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RFC1705 - Six Virtual Inches to the Left: The Problem with IPng

王朝other·作者佚名  2008-05-31
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Network Working Group: R. Carlson

Request for Comments: 1705 ANL

Category: Informational D. Ficarella

Motorola

October 1994

Six Virtual Inches to the Left:

The Problem with IPng

Status of this Memo

This memo provides information for the Internet community. This memo

does not specify an Internet standard of any kind. Distribution of

this memo is unlimited.

Abstract

This document was submitted to the IETF IPng area in response to RFC

1550. Publication of this document does not imply acceptance by the

IPng area of any ideas eXPressed within. Comments should be

submitted to the big-internet@munnari.oz.au mailing list.

Overview

This RFCsuggests that a new version of TCP (TCPng), and UDP, be

developed and deployed. It proposes that a globally unique address

(TA) be assigned to Transport layer protocol (TCP/UDP). The purpose

of this TA is to uniquely identify an Internet node without

specifying any routing information. A new version of TCP, and UDP,

will need to be developed describing the new header fields and

formats. This new version of TCP would contain support for high

bandwidth-delay networks. Support for multiple network layer

(Internet Protocol) protocols is also possible with this new TCP.

Assigning an address to TCP/UDP would allow for the support of

multiple network layer protocols (IPng's). The TA would identify the

location of an Internet node. The IPng layer would provide routing

information to the Internet. Separating the location and routing

functions will greatly increase the versatility of the Internet.

Table of Contents

1. IntrodUCtion . . . . . . . . . . . . . . . . . . . . . . . . . 2

2. Historical perspective . . . . . . . . . . . . . . . . . . . . 3

2.1 OSI and the 7 layer model . . . . . . . . . . . . . . . 3

2.2 Internet Evolution . . . . . . . . . . . . . . . . . . . 4

2.3 The Reasons for Change . . . . . . . . . . . . . . . . . 4

2.3.1 Class-B Address Exhaustion . . . . . . . . . . . 4

2.3.2 Routing Table Growth . . . . . . . . . . . . . . 5

3. The Problems with Change . . . . . . . . . . . . . . . . . . . 5

3.1 TCP/UDP Implementations . . . . . . . . . . . . . . . . 6

3.2 User Applications . . . . . . . . . . . . . . . . . . . 6

3.3 The Entrenched Masses . . . . . . . . . . . . . . . . . 6

4. Making TCP & UDP Protocol Independent . . . . . . . . . . . . 7

4.1 Transport Addressing . . . . . . . . . . . . . . . . . . 7

4.2 TCPng . . . . . . . . . . . . . . . . . . . . . . . . . 12

4.3 Mandatory Options . . . . . . . . . . . . . . . . . . . 15

4.4 Optional Options . . . . . . . . . . . . . . . . . . . . 16

4.5 Compatibility Issues . . . . . . . . . . . . . . . . . . 16

4.5.1 Backward Compatibility . . . . . . . . . . . . . 17

4.6 Level 4 Gateways . . . . . . . . . . . . . . . . . . . . 17

4.7 Error Conditions . . . . . . . . . . . . . . . . . . . . 18

5. Advantages and Disadvantages of this approach . . . . . . . . 18

6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 19

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Appendix A . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Appendix B . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Appendix C . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Appendix D . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Security Considerations . . . . . . . . . . . . . . . . . . . . . 27

Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27

1. Introduction

For more than a decade, network engineers have understood the

benefits of a multi-layer protocol stack. However, during its

development, the Transmission Control Protocol (TCP) was strongly

linked to the Internet Protocol (IP) [Postel, 1981a]. When the TCP/IP

protocol suite was developed, two important ideas were implemented.

The first was that each host would be uniquely identified by a

network layer number (i.e., IP number = 192.0.2.1). The second was to

identify an application with a transport layer port number (i.e., TCP

DNS number = 53). For host-to-host communications, the IP and port

numbers would be concatenated to form a socket (i.e., 192.0.2.1.53).

While this has lead to a very efficient and streamlined TCP layer, it

has tightly coupled the TCP and IP layers. So much so, in fact, that

it is nearly impossible to run TCP over any network layer except for

IP.

The motivation for writing this paper resulted from research into the

various Internet Protocol Next Generation (IPng) proposals put forth

by various IETF working groups. Each of the IPng proposals strives to

solve the impending IP address exhaustion problem by increasing the

size of the address field. They all allude to modifications to TCP

and User Datagram Protocol (UDP) to make them capable of supporting a

new network layer IPng protocol. The authors of this paper feel that

this points to an inherent TCP/IP design flaw. The flaw is namely

that the transport (TCP) and network (IP) layers are not protocol

independent. In this paper, we will propose a new TCP and UDP

implementation that will make the transport and protocol layers

independent and thus allow for any of the IPng protocols to operate

on the same internet without any further modification to the higher

layer protocols. TCP, and UDP would become extremely powerful

Application Programming Interfaces (APIs) that operate effectively

over multiple network layer technologies.

2. Historical perspective

2.1 OSI and the 7 layer model

Present day computer and communication systems have become

increasingly heterogeneous in both their software and hardware

complexity, as well as their intended functionality. Prior to the

establishment of computer communications industry standards,

proprietary standards followed by particular software and hardware

manufacturers prevented communication and information exchange

between different manufacturers products and therefore lead to many

"closed systems" [Halsal, 1992] incapable of readily sharing

information. With the proliferation of these types of systems in the

mid 1970s, the potential advantages of "open systems" where

recognized by the computer industry and a range of standards started

to be introduced [Halsal, 1992].

