the destination address for the IPsec packet is an IP multicast address rather than a unicast host address. A security gateway implementation of IPsec using the multicast extensions MUST use a tunnel mode SA, for the reasons described in [RFC2401BIS, Section 4.1]. In particular, the security gateway must use tunnel mode to encapsulate incoming fragments. New header construction semantics are required when tunnel mode is used to encapsulate IP multicast packets that are to remain IP multicast packets. This is due to unique requirements of IP multicast routing protocols (such as PIM-SM [RFC2362]). IP multicast routing protocols use the destination address on a packet to decide to where the packet should be routed. If the destination of an IP multicast packet is changed it will no longer be properly routed. To accommodate this routing requirement, the GKMP Subsystem may specify two actions. Firstly, the SPD-S entry for the traffic selectors must have the Remote Address PFP flag set. This Weis Expires December, 2005 [Page 4]
The Use of RSA Signatures with ESP and AH June, 2005 flag causes the remote address to be propagated to the IPsec SA. Secondly, a new IPsec SA attribute must be specified by the GKMP Subsystem that causes the tunnel mode header construction process to copy the remote address in the SA into the tunnel header remote address. IP multicast routing protocols also typically create multicast distribution trees based on the source address. An IPsec security gateway that changes the source address of an IP multicast packet may cause RPF checks on other routers to return a different result than the original plaintext IP multicast packet. As a result, multicast routing may drop the packet. To accommodate this routing requirement, the GKMP Subsystem may specify two actions. Firstly, the SPD-S entry for the traffic selectors must have the Source Address PFP flag set. This flag causes the remote address to be propagated to the IPsec SA. Secondly, a new IPsec SA attribute must be specified by the GKMP Subsystem that causes the tunnel mode header construction process to copy the source address in the SA into the tunnel header remote address. Some applications of address preservation may only require the remote address to be preserved. For this reason, the specification of remote address preservation and source address preservation are separated in the above description. In summary, retaining both the IP source and destination addresses of the inner IP header allow IP multicast routing protocols to route the packet irrespective of the packet being IPsec protected. This result is necessary in order for the multicast extensions to allow a security gateway to provide IPsec services for IP multicast packets. This method of tunnel mode is known as tunnel mode with address preservation. 4.0 Security Association 4.1 Major IPsec Databases The following sections describe the GKMP Subsystem and IPsec extension interactions with the major IPsec databases. Major IPsec databases need to be expanded in order to fully support multicast. 4.1.1 SPD A new SPD attribute is introduced - SPD entry directionality. Directionality can take three types. Each SPD entry can be marked symmetric, sender or receiver only. Symmetric SPD entries are the common entries as specified by RFC2401bis. Symmetric SHOULD be the default directionality unless specified otherwise. SPD entries marked as sender or receiver only SHOULD support multicast IP addresses in their destination address selectors. If the processing requested is bypass or discard and a sender only type is configured the entry Weis Expires December, 2005 [Page 5]
The Use of RSA Signatures with ESP and AH June, 2005 SHOULD be put in SPD-O only. Reciprocally, if the type is receiver only, the entry SHOULD go to SPD-I only. SSM is supported by the use of unicast IP address selectors as documented in IPsec RFCs. SPD entries created by a GCKS may have identical SPIs as some of the IKE created ones. This is not a problem for the inbound traffic as the appropriate SA's can be matched using the algorithm described in RFC2401bis and SA's contain a link to their parent SPD entries if such an entry exists (i.e. they are not manually keyed in). However, the outbound traffic needs to be matched against the SPD selectors so that the appropriate SA can be created on packet arrival. IPsec implementations that support multicast SHOULD use the destination address as the additional selector and match it against the SPD entries marked sender only. 4.1.2 SAD The SAD can support multicast SAs, if manually configured. An outbound multicast SA has the same structure as a unicast SA. The source address is that of the sender and the destination address is the multicast group address. An inbound, multicast SA must be configured with the source addresses of each peer authorized to transmit to the multicast SA in question. The SPI value for a multicast SA is provided by a multicast group controller, not by the receiver, as for a unicast SA. Because an SAD entry may be required to accommodate multiple, individual IP source addresses that were part of an SPD entry (for unicast SAs), the required facility for inbound, multicast SAs is a feature already present in an IPsec implementation. However, SPD needs provisions for accommodating multicast entries in order to enable automatic multicast SA creation. PAD needs to be extended in order to accommodate peers that may take on specific roles in the group. Such roles can be GCKS, speaker (in case of SSM) or just a member. It may also contain root certificates for PKI used by the group. 4.1.2.1 Anti-Replay for Multi-Sender SAs TBD 4.1.3 PAD 4.1.3.1 GKMP/IPsec Interactions with the PAD The RFC2401-bis section 4.4.3 introduced the Peer Authorization Database (PAD). In summary, the PAD manages the IPsec entity authentication mechanism(s) and authorization of each such peer identity to negotiate modifications to the SPD/SAD. Within the context of the GKMP/IPsec subsystem, the PAD defines for each group: Weis Expires December, 2005 [Page 6]
