Charles M. Kozierok The TCP-IP Guide

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☯ Internet Architecture Board (IAB): Formerly the Internet Activities Board, the IAB is

charged with overall management of the development of Internet standards. It makes

“big picture” policy decisions related to how Internet technologies and structures

should work, to ensure that various standardization efforts are coordinated and

consistent with overall development of the Internet. It is responsible for publishing

Internet standards (RFCs). It advises the ISOC, and oversees the IETF and IRTF; it

also acts as an appeals body for complaints about the standardization activities

performed by the IETF. The charter of the IAB is described in RFC 2850.

☯ Internet Engineering Task Force (IETF): The IETF focuses on issues related to the

development of current Internet and TCP/IP technologies. It is divided into a number of

working groups (WGs), each of which is responsible for developing standards and

technologies in a particular area, such routing or security. Each area is managed by an

area director (AD), who serves on the IESG. The IETF is overseen directly by the IESG

and in turn by the IAB; it is described in RFC 3160.

Figure 7: Internet Standards Organizations

The Internet Society (ISOC) oversees the IAB, which in turn directs the IETF and IRTF. The IETF develops

current Internet and TCP/IP standards, and is headed by the IESG, which manages IETF working groups

(WGs). The IRTF is the IETF’s research counterpart, containing research groups (RGs) led by the IRSG.

Internet Society (ISOC)

Internet Architecture

Board (IAB)

Internet Engineering

Steering Group (IESG)

Internet Engineering Task Force (IETF) Internet Research Task Force (IRTF)

Internet Research

Steering Group (IRSG)

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Group #1

Wor k ing

Group #3

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Group #2

...

Research

Group #1

Research

Group #3

Research

Group #2

...

☯ Internet Engineering Steering Group (IESG): The IESG is directly responsible for

managing the IETF and the Internet standards development process. It consists of

each of the area directors of the IETF, who make final decisions about the approval of

proposed standards, and works to resolve any issues that may arise in the standard-

ization process. The IESG is technically considered part of the IETF and is also

described in RFC 3160.

☯ Internet Research Task Force (IRTF): Where the IETF is focused primarily on short-

term development issues, the IRTF is responsible for longer-term research related to

the Internet and TCP/IP technologies. It is a much smaller organization than the IETF,

consisting of a set of research groups (RGs), which are analogous to the IETF’s

working groups. The IRTF is overseen by the IRSG and IAB. It is described in RFC

2014.

☯ Internet Research Steering Group (IRSG): The IRSG manages the IRTF in a similar

way to how the IESG manages the IETF. It consists of the chairs of each of the IRTF

research groups and works with the chair of the whole IRTF to make appropriate

decisions on research activities. It is also discussed in RFC 2014.

The Importance of the IETF

Of these organizations, the IETF is the one that you will most often hear referenced,

because that is the organization directly responsible for the development of the majority of

Internet standards. It is for this reason that throughout this Guide, whenever I mention

Internet standards development efforts, I refer to the IETF as doing the work. This is of

course a bit of an oversimplification, since all of these organizations play a role in the

standards development process, described in more detail in a separate topic.

Other Responsibilities of Standards Organizations

I also feel I should re-emphasize that many of these organizations are responsible for a

great deal more than just standards development. This is especially true of the Internet

Society, for which standardization is just one of many activities. The IAB also performs a

number of functions not strictly associated with standards development, including

managing the assignment of protocol values done by IANA and acting as a liaison between

the Internet standards organizations and other standards bodies.

Key Concept: A group of related organizations is responsible for the development of

TCP/IP standards and Internet technologies. The Internet Society (ISOC) has overall

responsibility for many Internet activities including standards development. It

oversees the Internet Architecture Board (IAB), which makes high-level decisions about

Internet technology development. Most of the actual work of creating current Internet

standards is performed by the Internet Engineering Task Force (IETF), which is managed

by the Internet Engineering Steering Group (IESG). Longer-term research is done by the

IETF’s sibling organization, the Internet Research Task Force (IRTF), led by the Internet

Research Steering Group (IRSG).

