Network connection problems for moveable computers.



Why won't my computer work on the Branner Library network?
How do I make my computer connect to the network in non-Earth Sciences buildings?
Why do I lose my wireless connection when I take my laptop from Geology Corner to Mitchell?

Last revision June 25, 2010

To use the network, your computer must have a known and unique IP address that is valid for the network to which you have connected. This set of questions all relate to problems getting such an address when you move your computer from its normal "home" network connection.

When you register your computer on the Earth Sciences wired network, a unique static IP address is assigned to that computer. When your computer is configured correctly, that assigned IP address is provided automatically to your computer by the campus DHCP servers whenever it connects to the network. This IP address is only valid on the Earth Sciences network.

To access the wired campus network outside Earth Sciences, you must register your computer with the roaming attribute, so the DHCP servers can give it a temporary IP address valid for that other part of campus. This attribute is automatically applied in the self-registration process, but must be specifically requested for manual registration.

The Branner Library is not part of the Earth Sciences wired network, even though it is housed in the Mitchell Earth Sciences Building. Futhermore, Earth Sciences offices in the Yang and Yamazaki Environment and Energy Building (Y2E2) are also part of a network separate from the rest of Earth Sciences. So, if your computer is registered in Mitchell or Geology Corner, for example, to use it on wired jacks in Branner Library or Y2E2, you must register with the roaming attribute.

Similarly, when you access the wireless network, the DHCP servers will give your computer a valid temporary IP address. The wireless network is always "roaming"; you never have a static IP address there. You must register your wireless card in order to get DHCP service.

Furthermore, the wireless network is divided into multiple zones, each with a different range of valid temporary IP addresses. If you move from one zone to another, your computer needs to ask the DHCP servers for a new address. The Earth Sciences buildings are not all in the same wireless zone. Geology Corner is in the Main Quad zone, while Mitchell Earth Sciences, Green Earth Sciences, and Y2E2 are in the Quad 4 zone.

How to solve these connection problems.

First of all, make sure that your computer is properly registered and configured. If you missed any of these steps, contact the network manager.

Next, learn how to "renew your DHCP lease".

Your computer acquires its IP address, whether it be the normal one for Earth Sciences, or a roaming or wireless one, by contacting the DHCP server, which supplies a "lease" on that IP address that is good for a specific amount of time.

The problem is that your computer may not realize that it has been moved to a new network and needs a different IP address. It may have plenty of time left on its original DHCP lease and keep trying to use that old IP address, which is no longer valid in the new location.

Modern laptops, particularly those from Apple, are generally very good about noticing when they are connected or disconnected from a wired network, or when they are put to sleep and re-awakened while using wireless. In that case, they automatically contact the DHCP sever again to verify or get a new IP address.

But not all computers work that well. If you move your properly registered and configured computer to another network (or another wireless zone) and it does not work on that network, you need to force it to contact the DHCP server again. This is called "renewing your DHCP lease".

How to renew your DHCP lease.

Windows 2000, XP, or Vista

  • Open a command prompt window (Select Run from the Start menu, then type in cmd and press the RETURN key).
  • In the command prompt window, type this command (don't forget to press the RETURN key):

    ipconfig /release

  • Now, type this command (and press the RETURN key):

    ipconfig /renew

  • Close the command prompt window.

Mac OS X 10.5

  • Open the Network System Preference Pane.

  • Select the connection method you are using from the menu on the left side: Built-in Ethernet for a wired connection; or AirPort for a wireless connection.

  • Click on the Advanced button at the bottom right of the window

  • In the new window that opens with advanced settings, make sure Using DHCP is selected in the Configure IPv4: drop-down menu.

  • Click the Renew DHCP Lease button on the right side. Wait a few seconds until you see the IP address fields repopulated. Then click the OK button and close the Network System Preference Pane.

Mac OS X versions earlier than 10.5

  • Open the Network System Preference Pane.
  • In the Show: drop-down menu, make sure that the connection method you are using is selected, for example, Built-in Ethernet for normal wired connections, or Airport for wireless.
  • Make sure the TCP/IP tab is selected.
  • The Configure IPv4: drop-down menu should be set to Using DHCP. Fix it if needed.
  • In Mac OS X versions 10.4 and 10.3, there will now be a Renew DHCP Lease button below and to the right of the Configure IPv4: drop-down menu. Click on that button.

  • Older versions of Mac OS X may not have the Renew DHCP Lease button. They may also have the name Configure: for the drop-down menu. For these older versions, click on the Apply Now button on the bottom of the page. If that button is not available (grayed out), then first reset the Configure: drop-down menu to the Manually option and then back again to Using DHCP. Now the Apply Now button should be available. Click it.
  • After a few seconds, a new IP address should appear.
  • Close the Network System Preference Pane.

Legacy operating systems

See this page for information on how to renew a DHCP lease for some older operating systems that are no longer supported on the Earth Sciences network.

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