The Use of RSA Signatures with ESP and AH June, 2005 . For those groups that authenticate identities using a Public Key Infrastructure, the PAD contains the group's set of one or more trusted root public key certificates. The PAD may also include the PKI configuration data needed to retrieve supporting certificates needed for an end entity's certificate path validation. . A set of one or more group membership authorization rules. The GCKS examines these rules to determine a candidate group member's acceptable authentication mechanism and to decide whether that candidate has the authority to join the group. . A set of one or more GKCS role authorization rules. A group member uses these rules to decide which systems are authorized to act as a GCKS for a given group. These rules also declare the permitted GCKS authentication mechanism(s). . A set of one or more Group Speaker role authorization rules. A GCKS uses these rules to authorize candidate group members that request the speaker privilege. For an authorized speaker, the GCKS creates a GSA description, and a subsequent RKE multicast configures that speaker's GSA in the group SPD/SAD. Some GKMP (e.g. GSAKMP) distribute their group's PAD configuration in a security policy token [COREPT] signed by the group's policy authority, also known as the "Group Owner" (GO). The GCKS re-key multicast includes the current policy token. At each of the group's endpoints, the GKMP subsystem is statically pre-configured with the Group Owner's signature public key certificate or else the information needed to acquire that certificate. All authorized group members receive the GCKS re-key multicast and verify the Group Owner's signature on the revised policy token. If that GO signature is accepted, then all group members dynamically update their respective PAD with the policy token's contents. All compliant IPsec subsystems MUST provide a trusted mechanism for a GKMP subsystem to update the PAD's per group configuration as described in the above list. The details of that trusted mechanism are implementation-specific and they are outside the scope of this standardization. The PAD MUST provide a management interface capability that allows an administrator to enforce that the scope of a GKMP group's policy specified SPD/SAD modifications are restricted to only those traffic data flows that belong to that group. This authorization MUST be configurable at GKMP group granularity. In the inverse direction, the PAD management interface MUST provide a mechanism(s) to enforce that IKE-v2 security associations do not negotiate traffic selectors that conflict or override GKMP group policies. An implementation SHOULD offer PAD configuration capabilities that authorize the GKMP policy configuration mechanism to set security policy for other aspects of an endpoint's SPD/SAD configuration, not confined to its group security associations. This capability allows the group's policy to Weis Expires December, 2005 [Page 7]
The Use of RSA Signatures with ESP and AH June, 2005 inhibit the creation of back channels that might otherwise leak confidential group application data. This document refers to re-key mechanisms as being multicast because of the inherent scalability of IP multicast distribution. However, there is no particular reason that re-key mechanisms must be multicast. For example, [ZLLY03] describes a method of re-key employing both unicast and multicast messages. 4.1.4 GSA A IPsec implementation supporting these extensions has a number of security associations: one or more IPsec SAs, and one or more group key management SAs used to download IPsec SAs [RFC3740, Section 4]. These SAs are collectively referred to as a GSA. 4.1.4.1 Concurrent GSA Life Spans and Re-key Rollover During a cryptographic group's lifetime, multiple group security associations can exist concurrently. This occurs principally due to two reasons: - There are multiple Group Speakers authorized in the group, each with its own GSA that maintains anti-replay state. A group that does not rely on IP Security anti-replay services can share one GSA for all of its Group Speakers. - The life spans of a Group Speaker's two (or more) GSA are allowed to overlap in time, so that there is continuity in the multicast data stream across group re-key events. This capability is referred to as "re-key rollover continuity". Each group re-key multicast message sent by a GCKS signals the start of a new Group Speaker time epoch, with each such epoch having an associated GSA. The group membership interacts with these GSA as follows: - As a precursor to the Group Speaker beginning its re-key rollover continuity processing, the GCKS periodically multicasts a Re-Key Event (RKE) message to the group. The RKE multicast contains group membership management directives (e.g. LKH), a new Group Traffic Protection Key (GTPK), and for some GKMP the RKE may include a revised group policy token. In the absence of a reliable multicast transport protocol, the GCKS may re-transmit the RKE a policy defined number of times to improve the availability of re-key information. - The RKE multicast configures the group's SPD/SAD with the new "leading edge" GSA state information. The leading edge GSA allocates a new Security Parameter Index and it is keyed by the GTPK distributed by the most recent RKE multicast. For a short Weis Expires December, 2005 [Page 8]
