RFC2517 - Building Directories from DNS: Experiences from WWWSeeker

Network Working Group R. Moats

Request for Comments: 2517 R. Huber

Category: Informational AT&T

February 1999

Building Directories from DNS: EXPeriences from WWWSeeker

Status of this Memo

This memo provides information for the Internet community. It does

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

memo is unlimited.

Abstract

There has been mUCh discussion and several documents written about

the need for an Internet Directory. Recently, this discussion has

focused on ways to discover an organization's domain name without

relying on use of DNS as a directory service. This memo discusses

lessons that were learned during InterNIC Directory and Database

Services' development and operation of WWWSeeker, an application that

finds a web site given information about the name and location of an

organization. The back end database that drives this application was

built from information oBTained from domain registries via WHOIS and

other protocols. We present this information to help future

implementors avoid some of the blind alleys that we have already

explored. This work builds on the Netfind system that was created by

Mike Schwartz and his team at the University of Colorado at Boulder

[1].

1. Introduction

Over time, there have been several RFCs [2, 3, 4] about approaches

for providing Internet Directories. Many of the earlier documents

discussed white pages directories that supply mappings from a

person's name to their telephone number, email address, etc.

More recently, there has been discussion of directories that map from

a company name to a domain name or web site. Many people are using

DNS as a directory today to find this type of information about a

given company. Typically when DNS is used, users guess the domain

name of the company they are looking for and then prepend "www.".

This makes it highly desirable for a company to have an easily

guessable name.

There are two major problems here. As the number of assigned names

increases, it becomes more difficult to get an easily guessable name.

Also, the TLD must be guessed as well as the name. While many users

just guess ".COM" as the "default" TLD today, there are many two-

letter country code top-level domains in current use as well as other

gTLDs (.NET, .ORG, and possibly .EDU) with the prospect of additional

gTLDs in the future. As the number of TLDs in general use increases,

guessing gets more difficult.

Between July 1996 and our shutdown in March 1998, the InterNIC

Directory and Database Services project maintained the Netfind search

engine [1] and the associated database that maps organization

information to domain names. This database thus acted as the type of

Internet directory that associates company names with domain names.

We also built WWWSeeker, a system that used the Netfind database to

find web sites associated with a given organization. The experienced

gained from maintaining and growing this database provides valuable

insight into the issues of providing a directory service. We present

it here to allow future implementors to avoid some of the blind

alleys that we have already explored.

2. Directory Population

2.1 What to do?

There are two issues in populating a directory: finding all the

domain names (building the skeleton) and associating those domains

with entities (adding the meat). These two issues are discussed

below.

2.2 Building the skeleton

In "building the skeleton", it is popular to suggest using a variant

of a "tree walk" to determine the domains that need to be added to

the directory. Our experience is that this is neither a reasonable

nor an efficient proposal for maintaining such a directory. Except

for some infrequent and long-standing DNS surveys [5], DNS "tree

walks" tend to be discouraged by the Internet community, especially

given that the frequency of DNS changes would require a new tree walk

monthly (if not more often). Instead, our experience has shown that

data on allocated DNS domains can usually be retrieved in bulk

fashion with FTP, HTTP, or Gopher (we have used each of these for

particular TLDs). This has the added advantage of both "building the

skeleton" and "adding the meat" at the same time. Our favorite

method for finding a server that has allocated DNS domain information

is to start with the list maintained at

http://www.alldomains.com/countryindex.Html and go from there.

Before this was available, it was necessary to hunt for a registry

using trial and error.

When maintaining the database, existing domains may be verified via

direct DNS lookups rather than a "tree walk." "Tree walks" should

therefore be the choice of last resort for directory population, and

bulk retrieval should be used whenever possible.

2.3 Adding the meat

A possibility for populating a directory ("adding the meat") is to

use an automated system that makes repeated queries using the WHOIS

protocol to gather information about the organization that owns a

domain. The queries would be made against a WHOIS server located

with the above method. At the conclusion of the InterNIC Directory

and Database Services project, our backend database contained about

2.9 million records built from data that could be retrieved via

WHOIS. The entire database contained 3.25 million records, with the

additional records coming from sources other than WHOIS.