Internet Registration Authorities and Registries (IANA, ICANN,

APNIC, ARIN, LACNIC, RIPE NCC)

The success of the global Internet relies on the development of universally-accepted

standards for protocols and other technologies. Internet standards organizations such as

the IETF are thus critically important; they manage the standards development process, to

ensure that everyone agrees on how to create hardware and software that will work

together to communicate world-wide.

Important Standardization Functions

While the need to standardize protocols seems obvious, there are a couple of other aspects

to Internet standardization that are equally important but perhaps not quite as well

understood:

☯ Parameter Standardization: Most protocols rely on the use of parameters that control

how they function. As just two of many, many examples, the Internet Protocol has a set

of numbers that define different IP options, and the Address Resolution Protocol (ARP)

has an Operation Code field that can take on many different values. Just as it is

essential for devices to agree on what protocols to use, they must also agree on what

parameters to use for those protocols, if communication is to be successful.

☯ Global Resource Allocation and Identifier Uniqueness: There are a number of

resources that are used on the Internet that must be allocated from a fixed set of

values and where uniqueness in assignment is essential. The most obvious example

is that each TCP/IP host must have a unique IP address; another important example is

ensuring that only one organization uses a given DNS domain name. If two devices

have the same IP address or two organizations try to use the same domain name, the

results would be unpredictable, but almost certainly bad.

Internet Centralized Registration Authorities

In both of the cases above, some sort of centralized organization is required. We need a

group to take responsibility for managing parameters and ensuring that everyone uses the

same ones, just as they use the same protocols. We also need to coordinate the

assignment of identifiers such as addresses and names, to ensure that they are created

and allocated in a way that is acceptable to all. In the world of the Internet, these are

sometimes called management authorities or registration authorities.

The organization originally responsible for this task was the Internet Assigned Numbers

Authority (IANA). Amazingly, while the name makes it sound like the IANA was a huge

bureaucracy, it was effectively one man: Jonathan B. (Jon) Postel, one of the most

important pioneers of Internet and TCP/IP technologies. Jon Postel ran IANA until his

untimely and unfortunate death in 1998.

IANA was originally charged with the task of managing which IP address blocks had been

assigned to different companies and groups, and maintaining periodically-published lists of

Internet parameters such as UDP and TCP port numbers. It also was in charge of registra-

tions of DNS domain names, which were more directly handled by the Internet Network

Information Center (InterNIC), a service managed by the United States government.

Network Solutions Inc. (NSI) was later granted the contract to manage the InterNIC, and

was eventually purchased by Verisign.

As the Internet continued to grow, an effort commenced in the mid-1990s to define a new

organization that would be responsible for the central registration of Internet addresses and

names. This took the form of a new private, non-profit company called the Internet Corpo-

ration for Assigned Names and Numbers (ICANN). ICANN is officially charged with all of the

centralized registration tasks I have mentioned so far in this topic, including IP address

assignment, DNS domain name assignment, and protocol parameters management.

In a simpler world, this development would have meant that ICANN would have replaced

IANA, which would no longer exist. Instead, ICANN kept IANA around, leaving that organi-

zation in charge of overseeing IP address registration and Internet parameters. ICANN is of

course now in charge of IANA, so really both organizations are responsible for IP

addresses and parameters. This often leads to confusion, and to make things worse, it is

common to see IANA and ICANN mentioned in conjunction as “IANA/ICANN” or “ICANN/

IANA”.

Key Concept: Internet registration authorities are centralized organizations respon-

sible for coordinating protocol parameters and globally-assigned resources such as

IP addresses. The first such organization was the Internet Assigned Numbers

Authority (IANA), which was initially in charge of IP address assignment, DNS domain

name management and protocol parameters.Today the Internet Corporation for Assigned

Names and Numbers (ICANN) has overall responsibility for these activities; the IANA

operates under the auspices of ICANN and is still responsible for IP address assignment

and parameter coordination.

Modern Hierarchy of Registration Authorities

In the original “classful” IP addressing scheme, addresses were assigned to organizations

directly by IANA in address blocks: Class A, Class B and Class C addresses. Today, a

hierarchical, classless addressing system called Classless Inter-Domain Routing (CIDR) is

used instead. Address assignment in CIDR involves the hierarchical allocation of blocks of

addresses, starting with large blocks that are given to big organizations, which split them to

assign to smaller groups. (Much more detail on these methods can be found in the large

section on IP addressing.)

