Internet Draft J. Curran
November 1992 BBN
TCP & UDP with Network-independent Endpoints (TUNE)
Status of this Memo
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Abstract
This memo proposes a strategy for providing TCP and UDP services over
_multiple_ network services in a manner compatible with existing
TCP/IP applications. By introducing network-independent endpoint
identifiers for transport entities, TUNE makes it possible to change
network addresses (and potentially network protocols) without impact
to the application layer. While this paper describes the use of
Connection-Less Network Protocol [1] as a possible long-term network
service for the Internet, the overall approach differs from the "TCP
& UDP with Bigger Addresses" [2] initiative due to the addition of
network-independent endpoint identifiers. TUNE also provides network
layer programming interfaces which are unchanged from those of the
current Internet Protocol (IP) suite and hence alleviate the need for
application code changes during initial deployment.
Comments should be sent to the author (jcurran@nic.near.net).
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Acknowledgments
Sincere thanks to the members of the TUBA mailing list who had to
endure these ideas at very early stage, and in particular, thanks to
Ross Callon, Dave Piscitello, and Paul Tsuchiya for bearing with my
endless questions.
Table of Contents
1 Introduction
2 TUNE Architecture
2.1 Endpoint Identifiers (EIDs)
2.2 EID Resolution
2.3 TUNE Header Format
3 TUNE Administration
3.1 Autoconfiguration
3.2 Portability
3.3 Mobility
4 Appendixes
5 Security Considerations
6 References
7 Author's Address
1.0 Introduction
Recent growth in the Internet has revealed several significant
scaling problems in the current Internet routing and addressing
architecture. It is generally acknowledged that continued deployment
of non-hierarchical addresses will result in unacceptable growth to
transit routing tables in the Internet. While the "Classless Inter-
Domain Routing" [3] approach to address assignment and route
aggregation should minimize routing table explosion for the immediate
future, it is not positioned as a long-term solution to the routing,
addressing, and scaling problems.
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From a purely technical viewpoint, strict hierarchical addressing
could be used to create a highly-scalable Internet routing
architecture. Topologically-assigned addresses for network attachment
points would minimize the need for routing information exchange. It
would be necessary to use addresses of sufficient size to fully
represent the network topology, but large hierarchical addressing
plans have already been proposed for some protocol suites [4].
There are two minor administrative problems in using topologically-
assigned addresses as a basis for long-term solution to the routing
problem:
Topologically-assigned addresses cannot provide organizations with
geographic and service provider mobility. As a result,
organizations using topologically-assigned addresses are forced
into address migrations when relocating. While autoconfiguration
and directory services may eventually minimize the use of network
addresses in configurations, these services do not currently
provide relief for network address changes.
Furthermore, the existence of larger hierarchically-assigned
addresses does not insure their usage by the thousands of
applications which currently work over today's Internet. Several
of the proposed routing and addressing solutions call for changing
the programming interfaces for TCP and UDP services to support
larger addresses. As a consequence, every existing network
application will have be revised, and organizations will have to
insure that they have the "upgraded" versions of all their network
applications before moving to the new architecture. It will be
necessary to phase in the usage of larger addresses in a
controlled manner in order to bring about their acceptance by the
Internet community.
TCP & UDP with Network-independent Endpoints (TUNE) is one possible
strategy for resolving the routing and addressing problems in the
current Internet while accommodating existing applications. The TUNE
architecture provides for the delivery of TCP and UDP messages in a
manner similar to IP, but goes further by formally separating
endpoint identification from network attachment information to
improve mobility and scaling. By allowing the use of existing IP
addresses as one class of endpoint identifiers, TUNE provides for an
initial transition to TUNE services without application code changes.
This document describes the overall TUNE architecture and a migration
plan for transition to CLNP network services. While TUNE will
function over almost any network service, CLNP's existing
hierarchical network addressing will require minimal routing
information exchange once TUNE is deployed. In addition, the
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availability of CLNP services in the current Internet will accelerate
the deployment process and eliminate the risks associated with the
development of a new network layer service.
2.0 TUNE Architecture
TCP & UDP with Network-independent Endpoints (TUNE) details a
convergence layer between the Internet transport and underlying
network datagram delivery services. The purpose of this layer is to
allow identification of transport endpoints independent of the
underlying network addressing scheme. This is analogous to the role
that the Address Resolution Protocol [5] plays in allowing network
address selection unconstrained by physical interface address.
