HP ProCurve 7000dl Series Basic Management And Configuration Manual page 330

Configuring the Data Link Layer Protocol for E1, T1, and Serial Interfaces
Configuring the Logical Interface
N o t e
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Before configuring the Frame Relay subinterface as an unnumbered interface,
you should be aware of a potential disadvantage: If the interface to which the
IP address is actually assigned goes down, the Frame Relay subinterface will
be unavailable. For example, suppose you configure Frame Relay 1.16 as an
unnumbered interface that takes its IP address from the Ethernet 0/1 interface.
If the Ethernet 0/1 interface goes down, the Frame Relay 1.16 subinterface will
be unavailable as well.
To minimize the chances of the interface with the IP address going down, you
can assign the IP address to a loopback interface, which typically does not
go down.
To configure a Frame Relay subinterface as an unnumbered interface, enter
the following command from the Frame Relay subinterface configuration
mode context:
Syntax: ip unnumbered <interface>
Valid interfaces include:
Ethernet interfaces and subinterfaces
other Frame Relay subinterfaces
PPP interfaces
HDLC interfaces
loopback interfaces
Asynchronous Transfer Mode (ATM) subinterfaces
demand interfaces
For example, you would enter the following commands to configure a loop-
back interface and then configure the Frame Relay 1.16 subinterface to use
the IP address assigned to that loopback interface:
ProCurve(config)# interface loopback 1
ProCurve(config-loop 1)# ip address 10.1.1.1 /30
ProCurve(config-loop 1)# interface fr 1.16
ProCurve(config-fr 1.16)# ip unnumbered loopback 1
You do not have to enter no shutdown to activate a loopback interface. The
status of a loopback interface changes to up after you enter the interface
loopback <interface number> command.