The Use of RSA Signatures with ESP and AH June, 2005 period after the GCKS multicasts the RKE, a Group Speaker does not transmit data using the leading edge GSA. Meanwhile, the Group Receiver endpoints prepare to use this GSA by installing the RKE directed changes to their respective SPD/SAD. - After waiting a sufficiently long enough period such that all of the Group Receiver endpoints have processed the RKE multicast, the Group Speaker begins to transmit using the leading edge GSA with its data encrypted by the new GTPK. Only authorized Group Members can decrypt these GSA multicast transmissions. The time delay that a Group Speaker waits before starting its first leading edge GSA transmission is a GKMP/IPsec policy parameter. This value SHOULD be configurable at the Group Owner management interface on a per group basis. - The Group Speaker's "trailing edge" GSA is the oldest group security association in use by the group for that speaker. All authorized Group Receiver endpoints can receive and decrypt data for this GSA, but the Group Speaker does not transmit new data using the "trailing edge" GSA after it has transitioned to the "leading edge GSA". The trailing edge GSA is deleted by the group's endpoints according to group policy (e.g., after a defined period has elapsed)" This re-key rollover strategy allows the group to drain its in transit datagrams from the network while transitioning to the leading edge GSA. Staggering the roles of each respective GSA as described above improves the group's synchronization even when there are high network propagation delays. Note that due to group membership joins and leaves, each Group Speaker time epoch may have a different group membership set. It is a group policy decision whether the re-key event transition between epochs provides forward and backward secrecy. The group's re- key protocol keying material and algorithm (e.g. Logical Key Hierarchy) enforces this policy. Implementations MAY offer a Group Owner management interface option to enable/disable re-key rollover continuity for a particular group This specification requires that a GKMP/IPsec implementation MUST support at least two concurrent GSA per Group Speaker and this re-key rollover continuity algorithm. 4.2 Data Origin Authentication As defined in [RFC2401BIS], data origin authentication is a security service that verifies the identity of the claimed source of data. While HMAC authentication methods are to used to provide data origin authentication, they are not sufficient to provide data origin authentication for groups. With an HMAC, every group member can use the HMAC key to create a valid authentication tag whether or not they are the authentic origin. Weis Expires December, 2005 [Page 9]
The Use of RSA Signatures with ESP and AH June, 2005 When the property of data origin authentication is required for an IPsec SA distributed from a GKMP, an authentication transform where the originator keeps a secret should be used. Two possible algorithms are TESLA [RFC4082] or RSA [W05]. In some cases, (e.g., RSA) the processing cost of the algorithm is significantly greater than an HMAC authentication method. To protect against denial of service attacks from device that is not authorized to join the group, the IPsec SA using this algorithm may be encapsulated with an IPsec SA using an HMAC authentication algorithm. However, doing so requires the packet to be sent across the IPsec boundary for additional inbound processing [RFC2401BIS, Section 5.2]. 4.3 Group SA and Key Management 4.3.1 Co-Existence of Multiple Key Management Protocols Often, the GKMP will be introduced to an existent IPsec subsystem as a companion key management protocol to IKE-v2 [IKE-v2]. A fundamental GKMP IP Security subsystem requirement is that both the GKMP and IKE- v2 can simultaneously share access to a common Security Policy Database and Security Association Database. The mechanisms that provide mutually exclusive access to the common SPD/SAD data structures are a local matter. This includes the SPD-outbound cache and the SPD-inbound cache. However, implementers should note that IKE-v2 SPI allocation is entirely independent from GKMP SPI allocation because group security associations are qualified by a destination multicast IP address and may optionally have a source IP address qualifier. See [RFC2406-bis] section 2.1 for further explanation. The Peer Authorization Database does require explicit coordination between the GKMP and IKE-v2. Section X.Y describes these interactions. This document discusses the coordination of multiple GKMP group owner and endpoint local management systems in section 4.11. 5.0 IP Traffic Processing Processing of traffic follows [RFC2401BIS, Section 5], with the additions described below when these IP multicast extensions are supported. 5.1 Outbound IP Multicast Traffic Processing If an IPsec SA is marked as supporting tunnel mode with address preservation (as described in Section 3.0), either or both of the outer header source or destination addresses is marked as being preserved. If the source address is marked as being preserved, during header construction the "src address" header field MUST be "copied from inner hdr" rather than "constructed" as described in [RFC2401BIS]. Similarly, If the destination address is marked as Weis Expires December, 2005 [Page 10]
The Use of RSA Signatures with ESP and AH June, 2005 being preserved, during header construction the "dest address" header field MUST be "copied from inner hdr" rather than "constructed". 5.2 Inbound IP Multicast Traffic Processing If an IPsec SA is marked as supporting tunnel mode with address preservation (as described in Section 3.0), the marked address (i.e., source and/or destination address) on the outer IP header MUST be verified to be the same value as the inner IP header. If the addresses are not consistent, the IPsec system MUST treat the error in the same manner as other invalid selectors, as described in [RFC2401BIS, Section 5.2]. In particular the IPsec system MUST discard the packet, as well as treat the inconsistency as an auditable event. 5.0 Networking Issues 5.1 Network Address Translation With the advent of NAT and mobile Nodes, IPsec multicast applications must overcome several architectural barriers to their successful deployment. This section surveys those problems and identifies the SPD/SAD state information that the GKMP must synchronize across the group membership. 5.1.1 SPD Losses Synchronization with Internet Layer's State The most prominent problem facing GKMP IPsec is that the GKMP group security policy mechanism can inadvertently configure the group's SPD traffic selectors with unreliable transient IP addresses. The IP addresses are transient because of either Node mobility or Network Address Translation (NAT), both of which can unilaterally change a multicast speaker's source IP address without signaling the GKMP. The absence of a SPD synchronization mechanism can cause the group's data traffic to be discarded rather than processed correctly. 5.1.1.1 Mobile Multicast Care-Of Address Route Optimization Both Mobile IP-v4 [RFC3344] and Mobile IP-v6 [MIPV6] provide transparent unicast communications to a mobile Node. However, comparable support for secure multicast mobility management is not specified by these standards. The goal is the ability to maintain an end-to-end transport mode group SA between a Group Speaker mobile node that has a volatile care-of-address and a Group Receiver membership that also may have mobile endpoints. In particular, there is no secure mechanism for route optimization of the triangular multicast path between the correspondent Group Receiver Nodes, the home agent, and the mobile Node. Any proposed solution must be secure against hostile re-direct and flooding attacks. Weis Expires December, 2005 [Page 11]
