# Configuring Dynamic Subscriber Interfaces

You can configure dynamic subscriber interfaces in the following configurations:

- IP over Ethernet
- IP over VLAN over Ethernet
- IP over bridged Ethernet over ATM
- GRE tunnels

The following sections describe how to create each of these basic configurations. In addition, Dynamic Subscriber Interface Configuration Example, provides a detailed sample configuration.

## Configuring Dynamic Subscriber Interfaces over Ethernet

To configure a dynamic subscriber interface in an IP over Ethernet configuration by using DHCP events, perform the following steps:

1. Configure the DHCP server.

   For instructions, see Configuring the DHCP Local Server .

2. Specify a Fast Ethernet, Gigabit Ethernet, or 10-Gigabit Ethernet port.
   host1(config)#interface fastEthernet 4/1
3. Create the primary IP interface by assigning an IP address and mask to the Ethernet interface (or make it unnumbered).
   host1(config-if)#ip address 192.168.2.1 255.255.255.0
4. Configure the primary IP interface to enable dynamic creation of subscriber interfaces.
   host1(config-if)#ip auto-configure ip-subscriber
5. (Optional) Specify the source address of traffic that is destined for the primary IP interface.
   host1(config-if)#ip source-prefix 192.168.2.1 255.255.255.0

Figure 24 shows the interface stack built for this configuration.

Figure 24: IP over Ethernet Dynamic Subscriber Interface Configuration

## Configuring Dynamic Subscriber Interfaces over VLANs

To configure a dynamic subscriber interface in an IP over VLAN over Ethernet configuration by using DHCP events, perform the following steps:

1. Configure the DHCP server.

   For instructions, see Configuring the DHCP Local Server .

2. Specify a Fast Ethernet, Gigabit Ethernet, or 10-Gigabit Ethernet port.
   host1(config)#interface gigabitEthernet 1/0
3. Specify VLAN as the encapsulation method on the interface. This command creates the VLAN major interface.
   host1(config-if)#encapsulation vlan
4. Create a VLAN subinterface by adding a subinterface number to the interface identification command.
   host1(config-if)#interface gigabitEthernet 1/0.1
5. Assign a unique VLAN ID to the VLAN subinterface.
   host1(config-if)#vlan id 101
6. Create the primary IP interface by assigning an IP address and mask to the VLAN subinterface (or make it unnumbered).
   host1(config-if)#ip address 192.168.2.10 255.255.255.0
7. Configure the primary IP interface to enable dynamic creation of subscriber interfaces.
   host1(config-if)#ip auto-configure ip-subscriber
8. (Optional) Specify the source address of traffic that is destined for the primary IP interface.
   host1(config-if)#ip source-prefix 192.168.2.10 255.255.255.0

Figure 25 shows the interface stack built for this configuration.

Figure 25: IP over VLAN over Ethernet Dynamic Subscriber Interface Configuration

## Configuring Dynamic Subscriber Interfaces over Bridged Ethernet

To configure a dynamic subscriber interface in an IP over bridged Ethernet over ATM configuration by using DHCP events, perform the following steps:

1. Configure DHCP server.

   For instructions, see Configuring the DHCP Local Server .

2. Create an ATM major interface.
   host1(config)#interface atm 3/3
3. Create an ATM 1483 subinterface.
   host1(config-if)#interface atm 3/3.1
4. Configure an associated PVC for the ATM 1483 subinterface by specifying the VCD, the VPI, the VCI, and the encapsulation type.
   host1(config-subif)#atm pvc 10 100 22 aal5snap
5. Specify bridged Ethernet as the encapsulation method on the ATM 1483 subinterface.
   host1(config-subif)#encapsulation bridge1483
6. Create the primary IP interface by assigning an IP address and mask to the bridged Ethernet interface (or make it unnumbered).
   host1(config-subif)#ip address 192.168.2.20 255.255.255.0
7. Configure the primary IP interface to enable dynamic creation of subscriber interfaces.
   host1(config-subif)#ip auto-configure ip-subscriber
8. (Optional) Specify the source address of traffic that is destined for the primary IP interface.
   host1(config-subif)#ip source-prefix 192.168.2.20 255.255.255.0

Figure 26 shows the interface stack built for this configuration.

Figure 26: IP over Bridged Ethernet over ATM Dynamic Subscriber Interface Configuration

## Configuring Dynamic Subscriber Interfaces over GRE Tunnels

To configure a dynamic subscriber interface in an GRE tunnel configuration by using packet detection, perform the following steps:

1. Create a GRE tunnel interface.

   For instructions, see the Configuration Tasks section in JunosE IP Services Configuration Guide .