TUNE's relationship to other network services can be depicted as
follows:
+---------------------------------------+
| (Applications) |
+ +------------------+
+====================+ DNS | Name Resolution
| Transport Layer +__________________+
| TCP, UDP, etc. |
+ +------------------+
|====================+ TUNE | Endpoint Resolution
| Network Layer +__________________+
| IP, CLNP, IPAE, SIP, etc. |
| +------------------+
+====================+ ARP | Address Resolution
| Data Link Layer +__________________+
| 802.3, DIX, SLIP, PPP, etc. |
| |
+---------------------------------------+
TUNE provides two functions: a mapping function from endpoint
identifiers to network protocols and addresses, and the labeling of
messages with transport endpoint identifiers.
While TUNE is not required for successful implementation of TCP and
UDP over new network protocols, the benefits of using TUNE include:
o Globally unique endpoint identifiers which are independent
of network attachment point.
o Endpoint identifiers translated to network addresses in a
manner transparent to the applications.
o Underlying transport provided via multiple network services
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with diverse address formats.
o Hiding of network layer information from higher layers.
o Backward-compatible programming interfaces for TCP and UDP
services, and application compatibility during transition.
o Full utilization of the 32-bit Internet Protocol address
space and its existing allocation infrastructure.
o Interoperability between IP and TUNE hosts during transition.
2.1 Endpoint Identifiers (EIDs)
Datagram-oriented transport protocols have traditionally used network
layer addresses during the specification of communication endpoints.
It is common for such network addresses to contain has some embedded
information regarding the underlying network topology. IP addresses,
for instance, implicitly identify the particular network which serves
the end system. In the case of CLNP, addresses that are compatible
with OSI Intra-domain IS-IS routing protocol [6] include explicit
topological information in the "Area Address" (formed from the
Initial Domain Part (IDP) and the High-order portion of the Domain
Specific Part (HO-DSP) of a given NSAP.) Neither IP nor CLNP provide
a endpoint identifier which is independent of network topology. As a
result, topological information which is specific to the network must
be made available to the applications for inclusion in their
transport service requests. Likewise, applications using transport
services become dependent upon the specific network attachment points
at the time of configuration.
TUNE transport services do not require specification of topology
information (implied or otherwise) by applications. Communication is
provided between globally unique "endpoint identifiers". These
endpoint identifiers (EIDs) are assigned hierarchically (for
administrative convenience and directory manageability) but do not
embody any network topology information. A system with two interfaces
(on the same or different networks) will use a single EID for normal
communications. Additionally, when a system moves from one network to
another, the endpoint identifier does not change. This provides TUNE
with endpoint identifiers that are independent of network topology
and inherently mobile.
The success of a globally unique identification system depends
ultimately upon the ease of obtaining identifiers. If the process
for acquiring such an identifier is burdensome, then the probability
of duplicate identifiers being used increases dramatically. For this
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reason, TUNE make use of existing allocation schemes for endpoint
identifiers whenever possible. Appendix A contains a preliminary
specification of the format and allocation process for EIDs.
2.2 EID Resolution
In order to transport a TCP or UDP message to the appropriate
endpoint, it will be necessary to determine the corresponding network
service and address for any given EID. Given the current state of
directory services in the Internet, the Domain Name System [7] is a
likely choice for providing the EID to network address mapping
function. One consequence of using DNS is that each TUNE system will
require access to a DNS nameserver via a supported network protocol.
Initially, it is anticipated that the existing IP nameservers will be
used (with CLNP-only systems using transition services), but
deployment of TUNE-supporting nameservers will occur as TUNE systems
become more common. Appendix B specifies a DNS services plan for
TUNE using the existing DNS software. This plan supports any NSAP
format and provides flexibility in the selection of NSEL values for
the TUNE service.
Once the destination network service is determined, the TUNE message
is passed to the appropriate network service along with the
destination network address. Delivery of the message is handled as
is normal for the particular network service selected; TUNE does not
affect the datagram forwarding process in any manner.
2.3 TUNE Header Format
Both TCP and UDP currently include a "pseudo-header" during checksum
calculation. The pseudo-header includes the network-level source and
destination along with the protocol identifier and transport message
length. The purpose of this checksum is to insure that the message
was delivered to the appropriate endpoint.