IANA, as the organization in charge of all IP addresses, assigns the largest blocks of

addresses to regional Internet registries (RIRs) that are responsible for further allocation

activities. Each RIR manages IP addresses and other Internet number resources (such as

autonomous system numbers) for a particular region. The four regional registries are:

☯ Asia Pacific Network Information Centre (APNIC): Covers the Asia/Pacific region.

☯ American Registry for Internet Numbers (ARIN): Manages North America, part of

the Caribbean, and sub-equatorial Africa.

☯ Latin American and Caribbean Internet Addresses Registry (LACNIC): Respon-

sible for Latin America and part of the Caribbean.

☯ Réseaux IP Européens Network Coordination Center (RIPE NCC): Takes care of

Europe, the Middle East, Central Asia, and Africa north of the equator.

Each registry may assign address blocks to Internet service providers (ISPs) directly, or

further delegate them to national Internet registries (NIRs) or smaller local Internet regis-

tries (LIRs). See the topic on IP address allocation issues for more details.

Name registration has changed over the last several years. It is no longer part of IANA’s

responsibilities, and ICANN has opened up the name registration business so it is no longer

the province of a single organization such as InterNIC/Network Solutions/Verisign. Now,

many different accredited registrars can be used for name registration in many of the

popular top-level domains. This is discussed in the topic on DNS public registration.

On The Web: The complete list of documents containing Internet and TCP/IP

protocol parameters can be found on the IANA’s web site at: http://www.iana.org/

numbers.html

Internet Standards and the Request For Comment (RFC)

Process

The precursors of the modern Internet were diminutive networks developed and run by a

small group of computer scientists and engineers. These technologists knew that devel-

oping open, widely-adopted standards would be essential to the eventual growth of the

Internet and the TCP/IP protocol suite. But there was no formalized standards development

mechanism back then.

Consensus-Based Standardization Using Requests For Comments (RFCs)

Standardization was achieved largely through building consensus through discussion about

new technologies and protocols. If someone had a proposal for a new protocol or

technology, or an idea for a change to an existing one, that person would create a

memorandum describing it and circulate it to others. Since the goal was to solicit comments

on the proposal, these memos were called requests for comments (RFCs). Not all RFCs

described formalized standards: many were just descriptive documents, clarifications or

miscellaneous information.

Note: The documents defining early standards were originally called Internet

Engineering Notes (IENs) before they were called RFCs.

Today, of course, the Internet is enormous and there is an official structure of Internet

standards organizations that is responsible for creating new Internet and TCP/IP standards.

Due to the many thousands of people who play an active role in developing Internet

technologies, having an informal system where anyone could just write an RFC would lead

to chaos. Thus, Internet and TCP/IP standards are still called RFCs, but the process of

creating one is much more formal and organized today.

The Internet Engineering Task Force (IETF) is the standards body that is most directly

responsible for the creation of Internet standards. The IETF’s working groups, overseen by

the Internet Engineering Steering Group (IESG) and the Internet Architecture Board (IAB),

develop new protocols and technologies continuously, and these developments are

formalized in RFCs.

The publishing of RFCs is handled by the office of the RFC Editor. From nearly thirty years,

starting in 1969, “the” RFC Editor was Internet pioneer Jon Postel. After his death in 1998,

the function was assigned to the Networking Division of the USC Information Sciences

Institute (ISI), where Jon Postel was once director. The function of the RFC Editor is to

publish and archive RFCs, and maintain an online repository of these documents so that

they can accessed and used by the Internet community.

The open and free access to RFCs has greatly contributed to the Internet’s success. If you

consider that even today there are standards bodies that charge thousands of dollars for

access to a single standard, the ability to log on and immediately retrieve any of the

thousands of RFCs is noteworthy.

On The Web: An up-to-date list of RFCs with hyperlinks to each document (except

for some of the early ones) can be found at the office of the RFC Editor: http://

www.rfc-editor.org/rfc-index.html

RFC Categories

As before, not all RFCs are official Internet standards, which is important to remember.

