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        Network Working Group                                  Ross Callon        Request for Comments: 1347                                     DEC                                                                 June 1992TCP and UDP with Bigger Addresses (TUBA),A Simple Proposal for Internet Addressing and Routing                                Status of the Memo                This memo provides information for the Internet community. It        does not specify an Internet standard. Distribution of this        memo is unlimited.1 Summary                The Internet is approaching a situation in which the current IP        address space is no longer adequate for global addressing        and routing. This is causing problems including: (i) Internet        backbones and regionals are suffering from the need to maintain        large amounts of routing information which is growing rapidly in        size (approximately doubling each year); (ii) The Internet is        running out of IP network numbers to assign. There is an urgent        need to develop and deploy an approach to addressing and routing        which solves these problems and allows scaling to several orders        of magnitude larger than the existing Internet. However, it is        necessary for any change to be deployed in an incremental manner,        allowing graceful transition from the current Internet without        disruption of service. [1]                This paper describes a simple proposal which provides a long-term        solution to Internet addressing, routing, and scaling. This        involves a gradual migration from the current Internet Suite        (which is based on Internet applications, running over TCP or        UDP, running over IP) to an updated suite (based on the same        Internet applications, running over TCP or UDP, running over CLNP        [2]). This approach is known as "TUBA" (TCP & UDP with Bigger        Addresses).                This paper describes a proposal for how transition may be        accomplished. Description of the manner in which use of CLNP,        NSAP addresses, and related network/Internet layer protocols        (ES-IS, IS-IS, and IDRP) allow scaling to a very large ubiquitous        worldwide Internet is outside of the scope of this paper.                Originally, it was thought that any practical proposal needed to        address the immediate short-term problem of routing information        explosion (in addition to the long-term problem of scaling to a        worldwide Internet). Given the current problems caused by        excessive routing information in IP backbones, this could require        older IP-based systems to talk to other older IP-based systems        over intervening Internet backbones which did not support IP.        This in turn would require either translation of IP packets intoCallon                                                    [Page 1]

RFC 1347   TUBA: A Proposal for Addressing and Routing   June 1992                        CLNP packets and vice versa, or encapsulation of IP packets        inside CLNP packets. However, other shorter-term techniques (for        example [3]) have been proposed which will allow the Internet to        operate successfully for several years using the current IP        address space. This in turn allows more time for IP-to-CLNP        migration, which in turn allows for a much simpler migration        technique.                The TUBA proposal therefore makes use of a simple long-term        migration proposal based on a gradual update of Internet Hosts        (to run Internet applications over CLNP) and DNS servers (to        return larger addresses). This proposal requires routers to be        updated to support forwarding of CLNP (in addition to IP).        However, this proposal does not require encapsulation nor        translation of packets nor address mapping. IP addresses and NSAP        addresses may be assigned and used independently during the        migration period. Routing and forwarding of IP and CLNP packets        may be done independently.                This paper provides a draft overview of TUBA. The detailed        operation of TUBA has been left for further study.2 Long-Term Goal of TUBA                This proposal seeks to take advantage of the success of the        Internet Suite, the greatest part of which is probably the use of        IP itself. IP offers a ubiquitous network service, based on        datagram (connectionless) operation, and on globally significant        IP addresses which are structured to aid routing. Unfortunately,        the limited 32-bit IP address is gradually becoming inadequate        for routing and addressing in a global Internet. Scaling to the        anticipated future size of the worldwide Internet requires much        larger addresses allowing a multi-level hierarchical address        assignment.                If we had the luxury of starting over from scratch, most likely        we would base the Internet on a new datagram internet protocol        with much larger multi-level addresses. In principle, there are        many choices available for a new datagram internet protocol. For        example, the current IP could be augmented by addition of larger        addresses, or a new protocol could be developed. However, the        development, standardization, implementation, testing, debugging        and deployment  of a new protocol (as well as associated routing        and host-to-router protocols) would take a very large amount of        time and energy, and is not guaranteed to lead to success. In        addition, there is already such a protocol available. In        particular, the ConnectionLess Network Protocol (CLNP [1]) is        very similar to IP, and offers the required datagram service and        address flexibility. CLNP is currently being deployed in the        Internet backbones and regionals, and is available in vendor        products. This proposal does not actually require use of CLNP        (the main content of this proposal is a graceful migration path        from the current IP to a new IP offering a larger address space),Callon                                                    [Page 2]

