Network Working Group                                  Ross Callon
        Request for Comments: 1347                                     DEC
                                                                 June 1992



                    TCP 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 into

        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),

        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).

                         ................    ................
                         .    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 in
        section 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 use

        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 CLNP

        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-address

        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 Details

6.1 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 network

        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 Internet

        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 Corporation
        550 King Street, LKG 1-2/A19
        Littleton, MA  01460-1289

        Phone: 508-486-5009

        Email: Callon@bigfut.lkg.dec.com