INTERNET DRAFT Jeffrey Lo Expires July 1999 NEC USA Michael Borella David Grabelsky 3Com Corp Realm Specific IP: A Framework 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 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 This document examines the general framework of Realm Specific IP (RSIP). All RSIP solutions must solve the same set of problems, and all RSIP-related proposals to date are similar in many ways. We attempt to enumerate the similarities and differences of these proposals, and expand the scope of RSIP to include several other possible mechanisms. We do not advocate any one RSIP solution over the other; instead, we present these solutions in the hope to clarify RSIP issues and generate further discussion towards adoption of RSIP. 1. Introduction While NAT has become a popular mechanism of sharing IP addresses amongst a number of hosts, it suffers from a lack of flexibility. In particular, a NAT router must examine and change the network and Lo et. al. Expires August 1999 [Page 1] INTERNET DRAFT Realm Specific IP: Framework February 1999 possibly the transport layer headers of each packet to or from the NAT subnet(s) sharing its IP address(es). This causes NAT to break the end-to-end nature of Internet connectivity, and disrupts network layer]] security protocols, such as IPSec. Furthermore, any application that transmits IP address or port content, such as FTP, will require a proxy module within the NAT router. Given these limitations, RSIP has emerged as an attempt to avoid the worst complications of NAT. RSIP is based on the concept of granting host from one realm (e.g., privately addressed realm) a presence in another realm (e.g., globally addressed realm) by granting it resources from the second realm. While this document is limited to the discussion of IPv4 networks, RSIP is general and may be applied well beyond the limitations of IPv4 networks, such as IPv4/IPv6 translators. In this document we discuss the approaches of several possible RSIP systems and address the issues that any RSIP solution must face. Since, at this preliminary stage, we most likely have missed out certain issues in the implementation of RSIP, we welcome thoughts and comments from the experienced. 2. Terminology Private Realm A routing realm in which RSIP hosts assumes temporary presence in another realm, the global realm. Examples of private realms are privately addressed (10/8, 172.16/12, 192.168/16) IPv4 realms or private IPv4 realms within IPv6 networks. Global Realm A routing realm with unique network addressed assigned by Internet Assigned Number Authority (IANA) or an equivalent address registry. RSIP-server An entity situated on the boundary between a private realm and a global realm which is responsible for global parameter management and assignment to RSIP-clients. In all cases, an RSIP-server may act as a normal NAT box at the same time for hosts within the private realm that are not RSIP enabled. RSIP-client An entity within the private realm that assumes globally unique parameters from the RSIP server through the use of RSIP. Lo et. al. Expires August 1999 [Page 2] INTERNET DRAFT Realm Specific IP: Framework February 1999 All other terminology found in this document is consistent with that of [1]. 3. Specification of Requirements The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this documents are to be interpreted as described in RFC 2119. 4. Architecture In a typical scenario where RSIP is deployed, there is some number of hosts in the private realm without globally-routable IP addresses connected to the global realm by the RSIP server. The hosts are likely to use private addresses from the range assigned by IANA (10/8, 172.16/12 and 192.168/16), while the RSIP server is multi- homed with one or more private addresses from this range and one or more publicly-routable addresses. The RSIP-server may act as a normal NAT device while at the same time facilitating RSIP implementations by dynamically carrying out global resource and/or parameter negotiation and assignments with RSIP- clients. Using the global parameters assigned by the RSIP-server, RSIP-clients route (usually tunnel) data packets to the RSIP-server within the private realm. If tunneling is used, the RSIP-server acts as the end point of such tunnels, stripping off the outer headers and routing the inner packets onto the global realm. An RSIP-server maintains a mapping of the demultiplexing tuples to RSIP-client private addresses, such the mapping can be used to demultiplex data traffic to RSIP-clients. 5. RSIP Fundamentals We discuss the issues that all RSIP schemes must address in this section. Note that these issues are not orthogonal; thus, by addressing one, in some cases another issue is also addressed sufficiently. 