Each RFC has a category or status associated with it that indicates its disposition:

☯ Proposed Standard / Draft Standard / Standard: These are documents that describe

technologies said to be on the “standards track”. That means they are either already

formally approved as standards, or they are likely to become standards in the future. In

many cases, the document is just given as “Standards Track” as opposed to one of

those three precise labels. See below for more information.

☯ Best Current Practice: A document providing guideline information or recommenda-

tions from the IETF that is not a formal standard.

☯ Informational: A document that provides general information or commentary.

☯ Experimental: A proposal for an experimental standard that is not on the standards

track. In some cases, protocols or proposed changes to existing protocols that are not

accepted as formal standards are changed to “experimental” status.

☯ Historic: Former standards that have been obsoleted.

The Internet Standardization Process

The full process for creating and publishing an Internet standard is lengthy and beyond the

scope of this Guide. It is interesting, however, so I will outline it here briefly. The full details

of the standards process can be found in… where else, an Internet RFC: 2026. ☺

Before a proposal will be considered for the Internet standardization process, it must be

published as an Internet Draft (ID). The IETF publishes a set of guidelines that specify how

IDs must be created and submitted. Most IDs are written by members of working groups

within the IETF who are involved in specific projects. However, since the standards process

is open, any member of the public can make an independent submission for review as a

standard, by creating an ID for consideration by the IETF and IESG. Internet Drafts are

usually revised many times based on feedback from others in various working groups within

the IETF.

If an Internet Draft has been reviewed and is considered valuable, well-understood and

stable (meaning that it is not being rapidly updated with new revisions) it may become a

candidate for standardization. The IESG can place the Draft on the Internet standards track

by changing its status to Proposed Standard. Documents of this status are considered

mostly complete, but may still be revised based on further review, testing and experimen-

tation with the technology.

Once the specification is sufficiently mature and widely accepted, it may be elevated from

Proposed Standard to Draft Standard. A key requirement for such advancement is that the

technology must be demonstrated to be functional on at least two independent and interop-

erable implementations. This proves that the standard is sufficiently clear and complete that

at least two different groups have been able to implement it compatibly.

A document only reaches Draft Standard when the IETF community believes it is technically

mature and the specification is complete. Changes are usually made to Draft Standards

only to correct problems encountered in testing, or resolve new issues that arise.

The final “station” on the Internet standards track is Internet Standard. This designation is

only applied to very mature specifications that are popular and that have been widely imple-

mented. A document that reaches this status often describes a technology that is or will

become universally-implemented, and is assigned an “STD” (“standard”) number.

The RFC development process can take months or even years, depending on how complex

the technology is, how many changes are required to the documents, and whether or not

the proposal is considered important or interesting. Many RFCs never make it officially to

Internet Standard status; Draft Standard status is generally considered sufficiently stable

that the technology is often just implemented by companies when that level is reached.

Some RFCs never even make it to Draft Standard status and the technologies they

describe are still used in products.

Once an RFC is published, it cannot be changed. This is a specific policy decision intended

to avoid the confusion that would otherwise result due to there being multiple versions of

the same RFC. The RFC publication process incorporates a number of steps at which RFC

authors can revise their documents, and check for editorial omissions and errors.

This need for a new document whenever a change is made is also why proposals are

typically published with a category designation of “Standards Track” rather than “Proposed

Standard”, “Draft Standard” and “Internet Standard”. This eliminates the need to publish a

new RFC that has no changes other than a different category designation, if a proposal

advances down the standards track without requiring any real changes.

Key Concept: Internet standards are described in a series of documents called

requests for comments (RFCs). The RFC process describes how an Internet

standard is usually created. An idea for a new technology or enhancement begins

with the creation of an Internet Draft (ID). After review and feedback, if the proposal has

support, it may be placed on the Internet standards track, and its status changed to

Proposed Standard. As the fledgling standard matures, its status may advance to Draft

Standard and eventually, Internet Standard. However, many RFCs are implemented in

products without reaching Internet Standard status. There are also other RFCs that define

experimental technologies or provide information without describing official Internet

standards.