The first and perhaps most important of these standards was the

International Standards Organization (ISO) reference model for Open

Systems Interconnection standard (OSI), describing the complete

communication subsystem within each computer. The goal of this

standard model was to "allow an application process in any computer

that supports a particular set of standards to communicate freely

with an application process in any other computer that supports the

same standards, irrespective of its origin of manufacture" [Halsal,

1992]. The last statement above describes the OSI 7-layer model

which has now, in concept, become the fundamental building block of

computer networks. Though there are arguably no present day

computers and networks completely compliant to all 7 layers of the

OSI protocol stack, most protocol stacks do embrace the fundamental

concept of independent layers, thus allowing the flexibility for

computers operating with dissimilar protocol stacks to communicate

with one another.

Take for example, the datalink layers as supported by TCP/IP. TCP/IP

will run equally well in either the local area network (LAN) or wide

area network (WAN) environments. Even though the LAN may use Ethernet

802.3 and the WAN may use T1 serial links. This function was designed

to present a "standardized set of network functions (i.e., a logical

network)", to the upper network layer, "regardless of the exact

details of the lower level implementations" [Meyer, Zobrist, 1990].

2.2 Internet Evolution

"The internet architecture, the grand plan behind the TCP/IP protocol

suite" was developed and tested in the late 1970s, [Braden, et al,

1991] and but for the addition of subnetting, autonomous systems, and

the domain name system in the early 1980s and the more recent IP

multicasting implementation, stands today essentially unchanged. Even

with the understood benefits of a multi-layer protocol stack, all

steps taken to enhance the internet and its services have been very

incremental and narrowly focused.

2.3 The Reasons for Change

The reasons for change from IP to IPng can be described in terms of

problems for which the current IP will simply become inadequate and

unusable in the near future (~2-4 years). These problems are the

exhaustion of IP class B address space, the exhaustion of IP address

space in general, and the non-hierarchical nature of address

allocation leading to a flat routing space [Dixon, 1993].

2.3.1 Class-B Address Exhaustion

One of the fundamental causes of this problem is the lack of a class

of network address appropriate for a mid-sized organization. The

class-C address, with a maximum of 254 unique host addresses is to

small, while class-B, with a maximum of in excess of 65 thousand

unique host addresses is to large [Fuller, et al, 1992]. As a

result, class-B addresses get assigned even though nowhere near the

number of available addresses will ever get used. This fact, combined

with a doubling of class-B address allocation on a yearly basis lead

the Internet Engineering Steering Group (IESG) to conclude in

November, 1992 that the class-B address space would be completely

exhausted within 2 years time. At that point, class-C addresses

would have to be assigned, sometimes in multiples, to organizations

needing more than the 254 possible host addresses from a single

class-C address [Almquist, Gross, 1992].

2.3.2 Routing Table Growth

Based on research conducted by the IESG in November 1992, definite

routing table size explosion problems were identified. Namely, it was

determined that current router technology at that point could support

a maximum of 16,000 routes, which in turn could support the internet

for an additional 12 to 18 months (~May, 1994) at the then twofold

annual network growth rate. However, vendor router maximum

capabilities were in the process of being increased to 64,000 routes,

which at the two-fold annual network growth rate, could bring us an

additional 2 years of lead time, (at best bringing us to May, 1996,

and at worst to November, 1995) assuming the class-B address

exhaustion problem mentioned above could be solved in the interim

[Almquist, Gross, 1992].

As a short term, incremental solution to this routing table growth

problem, and to aid in the class-B address exhaustion problem the

IESG endorsed the CIDR supernetting strategy proposal (see RFC-1338

for full details of this proposal). However, this strategy was

estimated to have a viability of approximately 3 years, at which

point the internet would run out of all classes of IP addresses in

general. Hence, it is clear that even CIDR only offers temporary

relief. However, if implemented immediately, CIDR can afford the

Internet community time to develop and deploy an approach to

addressing and routing which allows scaling to orders of magnitude

larger than the current architecture (IPng).

3. The Problems with Change

There are many problems, both philosophical and technical, which

greatly contribute to the difficulties associated with a large scale

change such as the one proposed in the conversion from IP to IPng.

These problems range from having to rewrite highly utilized and

entrenched user applications, such as NFS, RPC, etc, to potentially

having to invest additional capital to purchase hardware that

supports the new protocol(s). This proposal solves the urgent

internet problems listed above, while simultaneously limiting the

amounts of retraining and re- investing that the user community would

have to undertake. The TCP layer will once and for all be changed to

support a multiprotocol internet. The net affect is that while

administrators will necessarily be trained in the operations and

details of this new TCP, the much larger operator and end user

community will experience no perceptible change in service and

network usage.

3.1 TCP/UDP Implementations

Both TCP and UDP are highly dependent on the IPv4 network layer for 2

very low level reasons. 1) a TCP/UDP socket is formed by

concatenating a network layer address (IP address) and the transport

layer TCP/UDP port number. 2) included in the TCP/UDP checksum

calculation are the IP layer source and destination addresses

mentioned above which are transferred across the TCP/IP [Postel,

1981b] or UDP/IP [Postel, 1980] interfaces as procedure call

arguments. It should be noted at this point that the reason for such

strong dependence between the transport and network layers in TCP/IP

or UDP/IP is to insure a globally unique TCP/UDP layer address, such

that a unique connection could be identified by a pair of sockets.

