NBER Help: Working Papers

NBER Working Papers Technical FAQ

The following list is designed to supplement our regular Working Paper help pages, which cover more common issues. We recommend that you read those pages before reading these more technical questions and answers.

What is an 'IP address'?

An IP address is a unique identifying number for a computer or device on the Internet. It is written as four numbers between 0 and 255, each separated by periods. For example,

What is a 'network number'?

The range of IP addresses assigned to a particular network can be expressed in two ways. The NBER network range is usually written as, which means NBER computers can be assigned numbers from to You may see either notation.

What is a 'domain name'?

A domain name identifies one or more IP addresses. For example, the domain name nber.org represents the IP addresses for the NBER computers. Domain names are often used in URLs (such as www.nber.org), and in email addresses (such as webmaster@nber.org).

What is an 'ISP' or 'Internet Service Provider'?

An Internet Service Provider (such as America Online (AOL), CompuServe, or MediaOne) is a company that provides access to the Internet. The ISP typically gives users a software package, username, password, and access phone number. With a modem, users can then log on to the Internet and browse the World Wide Web and send and receive e-mail.

ISPs can serve both individuals and large companies, providing a connection from the company's networks to the Internet.

What is a 'nameserver'?

A nameserver translates names from one form into another. For example, the Internet uses Domain Name Servers (DNSs) to translate domain names into IP adresses.

What is a 'Domain Name Server' or 'Domain Name System' (DNS)?

Domain Name System (or Service), is an Internet service that translates domain names into IP addresses. Because domain names use letters instead of numbers, they are easier for people to remember than IP addresses (instead of remembering, people can remember www.nber.org). The Internet however, really uses IP addresses. Therefore, every time you use a domain name, a DNS service must translate the name into the corresponding IP address.

What is 'reverse name lookup'?

Every computer on the Internet has a unique identifying number called an IP address. The NBER server can compare this number to a database of domain names and network numbers to determine who owns that number. We then issue a request to the nameserver on that network to identify the domain name of that specific computer. A request of this nature is called a "reverse name lookup" (RNL) and is a standard part of networking protocol.

What is 'PDF'?

The PDF (Portable Document File) format is a virtually universal publishing format designed to be portable across all computer platforms, making documents look and print the same on all systems. To view these files, you need the free Adobe Acrobat Reader. We recommend that all users download and install Version 4.0 or higher.

What is 'web caching'?

Web cache engines store Web pages that are frequently requested by users. Users do not actually get Web pages directly from Web sites, but rather from the caching computer. Caching computers feed pages to users either from pages that have already been stored, or by accessing Web sites to retrieve new pages which are then passed on to the user.

How does Web caching affect free download authorization?

Web caching can create problems for free download authorization since the NBER Web server sees download requests coming from the caching machine, not from the individual user. If the cache engine only serves a network which is authorized for free downloads, the NBER can authorize the caching computer for free downloads. However, if the cache engine serves non-authorized users as well, the problem can be more complicated. Visit our trouble shooting guide for more information.

How does the NBER authenticate users?

With every WWW query, we are provided with the IP address of the querying computer. By comparing this IP number with our list of authorized numbers, we can determine whether the querying computer is authorized for free downloads, in which case we offer a full-text download. If the IP address is not on our authorization list, we do a reverse name lookup. If that returns with the host name of a machine in an authorized domain, the full-text download is made available.

Users who are not offered a free download on the "Bibliographic Page" are offered a link for Users expecting free downloads, as well as an order basket. If you select the link, you will be asked for your email address. The address will be checked for authorization, and if your are authorized, you will receive an email with special instructions.

Must I supply my network number?

If your network Domain Name Server can correctly resolve reverse name lookups, the network number is redundant and therefore unnecessary. However, many networks are unable to correctly resolve reverse name lookups, which makes it necessary for the NBER to know the network number.

Is my network number the same as my IP address?

No. The network number covers all the computers on your 'subnet', possibly your entire organization. Your IP address is only one address among the many in use at your site. Online Working Papers are offered to the whole organization, not just your computer.

Why may reverse name lookups not work?

RNL's may fail for a variety of reasons, including firewalls, caching, or poorly designed security policy on your network or at your ISP (Internet Service Provider). Lookups might fail also on a very overloaded network, but this would be temporary.

Can we participate if we use a Web proxy server or firewall that hides our address?

If the proxy server or firewall is part of your domain, there is no problem. If it is shared by other customers of your ISP, or otherwise combines the requests of multiple sites, our system may not recognize the requests as coming from you, and you will not automatically be offered free access. There are two solutions to this problem.

    HTTP 1.1 compliant cache engines provide a 'Via' header that provides the names of each cache in the chain of caches. If the first of these is an authorized cache, free access is offered.

    Another way around proxies and firewalls is to request the paper at a non-standard port which we have allocated for this purpose. For example,

    if your request to view http://papers.nber.org/papers/w0000.pdf is refused,

    try browsing http://papers.nber.org:81/papers/w0000.pdf.

    You will have to enter the URL by hand, but the request will bypass your cache and come straight to our web server.

Can we participate through a commercial ISP such as AOL, Compuserve, etc.
or when accessing the Internet away from our organization's network?

If you:

    access the Internet via a commercial ISP (such as AOL) which shares host names and IP addresses with other institutions

    access the Internet via an ISP which assigns you a new IP address each time you connect

    need access while away from your organization's network
We offer individual logins that allow you to access Working Papers from any computer.

Once I am authorized, can anything else go wrong?

An extensive trouble-shooting guide is available.

Working Papers Technical Support
Questions and comments about our web site are always welcome.