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Connection Issues When Using a
Commercial Internet Service Provider

Overview of Internet Communication
Determine your computer's IP address
Is your IP address registered properly?
IP Address is Registered, but Still Can't Connect?

IMPORTANT

For SFSU users who connect to the Internet with a commercial Internet Service Provider (ISP), and access SFSU E-mail using a POP E-mail program (e.g., Eudora), or connect to the SFSU servers using Telnet or FTP.

The IP address assigned to your computer AND the domain name associated with the IP address MUST be registered with the 
Internet Corporation for Assigned Names and Numbers (ICANN) or access to the SFSU servers will fail.

Read through this document for more details on how to find your IP number and domain name associated with the IP number. If you have a problem contact your ISP and have them properly register both the IP # and the domain name associated with the IP #.

The Division of IT can NOT register your IP # or the domain name associated with your IP # - only your ISP can do this.

 

Overview of Internet Communication

An Internet Service Provider (ISP) is a company that provides Internet connectivity to computer users.  To bring about this connectivity, the user's computer must have a unique Internet Protocol (IP) address.  In fact, all computers on the Internet must have an IP address.  The IP address is a number that identifies the computer on the Internet and it is written as four numbers separated by periods.  Each of the numbers can be from 0 to 255.  For example, 130.212.1.240 could be an IP address for a computer.  The ISP provides the IP address for your computer.  With a valid IP address, you will be able to successfully connect to the Internet and browse the Web, access your e-mail or download files. 

An Internet domain is a group of computers on the Internet that are administered by a single organization. Domain names are the familiar, easy-to-remember names for computers on the Internet and are used generally as a convenient way of locating information and reaching others on the Internet.  A domain name translates to an IP address and is what Internet users are most familiar with when referring to a Web address, or an e-mail address.  For example, sfsu.edu is the Internet domain for the group of computers at SFSU.  Specifically, www.sfsu.edu is the domain name for the SFSU Web server and that domain name translates to the IP address, 130.212.10.101.

The ISP maintains an Internet Domain Name System (DNS), which consists of a directory of domain names and their corresponding IP addresses.  One of the main functions of the DNS is to translate the domain name into its corresponding IP address.  The DNS also contains information on the companies or people to which the domain names are registered.  Your ISP will register the IP address that is assigned to your computer with a commercial Domain Name Registrar.

SFSU users who are customers with a commercial ISP must have an IP address that is registered with ICANN, if they want to access campus resources using one of the following Internet access programs:

If you can successfully connect to the Internet and use a Web browser (e.g., Netscape Navigator), then you have a valid IP address for accessing the Internet.  But if you have problems accessing your SFSU e-mail using a POP mail program, or connecting to one of SFSU’s computers using a telnet program, or an FTP program, then the problem could be that your computer’s IP address is not registered with ICANN.  One thing that you can do to troubleshoot your connection problem is to check your computer's IP address.

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How to Determine Your Computer’s IP Address

To troubleshoot your connection problem, you will need to know your computer’s IP address.  To determine the IP address of your computer, perform the following procedure below that corresponds to the version of the operating system for the type of computer that you have.

Microsoft Windows XP Computer

  1. Start-up your computer and connect to your ISP as you do normally:
    1. If you have DSL or a Cable modem, when you startup your computer you automatically connect to your ISP.
    2. If you have a modem, connect to your ISP as you do normally using the Dial-up Networking icon.
  2. Once you are connected, click on the Start button, select the Run command. The Run dialogue box will appear.
  3. Type command in the Open field. Then click the OK button. A DOS window will appear.
  4. Type ipconfig and press the return/enter key.
  5. The IP Configuration dialogue box will appear.
  6. The IP address is displayed in the IP Address field.  Write it down.
  7. Click the Close box, to close the DOS window box. 

Microsoft Windows 98/NT4.0/2000/ME Computer

  1. Start-up your computer and connect to your ISP as you do normally:
    1. If you have DSL or a Cable modem, when you startup your computer you automatically connect to your ISP.
    2. If you have a modem, connect to your ISP as you do normally using the Dial-up Networking icon.
  2. Once you are connected, click on the Start button, select the Run command. The Run dialogue box will appear.
  3. Type winipcfg in the Open field. Then click the OK button. The IP Configuration dialogue box will appear.
  4. The IP address is displayed in the IP Address field.  Write it down.
  5. Click the Close box, to close the IP Configuration dialogue box. 