5.1. Negotiation and/or determination of Demultiplexing Fields Assume that an RSIP-client within a private realm has transmitted a request to a public server within a global realm, and the server has sent a response packet that successfully arrived at the RSIP server. Based on a pre-arranged mapping, the RSIP-server must be able to determine the private IP address of the packet's destination; i.e., the RSIP-client. The only information that the RSIP-server may use is what is already contained within the headers of the inbound data packet. We will refer to these header Lo et. al. Expires August 1999 [Page 3] INTERNET DRAFT Realm Specific IP: Framework February 1999 fields as the "demultiplexing fields" as they are used to spread the incoming streams of packets to multiple destinations within the private realm. Depending on the type of mapping used by the RSIP server, demultiplexing parameters could either be global IPv4 addresses or port. Demultiplexing of incoming streams of packet require pre- assignment of the demultiplexing fields to RSIP clients. Hence there exist a requirement for a negotiation process that enable these parameters to be negotiated between RSIP server and RSIP clients. Such a negotiation process can be based on the following approaches. As an extension of current host configuration or policy protocols such as DHCP, COPS, RADIUS, DIAMETER, or SOCKS. During tunnel establishment, for example as an extension to L2TP parameter negotiation. As a specialized RSIP-specific protocolm such as described in [2]. 5.2. Determination of other RSIP parameters Apart from negotiation of demultiplexing parameters, other information pertaining to the assignment of those demultiplexing fields may also need to be negotiated. Examples of such parameters are: A binding identifier may be assigned for each global parameter assignment. The binding identifier serves to uniquely identify the resource that has been allocated by an RSIP server. It may also be used during lookup to efficiently index existing bindings. A time duration may be associated with each bind of global parameters to a RSIP clients. If such time information are used, it has to be negotiated. RSIP-clients may require that the RSIP-server specify how it allocates address and port resources. RSIP-servers may only allocate a global IP address to each unique host, resulting in a Basic-NAT-like operation. Or, RSIP-servers may distribute a (potentially shared) global IP address and a unique port range per that IP address to eachhost, resulting in a NAPT-like operation. The negotiation and assignment mechanism SHOULD facilitate vendor specific parameters. Lo et. al. Expires August 1999 [Page 4] INTERNET DRAFT Realm Specific IP: Framework February 1999 5.3. Tunnel Use and Establishment RSIP generally requires the use of tunnels within the private realm, between the RSIP clients and the RSIP server. While it is possibly to imagine an RSIP implementation that does not require tunneling, it seems that tunneling is a flexible method for solving a address ambiguity problems. The type of tunnel may be IP-IP, GRE, an IPSEC mode, L2TP, or another form of tunnel. Tunnels may be established statically or dynamically between RSIP clients and servers. A static tunnel is established at host boot and remains in service until the host is no longer using the network. A dynamic tunnel is established at the beginning of a session or flow and exists only for the lifetime of the session. Both types of tunnels may allow for on-the-fly re-negotiation of demultiplexing fields and re-assignment of parameters to RSIP clients. If tunneling is used to route the globally addressed packet within private realm, global parameter negotiation could be associated with tunnel establishment mechanisms. Alternatively, a negotiation protocol may enable the negotiation of tunnel type as well. 5.4. Policy and Accounting Having an RSIP MIB may be useful as a means of pre-configuring RSIP-clients at set up and as a method for introducing RSIP policy. It is particularly valuable in large-scale implementations with thousands of RSIP-clients. In such cases, push technology could be used to update RSIP-clients with the configuration and policy information. All RSIP-clients SHOULD have a mechansims of authenticating themselves to RSIP-servers, in order to alleviate possible denial of service attacks in which a malicious RSIP-client attempts utilize the resources assigned to a different RSIP-client. Any RSIP implementation SHOULD implement accounting of irregular event seen by the RSIP-server. Events such as denial of service attacks, illegal use of resources (traffic without bindings or after binding expirations) and global resource depletion SHOULD be logged. 6. Open Problems The resolution of a number of RSIP issues are still open. Although solutions may exist for these problems, they may have unattractive side effects. In this section we discuss several such issues. Lo et. al. Expires August 1999 [Page 5] INTERNET DRAFT Realm Specific IP: Framework February 1999 6.1. Contacting Internal Servers In order for an RSIP implementation to allow private hosts to run servers that can be contacted from the public network, these servers must be registered with the RSIP server. Registration of servers with unique and/or well known listen ports may be limited to one per private realm. 