The Use of RSA Signatures with ESP and AH June, 2005 5.1.1.2 NAT Translation Mappings Are Not Predictable The following spontaneous NAT behaviors adversely impact source- specific secure multicast groups. When a NAT gateway is on the path between a Group Speaker endpoint residing behind a NAT and a public IP-v4 multicast Group Receiver, the NAT gateway alters the private source address to a public IP-v4 address. This translation must be coordinated with every Group Receiver's inbound Security Policy Database (SPD) multicast entries that depend on that source address as a traffic selector. One might mistakenly assume that the GC/KS could set up the group endpoints with a SPD entry that anticipates the value(s) that the NAT translates the packet's source address. However, there are known cases where this address translation can spontaneously change without warning: - NAT gateways may re-boot and lose their address translation state information. - The NAT gateway may de-allocate its address translation state after an inactivity timer expires. The address translation used by the NAT gateway after the resumption of data flow may differ than that known to the SPD selectors at the group endpoints. - The GC/KS may not have global consistent knowledge of a group endpoint's current public and private address mappings due to network errors or race conditions. For example, an endpoint's address may change due to a DHCP assigned address lease expiration. - Alternate paths may exist between a given pair of group endpoints. If there are parallel NAT gateways along those paths, then the address translation state information at each NAT gateway may produce different translations on a per packet basis. The consequence of this problem is that the GC/KS can not be pre- configured with NAT mappings, as the SPD at the group's endpoints will lose synchronization as soon as a NAT mapping changes due to any of the above events. In the worst case, group endpoints in different sections of the Internet will see different NAT mappings, because the multicast packet traversed multiple NAT gateways. 5.1.2 Secondary Problems Created by NAT Traversal 5.1.2.1 SSM Routing Dependency on Source IP Address Source-Specific Multicast (SSM) routing depends on a multicast packet's source IP address and multicast destination IP address to make a correct forwarding decision. However, a NAT gateway alters that packet's source IP address as its passes from a private network into the public Internet. Mobility changes a Node's point of attachment to the Internet, and this will change the packet's source IP address. Regardless of why it happened, this alteration in the Weis Expires December, 2005 [Page 12]
The Use of RSA Signatures with ESP and AH June, 2005 source IP address makes it infeasible for transit multicast routers in the public Internet to know which SSM speaker originated the multicast packet, which in turn selects the correct multicast forwarding policy. 5.1.2.2 ESP Cloaks Its Payloads from NAT Gateway When traversing NAT, application layer protocols that contain IP-v4 addresses in their payload need the intervention of an Application Layer Gateway (ALG) that understands that application layer protocol [RFC3027] [RFC3235]. The ALG massages the payload's private IP-v4 addresses into equivalent public IP-v4 addresses. However, when encrypted by end-to-end ESP, such payloads are opaque to application layer gateways. When multiple Group Speaker endpoints reside behind a NAT with a single public IP-v4 address, the NAT gateway can not do UDP or TCP protocol port translation (i.e. NAPT) because the ESP encryption conceals the transport layer protocol headers. The use of UDP encapsulated ESP [UDPESP] avoids this problem. However, this capability must be configured at the GC/KS as a group policy, and it must be supported in unison by all of the group endpoints within the group, even those that reside in the public Internet. 5.1.2.3 UDP Checksum Dependency on Source IP Address A GKMP/IPsec multicast application that uses UDP within an ESP payload will encounter NAT induced problems. The original IP-v4 source address is an input parameter into a receiver's UDP pseudo- header checksum verification, yet that value is lost after the IP header's address translation by a transit NAT gateway. The UDP header checksum is opaque within the encrypted ESP payload. Consequently, the checksum can not be manipulated by the transit NAT gateways. UDP checksum verification needs a mechanism that recovers the original source IP-4 address at the Group Receiver endpoints. In a transport mode multicast application GSA, the UDP checksum operation requires the origin endpoint's IP address to complete successfully. In IKE-v2 [IKE-v2], this information is exchanged between the endpoints by a NAT-OA payload (NAT original address). See also reference [IPSECNAT]. A comparable facility must be exist in a GKMP payload that defines the multicast application GSA attributes for each Group Speaker endpoint. 5.1.2.4 Can Not Use AH with NAT Gateway The presence of a NAT gateway makes it impossible to use an Authentication Header, keyed by a group-wide key, to protect the integrity of the IP header for transmissions between members of the cryptographic group. Weis Expires December, 2005 [Page 13]
