HP ProCurve Secure 7000dl Series Basic Management And Configuration Manual page 417

Configure the Demand Interface as an Unnumbered Interface. To
conserve IP addresses on your network, you may want to create the demand
interface as an unnumbered interface. When you assign a logical interface on
the router an IP address, that IP address cannot overlap with the IP addresses
assigned to other logical interfaces. As a result, each interface that has an IP
address represents an entire subnet. Depending on the subnetting scheme you
use, you may not have enough IP addresses to assign to each active interface
on your router.
To conserve IP addresses, you may want the demand interface to use the IP
address of another interface. However, if the interface to which the IP address
is actually assigned goes down, the demand interface will be unavailable as
well. Because there is little chance that a loopback interface will go down, you
may want to assign the IP address to a loopback interface.
To configure the demand interface as an unnumbered interface, enter the
following command from the demand interface configuration mode context:
Syntax: ip unnumbered <interface ID>
Valid interfaces from which the demand interface can takes its address
include:
Ethernet interfaces and subinterfaces
Frame Relay subinterfaces
PPP interfaces
loopback interfaces
Asynchronous Transfer Mode (ATM) subinterfaces
For example, you would enter the following commands to configure a loop-
back interface and then configure the demand 1 interface to use the IP address
assigned to that loopback interface:
ProCurve(config)# interface loopback 1
ProCurve(config-loop 1)# ip address 192.168.115.1 /24
ProCurve(config-loop 1)# interface demand 1
ProCurve(config-demand 1)# ip unnumbered loopback 1
Spoofing. After you configure an IP address for the demand interface, its
status should change to "up (spoofing)," and it should be listed as a directly
connected interface in the routing table. To check the status of the demand
interface, use the do command to enter a show command from the demand
interface configuration mode context:
ProCurve(config-demand 1)# do show interface demand 1
Configuring Demand Routing for Primary ISDN Modules
Using Demand Routing for ISDN Connections
8-25