Since an endpoint identifier is no longer related to the network
layer addresses, the use of these pseudo-headers by TCP or UDP must
be revised with new endpoint semantics. Under TUNE, the destination
of TCP or UDP datagrams can be uniquely identified by the EID and the
port number alone. It is not necessary for pseudo-headers to contain
network addresses at all, since EIDs are globally unique. In
addition, maintaining network addresses in these headers can actually
prevent communications in some instances because the messages arrived
via a different network protocol or interface than the sender
intended. The elimination of network address information in these
headers provides for consistent endpoint specification during
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mobility, and allows the use of multiple network services (with
potentially different characteristics) by a single endpoint.
The revised TCP and UDP pseudo-header for TUNE operations is:
0 7 8 15 16 23 24 31
+---------+---------+---------+---------+
| source endpoint id (octets 1-4) |
+---------+---------+---------+---------+
| source endpoint id (octets 5-8) |
+---------+---------+---------+---------+
| destination endpoint id (octets 1-4) |
+---------+---------+---------+---------+
| destination endpoint id (octets 5-8) |
+---------+---------+---------+---------+
| flags | protocol| data length |
+---------+---------+---------+---------+
Since TUNE decouples the one-to-one relationship between network
attachment points and transport endpoints, the specific destination
EID must be available in the network or transport message so that
messages for the destination system may recognized and processed.
Source EIDs may also be desired in transport messages for logging,
accounting, or authorization purposes.
As part of the TUBA discussions, it has been suggested that these
EIDs might be embedded in network addresses via various mappings.
This restricts the choice of network addresses (to those conforming
to the mapping algorithm), and such mapping may not be available over
other network services. Another consequence of embedding EIDs into
network addresses is that the resulting transport identifiers used by
applications become dependent on network addressing structures and
thus subject to change with network changes.
TUNE maintains independence from network layer addresses by
prepending TCP and UDP messages with the revised pseudo-header during
delivery. This revised header (referred to as the "TUNE header")
precedes the TCP or UDP data in a TUNE datagram and contains the
protocol field needed for demultiplexing at the destination TUNE
system. This is a significant departure from current IP
architecture, and will result in larger network layer datagrams in
most cases. While the addition of 24 octets to the average Internet
datagram is considered heresy by many, the header will result in a
minimal performance impact when used with large datagram sizes. The
impact on low-speed circuits would be much greater, but may be
alleviated through the use of header compression techniques in a
manner similar to IP [8].
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3.0 TUNE Administration
By introducing organizational endpoint identifiers, TUNE creates
basic infrastructure for several administrative features which have
been previously viewed as network-layer services. In particular, EID
identification of transport messages can simplify the deployment of
autoconfiguration, portability, and mobility for end-systems.
3.1 Autoconfiguration
In order for a TUNE system to properly interact with other TUNE
systems, it must:
o Have an operational network service
o Know its own EID
o Have access to the EID resolution service
Autoconfiguration of network layer services has been sucessfully
deployed for IP [9, 10], and is under development for CLNP services.
As TUNE operates on top of network services, it does not interfere
with the operation of any network-layer mechanisms.
TUNE does provide an additional key which autoconfiguration
techniques could use to gain hardware independence. Rather than
utilizing an IEEE identifier from one of its network interfaces as a
key for system information, (such as name and bootfile selection) it
becomes possible to index such information by the EID, and have
systems store (in a non-volatile memory) their EID. Changing either
the network level address or the hardware address (such as board
swap) would not affect the boot process. In some environments, it
may be useful to store a secret key in addition to the EID for use
via ticket granting service authorizing use of the EID.
TUNE operation will require either non-volatile storage of the EID
resolution service configuration or use of the autoconfiguration
process to obtain such information. BOOTP is already capable of
returning the necessary DNS information, but any additional
information (such as network service preference) will have to be
added as BOOTP extension or stored locally.
3.2 Portability
Portability, loosely defined as the ability to carry a system
somewhere and have it operate at the destination, has been considered
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a desirable characteristic of the Internet's next architecture. This
is particularly true if portability is going to be used to maintain
topologically-assigned network addresses.
Since EIDs are not dependent upon any particular physical network,
TUNE systems which are moved to a new network attachment point only
need to update the EID-to-network-address mapping in order to achieve
portability. This works regardless of the cause of the address
change (physical move, provider change, etc.) Such address changes
are completely transparent to applications under TUNE, since
applications use EIDs.