The authors of this paper propose that the IP address requirement

with TCP and UDP be replaced with a globally unique transport address

(TA) concatenated with a transport layer port address. This solution

offers the capability to still maintain a globally unique address and

host unique port number with the added benefit of eliminating the

transport and network layer dependence on one another.

3.2 User Applications

In addition to TCP and UDP, there are a large number of firmly

entrenched higher level applications that use the IP network layer

address embedded internally, and would therefore require modification

for use with the proposed IPng network layer schemes. These

applications include, but are not limited to Network File System

(NFS), Remote Procedure Call (RPC), and File Transfer Protocol (FTP).

All of these applications should be modified to use the Internet

Domain name to identify the remote node, and not an embedded,

protocol dependent IP address.

3.3 The Entrenched Masses

Will users voluntarily give up their IPv4 systems to move to IPng?

It seems likely that many users will resist the change. They will

perceive no benefit and will not install the new software. Making

the local Internet contact responsible may not be feasible or

practical in all cases. Another issue is backward compatibility

issues. If a host needs to run IPng and IPv4 to support old hosts,

then 1) where is the address savings IPng promised. 2) Why change if

the host you are talking to has IPv4 anyway?

On the other hand, replacing the existing TCP (TCPv6) with this new

version (TCPng) will benefit users in several ways. 1) Users will be

able to connect to unmodified TCPv6 hosts. 2) As nodes upgrade to

TCPng, new features will be enabled allowing TCP to communicate

effectively over high bandwidth*delay network links. 3) System

administrators will be able to incrementally upgrade nodes as needed

or as local conditions demand. 4) Upgraded nodes may return their

IPv4 address and use an IPng address and TCP transporter function,

described later, to communicate with IPv4 hosts.

4. Making TCP & UDP Protocol Independent

The OSI 7 layer model specifies that each layer be independent of the

adjacent layers. What is specified is the interface between layers.

This allows layers to be replaced and/or modified without making

changes to the other layers. As was pointed out previously, the TCP

and UDP transport layers violate this precept. In the following

discussion, when we refer to TCP we mean both the TCP and UDP

protocols. The generic term transport layer and TCP will be used

interchangeably.

Overcoming TCP's dependence on IP will require changes to the

structure of the TCP header. The developers and implementors will

also have to change the way they think about TCP and IP. End users

will also have to change the way they view the Internet. Gone will

be the days when Internet node names and IP addresses can be used

interchangeably. The goal of this change is to allow end users to

migrate from the current IPv4 network layer to an IPng layer. What

this IPng protocol is will be left to the Internet Architecture

Board/Internet Engineering Steering Group/Internet Engineering Task

Force (IAB/IESG/IETF) to decide. By adopting this proposal, the

migration will be greatly enhanced.

One of the stated goals of the IAB is to promote a single Internet

protocol suite [Leiner, Rekhter, 1993]. While this is a laudable

goal, we should not be blinded by it. The addition of a Transport

layer address (TA) does not invalidate the IAB's stated goals. It

merely brings the implementation into compliance with standard

networking practices. The historical reasons for concatenating TCP

port numbers to IP numbers has long since passed. The increasing

throughput of transmission lines and the negligible effect of packet

overhead (see appendix A) prove this. The details of assigning and

using TA's are discussed in the next few sections.

4.1 Transport Addressing

A Transport Address (TA) will be assigned to the TCP transport layer

on each Internet node. The purpose of this address is to allow a TCP

on one node to communicate with a TCP on a remote node. Some of the

goals defined in developing this address are:

1. Fixed size -- A fixed size will make parsing easier for

decoding stations.

2. Minimum impact on TCP packet size -- This information

will need to be carried each TCP packet.

3. Global Uniqueness -- It is desirable (required) to have a

globally unique Transport Address.

4. Automatic Registration -- To reduce implementation

problems, an automatic registration of the TA is

desirable.

The TA will be used when an Internet node attempts to communicate

with another Internet node. Conceptually you can view the TA as

replacing the IP number in every instance it now appears in the

transport layer (i.e., a socket would change from IP#.Port# to

TA#.Port#). A connection setup would thus be:

1. A user starts an application on Node-A and requests

service from Node-B. The user identifies Node-B by

referencing it's Internet Domain Name.

2. The TCP on Node-A makes a Domain Name Service (DNS) call

to determine the TA of Node-B.

3. Node-A constructs a TCP packet using the header Src = TA-

A.port and Dest = TA-B.port and passes this packet down to

the network layer.

4. The IP on Node-A makes a DNS call to determine the IP

address of Node-B. The IP will cache this TA/IP pair for

later use.

5. Node-A constructs an IP packet using the header Src = IP-A

and Dest = IP-B and passes this packet down to the Media

Access layer.

6. Delivery of the packet is identical to the delivery of an

existing Internet IP packet.

7. The IP on Node-B examines the IP Dest address and if it

matches it's own, strips off the header and passes the

data portion up to the TCP. (Note: the packet may have

passed through several IP routers between the source and

destination hosts.)

8. The TCP on Node-B examines the header to determine if the

Dest TA is it's own, if so it passes the data to the

application specified by the port address. If not it

determines if it should perform the transporter function.

The packet will be forwarded toward the destination or an

error message will be returned.

The above steps represent a quick synopsis of how user applications

may pass data between different Internet nodes. The exact structure

of the network is hidden from the application, allowing the network

to be modified and improved as needed. Using the transporter

function, several different network layers may be traversed when

moving from source to destination (several examples are provided in

appendix D).