In our experience this information contains many factual and

typographical errors and requires further examination and processing

to improve its quality. Further, TLD registrars that support WHOIS

typically only support WHOIS information for second level domains

(i.e. ne.us) as opposed to lower level domains (i.e.

windrose.omaha.ne.us). Also, there are TLDs without registrars, TLDs

without WHOIS support, and still other TLDs that use other methods

(HTTP, FTP, gopher) for providing organizational information. Based

on our experience, an implementor of an internet directory needs to

support multiple protocols for directory population. An automated

WHOIS search tool is necessary, but isn't enough.

3. Directory Updating: Full Rebuilds vs Incremental Updates

Given the size of our database in April 1998 when it was last

generated, a complete rebuild of the database that is available from

WHOIS lookups would require between 134.2 to 167.8 days just for

WHOIS lookups from a Sun SPARCstation 20. This estimate does not

include other considerations (for example, inverting the token tree

required about 24 hours processing time on a Sun SPARCstation 20)

that would increase the amount of time to rebuild the entire

database.

Whether this is feasible depends on the frequency of database updates

provided. Because of the rate of growth of allocated domain names

(150K-200K new allocated domains per month in early 1998), we

provided monthly updates of the database. To rebuild the database

each month (based on the above time estimate) would require between 3

and 5 machines to be dedicated full time (independent of machine

architecture). Instead, we checkpointed the allocated domain list

and rebuild on an incremental basis during one weekend of the month.

This allowed us to complete the update on between 1 and 4 machines (3

Sun SPARCstation 20s and a dual-processor Sparcserver 690) without

full dedication over a couple of days. Further, by coupling

incremental updates with periodic refresh of existing data (which can

be done during another part of the month and doesn't require full

dedication of machine hardware), older records would be periodically

updated when the underlying information changes. The tradeoff is

timeliness and accuracy of data (some data in the database may be

old) against hardware and processing costs.

4. Directory Presentation: Distributed vs Monolithic

While a distributed directory is a desirable goal, we maintained our

database as a monolithic structure. Given past growth, it is not

clear at what point migrating to a distributed directory becomes

actually necessary to support customer queries. Our last database

contained over 3.25 million records in a flat ASCII file. Searching

was done via a PERL script of an inverted tree (also produced by a

PERL script). While admittedly primitive, this configuration

supported over 200,000 database queries per month from our production

servers.

Increasing the database size only requires more disk space to hold

the database and inverted tree. Of course, using database technology

would probably improve performance and scalability, but we had not

reached the point where this technology was required.

5. Security Considerations

The underlying data for the type of directory discussed in this

document is already generally available through WHOIS, DNS, and other

standard interfaces. No new information is made available by using

these techniques though many types of search become much easier. To

the extent that easier Access to this data makes it easier to find

specific sites or machines to attack, security may be decreased.

The protocols discussed here do not have built-in security features.

If one source machine is spoofed while the directory data is being

gathered, substantial amounts of incorrect and misleading data could

be pulled in to the directory and be spread to a wider audience.

In general, building a directory from registry data will not open any

new security holes since the data is already available to the public.

Existing security and accuracy problems with the data sources are

likely to be amplified.

6. Acknowledgments

This work described in this document was partially supported by the

National Science Foundation under Cooperative Agreement NCR-9218179.

7. References

[1] M. F. Schwartz, C. Pu. "Applying an Information

Gathering Architecture to Netfind: A White Pages Tool for a

Changing and Growing Internet", University of Colorado Technical

Report CU-CS-656-93. December 1993, revised July 1994.

URL:ftp://ftp.cs.colorado.edu/pub/cs/techreports/schwartz/Netfind

[2] Sollins, K., "Plan for Internet Directory Services", RFC1107,

July 1989.

[3] Hardcastle-Kille, S., Huizer, E., Cerf, V., Hobby, R. and S.

Kent, "A Strategic Plan for Deploying an Internet X.500 Directory

Service", RFC1430, February 1993.

[4] Postel, J. and C. Anderson, "White Pages Meeting Report", RFC

1588, February 1994.

[5] M. Lottor, "Network Wizards Internet Domain Survey", available

from http://www.nw.com/zone/WWW/top.html

8. Authors' Addresses

Ryan Moats

AT&T

15621 Drexel Circle

Omaha, NE 68135-2358

USA

EMail: jayhawk@att.com

Rick Huber

AT&T

Room C3-3B30, 200 Laurel Ave. South

Middletown, NJ 07748

USA

EMail: rvh@att.com

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