RFC 1347   TUBA: A Proposal for Addressing and Routing   June 1992                        but use of CLNP will be assumed.                This proposal seeks to minimize the risk associated with        migration to a new IP address space. In addition, this proposal        is motivated by the requirement to allow the Internet to scale,        which implies use of Internet applications in a very large        ubiquitous worldwide Internet. It is therefore proposed that        existing Internet transport and application protocols continue to        operate unchanged, except for the replacement of 32-bit IP        addresses with larger addresses. The use of larger addresses will        have some effect on applications, particularly on the Domain Name        Service. TUBA does not mean having to move over to OSI        completely. It would mean only replacing IP with CLNP. TCP, UDP,        and the traditional TCP/IP applications would run on top of CLNP.                The long term goal of the TUBA proposal involves transition to a        worldwide Internet which operates much as the current Internet,        but with CLNP replacing IP and with NSAP addresses replacing IP        addresses. Operation of this updated protocol suite will be very        similar to the current operation. For example, in order to        initiate communication with another host, a host will obtain a        internet address in the same manner that it normally does, except        that the address would be larger. In many or most cases, this        implies that the host would contact the DNS server, obtain a        mapping from the known DNS name to an internet address, and send        application packets encapsulated in TCP or UDP, which are in turn        encapsulated in CLNP. This long term goal requires a        specification for how TCP and UDP are run over CLNP. Similarly,        DNS servers need to be updated to deal with NSAP addresses, and        routers need to be updated to forward CLNP packets. This proposal        does not involve any wider-spread migration to OSI protocols.                TUBA does not actually depend upon DNS for its operation. Any        method that is used for obtaining Internet addresses may be        updated to be able to return larger (NSAP) addresses, and then        can be used with TUBA.3 Migration                Figure 1 illustrates the basic operation of TUBA. Illustrated is        a single Internet Routing Domain, which is also interconnected        with Internet backbones and/or regionals. Illustrated are two        "updated" Internet Hosts N1 and N2, as well as two older hosts H1        and H2, plus a DNS server and two border routers. It is assumed        that the routers internal to the routing domain are capable of        forwarding both IP and CLNP traffic (this could be done either by        using multi-protocol routers which can forward both protocol        suites, or by using a different set of routers for each suite).Callon                                                    [Page 3]

RFC 1347   TUBA: A Proposal for Addressing and Routing   June 1992                                                         ................    ................                         .    H1        .    .  Internet    .                         .              .-R1-.              .                         .  H2          .    .  Backbones   .                         .        DNS   .    .              .                         .              .    .     and      .                         .      N1      .    .              .                         .              .    .  Regionals   .                         .          N2  .-R2-.              .                         ................    ................                                   Key                              DNS    DNS server                       H     IP host                       N     Updated Internet host                       R     Border Router                                    Figure 1 - Overview of TUBA                                Updated Internet hosts talk to old Internet hosts using the        current Internet suite unchanged. Updated Internet hosts talk to        other updated Internet hosts using (TCP or UDP over) CLNP. This        implies that updated Internet hosts must be able to send either        old-style packets (using IP), or new style packet (using CLNP).        Which to send is determined via the normal name-to-address        lookup.                Thus, suppose that host N1 wants to communicate with host H1. In        this case, N1 asks its local DNS server for the address        associated with H1. In this case, since H1 is a older        (not-updated) host, the address available for H1 is an IP        address, and thus the DNS response returned to N1 specifies an IP        address. This allows N1 to know that it needs to send a normal        old-style Internet suite packet (encapsulated in IP) to H1.                Suppose that host N1 wants to communicate with host N2. In this        case, again N1 contacts the DNS server. If the routers in the        domain have not been updated (to forward CLNP), or if the DNS        resource record for N2 has not been updated, then the DNS server        will respond with a normal IP address, and the communication        between N1 and N2 will use IP (updated hosts in environments        where the local routers do not handle CLNP are discussed insection 6.3). However, assuming that the routers in the domain        have been updated (to forward CLNP), that the DNS server has been        updated (to be able to return NSAP addresses), and that the        appropriate resource records for NSAP addresses have been        configured into the DNS server, then the DNS server will respond        to N1 with the NSAP address for N2, allowing N1 to know to useCallon                                                    [Page 4]