6.2. Determining Locality of Destinations In general, an RSIP client must know, for a particular IP address, whether it should transmit the packet normally for local delivery, or tunnel the packet to the RSIP-server. Since more than one subnet may be behind an RSIP-server, looking at a local subnet mask will not work. We'd rather not have to propagate routing tables to all RSIP-clients. A simple alternative, proposed in [2], that will solve this problem is to require that the RSIP- server knows all of the subnets that are on the private network This information can be manually entered because it is not expected to change often. Then, if an IP address in question is not on a host's local subnet, the host can query the server with the address. The RSIP server will return a simple "yes or "no" answer - yes, this address is local, or no, it is not. Alternatively, RSIP-clients could send all packets for destinations without an explicit static route to the RSIP server. If they arrive at the RSIP server, it informs the host that it should instead tunnel the packet. The host then acquires the necessary global parameters and tunnels the packet, to the RSIP server. This approach may require further changes to the TCP/IP stack at the host, since, in the case of TCP traffic, a half-open TCP socket must be discarded. Likewise, the RSIP client could at first tunnel the packets to the RSIP server. If the server determines that the destination is local, it would inform the host of this fact and the host could then transmit the packet in the standard fashion. Regardless of the solution chosen, RSIP clients caching the "locality" of recently-contacted IP addresses may be beneficial. 7. Cascaded RSIP It is possible for RSIP to allow for cascading of RSIP-servers. For example, consider an ISP that uses RSIP for address sharing amongst its customers. It might assign resources (e.g., IP addresses and ports) to a particular customer. This customer may further subdivide the port ranges and address(es) amongst individual end hosts. A reference architecture is depicted below. Lo et. al. Expires August 1999 [Page 6] INTERNET DRAFT Realm Specific IP: Framework February 1999 +-----------+ | | | RSIP | | server +---- 10.0.0.0/8 | B | | | +-----+-----+ | | 10.0.1.0/24 +-----------+ | (149.112.240.0/25) | | | 149.112.240.0/24| RSIP +--+ ----------------+ server | | A +--+ | | | +-----------+ | 10.0.2.0/24 | (149.112.240.128/25) | +-----+-----+ | | | RSIP | | server +---- 10.0.0.0/8 | C | | | +-----------+ RSIP-server A is in charge of the IP addresses of subnet 149.112.240.0/24. It distributes these addresses to RSIP-clients and RSIP-servers. In the given configuration, it distributes addresses 149.112.240.0 - 149.112.240.127 to RSIP-server B, and addresses 149.112.240.128 - 149.112.240.254 to RSIP-server C. Note that the subnet broadcast address, 149.112.240.255, must remain unclaimed, so that broadcast packets can be distributed to arbitrary hosts behind RSIP-server A. Also, the subnets between RSIP-server A and RSIP- servers B and C will use private addresses. Due to the tree-like fashion in which addresses will be cascaded, we will refer to RSIP-servers A as the 'parent' of RSIP-servers B and C, and RSIP-servers B and C as 'children' of RSIP-servers A. An arbitrary number of levels of children may exist under a parent RSIP- server. A parent RSIP-server will not necessarily be aware that the address(es) and port blocks that it distributes to a child RSIP- server will be further distributed. Thus, the RSIP-clients MUST tunnel their outgoing packets to the nearest RSIP-server. This server will then verify that the sending host has used the proper address and port block, and then tunnel the packet on to its parent Lo et. al. Expires August 1999 [Page 7] INTERNET DRAFT Realm Specific IP: Framework February 1999 RSIP-server. For example, in the context of the diagram above, host 10.0.0.1, behind RSIP-server C will use its assigned external IP address (say, 149.112.240.130) and tunnel its packets over the 10.0.0.0/8 subnet to RSIP-server C. RSIP-server C strips off the outer IP header. After verifying that the source public IP address and source port number is valid, RSIP-server C will tunnel the packets over the 10.0.2.0/8 subnet to RSIP-server A. RSIP-server A strips off the outer IP header. After verifying that the source public IP address and source port number is valid, RSIP-server A transmits the packet on the public network. While it may be more efficient in terms of computation to have a RSIP-client tunnel directly to the overall parent of an RSIP-server tree, this would introduce significant state and administrative difficulties. A RSIP-server that is a child MUST take into consideration the parameter assignment constraints that it inherits from its parent when it assigns parameters to its children. For example, if a child RSIP-server is given a lease time of 3600 seconds on an IP address, it MUST compare the current time to the lease time and the time that the lease was assigned to compute the maximum allowable lease time on the address if it is to assign the address to a RSIP-client or child RSIP-server. 8. References [1] P. Srisuresh and Matt Holdrege, "IP Network Address Translator (NAT) Terminology and Considerations," , Work in progress [2] Michael Borella, David Grabelsky, Jeffrey Lo and Kuni Taniguchi, "Realm Specific IP: Protocol Specification," , Work in progress. 9. Authors' Addresses Jeffrey Lo NEC USA C&C Research Labs. 110 Rio Robles San Jose, CA 95134 (408) 943 3033 jlo@ccrl.sj.nec.com Michael Borella Lo et. al. Expires August 1999 [Page 8] INTERNET DRAFT Realm Specific IP: Framework February 1999 3Com Corp. Advanced Technologies Research Center 1800 W. Central Rd. Mount Prospect IL 60056 (847) 842 6093 mike_borella@3com.com David Grabelsky 3Com Corp. Advanced Technologies Research Center 1800 W. Central Rd. Mount Prospect IL 60056 (847) 222 2483 david_grabelsky@3com.com Copyright (c) The Internet Society (1999). 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. Lo et. al. Expires August 1999 [Page 9]