Backgrounder: Data Representation and the

Mathematics of Computing

Humans use decimal (base 10) numbers to represent numeric information, and various

alphabets and symbol systems to represent other types of information. In contrast,

computers understand only one basic type of information: ones and zeroes, which

themselves are representative of either an “on” or “off” electrical or light state within the

hardware of the device. These ones and zeroes are combined in various ways to form all

the more common data elements we are used to finding in computers: regular numbers,

characters and files. However, all of these are really only abstractions; the ones and zeroes

are always “underneath” whatever logical structures used within the computer.

This same basic foundation of ones and zeroes applies to networking as well. Even though

most of the information in a network is exchanged in a logical fashion between higher-layer

protocols, underlying all networking structures are the ones and zeroes sent over the

network medium. Understanding how data is represented and manipulated in computer

systems is important background information that will help you comprehend many of the

different technologies. Not only are computer data representation and mathematics

important for explaining how low-level physical layer modulation and encoding techniques

work, they come into play even for higher-level concepts, such as how IP addresses are set

up and used on the Internet.

In this section I provide some general background information on how numerical data is

represented, stored and manipulated within computers and networking hardware. I begin

with a description of binary numbers and the different terms used to refer to collections of

binary information of various sizes. I describe the different types of numbering systems

used in computer systems, such as octal, decimal and hexadecimal, and how data can be

converted between these different types. I explain how arithmetic is performed on binary

and hexadecimal numbers. I then discuss boolean logic and how logical functions are used

to manipulate binary data.

These explanations then form the basis for a discussion of how logical functions are used

for setting, clearing, inverting and masking bits. These operations are employed extensively

in certain networking technologies and protocols. Masking operations are especially often

used in IP addressing, so even though this section seems rather low-level it is quite relevant

to the world of TCP/IP.

Needless to say, many of you reading this Guide know most or all of the information in this

section, so feel free to skip (or just skim) those topics that you already know. However, I

wanted to provide this background detail for the sake of those new to computing, or those

needing a refresher. The pages are somewhat long and I try to assume little in the descrip-

tions, so you may want to breeze through the parts that seem familiar. However, even those

of you who know what a bit and byte are and the difference between binary and decimal

numbers may find the discussion of bit masking worth perusing.

Note: There is only so much detail on the rudimentary basics of computing that I

can cover in a Guide of this sort without getting too far afield. If the contents of this

section are not sufficient to get you up to speed, I would recommend consulting a

more comprehensive reference specific to computing theory and mathematics.

Binary Information and Representation: Bits, Bytes, Nibbles,

Octets and Characters

The essence of computing is information. Computer hardware and software products are

designed to allow the input, storage, transfer and expression of various types of infor-

mation. A primary way in which types of information are differentiated is based on whether

they are analog or digital. In highly simplified terms, analog information is continuous, while

digital is discrete. The distinction between them can be seen by considering, for example, a

light switch and a dimmer. A light switch allows a light to be turned on or off only—no “in-

between” states. That's digital information—on or off. In contrast, a dimmer allows you to

fine-tune the light output from fully on to fully off, with an infinite number of intermediate

states in between: this is analog.

Binary Information

Modern digital computers store all of their information in digital form, because of how they

work at a fundamental level. Much the way a light bulb has only an “on” or “off” value, so too

do the components that store and manipulate information within computers. Millions of

transistors comprise computer processors and other circuits, and are, in highly-simplified

form, digital switches. Thus, all information in computers is manipulated as collections of

information pieces that can be only “on” or “off”, like a switch.

Since there are only two possible states, “on” or “off”, this is called binary information (the

prefix “bi” meaning “two”, of course.) There are several advantages to using binary repre-

sentation for information. It is a simple way to represent many types of information, such as

the state of a light bulb, or whether a file has been successfully copied, or whether a

temperature should be expressed in Celsius or Fahrenheit. It is also possible to collect

multiple binary values together to represent more complex information.

Perhaps most importantly, binary information is unambiguous. “On” is “on” and “off” is “off”,

and this is important as it allows devices to detect clearly the value of a particular piece of

information. Computers like black and white; they are not particularly good at dealing with

“shades of gray”. This becomes especially important in the field of networking when trans-

mission of data can cause signals to become polluted by noise.

The “on” or “off” condition of a binary value can be expressed in a number of different ways.

In logical expressions, we may consider the value to be “true” or “false”. For representing

mathematical values, the most common representation is “one” (“on”) or “zero” (“off”).