RFC 1347   TUBA: A Proposal for Addressing and Routing   June 1992                        CLNP (instead of IP) for communication with N2.                A new resource record type will be defined for NSAP addresses.        New hosts ask for both the new and old (IP address) resource        records. Older DNS servers will not have the new resource record        type, and will therefore respond with only IP address        information. Updated DNS servers will have the new resource        record information for the requested DNS name only if the        associated host has been updated (otherwise the updated DNS        server again will respond with an IP address).                Hosts and/or applications which do not use DNS operate in a        similar method. For example, suppose that local name to address        records are maintained in host table entries on each local        workstation. When a workstation is updated to be able to run        Internet applications over CLNP, then the host table on the host        may also be updated to contain updated NSAP addresses for other        hosts which have also been updated. The associated entries for        non-updated hosts would continue to contain IP addresses. Thus,        again when an updated host wants to initiate communication with        another host, it would look up the associated Internet address in        the normal manner. If the address returned is a normal 32-bit IP        address, then the host would initiate a request using an Internet        application over TCP (or UDP) over IP (as at present). If the        returned address is a longer NSAP address, then the host would        initiate a request using an Internet application over TCP (or        UDP) over CLNP.4 Running TCP and UDP Over CLNP                TCP is run directly on top of CLNP (i.e., the TCP packet is        encapsulated directly inside a CLNP packet - the TCP header        occurs directly following the CLNP header). Use of TCP over CLNP        is straightforward, with the only non-trivial issue being how to        generate the TCP pseudo-header (for use in generating the TCP        checksum).                Note that TUBA runs TCP over CLNP on an end-to-end basis (for        example, there is no intention to translate CLNP packets into IP        packets). This implies that only "consenting updated systems"        will be running TCP over CLNP; which in turn implies that, for        purposes of generating the TCP pseudoheader from the CLNP header,        backward compatibility with existing systems is not an issue.        There are therefore several options available for how to generate        the pseudoheader. The pseudoheader could be set to all zeros        (implying that the TCP header checksum would only be covering the        TCP header). Alternatively, the pseudoheader could be calculated        from the CLNP header. For example, the "source address" in the        TCP pseudoheader could be replaced with two bytes of zero plus a        two byte checksum run on the source NSAP address length and        address (and similarly for the destination address); the        "protocol" could be replaced by the destination address selector        value; and the "TCP Length" could be calculated from the CLNPCallon                                                    [Page 5]

RFC 1347   TUBA: A Proposal for Addressing and Routing   June 1992                        packet in the same manner that it is currently calculated from        the IP packet. The details of how the pseudoheader is composed is        for further study.                UDP is transmitted over CLNP in the same manner. In particular,        the UDP packet is encapsulated directly inside a CLNP packet.        Similarly, the same options are available for the UDP pseudo-        header as for the TCP pseudoheader.5 Updates to the Domain Name Service                TUBA requires that a new DNS resource record entry type        ("long-address") be defined, to store longer Internet (i.e.,        NSAP) addresses. This resource record allows mapping from DNS        names to NSAP addresses, and will contain entries for systems        which are able to run Internet applications, over TCP or UDP,        over CLNP.                The presence of a "long-address" resource record for mapping a        particular DNS name to a particular NSAP address can be used to        imply that the associated system is an updated Internet host.        This specifically does  not imply that the system is capable of        running OSI protocols for any other purpose. Also, the NSAP        address used for running Internet applications (over TCP or UDP        over CLNP) does not need to have any relationship with other NSAP        addresses which may be assigned to the same host. For example, a        "dual stack" host may be able to run Internet applications over        TCP over CLNP, and may also be able to run OSI applications over        TP4 over CLNP. Such a host may have a single NSAP address        assigned (which is used for both purposes), or may have separate        NSAP addresses assigned for the two protocol stacks. The        "long-address" resource record, if present, may be assumed to        contain the correct NSAP address for running Internet applications        over CLNP, but may not be assumed to contain the correct NSAP        address for any other purpose.                The backward translation (from NSAP address to DNS name) is        facilitated by definition of an associated resource record. This        resource record is known as "long-in-addr.arpa", and is used in a        manner analogous to the existing "in-addr.arpa".                Updated Internet hosts, when initiating communication with        another host, need to know whether that host has been updated.        The host will request the address-class "internet address",        entry-type "long-address" from its local DNS server. If the        local DNS server has not yet been updated, then the long address        resource record will not be available, and an error response will        be returned. In this case, the updated hosts must then ask for        the regular Internet address. This allows updated hosts to be        deployed in environments in which the DNS servers have not yet        been updated.                An updated DNS server, if asked for the long-addressCallon                                                    [Page 6]