One of the underlying assumptions is that the user application must

refrain from making assumptions about the network structure. As

pointed out in section 3, this is not the case for the current

Internet network. User applications that are deployed with this new

TCP must be capable of making this assumption. This means that the

user application should store the Internet Domain Name in it's

internal structure instead of the IPng network number. The domain

name is globally unique and provides enough information to the system

to find the transport and network layer addresses. The user

application must pass the following parameters down to TCP:

1. Destination domain name (Text string)

2. Pointer to data buffer

3. Quality of service indicators

4. Options

When the user application writes data to the network, TCP will return

a nonzero integer to indicate an error condition, or a zero integer

to indicate success. When the user application reads data from the

network, TCP will deliver a pointer to a data buffer back to the

application.

TCP will receive the users request and it will make a DNS call to

determine the destination nodes TA. If DNS returns a TA, TCP will

build a Transmission Control Block (TCB) (see the paragraph below)

and call the network layer. Otherwise, TCP will make a DNS call

looking for the destination nodes IPv4 address. If an address is

returned, TCP will takes the steps listed below in building a TCB,

and call the proper network layer. If DNS returns a host unknown

indication, exit back to the user with a "host unknown" error. TCP

should maintain a cache of domain names and addresses in lieu of

making repeated DNS calls. This feature is highly recommended, but

not required.

The state information needed to keep track of a TCP connection is

kept in the Transmission Control Block (TCB). Currently this

structure has fields for the TCP parameters, source port, destination

port, window size, sequence number, acknowledgment number, and any

TCP options. The network layer source and destination IP numbers are

also stored here. Finally, the status of the connection (LISTEN,

ESTABLISHED, CLOSING, of the TCP parameters and include the new

source and destination Transport addresses. The existing space for

the IPv4 addresses will be left in place to allow for backward

compatibility. The IPv4 fields will be used if the source is

communicating directly with an unmodified TCP/IP host.

The existing status indicators will remain with their meaning

unchanged. Connection setup will retain the current 3-way handshake.

When performing transporter functions, TCP will NOT build a TCB,

unless the destination is an unmodified IPv4 host (see appendix D).

The TCP connection remains an end-to-end reliable transport service,

regardless of the number of intermediate transporter nodes.

TCP will build an old or new header (defined below) placing the user

application data in the data field. If TCP is communicating directly

with an unmodified IPv4 host, the existing TCP header (STD 7, RFC

793) will be used for comparability reasons. If the destination host

is an unmodified host, and an intermediate transporter node is being

used, this new TCP header must be used with the 'C' bit set to 1.

The destination TA will be set to the IPv4 address, and the packet

will be delivered to the transporter node. If the destination host

is modified with this new TCP, the destination address will be set to

the TA and the packet will be delivered, possibly through a

transporter, to the remote host.

TCP will communicate with it's underlying network layer(s) to deliver

packets to remote hosts. The Internet Assigned Number Authority

(IANA) will assign unique identifiers to each network layer TCP will

support. TCP will maintain a cache of TA's and IANA network layers

numbers, to allow support of multiple network layers. When TCP

wishes to send data, it will consult this cache to determine which

network to send the packet to. If the destination TA is not in this

cache, TCP will send a request to each of it's network layer(s)

aSKINg if they know how to deliver data to this TA. All of the

network layers supported by the sending host will be probed, in an

order defined by the system administrator, until one responds 'yes'

or they all have said 'no'. The first layer to say 'yes' will be

used. If no path exists, an error message will be returned to the

user application. Once a network layer is identified, TCP will

communicate with it by passing the following parameters:

1) Destination address (TA or IPv4).

2) A pointer to the data buffer.

3) Options.

The network layer will use the destination address as an index into a

cache to determine the network address to send to. In the entry is

not in the cache, it will make a DNS call to determine the network

address and a cache entry will be build (see appendix D). It is

mandatory that a cache be maintained. If a host is attached to

several different networks (i.e., a transporter) each layer will

maintain it's own cache.

When IP receives a data packet from a remote node, it will strip off

the IP header and pass a pointer to the data buffer up to TCP. IP

will also supply TCP with it's IANA network layer number. TCP may

use the source TA and the IANA number to update it's cache.

The structure of a TA is to concatenate a unique manufacture code

with a manufacturer defined variable to form a unique 64 bit number.

The unique manufacture code will be a 24 bit number, possibly the

same code as the IEEE 802.3 MAC address code. The remaining 40 bits

will be supplied by the manufacture to uniquely identify the TCP. It

is recommended that this field be built by encoding the

manufacturer's serial number. An integer serial number will be

viewed as an integer number and converted into it's hexadecimal

equivalent, left padded with 00 octets if necessary. If a serial

number contains Alpha characters, these alpha characters will be

converted into octets using the international standard ASCII code.

The integer values will then be converted to their hexadecimal

equivalent and the 2 values will be concatenated to form the unique

identifier. These structure will allow 2^24 (16,777,216)

manufactures to build 2^40 (1,099,511,627,776) transport addressable

entities. Each of these entities may have 1 or more network

interfaces using IPv4, IPng, or any other network layer protocol.

The current growth of the Internet may indicate that this amount of

address space is inadequate. A larger fixed space (i.e., 96 or 128

bits) or a variable length field may be required. The disadvantage

is that this address must be transmitted in every packet.

4.2 TCPng

The new TCP header is as shown.

1 2 3

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

+ Destination TA +

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

+ Source TA +

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Destination Port Number ver

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Source Port Number QoS

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Window Size

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

+ Sequence Number +

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

+ Acknowledgment Number +

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

data offset XXCAPRSF Checksum

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

/ Variable length option 1 /

\ : / : /

\ Variable length Option n +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1

Destination TA: 64 bits.