Due to the use of DNS services for EID->address mapping, TUNE cannot
provide "instant" portability during its initial deployment. This
stems from the inability to perform distributed updates to the DNS
database from remote systems. Organizations will enjoy portability
for all of their TUNE systems, but will have to manually update the
EID mapping when systems are moved.
The addition of dynamic update facilities could be done via DNS
extensions for dynamic database update, or could be done as a
separate facility which interacts directly with the master nameserver
as needed. The advantage of a separate facility is the ability to
readily add site-defined validation for such updates, whereas a DNS-
based solution can readily be found during autoconfiguration and
would not require specific autoconfiguration support as a result.
Additional work is needed before making a determination for this
topic.
3.3 Mobility
Mobility, defined here as the ability to operate a system
continuously while changing network location, has been expressed by
many as a desirable characteristic of the next Internet architecture.
Several mobile technologies including wireless LAN's, microwave
personal communications services, and digital celluar services will
become generally available over the next few years and could make
significant demands upon our routing architecture if pressed to
provide mobility to systems.
In the TUNE model, mobility is provided at the transport layer. The
TUNE header allows direction of transport messages without affecting
the endpoint identifiers. Given two systems, EID XXX with network
address NX1, and EID YYY with network address NY1, it is possible for
XXX to move to a new network address (NX2) while communicating over
CLNP as follows:
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XXX YYY
--- ---
Disconects from NX1/
connects to NX2
Sends dynamic update to
EID map (identical to
portability case)
Cached mapping for XXX incorrect/
messages timeout.
Cached ES info expires at
last IS router based on
holding timer.
(holding timer presumably
low for mobile host)
Cached mapping for XXX incorrect/
messages report Host Unreachable.
Failure causes reacquisition of EID ->
address mapping.
Mapping returns new information/
Messages to XXX/NX2 succeed.
For TCP connections, the reaction time to network address changes can
be minimized by using a "refresh EID" flag in the TUNE header. When
a system changes its network address, this flag should be set in the
next datagram to each outstanding TCP connection.
4.0 Appendix A: EID Allocation and Format
TUNE Endpoint Identifiers are 64 bits in length, and may be
represented in the familiar "dotted-decimal" notation used for IP
addresses. The EIDs are allocated by the Internet Assigned Numbers
Authority and its delegated authorities in accordance with the
recommendations of the IETF.
The IANA should allocate EIDs in contiguous blocks of EIDs to
subordinate allocation authorities as necessary to insure an adequate
supply of EIDs for TUNE-using organizations. It is recommended that
the IANA make use of multiple channels for distribution of EIDs
including network service providers, professional organizations,
standards organizations, and others as necessary.
In order to insure an plentiful supply of EID authorities, the first
two octets of the EID are reserved for an allocation authority
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prefix. This allows for 64K allocation authorities. It is
foreseeable that the IANA might supply multiple authority prefixes to
some authorities so that further delegation of authority may occur.
An example of this would be if the IANA were to allocate sufficient
prefixes to ISO so that each country could have a unique authority
prefix.
Allocation authorities may allocate EIDs in any of the following
sized blocks: 2**8, 2**16, 2**24, 2**32, 2**40, and 2**48.
Authorities are required to maintain records of blocks assigned and
provide support infrastructure (such as top-level directory servers)
to allow successful EID resolution process for each block assigned.
The requirements for directory services are intended to discourage
small allocations by authorities, and it is expected that typical EID
block allocations will consist of 2**16 or 2**24 EIDs per
organization.
In order to provide interoperability between IPv4 and TUNE systems,
it is necessary to "map" existing IP addresses into TUNE EIDs. It is
recommended that the following EIDs be reserved for this purpose:
128.0.x.y.z.0.0.n
where
128.0 Authority Prefix
x.y.z IP address (high 3 octets)
0.0.n IP address (low octet)
Although this method of allocation does not provide a straightforward
translation for existing IP addresess, it will allow existing network
(and subnet) allocations to evolve into large EID namespaces prior to
the establishment of multiple EID allocation authorities.
4.0 Appendix B: DNS Support for EID Resolution
TUNE requires a distributed mapping function from a given EID to the
appropriate network service and address used to reach it. This
function will be initially provided through existing DNS services in
order to allow timely deployment in the Internet.