RFC 1347   TUBA: A Proposal for Addressing and Routing   June 1992                        corresponding to a particular DNS name, does a normal DNS search        to obtain the information. If the long-address corresponding to        that name is not available, then the updated DNS server will        return the resource record type containing the normal 32-bit IP        address (if available). This allows more efficient operation        between updated hosts and old hosts in an environment in which        the DNS servers have been updated.                Interactions between DNS servers can be done over either IP or        CLNP, in a manner analogous to interactions between hosts. DNS        servers currently maintain entries in their databases which allow        them to find IP addresses of other DNS servers. These can be        updated to include a combination of IP addresses and NSAP        addresses of other servers. If an NSAP address is available, then        the communication with the other DNS server can use CLNP,        otherwise the interaction between DNS servers uses IP. Initially,        it is likely that all communication between DNS servers will use        IP (as at present). During the migration process, the DNS servers        can be updated to communicate with each other using CLNP.6 Other Technical Details6.1 When 32-Bit IP Addresses Fail                Eventually, the IP address space will become inadequate for        global routing and addressing. At this point, the remaining older        (not yet updated) IP hosts will not be able to interoperate        directly over the global Internet. This time can be postponed by        careful allocation of IP addresses and use of "Classless        Inter-Domain Routing" (CIDR [3]), and if necessary by        encapsulation (either of IP in IP, or IP in CLNP). In addition,        the number of hosts affected by this can be minimized by        aggressive deployment of updated software based on TUBA.                When the IP address space becomes inadequate for global routing        and addressing, for purposes of IP addressing the Internet will        need to be split into "IP address domains". 32-bit IP addresses        will be meaningful only within an address domain, allowing the        old IP hosts to continue to be used locally. For communications        between domains, there are two possibilities: (i) The user at an        old system can use application layer relays (such as mail relays        for 822 mail, or by Telnetting to an updated system in order to        allow Telnet or FTP to a remote system in another domain); or        (ii) Network Address Translation can be used [4].6.2 Applications which use IP Addresses Internally                There are some application protocols (such as FTP and NFS) which        pass around and use IP addresses internally. Migration to a        larger address space (whether based on CLNP or other protocol)        will require either that these applications be limited to local        use (within an "IP address domain" in which 32-bit IP addresses        are meaningful) or be updated to either: (i) Use larger networkCallon                                                    [Page 7]

RFC 1347   TUBA: A Proposal for Addressing and Routing   June 1992                        addresses instead of 32-bit IP addresses; or (ii) Use some other        globally-significant identifiers, such as DNS names.6.3 Updated Hosts in IP-Only Environments                There may be some updated Internet hosts which are deployed in        networks that do not yet have CLNP service, or where CLNP service        is available locally, but not to the global Internet. In these        cases, it will be necessary for the updated Internet hosts to        know to initially send all Internet traffic (or all non-local        traffic) using IP, even when the remote system also has been        updated. There are several ways that this can be accomplished,        such as: (i) The host could contains a manual configuration        parameter controlling whether to always use IP, or to use IP or        CLNP depending upon remote address; (ii) The DNS resolver on the        host could be "lied to" to believe that all remote requests are        supposed to go to some particular server, and that server could        intervene and change all remote requests for long-addresses into        requests for normal IP addresses.6.4 Local Network Address Translation                Network Address Translation (NAT [4]) has been proposed as a        means to allow global communication between hosts which use        locally-significant IP addresses. NAT requires that IP addresses        be mapped at address domain boundaries, either to globally        significant addresses, or to local addresses meaningful in the        next address domain along the packet's path. It is possible to        define a version of NAT which is "local" to an addressing domain,        in the sense that (locally significant) IP packets are mapped to        globally significant CLNP packets before exiting a domain, in a        manner which is transparent to systems outside of the domain.                NAT allows old systems to continue to be used globally without        application gateways, at the cost of significant additional        complexity and possibly performance costs (associated with        translation or encapsulation of network packets at IP address        domain boundaries). NAT does not address the problem of        applications which pass around and use IP addresses internally.                The details of Network Address Translation is outside of the        scope of this document.6.5 Streamlining Operation of CLNP                CLNP contains a number of optional and/or variable length fields.        For example, CLNP allows addresses to be any integral number of        bytes up to 20 bytes in length. It is proposed to "profile" CLNP        in order to allow streamlining of router operation. For example,        this might involve specifying that all Internet hosts will use an        NSAP address of precisely 20 bytes in length, and may specify        which optional fields (if any) will be present in all CLNP        packets. This can allow all CLNP packets transmitted by InternetCallon                                                    [Page 8]

RFC 1347   TUBA: A Proposal for Addressing and Routing   June 1992                        hosts to use a constant header format, in order to speed up        header parsing in routers. The details of the Internet CLNP        profile is for further study.7 References                [1]    "The IAB Routing and Addressing Task Force: Summary               Report", work in progress.                [2]    "Protocol for Providing the Connectionless-Mode Network               Service", ISO 8473, 1988.                [3]    "Supernetting: An Address Assignment and Aggregation               Strategy", V.Fuller, T.Li, J.Yu, and K.Varadhan, March               1992.                [4]    "Extending the IP Internet Through Address Reuse", Paul               Tsuchiya, December 1991.8 Security Considerations                Security issues are not discussed in this memo.9 Author's Address                Ross Callon        Digital Equipment Corporation550 King Street, LKG 1-2/A19        Littleton, MA  01460-1289                Phone: 508-486-5009                Email: Callon@bigfut.lkg.dec.com                                                                                                                                                                        Callon                                                    [Page 9]