The Destination Transport Address. The concatenation of

the 24 bit IEEE assigned Ethernet address and the 40 bit

representation of the machines serial number for the

remote node.

Source TA: 64 Bits.

The Source Transport Address. The concatenation of the

24 bit IEEE assigned Ethernet address and the 40 bit

representation of the machines serial number for the

local node.

Destination Port Number: 28 Bits.

Identifies the specific application on the remote node.

Ver: 4 bits.

Version number. This is TCPng. RFC793

references 9 earlier editions of ARPA TCP. The current

TCP is version 10.

Source Port Number: 28 Bits.

Identifies the specific application on the local node.

QoS: 4 bits.

The Quality of Service parameter may be set by the user

application and passed down to a network layer that

supports different levels of service.

Window: 32 Bits.

The number of data octets beginning with the one

indicated in the acknowledgment field which the sender

of this segment is willing to accept.

Sequence Number: 64 Bits.

The sequence number of the first data octet in this segment

(accept when the S bit is present). If S bit is on, the

sequence number is the initial sequence number (ISN) and

the first data octet is ISN+1. (The ISN is computed using

the existing algorithm).

Acknowledgment Number: 64 Bits.

If the A bit is set, this field contains the value of

the next sequence number the sender of this segment is

expecting to receive. Once a connection is established,

this is always sent.

Data Offset: 8 Bits.

This is the number of 32 bit Words in the TCP header. This

indicates where the data begins. The TCP header is an

integral number of 32 bit words long. The minimum value is

12 and the maximum is 256. If options are used, they must

pad out to a 32 bit boundary.

Flags: 8 Bits.

The A, P, R, S, and F flags carry the same meaning as in

the current version of TCP. They are:

1. A = Ack, and acknowledgment field significant

2. P = Push, the push function

3. R = Reset, reset the connection

4. S = Sync, synchronize sequence numbers

5. F = Fin, No more data from sender

The C bit, C = Compatibility, is used to indicate that one

end of the connection is an unmodified TCP/IP host. When

the C bit is set, all header values must conform to the

TCPv6 specifications. The source port, destination port,

and window size must be 16 bits and the Sequence and

Acknowledgment numbers must be 32 bits. These values are

stored in the lower half of the proper area with null octet

pads filling out the rest of the field.

The 2 X bits, X = Reserved, are not defined and must be

ignored by a receiving TCP.

Checksum: 16 Bits.

The checksum field has the same meaning as in the current

version of TCP. The current 96 bit pseudo header is NOT

used in calculating the checksum. The checksum covers only

the information present in this header. The checksum field

itself is set to zero for the calculation.

Variable Length Options:

There are two types of options, mandatory and optional. A

TCP must implement all known mandatory options. It must

also be capable of ignoring all optional options it does

not know about. This will allow new options to be

introduced without the fear of damage caused by unknown

options. An option field must end on a 32 bit boundary.

If not, null octet pad characters will be appended to the

right of the option. The structure of an option is shown

in figure 2 below:

1 2 3

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type Length

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Option data pad

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2

4.3 Mandatory Options

There are three mandatory options defined by this implementation of

TCP. Each of these options is implemented using the structure

pictured in figure 2 above.

A description of each field follows:

Type: 16 bits

The type field identifies the particular option.

Length: 16 bits

The length field represents the size of the option

data to follow, in octets.

Option Data: Variable Length

The option data is of variable length specified by

the length field, plus 0-3 bytes of zeros to pad to a

32-bit boundary.

The following are the 3 mandatory options that must be implemented:

Null: 8 bits

The null option, (type=0) is represented by the bit

sequence [00000000], preceded by an additional 8, zero

padding bits to fill out the full 16-bit type field. The

data may be of any size, including 0 bytes. The option may

be used to force an option to be ignored.

Maximum Segment Size: 8 bits

The maximum segment size option, (type=1) is represented by

the bit sequence [00000001] preceded by an additional 8,

zero padding bits to fill out the full 16-bit type field.

If this option is present, then it communicates the maximum

receive segment size at the TCP which sends this segment.

This potion is mandatory if sent in the initial connection

request (SYN). If it is sent on any other segment it is

advisory. The data is a 32-bit word specifying the segment

size in octets [Ullmann, 1993].

Urgent Pointer: 8 bits

The urgent pointer, (type=2) is represented by the bit

sequence [00000010] preceded by an additional 8, zero

padding bits to fill out the full 16-bit type field. This

option emulates the urgent field in TCPv6. The data is a

64-bit sequence number identifying the last octet of urgent

data within the segment.

4.4 Optional Options

This version of TCP must be capable of accepting any unknown options.

This is to guarantee that when presented with an unrecognized option,

TCP will not crash, however it must not reject or ignore any option.

4.5 Compatibility Issues

The Internet community has a large installed base of IP users. The

resources required to operate this network, both people and machine,

is enormous. These resources will need to be preserved. The last

time a change like this took place, moving from NCP to TCP, there

were a few 100 nodes to deal with [Postel, 1981c]. A small close

knit group of engineers managed the network and mandated a one year

migration strategy. Today there are millions of nodes and thousands

of administrators. It will be impossible to convert any portion of

the Internet to a new protocol without effecting the rest of the

community.