It is necessary to represent the EID information in the DNS namespace
in a manner which supports delegation from the IANA to each
assignment authority, and from each assignment authority to each
organization. DNS has two restrictions upon how delegation may be
performed: delegation may only occur on token boundaries (where
tokens are delimited by periods in the name string), and information
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is organized with the rightmost tokens being most significant.
Considering these requirements, the following approach is recommend
for EID to network information mapping via DNS:
The IANA will establish DNS service for a new domain: IN-EID.ARPA.
For each authority prefix assignment, the IANA will delegate a
subdomain of IN-EID.ARPA for management by the assignment authority.
The subdomain may be determined by representing the authority prefix
in dotted-decimal notation and inverting the order of tokens (as is
done for the IN-ADDR domain currently)
Example:
Authority ABC is assigned prefix 0.47. A matching domain of
47.0.IN-EID.ARPA would be operated by or on behalf of the
authority.
For each organization prefix assigned, the authority will delegate a
subdomain of their domain for management by the organization. The
subdomain may be determined by representing the organization prefix
in dotted-decimal notation and inverting the order of tokens (as
above).
The IANA will delegate subdomains for any organizations using EIDs
based upon their IP network address allocation.
Example:
Organization XYZ is assigned prefix 0.47.255.238.0. A matching
domain of 0.238.255.47.0.IN-EID.ARPA would be operated by or on
behalf of organization XYZ.
Organizations are responsibility for providing a pointer (PTR) record
for each EID in use. The location for the PTR record may be
determined by representing the EID in dotted-decimal notation and
inverting the order of tokens (as above).
The PTR record will contain the name of the network service used to
reach the EID, a slash ("/") character, and a network address in a
format specific to the network service.
The valid names and address formats will be determined by the IANA.
The use of PTR resource records requires that all address formats end
with a period (".").
A network address may include a network layer protocol selector when
available (e.g. NSEL in NSAP addresses) as TUNE only requires a
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single dispatch point and performs transport protocol demultiplexing
internally based upon the TUNE header.
TUNE hosts should only process address records for supported network
protocols and should ignore all others received. The method for
selecting which network service and address to use in the presence of
multiple valid records is a local configuration issue, and not
addressed here. It is conceivable that address selection might take
local policy into consideration to provide limited source-specified
routing.
Examples:
A system with EID of 128.0.192.52.71.0.0.4 reachable via
CLNP might require a PTR record of the following form:
4.0.0.71.52.192.0.128.IN-EID.ARPA.
PTR CLNS/47000580FFEE00000000001100AA00040084AF10.
A system with EID of 0.47.255.238.0.0.1.178 reachable via
PIP might require a PTR record of the following form:
178.1.0.0.238.255.47.0.IN-EID.ARPA
PTR PIP/7.66000.77.18.2.
5.0 Security Considerations
Security considerations are not discussed in this memo, but should be
thoroughly explored before any future Internet architecture is
selected.
6.0 References
[1] "Protocol for Providing the Connectionless-Mode Network Service",
ISO 8473, 1988.
[2] Callon, R., "TCP and UDP with Bigger Addresses (TUBA), A Simple
Proposal for Internet Addressing and Routing", RFC1347, 1992 June.
[3] Fuller, V.; Li, T.; Yu, J.; Varadhan, K, "Supernetting: an
Address Assignment and Aggregation Strategy", RFC1338, 1992 June.
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[4] Collela, R.; Gardner, E.P.; Callon, R.W., "Guidelines for
OSI NSAP allocation in the internet", RFC1237, 1991 July.
[5] Plummer, D.C., "Ethernet Address Resolution Protocol: Or converting
network protocol addresses to 48.bit Ethernet address for transmission
on Ethernet hardware", RFC826, 1982 November.
[6] Oran, David, Ed., "OSI IS-IS Intra-domain Routing Protocol",
RFC1142, February 1990.
[7] Mockapetris, P., "Domain names - Concepts and Facilities", RFC1034,
November 1987.
[8] Jacobson, V., "Compressing TCP/IP headers for low-speed
serial links", RFC1144, 1990 February.
[9] Croft, W.J.; Gilmore, J., "Bootstrap Protocol", RFC951,
1985 September.
[10] Reynolds, J.K., "BOOTP vendor information extensions",
RFC1084, 1988 December.
7.0 Author's Address:
John Curran
Bolt Beranek and Newman, Inc.
10 Moulton Street
Cambridge, MA 02138
(617) 873-4398
jcurran@nic.near.net
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