Host Database: New "Mobile IP Only" Feature for Dormnet Subscriptions

The Host Database has been enhanced to provide a new feature for Dormnet subscribers.

Previously, the Ethernet interface of a Dormnet subscription always was assigned an OIT Static IP Address on the pu-dormnet-bb network. This is the network associated with OIT Ethernet Service in dormitory rooms, eating clubs, and apartments. As a result, the Ethernet interface relied on OIT Static IP Service when it was attached to the pu-dormnet-bb network, and relied on OIT Mobile IP Service when it was attached to any other network.

The traditional behavior remains available, but starting April 14 2008, a Dormnet subscriber may specify instead that the Ethernet interface should be assigned no OIT Static IP Address. That will result in the Ethernet interface relying on OIT Mobile IP Service when it is attached to OIT Ethernet Service in any location, even the pu-dormnet-bb network.

Customers who already have a Dormnet subscription need take no action; OIT has made no change to their subscriptions, so those subscriptions will continue to work exactly as they have in the past. If they would prefer to switch to the new behavior, they may use the Change Dormnet Entry form to choose between the two behaviors. On that form, the traditional behavior is entitled "Rely on OIT Static IP Service on pu-dormnet-bb; rely on OIT Mobile IP Service elsewhere". The new behavior is entitled "Always rely on OIT Mobile IP Service".

Beginning April 14 2008, new Dormnet subscriptions default to "Always rely on OIT Mobile IP Service" (the new behavior). The customer may still select the traditional behavior when subscribing to Dormnet. And the customer may use the Change Dormnet Entry form at a later date to switch between the two behaviors.

The change affects only Dormnet subscriptions; it does not affect "office" entries in the Host Database. Dormnet subscriptions are those Host Database entries where the canonical DNS hostname ends with student.princeton.edu.

Recommendations

If you have an existing Dormnet subscription, there is no need to take any action. If you wish to change the subscription so the Ethernet interface has no OIT Static IP Address assigned, you are welcome to do so; use the Change Dormnet Entry form.

For new subscriptions, the default on the subscription form is "Always rely on OIT Mobile IP Service" (the new behavior). We recommend you accept the default unless you have some reason to choose otherwise:

• OIT Mobile IP Service assigns a dynamic (non-static) IP address and hostname. These may vary over time; the Ethernet interface may be assigned a different IP address and hostname each time it is connected to the network.

• OIT Static IP Service assigns a static (unchanging) IP address and hostname.

• One reason to select OIT Static IP Service is if you know the device is unsuitable for use with OIT Mobile IP Service. For example, perhaps OIT notified you of a problem with your device that makes it unsuitable for use with OIT Mobile IP Service. (Such problems are common with standalone appliances, such as printers and NAT routers.) In that case, by relying on OIT Static IP Service you would be able to use the device as long as you attach the device's Ethernet interface to the pu-dormnet-bb network.

• If the device is attached solely via Ethernet to the pu-dormnet-bb network, and the device provides some well-known service (say, a Web server) that you want other clients to be able to locate using an unchanging DNS hostname or IP address, you will want to rely on OIT Static IP Service.

Technical Details

This change involves only the Ethernet interface in the Dormnet subscription. A Dormnet subscription's wireless interface (in any) continues to be assigned no OIT Static IP Address; it has always relied on OIT Mobile IP Service.

Depending on which behavior is selected, the Ethernet interface is assigned an IP address on the pu-dormnet-bb network or the driftnet network:

• If the Dormnet subscription's Ethernet interface is registered to "Rely on OIT Static IP Service on pu-dormnet-bb; rely on OIT Mobile IP Service elsewhere" (the traditional behavior), the Host Database entry will have a pu-dormnet-bb IP address assigned to the Ethernet interface. This is an OIT Static IP Address.

• If the Dormnet subscription's Ethernet interface is registered to "Always rely on OIT Mobile IP Service" (the new behavior), the Host Database entry will have a driftnet IP address assigned to the Ethernet interface. This is not an OIT Static IP Address.

  The driftnet subnet is an "imaginary" one; no location on campus is actually wired to this network. A driftnet IP address would never be used by a device on the campus network.

  Because no location on campus is actually wired to driftnet, when the device's Ethernet interface is attached to the campus network via OIT Ethernet Service, it will be attached to a subnet other that driftnet, that is, a subnet other than its "home" network. Since it is "visiting" a subnet other than its home network, it will rely on OIT Mobile IP Service.

  Because a Dormnet subscription is exempt from being declared a Mobile IP Camper, regardless of how long the Ethernet interface "visits" a subnet, we will not change the Host Database entry to assign the Ethernet interface an OIT Static IP Address on the network it is visiting. The interface will remain registered on driftnet; this ensures it does not unexpectedly switch to using OIT Static IP Service.

  Some may wonder why we insert a driftnet IP address into the Host Database entry, instead rather than inserting no IP address. We we do because if we inserted no IP address, the network interface would be ineligible for OIT Mobile IP Service.