In the worst case, users will lose communications with their peers as

some systems upgrade and others do not. In the current global

environment, this will not be tolerated. Any attempt to simply

replace the current IPv4 protocol with a new IPng protocol that does

not address compatibility issues is doomed to failure. This

reasoning has recently been realized by Ullmann (CATNIP) and he

attempts to use translators to convert from one protocol to another

(i.e., CATNIP to IPv4). The problem is what to do when incompatible

parameters are encountered. Also CATNIP would need to be replaced

every time a new network layer protocol was developed.

This proposal attempts to solve these problems by decoupling the

transport and network protocols. By allowing TCP to operate over

different network layer protocols, we will create a more stable

environment. New network layer protocols could be developed and

implemented without requiring changes that are visible to the user

community. As TCP packets flow from host-to-host they may use

several different network layers, allowing users to communicate

without having to worry about how the data is moved across the

underlying network.

4.5.1 Backward Compatibility

It may be said that the maturity of a software package can be

determined by how much code is required to maintain compatibility

with previous versions. With the current growth of the Internet,

backward compatibility issues can not be dismissed or added in as an

after thought. This version of TCP was designed with backward

compatibility in mind. When the TCP communicates with an unmodified

IPv4 TCP/IP, it takes steps to insure compatibility. First off it

sets a bit in the header indicating that the TCP parameters (ack,

seq, port numbers, and window size) use the TCPv6 values. When

communicating directly with an unmodified host the existing TCP/IP

header is used. Only existing TCP options may be sent as well.

The advantage of this approach is that TCP transporter nodes will not

have to make decisions about how to modify packets just passing

through. It is up to the source node to build a header that is

compatible before sending it. This approach will allow any new TCP

to contact and communicate with any unmodified IPv4 host. The source

host may have an IPv4 address, or it may send data to a transporter

for delivery. The decision will be made based on the source and

destination addresses. During connection setup, the location of the

destination node is determined and the proper network layer is used

to send data.

An existing IPv4 host will be capable of opening a connection to any

new TCPng host that is directly connected to the network with an IPv4

protocol stack. If the TCPng host only has an IPng stack, the

connection attempt will fail. Some existing batch style services

(i.e., Simple Mail Transfer Protocol - SMTP) will continue to work

with the help of transporters. Interactive sessions (i.e., Telnet)

will fail. Thus, our new TCP is backward compatible, but the

existing IPv4 hosts are not forward compatible.

4.6 Level 4 Gateways

The ability to allow hosts with differing network layer protocols to

communicate will be accomplished by using a transport layer gateway

(called transporter in this paper). The transporter works just like

an IP router, receiving TCP packets from one network layer and

transporting them over to another. This switching is done by

examining the packets source and destination TA's. If a TCP packet

arrives with a destination TA that differs from this hosts TA, and

the transporter functionality is enabled, the packet should be

transported to another network layer. In some cases, the receiving

node is a host and not a transporter (i.e., transporter functionality

disabled). In this case the host will discard the packet and return

a TCMP (see below) error message.

A transporter is not responsible for reading or formatting the TCP

header of packets it receives. The header is simply examined to

determine where to deliver the packet. When forwarding, the packet

is sent to any of the network layers the transporter supports. The

exception is that the packet may not be presented back to the network

it was received from. It is the responsibility of the network layer

to destroy undeliverable packets. If a transporter is unable to

determine which network the packet should be forwarded to, the packet

is discarded and a TCMP message is generated and returned to the

original source host. Several examples of how transporting works are

presented in appendix D.

4.7 Error Conditions

It is recognized that from time to time certain error conditions will

occur at some intermediate transporter that will need to be

communicated back to the source host. To accomplish this a Transport

Control Message Protocol (TCMP) service facility will need to be

developed. This protocol will model itself after the Internet

Control Message Protocol (ICMP). The operational details are

discussed in a separate TCMP document.

5. Advantages and Disadvantages of this approach

This proposal offers the Internet community several advantages.

First, TCPng will operate over multiple network layer protocol

stacks. Users will be able to select the stack(s) that meets their

needs. The problem of IPv4 address exhaustion will be postponed as

sites move from IPv4 to IPng protocol stacks. Future IP3g protocol

stacks may be designed and deployed without major service

disruptions. The increased size of the sequence, acknowledge, and

window fields will allow applications to run effectively over high

bandwidth-delay network links. Lastly, TCPng will allow applications

to specify certain Quality of Service (QoS) parameters which may be

used by some network layer protocols (i.e., Asynchronous Transfer

Mode - ATM).

This protocol is not without it's share of design compromises. Among

these are a large packet header increased in size from 5 to 12 long

words. The addition of a TA means that network administrators must

deal with yet another network number that must be globally

maintained. Multiple network protocols may add to the complexity of

a site's network. Lastly, is the TA address space large enough so we

will not have to rebuild TCP.

6. Conclusions

In this paper, we have reviewed the current status of the Internet

society s IPng initiative. We were struck by the enormity of the

changes required by those proposals. We felt that a different

approach was needed to allow change to occur in a controlled manner.

This approach calls for replacing the current TCP protocol with one

that does not require a specific IP layer protocol. Once this is in

place, various IPng protocols may be developed and deployed as sites

require them. Communications between IPv4 and IPng hosts will be

maintained throughout the transition period. Modified hosts will be

able to remove their IPv4 protocol stacks, while maintaining

communications with unmodified hosts by using a TCP transporter.