The Use of RSA Signatures with ESP and AH June, 2005 5.1.3 Avoidance of NAT Using an IP-v6 Over IP-v4 Network A straightforward and standards-based architecture that effectively avoids the GKMP interaction with NAT gateways is the IP-v6 over IP-v4 transition mechanism [RFC2529]. In IP-v6 over IP-v4 (a.k.a. "6over4"), the underlying IP-v4 network is treated as a virtual multicast-capable Local Area Network. The IP-v6 traffic tunnels over that IP-v4 virtual link layer. Applying GKMP/IPsec in a 6over4 architecture leverages the fact that an administrative domain deploying GKMP/IPsec would already be planning to deploy IP-v4 multicast router(s). The group's IP-v6 multicast routing can execute in parallel to IP-v4 multicast routing on that same physical router infrastructure. In particular, the NAT gateways at administrative domain public/private boundaries are replaced by IP-v6 multicast routers operating with 6over4 mode enabled on their network interfaces. Within the GKMP, all references to IP addresses are IP-v6 addresses for all security association endpoints and these addresses do not change over the group's lifetime. This yields a substantial reduction in complexity and error cases over the NAT-based approaches. This reduction in complexity can translate into better security. Reliable scalable GKMP/IPsec based on 6over4 deployment is far more practical than an IP-v4 with NAT deployment. In particular, new GKMP/IPsec multicast applications SHOULD prefer IP-v6 native mode. However, the GKMP/IPsec architecture supports either choice. The following factors may weigh against the decision to deploy GKMP/IPsec using 6over4: - A drawback of the GKMP/IPsec 6over4 approach is that the secure multicast application must be (re-)written to an IP-v6 multicast socket API or equivalent, and it must interact with the Multicast Listener Discovery (MLD) API [RFC3590] [RFC3678] rather than IGMP. In addition, the application layer protocol itself must embed references to IP-v6 addresses rather than IP-v4 addresses within its payloads. For new applications, this may not be of consequence; it usually only becomes an issue if the application and its protocol has an embedded base. - An embedded base of GKMP/IPsec IP-v4 multicast applications that are only available in binary form will not be able to migrate to these transitional IP-v6 mechanisms. - The secondary drawbacks of GKMP/IPsec using 6over4 are that the IP hosts must be upgraded to dual-stack, the attendant overlay IP-v6 multicast network operational costs, and the perceived difficulty of deploying commercial wide-area IP-v6 multicast services. 5.1.4 GKMP/IPsec Multi-Realm IP-v4 NAT Architecture In a multi-realm group, GKMP/IPsec security association endpoints may straddle any combination of IP-v4 public addresses and private addresses [RFC1918]. In such cases, transport layer endpoint Weis Expires December, 2005 [Page 14]
The Use of RSA Signatures with ESP and AH June, 2005 identifiers when resolved to their underlying private or public IP-v4 addresses entangle the GKMP protocol with NAT gateway behaviors. The NAT translation of IP-v4 header addresses impacts the GKMP registration SA, the GKMP re-key GSA, and the secure multicast application GSA. This section overviews the GKMP/IPsec mechanisms that partially mitigate the inherent complexity spawned by IP-v4 NAT and Network Address Protocol Translation (NAPT) traversal. However, the attendant Group Owner configuration procedures are labor-intensive, prone to configuration mismatch errors between the GC/KS and NAT gateways, and they do not scale well to large groups. Given the large number of documented NAT problems and its erosion of end-to-end security, new GKMP/IPsec applications and deployments SHOULD strongly prefer the use of IP-v6. Section X.Y offers IP-v4 to IP-v6 transitional guidance in support of that objective. 5.1.4.1 GKMP/IPsec IP-v4 NAT Architectural Assumptions To make the multi-realm GKMP/IPsec IP-v4 NAT interaction problem tractable to a solution, this specification requires the following simplifying assumptions: - The secure multicast group destination address is a statically allocated public IP-v4 multicast address known to all group endpoints. - Wherever they are present in the GKMP, group endpoint addresses are expressed as permanent IP-v6 "6to4" addresses [RFC3056] to assure that the group endpoints that refer to hosts assigned private IP-v4 addresses are globally unique. In this context, a "permanent" 6to4 address means that the address is constant for the group's lifetime. - Each private IP-v4 address space has one or more NAT gateways directly connected to the IP-v4 public Internet, and a packet does not have to traverse multiple private networks to reach the public Internet. This can be thought of as a "spoke and hub" configuration wherein the public Internet is the hub. - A GC/KS may reside within one of the private networks, but it also MUST have a permanent public IP-v4 address on at least one of its network interfaces. This requirement applies to both the Primary- GC/KS and all of the group's Subordinate-GC/KS. - GKMP/IPsec group security associations are end-to-end transport mode. However, since the one or more GC/KS are constrained to straddle a public/private network boundary, they effectively terminate the GSA at a combined NAT/security gateway [RFC2709]. Weis Expires December, 2005 [Page 15]
