OIT Network Systems

OIT Mobile IP Service

OIT Mobile IP Service allows you to temporarily attach a device's network interface to a network other than the device's "home network", and receive IP service without reconfiguring the device or updating its Host Database entry.

The "home network" of a device's network interface is defined as the IP network (a.k.a. "subnet") specified for that network interface in the device's Princeton University Host Database entry. For example, if a device is registered in the Host Database as having two network interfaces, and the first interface is assigned an IP address on the libnet network, then that interface is deemed to be "homed" on libnet. If the second interface is assigned an IP address on the wirelessnet network, then the second interface is "homed" on wirelessnet.

Some networks span multiple buildings; conversely, some buildings contain several networks. For a list of buildings and networks, see the Princeton Network ("subnet") List.

Mobile IP service provides your device's network interface with a temporary IP (Internet) address and Internet hostname when the device's network interface is attached to parts of the Campus Data Network (CDN) outside the device's "home network." The service is available on these parts of the Campus Data Network (CDN):

Because of the special demands associated with mobile networking, there are some guidelines you'll need to be particularly aware of. Those guidelines are covered in this document.

If you have questions about the procedures below, or encounter difficulties related to them, please contact the OIT Support and Operations Center for assistance.

Contents

  1. General Procedures
  2. Requirements
  3. How Does it Work?
  4. Caveats
  5. Multiple Interface Devices
  6. Mobile IP Campers
  7. Related Resources
  8. If You Need Additional Assistance

General Procedures

The following procedures apply to all computers attached to the campus network, but are of special importance for mobile devices:


Requirements

To use OIT Mobile IP service, your computer must meet the following requirements:


How Does it Work?

For devices meeting the requirements above, Mobile IP service works as follows:


Caveats


Multiple Interface Devices

Our service supports devices with multiple network interfaces, for example, a computer with an Ethernet interface and a Wireless interface.

Each network interface that is eligible for DHCP service is treated as an independent device. Each has its own "home network", and is independently eligible for its own DHCP lease. Therefore, each such interface is independently eligible for Mobile IP Service. It is possible that one interface (attached to its home network) may be using OIT Static IP Service at the same time that the other interface (attached to a network other than its home network) may be using OIT Mobile IP Service.

Each network interface is subject to Mobile IP Camper identification (described elsewhere in this document) independent of the device's other interfaces.

This means, for example, that anywhere in this document that you read "device" or "computer", we are really referring to one of your device's network interfaces.

While our service support a device with multiple physical interfaces, it does not support a device with multiple logical interfaces running on a single physical interface. We treat each physical interface (as identified by its IEEE 802.2 MAC address) as a single unique client, which may be attached to a single network at a time, and is eligible for (at most) one DHCP lease at a time. A device which tries to simultaneously acquire multiple IP addresses on a single physical interface is not eligible for our service.


Mobile IP Campers

Mobile IP service is intended to provide your computer's network interface with a temporary IP (Internet) address and Internet hostname when it is attached to a network other than its "home network." It is not intended to provide a permanent IP address and hostname when your computer leaves its "home network" permanently, or for an extended period (more than 14 days). In either of those circumstances, you should instead update your computer's entry in the Princeton University Host Database to reflect that network interface's new "home network."

We impose the time limit both to ensure that Mobile IP Service is not used as a substitute for updating a computer's Host Database entry when it relocates permanently, and to ensure an adequate supply of Mobile IP addresses for devices that are truly mobile.

If OIT's DHCP servers detect that your device's network interface has received Mobile IP Service on a single network other that its home network for "an extended period", they will identify your device as a Mobile IP Camper. (Your device's network interface has been "mobile" on a single network other than "home network" for so long, it appears to be "camping" there, suggesting that your device's network interface has been relocated permanently, rather than just "visiting" the new network.)

Some devices are exempt from being identified as Mobile IP Campers. And devices visiting some networks are also exempt. These exemptions include:

If your device is identified as a Mobile IP Camper, OIT may update the device's Host Database entry on your behalf, to reflect its new home network. That is, we will assume that you must have relocated the device permanently (or for an extended period), but neglected to update the Host Database entry. After OIT updates the device's Host Database entry, you will need to reboot the device, so it switches from using an IP address assigned via Mobile IP Service, to using its new statically-assigned IP address. The device may experience some interruption to its network access until you reboot it.

Here are the specific details:

You might wonder why you should bother updating a device's Host Database entry after relocating it, since eventually OIT will do so for you. Recall that you will need to reboot the device after the change to the Host Database is complete; until you do so, the device's network access may be interrupted. By performing the change yourself, you exercise greater control over the timing of the change, and therefore, over any interruption in service. If you leave the change to us, it may happen an a time that is inconvenient for you. Additionally, OIT will only update the interface's IP-SUBNET-OR-ADDRESS field; since you'll eventually want to update the BUILDING and ROOM fields as well, you may as well change all three at once.


Related Resources


If You Need Additional Assistance

If you have questions or need assistance with any of the procedures in this document, please contact the OIT Support and Operations Center.


A service of OIT Network Systems
The Office of Information Technology,
Princeton University
Last Updated: April 17 2014