Macintosh OS X

  1. Start-up your computer and connect to your ISP as you do normally:
    1. If you have DSL or a Cable modem, when you startup your computer you automatically connect to your ISP.
    2. If you have a modem, connect to your ISP as you do normally by starting up Internet Connect.
  2. Once you are connected, click on the System Preferences icon located on the Dock.
  3. Click on the Network icon.
  4. In the Show field, select the method you are using to connect - either Internet Modem, built-in Ethernet or AirPort.
  5. The IP address will be displayed in the IP Address field.  Write it down.
  6. Click the Close box, to close the Network dialogue window.

Macintosh OS 7.6 - 9.x  with Open Transport TCP/IP or PPP

  1. Start-up your computer and connect to your ISP as you do normally:
    1. If you have DSL or a Cable modem, when you startup your computer you automatically connect to your ISP.
    2. If you have a modem, connect to your ISP as you do normally by starting up Remote Access (or PPP).
  2. Once you are connected, click on the Apple menu, point to Control Panels, select TCP/IP.  The TCP/IP Configuration dialogue box will open.
  3. The IP address is displayed in the IP Address field.  Write it down.
  4. Click the Close box, to close the TCP/IP Configuration dialogue box.

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Is Your IP Address Registered Properly?

In order for a user to access SFSU e-mail using a POP mail program like Eudora, the IP address assigned to your computer MUST be registered with the Internet Corporation for Assigned Names and Numbers (ICANN).  ICANN is the non-profit corporation that was formed to assume responsibility for some of the central coordination and management  functions of the Internet.  Its primary objective is ensuring the stability of the Internet's system of assigned domain names and IP addresses.  Although an IP address may be registered with one of the many commercial Domain Name Registrars, that Registrar may not be accredited with ICANN.

To verify that your IP address is registered properly with an accredited domain name registrar, you may use a Web browser to access the nslookup utility.  The nslookup utility sends queries to an Internet DNS and, if it is registered properly, determines the IP address associated with its domain name.

Using the nslookup Utility

  1. Once you have determined the IP address of your computer (as discuss in the previous section)
  2. Use a Web browser and access the nslookup utility at http://www.swhois.net/ to perform a domain name lookup
  3. Enter your IP address (e.g., 65.12.14.86 or 206.112.126.38) in the nslookup field and click the search button.
  1. If the IP address (e.g., 65.12.14.86) is NOT registered properly, then the nslookup utility will not be able to find an associated domain name.  The Web page will display a response like the following:

NSlookup results for: 65.12.14.86 

Reverse lookup produced no results.
The IP number 65.12.14.86
does not appear to be inverse-mapped to a domain name.

NOTE:

If your computer's IP address or the domain name associated with the IP address is NOT registered properly,
connections to SFSU using a POP mail, a telnet, or an ftp program will be denied.

If you have connection problems as a result of an improperly registered IP address, ask
 your ISP technical support consultant for an IP address with a domain name that is registered with an
 ICANN-accredited domain name registrar.

 

  1. If the IP address (e.g., 206.112.126.38) is registered properly, the nslookup utility will find the associated domain name.  The Web page will display a response like the following:

NSlookup results for: 206.112.126.38 

Server: localhost
Address: 127.0.0.1

Name: cust-P5-R15-38.POOL.ESR.SJO.wwc.com
Address: 206.112.126.38

Then you should perform the Reverse Domain Lookup by typing the domain name (e.g., cust-P5-R15-38.POOL.ESR.SJO.wwc.com) associated with your IP address into the nslookup field.  The Web page will display a response like the following:

NSlookup results for:
CUST-P5-R15-38.POOL.ESR.SJO.WWC.COM

Server: localhost
Address: 127.0.0.1

Name: CUST-P5-R15-38.POOL.ESR.SJO.WWC.COM
Address: 206.112.126.38

If you receive a non-authorative answer when performing a Reverse Domain Lookup you will not be able to connect to the SFSU servers and will need to contact your ISP and have them properly register the domain name associated with your IP number.

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IP Address is Fully Registered, but Still Can't Connect?

If your computer's IP address is registered with an ICANN-accredited domain name registrar but you still cannot connect to SFSU resources, then your computer may be on a network that resides behind a firewall.  A firewall is a system designed to prevent unauthorized access to or from a private network.  Therefore, your ability to communicate over the Internet is restricted by your ISP.

If you are using a cable modem or have DSL and are having sudden problems doing file transfer and/or telnet access try resetting your cable/dsl modem and or resetting your home network hardware. This will often give your home network a new IP number and resolve the problems you are having connecting to SFSU.

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Last Modified: 24 Oct 2005
doit@sfsu.edu