The Use of RSA Signatures with ESP and AH June, 2005 - The GC/KS domain name RR record should point to that public IP-v4 address, and it is recommended that it be protected by DNS-SEC. - Each of an administrative domain's NAT gateways are explicitly configured with static private/public address translation mappings for the GC/KS's GKMP re-key multicast ESP protected UDP packets inbound from the public Internet [RFC2588]. - The NAT gateways/firewalls are explicitly configured with stateless filter rules that simply pass through without any address translation the group's inbound multicast application packets arriving from the public Internet. The NAT gateway does not translate the multicast application packet's public multicast IP destination address into a private IP multicast address. - In the outbound direction, NAT gateways generally translate the multicast application packet's private source IP address into a dynamically selected public IP address. Exceptions to this policy for source specific multicast are noted in subsequent sections. - Within each administrative domain, a multicast routing protocol domain routes packets based on the group's destination multicast public IP-v4 address. The multicast routers will distribute the group's packets to all of the group's Group Receiver endpoints residing in that administrative domain. - The border routers of each of the administrative domains spanned by the group do cross-realm multicast routing and distribution on behalf of the group. The IP-v4 multicast routers that exchange reachability information regarding the group across trust boundaries authenticate that information. Weis Expires December, 2005 [Page 16]
The Use of RSA Signatures with ESP and AH June, 2005 "A" Admin . ISP Admin . "B" Admin Domain . Domain . Domain . . +---------------.--------------.-------------------+ | . . | | P U B L I C . I P - v 4 . I N T E R N E T | | . . | +------/\-------.-----A-----A--.----/\--------/\---+ || public. | | . || public || || IP-v4 . | | . || IP-v4 || +------\/------+. | | .+---\/---+ +--\/---+ |Grp.Z |NAT "A"|. | | .|Group Z | |NAT "B"| |S-GCKS|gateway|. | | .|P-GC/KS | |gateway| +---A--+---A---+. | | .+---A----+ +--A----+ | | .registratn | . | | regist. SA| . SA | . regist. SA | | | . | | . | | +-V-+ | . +-V-+ | . +-V-+ | |GM1| | . |GM2| | . |GM3| | +-A-+ | . +-A-+ | . +-A-+ | | | . | | . | | Group data SA . Group data SA. Group data SA rekey SA . rekey SA . and rekey SA | | . | | . | | +-V------V--+ . +---V-----V-+.+---V---------V-+ | Group "Z" | . | Group "Z" |.| Group "Z" | | multicast | . | multicast |.| multicast | | routing | . | routing |.| routing | | domain | . | domain |.| domain | +-----------+ . +-----------+.+---------------+ . . Figure 2 Representative GKMP/NAT architecture 5.1.4.2 Representative GKMP Multi-Realm Configuration Figure 2 illustrates a representative group "Z" wherein a GKMP/IPsec group security association spans two private IP-v4 networks and the public IP-v4 Internet. The Group "Z" GC/KS has two network interfaces, one attached to the public Internet and the other interface attached to the administrative domain "B" private network. The group member GM1 resides within the administrative domain "A" private network. It communicates with the group Z Group Speaker endpoint(s) through the administrative domain "A" NAT gateway. When GM1 multicasts application SA traffic to the group Z public multicast address, the Group Z peer members (i.e. GM2, and GM3) receive that multicast with the source address translated by NAT gateway "A" processing. In the inverse direction, the administrative domain "A" NAT gateway/firewall must be configured to allow Group Z multicast Weis Expires December, 2005 [Page 17]
The Use of RSA Signatures with ESP and AH June, 2005 application GSA traffic to enter the private network "A" from the public Internet (e.g. a multicast originating from GM3). The group member GM3 resides within the administrative domain "B" private network. Its interactions with Group Z are very similar to those discussed for member GM1. It uses private addresses when communicating with the P-GC/KS, as it is in private network "B". The group member GM2 is in a public Internet administrative domain operated by an ISP. It communicates with the P-GC/KS using public IP- v4 addresses without passage through a NAT gateway. When GM2 multicasts application SA traffic to the group Z public multicast address, the Group Z peer members behind NAT gateways receive that multicast with the source address unchanged by NAT processing. Each administrative domain operates an IP-v4 multicast routing domain instance. The multicast routers distribute both GKMP re-key messages and multicast application GSA data traffic. The multicast routing for group "Z" peers between these three multicast routing domains. 5.1.4.3 Registration Security Association NAT Traversal The GKMP registration protocol's unicast messages are exchanged between a GC/KS in the public IP-v4 Internet and a candidate Group Member that may be in a private network. A group member sends a registration SA GKMP message to the GC/KS public IP-v4 address and the GKMP reserved port number. The group member assigns a unique GKMP UDP source port number for each GKMP registration SA that it participates in. The group member SHOULD send the GKMP UDP packet without a checksum to avoid NAT alterations to that field. The UDP packet's transmission error detection depends on the GKMP signature within the payload. A NAT gateway on the path leading to the GC/KS translates the private source IP address and source UDP port number into a public address and a temporary UDP port number (assuming NAPT), then forwards the packet to the GC/KS. The NAT gateway creates state information for that public/private address mapping so it can do the inverse translation on the GKMP messages sent from the GC/KS to that group member. The GC/KS must process the GKMP messages that it receives from group members originating from any source IP address or source port number, even if those two values have changed since the last time that the GC/KS had interacted with a given group member. To identify the group member, the GC/KS MUST use the GKMP signature payload's identifying information and validate the message's digital signature. After processing a message from a group member that requires a GC/KS response, the GC/KS creates the GKMP UDP message destined for the same IP-v4 address and UDP port that the GC/KS found in the candidate Group Member message's source IP address and UDP source port. Weis Expires December, 2005 [Page 18]