The title of this paper "Six Virtual Inches to the Left" comes from a

talk the author once heard. In this talk an engineer from Control

Data Corporation (CDC) told a story of CDC's attempt to build a

cryogenically cooled super computer. The idea being that the power

consumption of such a computer would be far lower then that of a

conventional super computer. As the story goes, everyone thought

this was a great idea until someone pointed out what the power

requirements of the cryo system were. The result was that all the

assumed power savings were consumed by the cryo system. The

implication being that all the power requirements were not saved but

simply moved 6 feet from the CPU to the support equipment. The moral

being that the entire system should be analyzed instead of just one

small piece.

References

[Postel, 1981a] Postel, J., "Transmission Control Protocol - DARPA

Internet Program Protocol Specification", STD 7, RFC793, DARPA,

September 1981.

[Halsal, 1992] Data Communications, Computer Networks, and Open

Systems.

[Meyer, Zobrist, 1990] TCP/IP versus OSI, The Battle of the

Network Standards, IEEE Potentials.

[Braden, et al, 1991] Clark, D., Chapin, L., Cer, V., Braden, R., and

R. Hobby, "Towards the Future Internet Architecture", RFC1287,

MIT, BBN, CNRI, ISI, UCDavis, December 1991.

[Dixon, 1993] Dixon, T., "Comparison of Proposals for Next Version of

IP", RFC1454, RARE, May 1993.

[Fuller, et al, 1992] Fuller, V., Li, T., Yu, J., and K. Varadhan,

"Supernetting: an Address Assignment and Aggregation Strategy",

RFC1338, BARRNet, cicso, Merit, OARnet, June 1992.

[Almquist, Gross, 1992] Gross, P., and P. Almquist, "IESG

Deliberations on Routing and Addressing", RFC1380, IESG Chair,

IESG Internet AD, November 1992.

[Postel, 1981b] Postel, J., "Transmission Control Protocol - DARPA

Internet Program Protocol Specification", STD 7, RFC793, DARPA,

September 1981.

[Postel, 1980] Postel, J., "User Datagram Protocol", STD 6, RFC768,

USC/Information Sciences Institute, August 1980.

[Postel, 1981c] Postel, J., "NCP/TCP Transition Plan", RFC801,

USC/Information Sciences Institute, November 1981.

[Leiner, Rekhter, 1993] Leiner, B., and Y. Rekhter, "The

Multi-Protocol Internet" RFC1560, USRA, IBM, December 1993.

[Ullmann, 1993] Ullmann, R., "TP/IX: The Next Internet", RFC1475,

Process Software Corporation, June 1993.

Bibliography

Gilligan, Nordmark, and Hinden, "The SIPP Interoperability and

Transition Mechanism", IPAE, 1993.

Jacobson, V., and R. Braden, "TCP Extensions for Long-Delay Paths",

RFC1072, LBL, USC/Information Sciences Institute, October 1988.

Jacobson, V., Braden, R., and D. Borman, "TCP Extensions for High

Performance", RFC1323, LBL, USC/Information Sciences Institute, Cray

Research, May 1992.

Jacobson, V., Braden, R., and L. Zhang, "TCP Extension for High-Speed

Paths", RFC1185, LBL, USC/Information Sciences Institute, PARC,

October 1990.

Leiner, B., and Y. Rekhter, "The Multiprotocol Internet", RFC1560,

USRA, IBM, December 1993.

O'Malley, S., and L. Peterson, "TCP Extensions Considered Harmful",

RFC1263, University of Arizona, October 1991.

Westine, A., Smallberg, D., and J. Postel, "Summary of Smallberg

Surveys", RFC847, USC/Information Sciences Institute, February 1983.

Appendix A

The minimum size of an ethernet frame is 64 bytes. With the existing

TCP/IP protocol, a minimum size frame is 18 bytes (ethernet header &

trailer) + 20 bytes (IP header) + 20 bytes (TCP header) for a total

of 58 bytes. The transmitting station must add 6 null pad characters

to this frame to make it conform to the 64 byte minimum. This new

TCP will increase the size of the TCP header to 48 bytes.

SuBTracting 26 bytes (the old header and pad characters) we are left

with 22 bytes or 176 bits. The time it takes to transmit these

additional bits is the impact of this new TCP. The transmission time

for several types of media currently used is shown in the table

below. You will note that the increased times are all under 20

micro-seconds for anything over T1 speeds. User traffic patterns

vary of course but it is generally agreed that 80% of the traffic

stays at the local site. If this is true then the increased header

size has a negligible impact on communications.

Media Speed (Mbps) Rate (nsec/bit) time (usec)

------ ------------ --------------- ----------

T1 1.544 647.7 144.00

T3 44.736 22.4 3.91

Enet 10.00 100.0 17.60

FDDI 100.00 10.0 1.76

OC-1 51.84 19.3 3.40

OC-3 155.52 6.4 1.13

Appendix B

In order to support the TA, new DNS entries will need to be created.

It is hoped that this function will be accomplished automatically.

When a station is installed, the local DNS server is defined. On

power up, the station will contact this server and send it it's TA

and domain name. A server process will be listening for this type of

information, and it will collect the data, run an authorization

check, and install the TA into the DNS server. The following entry

will be made.

node.sub.domain.name IN TA xx.yy.zz.aa.bb.cc.dd.ee

ee.dd.cc.bb.aa.zz.yy.aa.in-addr.tcp IN PTR node.sub.domain.name.

Using these entries, along with the existing DNS A records, a

requesting node can determine where the remote node is located. The

format xx.yy.zz is the IEEE assigned portion and aa.bb.cc.dd.ee is

the encoded machine serial number as described in section 4.1.

