Figure 27 shows the interface
stack built for this configuration.
Figure 27: GRE Tunnel Dynamic Subscriber Interface
Configuration
Dynamic Subscriber Interface Configuration Example
The procedure in this section shows how to configure
dynamic subscriber interfaces by using the same loopback interface
referenced by multiple unnumbered IP interfaces. Instead of assigning
a different IP address to each physical interface, this example assigns
an IP address to a loopback interface (loopback 0). Each physical
interface is then configured as an unnumbered IP interface, referencing
the same loopback interface. This example uses a DHCP local server.
This approach has the following benefits:
A loopback interface provides a stable IP address that
can minimize the impact if a physical interface in the network goes
down.
Unnumbered IP interfaces preserve valuable IP address
space.
To configure dynamic subscriber interfaces, perform
the following steps:
Enable the DHCP local server for standalone mode.
host1(config)#service dhcp-local standalone
Access DHCP Local Pool Configuration mode for the local
address pool.
host1(config)#ip dhcp-local pool ispWestford
Specify the enduring IP addresses that the DHCP local
server can assign from the local address pool.
Create an unnumbered primary IP interface associated with
the loopback interface configured in Steps 6 and 7.
host1(config-if)#ip unnumbered loopback 0
Configure the primary IP interface to enable dynamic creation
of subscriber interfaces.
host1(config-if)#ip auto-configure ip-subscriber
Exit Interface Configuration
mode.
host1(config-if)#exit
Repeat Steps 9 through 12 for each Fast Ethernet interface
on which you want to configure dynamic subscriber interfaces. For
example:
host1(config)#interface fastEthernet 3/1
host1(config-if)#ip unnumbered loopback 0
host1(config-if)#ip auto-configure ip-subscriber
host1(config-if)#exit
host1(config)#interface fastEthernet 3/2
host1(config-if)#ip unnumbered loopback 0
host1(config-if)#ip auto-configure ip-subscriber
host1(config-if)#exit
atm pvc
Use to configure a PVC on an ATM interface.
Specify the VCD, the VPI, the VCI, and the encapsulation
type. (For more information about these parameters, see the Creating a Basic Configuration section in JUNOSe Link Layer Configuration Guide .)
Use to select a Fast Ethernet (FE) interface on a line
module or an SRP module.
Example
host1(config)#interface fastEthernet 1/0
Use the no version to remove
IP from an interface or subinterface. You must issue the no version from the highest level down; you cannot
remove an interface or a subinterface if the one above it still exists.
Note:
You can configure only the primary port, 0, on the Gigabit Ethernet
module. The router automatically uses the redundant port if the primary
port fails.
Example
host1(config)#interface gigabitEthernet 1/0
Use the no version to remove
IP from an interface. You must issue the no version from the highest level down; you cannot remove an interface
or a subinterface if the one above it still exists.
Use to select a 10-Gigabit Ethernet interface on the E120
router or the E320 router.
Use the slot/adapter/port format.
Example
host1(config)#interface tenGigabitEthernet
4/0/1
Use the no version to remove
IP from an interface. You must issue the no version from the highest level down; you cannot remove an interface
or subinterface if the one above it still exists.
You can use a loopback interface to provide a stable IP
address that can minimize the impact if a physical interface goes
down.
You cannot shut down a loopback interface.
Best Practice:
We recommend that you configure a 32-bit subnet mask for the
loopback interface. For example, if you configure a loopback interface
with the IP address and mask as 1.1.1.1/16, the 1.1.0.0/16 route entry
is entered on the line module and all traffic destined to the to 1.1.0.0/16
subnet is forwarded to the SRP module by the line module. Although
the SRP module responds only to traffic destined to the 1.1.1.1 subnet
and discards traffic to all other host IP addresses within that subnet
(1.1.1.1/16), if no specific or longer route entry is found or if
the SRP module receives too much traffic from subnets other than 1.1.1.1,
the CPU utilization on the SRP module reaches the saturation level.
If you use a subnet mask other than a /32 mask for the IP address
configured on the loopback interface, traffic from the entire subnet
is routed to the loopback interface. Therefore, that subnet cannot
be routed through any other interface on the router, unless a more
specific route points to another interface.
Use to set an IP address for an interface or a subinterface.
Specify the layer 2 encapsulation before you set the IP
address.
Issuing this command creates the primary IP interface.
You must create a primary IP interface on which to enable dynamic
creation of subscriber interfaces.
Use to configure an IP interface to support creation of
dynamic subscriber interfaces. The specified IP interface is considered
the primary interface.
The router creates the required dynamic subscriber interfaces
when the IP address is assigned to the associated subscriber. The
address might be assigned by an external DHCP server, the DHCP local
server, or the packet detect feature.
Use the include-primary keyword
to specify that the primary interface can be assigned to a subscriber.
Use the exclude-primary keyword to specify
that the primary interface is not used for subscribers. The primary
interface is not assigned to a subscriber by default.
You can issue this command from Interface Configuration
mode, Subinterface Configuration mode, or Profile Configuration mode.
Use the no version to disable
creation of dynamic subscriber interfaces associated with this primary
IP interface. Use the no version with the include-primary keyword to specify that the primary
interface is not assigned to a subscriber.
Use to set the router’s packet detect feature and
specify that IP automatically detect packets that do not match any
entries in the demultiplexer table. When an unmatched packet is detected,
an event is generated that determines whether to create a dynamic
subscriber interface.
Example
host1(config-if)#ip auto-detect ip-subscriber
Use the no version to restore
the default, in which packet detection is disabled.
Use to configure the inactivity timer value. A dynamically
created subscriber interface is deleted if it is inactive for a period
longer than the inactivity timer value.
The timer value can be in the range 1–65335 minutes.
A timer value of 0 specifies that dynamically created
subscriber interfaces are never deleted by the inactivity timer.
Example
host1(config-if)#ip inactivity-timer 100
Use the no version to restore
the default, in which inactivity timer feature is disabled.
Use to configure a subscriber interface or a primary IP
interface enabled for dynamic creation of subscriber interfaces to
demultiplex traffic with the specified source address.
You can issue this command from either Interface Configuration
mode or Subinterface Configuration mode.
This command enables IP processing on an interface without
assigning an explicit IP address to the interface.
You must specify an interface location, which is the identifier
of another interface on which the router has an assigned IP address.
This interface cannot be another unnumbered interface.
Examples
host1(config-if)#ip unnumbered fastEthernet
3/0
host1(config-if)#ip unnumbered loopback 10
Use the no version to disable
IP processing on the interface.
Use to configure a static primary IP interface to use
framed routes as source IP addresses when creating dynamic subscriber
interfaces. The router uses the Framed-Route RADIUS attribute [22]
sent in Access-Accept messages to apply framed routes to subscriber
interfaces associated with the primary interface.
Use the noversion to restore
the default in which DHCP relay builds dynamic subscriber interfaces
on the IP interface that is used for DHCP server-destined messages.