The Use of RSA Signatures with ESP and AH June, 2005 5.1.4.4 GKMP Re-key GSA NAT Traversal The GKMP Re-Key GSA is considerably simplified by the constraint that every Subordinate-GC/KS and Primary-GC/KS MUST straddle a public Internet/private network boundary adjacent to wherever it has Group Members behind a NAT gateway. Consequently, a GC/KS may have Group Members on either side of that boundary, but there is no intervening NAT gateway tampering with the GC/KS transmissions. The GC/KS multicasts the GKMP re-key message to the Re-Key GSA in an ESP protected UDP|GKMP packet addressed to its (sub-)group's destination public IP-v4 multicast address. The UDP destination port is set to the GKMP-UDP reserved port number. The group keyed ESP authenticator protects the UDP payload, so a UDP checksum MUST NOT be used. A multi-realm IP-v4 GKMP/IPsec group operates in autonomous distributed mode. Therefore, each of the group's Subordinate-GC/KS must relay to their respective sub-group membership the GTEK (and policy token, if any) that it extracts from the Primary-GC/KS rekey multicast. The S-GC/KS sends its re-key message to its sub-group membership from its public Internet interface. 5.1.4.5 Multicast Application GSA NAT Traversal Unlike the GKMP rekey message multicast to the Re-Key GSA, a multicast application message sent to the group may originate from a Group Speaker endpoint located behind a NAT gateway. Since the application's message is encrypted within an ESP payload, the transport layer protocol header port fields are concealed from NAT gateways and they can not participate in NAPT. The multicast application GSA must be handled differently depending on whether the application requires source-specific multicast. If the application requires source-specific multicast routing, then there must be a separate public IP-v4 address statically reserved at the NAT gateway for each Group Speaker endpoint private/public address mapping. This constraint allows the GC/KS to specify at every Group Member the inbound SPD traffic selector with a pre-determined public source address for each Group Speaker endpoint in the group. The traffic selector's public source address in combination with the group's destination multicast address and SPI selects the inbound SA. Keeping the NAT gateway's source address mapping static rather than dynamic also allows the multicast routers along the packet's path to apply source-specific routing policies. Note that the use of a static source address mapping NAT avoids the need for the group's policy token to specify UDP encapsulated ESP. The drawback of this approach is that the GC/KS SPD/SAD configuration database must be kept synchronized with the group's NAT gateway address mapping configurations. These operational procedures can be labor-intensive and error-prone, making large-scale group deployments difficult. A Weis Expires December, 2005 [Page 19]
The Use of RSA Signatures with ESP and AH June, 2005 more sophisticated GKMP may sidestep this problem by dynamically setting the Group Receiver endpoint's SPD/SAD entry traffic selector rather than relying on static GC/KS configuration. If the application requires the any-source multicast service model, then the NAT gateway's source address translation can use dynamically allocated public IP-v4 addresses rather than statically allocated IP- v4 addresses. However, unless the group uses UDP encapsulated ESP, then the NAT gateway must have a pool of public IP-v4 addresses reserved that is at least as large as the number of Group Speaker endpoints within its private network. The public IP address pool allows the NAT gateway to do a one-to-one mapping from every Group Speaker endpoint's private source address to a dynamically allocated public source address. In this case, the use of NAPT rather than NAT is not an option, since the transport layer protocol is within an opaque ESP payload. The GC/KS specifies the SPD/SAD traffic selector as the combination of the group's destination multicast address and the SPI. In some deployments, the number of public IP-v4 addresses assigned to a NAT gateway is very limited (e.g. only one public IP-4 address). Also, it may be difficult to predict how many Group Speaker endpoints will reside within the private network before the group begins its operation. For these cases, the group MAY use UDP encapsulated ESP. The NAT gateway applies NAPT to the UDP header's source port field, sidestepping the constraint of its limited public IP-v4 address pool. The Group Owner modifies the group policy token to specify that the outbound SPD processing must pre-append a UDP header in front of the ESP header. When a Group Speaker endpoint originates a multicast application packet, it inserts a UDP header in front of the ESP header, as per reference [UDPESP]. 6.0 Security Considerations [TBD] 7.0 Acknowledgements [TBD] 8.0 Appendix A - Multicast Application Service Models The vast majority of secure multicast applications can be catalogued by their service model and accompanying intra-group communication patterns. Both the Group Key Management Protocol (GKMP) Subsystem and the IPsec subsystem MUST be able to configure the SPD/SAD security policies to match these dominant usage scenarios. The SPD/SAD policies MUST include the ability to configure both Any-Source- Multicast groups and Source-Specific-Multicast groups for each of these service models. The GKMP Subsystem management interface MAY include mechanisms to configure the security policies for service models not identified by this standard. Weis Expires December, 2005 [Page 20]
The Use of RSA Signatures with ESP and AH June, 2005 8.1 Unidirectional Multicast Applications Multi-media content delivery multicast applications that do not have congestion notification or retransmission error recovery mechanisms are inherently unidirectional. RFC2401-bis only defines bi- directional unicast security associations (as per sections 4.4.1 and 5.1 with respect to security association directionality). The GKMP Subsystem requires that the IPsec subsystem MUST support unidirectional Group Security Associations (GSA). Multicast applications that have only one group member authorized to transmit can use this type of group security association to enforce that group policy. In the inverse direction, the GSA does not have a SAD entry, and the SPD configuration is optionally setup to discard unauthorized attempts to transmit unicast or multicast packets to the group. The GKMP Subsystem's Group Owner management interface MUST have the ability to setup a GKMP Subsystem group having a unidirectional GSA security policy. 