Appendix C

Proposed UDP Header

1 2 3

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

+ Destination TA +

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

+ Source TA +

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Destination Port Number ver

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Source Port Number QoS

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Length Checksum

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

/ Data /

\ : / : /

\ : +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Destination TA: 64 bits.

The Destination Transport Address. The concatenation of

the 24 bit IEEE assigned Ethernet address and the 40 bit

representation of the machines serial number for the remote

node.

Source TA: 64 Bits.

The Source Transport Address. The concatenation of the 24

bit IEEE assigned Ethernet address and the 40 bit

representation of the machines serial number for the local

node.

Destination Port Number: 28 Bits.

Identifies the specific application on the remote node.

Ver: 4 bits.

This parameter the UDP version number in use within this

packet.

Source Port Number: 28 Bits.

Identifies the specific application on the local node.

QoS: 4 bits.

The Quality of Service parameter may be set by the user

application and passed down to a network layer that

supports different levels of service.

Length: 16 bits

The length parameter represents the length of the data area

in octets. This value will be set to zero if no data is

sent within this packet.

Checksum: 16 bits

The checksum parameter has the same meaning as in the

current version of UDP. The current 96 bit pseudo header

is NOT used in calculating the checksum. The checksum

covers only the information present in this header. The

checksum field itself is set to zero for the calculation.

Data: Variable

This is the area in which the data for the datagram will be

sent. The length of this data in octets is specified by

the length parameter above.

Appendix D

______ ______

H1 H2

______ ______

\ / \ / ========================= / " "/

" (SIPP) "

" "

"========================="

====================

______ " "

" CLNP "

H4 " "

"===================="

______

\

\

=================== ______

" "

" "------- H3

" IPv4 "

" " _______

"=================="

Example 1: H1 Wishes to Establish Communication with H4 (Refer to the

figure above.)

1. A user on host H1 attempts to communicate with a user

on host H4 by referencing H4 s fully qualified domain name.

2. The TCP on H1 makes a DNS call to determine the TA

address of H4.

3. The DNS call returns only the IPv4 address since H4 is

determined to be an IPv4 only host.

4. The H1 TCP builds a transmission control block (TCB)

setting the C-Bit (compatibility) "ON" since H4 is an IPv4

host. Included in the TCB will also be DA = IP-H4, SA =

TA1, DP = 1234, SP = 5000 and any state parameters

describing the connection (port numbers are for example

purposes only).

5. The IP on H1 makes a DNS call to determine the network

IP address of H4 and correspondingly caches both the TA

address from the TCP as well as the network IP address for

later use.

6. The packet is now routed using standard SIPP procedures

to H2 this is the only path H1 has to H4.

7. H2 receives the packet from H1. The TCP on H2 checks

the destination TA of the packet and compares it to its

own. In this case it does not match, therefore the packet

should be forwarded.

8. H2 s TCP will interrogate the supported network

layer(s) and determines the packet must be forwarded to H3.

9. The TCP must now pass the packet the CLNP network

layer. The network layer checks its cache to determine if

there is a route specified for DA = IP-H4 already in the

cache. If so the cache entry is used, if not an entry is

created. H2 then routes the packet to H3 via NA3a, which

is the network layer address for IP-H4.

10. H3 receives the packet from H2. The TCP on H3 checks

the destination TA of the packet and compares it to its

own. Once again, it does not match.

11. H3, realizing that the destination address is an IPv4

host, and knowing that it itself is directly connected to

the IPv4 network constructs an IPv4 compatible header. H3

also constructs a TCB to manage the IPv4 connection.

12. The packet is sent down to be routed to the IP using

standard IP routing procedures.

13. H4 receives the packet at which point the IP on it

determines that the destination address is its own and thus

proceeds to strip off the IP header and pass the packet up

to the TCP layer.

14. The TCP layer than opens the corresponding IPV4_DP

port (2311) which forms the first half of the connection to

the application.

15. H4 will now reply with a connection accept message,

sending the packet back to H3.

16. H3 s TCP receives the packet and based on information

in the TCB determines the packet should be delivered to H1.

H3 uses the steps outlined above to route the packet back

through the network structure.

Example 2: H2 Wishes to Establish Communication with H3 (Refer to the

figure above.)

1. A user on host H2 attempts to communicate with a user

on host H3 by referencing H3 s fully qualified domain name.

2. The TCP on H2 makes a DNS call to determine the TA

address of H3.

3. The DNS call returns the TA address for H3.

4. The H2 TCP builds a transmission control block (TCB)

setting the C-Bit (compatibility) "OFF" since H3 is an IPng

host. Included in the TCB will also be DA = TA3, SA = TA2,

DP = 1111, SP = 2222 and any state parameters describing

the connection (port numbers are for example purposes

only).

5. The IPng on H2 makes a DNS call to determine the

network IPng address of H3 and correspondingly caches both

the TA address from the TCP as well as the network IPng

address for later use.

6. The packet is now routed to H3 over the IPng supported

on that network.

7. H3 receives the packet from H2. The TCP on H3 checks

the destination TA of the packet and compares it to its

own. In this case it matches.

8. H3 s TCP will construct a TCB and respond with an open

accept message.

9. H3 s TCP will interrogate the supported network

layer(s) to determine the packet must be delivered to H2

using NA2b which is specified in its cache.

Security Considerations

Security issues are not discussed in this memo.

Authors' Addresses

Richard Carlson

Argonne National Laboratory

Electronics and Computing Technologies

Argonne, IL 60439

Phone: (708) 252-7289

EMail: RACarlson@anl.gov

Domenic Ficarella

Motorola

Phone: (708) 632-4029

 
 
 
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