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
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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),
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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).
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................ ................
. 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
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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
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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
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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
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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
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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
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