8.2 Bi-directional Reliable Multicast Applications Some secure multicast applications are characterized as one group speaker to many receivers, but with inverse data flows required by a reliable multicast transport protocol (e.g. NORM). In such applications, the data flow from the speaker is multicast, and the inverse flow from the group's receivers is unicast to the speaker. Typically, the inverse data flows carry error repair requests and congestion control status. For such applications, the GSA SHOULD use IPsec anti-replay protection service for the speaker's multicast data flow to the group's receivers. Because of the scalability problem described in the next section, it is not practical to use the IPsec anti-replay service for the unicast inverse flows. Consequently, in the inverse direction the IPsec anti-replay protection MUST be disabled. However, the unicast inverse flows can use the group's IPsec group authentication mechanism. The group receiver's SPD entry for this GSA SHOULD be configured to only allow a unicast transmission to the speaker Node rather than a multicast transmission to the whole group. If ESP RSA signature mechanism is available, source authentication MAY be used to authenticate a receiver Node's transmission to the speaker. The GKMP MUST define a key management mechanism for the group speaker to validate the asserted signature public key of any receiver Node without requiring that the speaker maintain state about every group receiver. This multicast application service model is RECOMMENDED because it includes congestion control feedback capabilities. Refer to [RFC2914] for additional background information. Weis Expires December, 2005 [Page 21]
The Use of RSA Signatures with ESP and AH June, 2005 The GKMP Subsystem's Group Owner management interface MUST have the ability to setup a GKMP Subsystem GSA having a bi-directional GSA security policy and one group speaker. The management interface SHOULD be able to configure a group to have at least 16 concurrent authorized speakers, each with their own GSA anti-replay state. 8.3 Any-To-Any Multicast Applications Another family of secure multicast applications exhibits a "any to many" communications pattern. A representative example of such an application is a videoconference combined with an electronic whiteboard. For such applications, all (or a large subset) of the group's endpoints are authorized multicast speakers. In such service models, creating a distinct GSA with anti-replay state for every potential speaker does not scale to large groups. The group SHOULD share one GSA for all of its speakers. The GSA SHOULD NOT use IPsec anti-replay protection service for the speaker's multicast data flow to the group's listeners. The GKMP Subsystem's Group Owner management interface MUST have the ability to setup a group having an Any-To-Many Multicast GSA security policy. 9.0 References 9.1 Normative References [AH] Kent, S., "IP Authentication Header", draft-ietf-ipsec- rfc2402bis-10.txt, December 2004. [ESP] Kent, S., "IP Encapsulating Security Payload (ESP)", draft- ietf-ipsec-esp-v3-09.txt, September 2004. [RFC1112] Deering, S., "Host Extensions for IP Multicasting," RFC 1112, August 1989. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Level", BCP 14, RFC 2119, March 1997. [RFC2401BIS] Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", draft-ietf-ipsec-rfc2401bis-06.txt, March, 2005. [RFC3552] E. Rescorla, et. al., "Guidelines for Writing RFC Text on Security Considerations", RFC 3552, July 2003. 9.2 Informative References [IKEV2] C. Kaufman, "Internet Key Exchange (IKEv2) Protocol", draft- ietf-ipsec-ikev2-17.txt, September 23, 2004. Weis Expires December, 2005 [Page 22]
The Use of RSA Signatures with ESP and AH June, 2005 [RFC2526] D. Johnson, S. Deering., "Reserved IPv6 Subnet Anycast Addresses", RFC 2526, March, 1999. [RFC2914] S.Floyd, "Congestion Control Principles", RFC2914, September 2000. [RFC3171] Z. Albanni, et. al., "IANA Guidelines for IPv4 Multicast Address Assignments", RFC 3171, August, 2001. [RFC2362] Estrin, D., et. al., "Protocol Independent Multicast-Sparse Mode (PIM-SM): Protocol Specification", RFC 2362, June, 1998. [RFC3376] B. Cain, et. al., "Internet Group Management Protocol, Version 3", RFC 3376, October, 2002. [RFC3547] Baugher, M., Weis, B., Hardjono, T., and H. Harney, "The Group Domain of Interpretation", RFC 3547, December 2002. [RFC3569] S. Bhattacharyya, "An Overview of Source-Specific Multicast (SSM)", RFC 3569, July, 2003. [RFC3940] B. Adamson, et. al., "Negative-acknowledgment (NACK)- Oriented Reliable Multicast (NORM) Protocol", RFC 3940, November, 2004. [RFC4082] A. Perrig, et. al., "Timed Efficient Stream Loss-Tolerant Authentication (TESLA): Multicast Source Authentication Transform Introduction", RFC 4082, June 2005. [W05] B. Weis, "The Use of RSA/SHA-1 Signatures within ESP and AH", draft-ietf-msec-ipsec-signatures-06.txt, June 2005. [ZLLY03] X. Zhang, et. al., "Protocol Design for Scalable and Reliable Group Rekeying", IEEE/ACM Transactions on Networking (TON), Volume 11, Issue 6, December 2003. See http://www.cs.utexas.edu/users/lam/Vita/Cpapers/ZLLY01.pdf. Weis Expires December, 2005 [Page 23]
The Use of RSA Signatures with ESP and AH June, 2005 Author's Address Brian Weis Cisco Systems 170 W. Tasman Drive, San Jose, CA 95134-1706, USA (408) 526-4796 bew@cisco.com George Gross IdentAware Security 82 Old Mountain Road Lebanon, NJ 08833 908-268-1629 gmgross@identaware.com Dragan Ignjatic Polycom 1000 W. 14th Street North Vancouver, BC V7P 3P3 Canada tel: +1 604 982 3424 email: dignjatic@polycom.com Full Copyright Statement Copyright (C) The Internet Society (2005). 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. 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. Intellectual Property 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. Weis Expires December, 2005 [Page 24]
The Use of RSA Signatures with ESP and AH June, 2005 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. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Weis Expires December, 2005 [Page 25]