2. Create the primary IP interface by assigning an IP address and mask to the bridged Ethernet interface (or make it unnumbered).
   host1(config-subif)#ip address 192.168.2.20 255.255.255.0
3. Configure the packet detect feature and specify that IP automatically detect packets that do not match any entries in the demultiplexer table.
   host1(config-if)#ip auto-detect ip-subscriber
4. Configure the primary IP interface to enable dynamic creation of subscriber interfaces.
   host1(config-subif)#ip auto-configure ip-subscriber
5. (Optional) Specify the IP inactivity timer.
   host1(config-subif)#ip inactivity-timer 100
6. (Optional) Specify the source address of traffic that is destined for the primary IP interface.
   host1(config-subif)#ip source-prefix 192.168.2.1 255.255.255.0

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:

1. Enable the DHCP local server for standalone mode.
   host1(config)#service dhcp-local standalone
2. Access DHCP Local Pool Configuration mode for the local address pool.
   host1(config)#ip dhcp-local pool ispWestford
3. Specify the enduring IP addresses that the DHCP local server can assign from the local address pool.
   host1(config-dhcp-local)#network 10.20.0.0 255.255.192.0
4. Specify the router to forward traffic from the IP addresses to destinations on other subnets.
   host1(config-dhcp-local)#default-router 10.20.32.1
5. Exit DHCP Local Pool Configuration mode.
   host1(config-dhcp-local)#exit
6. Configure a loopback interface.
   host1(config)#interface loopback 0
7. Assign an IP address and mask to the loopback interface.
   host1(config-if)#ip address 10.20.32.1 255.255.255.255
8. Exit Interface Configuration mode.
   host1(config-if)#exit
9. Specify a Fast Ethernet port.
   host1(config)#interface fastEthernet 3/0
10. Create an unnumbered primary IP interface associated with the loopback interface configured in Steps 6 and 7.
    host1(config-if)#ip unnumbered loopback 0
11. Configure the primary IP interface to enable dynamic creation of subscriber interfaces.
    host1(config-if)#ip auto-configure ip-subscriber
12. Exit Interface Configuration mode.
    host1(config-if)#exit
13. 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 .)
- Example
  host1(config-subif)#atm pvc 10 100 22 aal5snap
- Use the no version to remove the specified PVC.
- See atm pvc

default-router

- Use to specify the IP address of the router for the subscriber’s computer to use for traffic destined for locations beyond the local subnet.
- Specify the IP address of a primary server, and optionally, specify the IP address of a secondary server.
- Example
  host1(config-dhcp-local)#default-router 10.10.1.1
- Use the no version to remove the association between the address pool and the router.
- See default-router

encapsulation bridge1483

- Use to configure bridged Ethernet as the encapsulation method on an interface.
- Example
  host1(config-subif)#encapsulation bridge1483
- Use the no version to remove bridged Ethernet as the encapsulation method on the interface.
- See encapsulation bridge1483

encapsulation vlan

- Use to configure VLAN as the encapsulation method on an interface.
- Issuing this command creates the VLAN major interface.
- Example
  host1(config-if)#encapsulation vlan
- Use the no version to disable VLAN encapsulation on the interface.
- See encapsulation vlan

interface atm

- Use to configure an ATM interface or subinterface type in the slot/port.subinterface format:
  - slot—Specifies router chassis slot
  - port—Specifies I/O module port
  - subinterface—Specifies subinterface number
- Example
  host1(config-if)#interface atm 9/1.1
- Use the no version to remove the ATM interface or subinterface.
- See interface atm

interface fastEthernet

- 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.
- See interface fastEthernet

interface gigabitEthernet

- Use to select a Gigabit Ethernet interface.

  | 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.
- See interface gigabitEthernet

interface tenGigabitEthernet

- 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.
- See interface tenGigabitEthernet

interface loopback

- Use to access and configure a loopback interface.
- 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.

- Example
  host1(config)#interface loopback 10 host1(config-if)#ip address 10.20.32.1 255.255.255.255
- Use the no version to delete the loopback interface.
- See interface loopback

ip address

- 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.
- Example
  host1(config-subif)#ip address 192.168.2.50 255.255.255.0
- Use the no version to remove the IP address or to disable IP processing.
- See ip address

ip auto-configure ip-subscriber

- 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.
- Example
  host1(config-if)#ip auto-configure ip-subscriber include-primary
- 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.
- See ip auto-configure ip-subscriber

ip auto-detect ip-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.
- See ip auto-detect ip-subscriber

ip dhcp-local pool

- Use to access DHCP Local Pool Configuration mode.
- The DHCP local server uses pool names other than default to maintain configuration information for subscribers to a particular domain.
- Example
  host1(config)#ip dhcp-local pool ispBoston
- Use the no version to prevent the DHCP local server from supplying IP addresses from the specified pool.
- See ip dhcp-local pool

ip inactivity-timer

- 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.
- See ip inactivity-timer

ip source-prefix

- 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.
- Example
  host1(config-if)#ip source-prefix 10.10.2.0 255.255.255.0
- Use the no version to remove the association between the interface and the specified IP source address and mask.
- See ip source-prefix

ip unnumbered

- Use to configure an unnumbered IP interface.
- 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.
- See ip unnumbered

ip use-framed-routes ip-subscriber

- 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.
- Example
  host1(config-if)#ip use-framed-routes ip-subscriber
- Use the no version to disable the use of framed routes when creating dynamic subscriber interfaces associated with this primary IP interface.
- See ip use-framed-routes ip-subscriber

network

- Use to specify the IP addresses that the DHCP local server can provide from an address pool.
- Example
  host1(config-dhcp-local)#network 10.10.1.0 255.255.255.0
- Use the no version to remove the network address and mask.
- See network

service dhcp-local

- Use to enable the DHCP local server to operate in either equal-access mode or standalone mode.
- Example
  host1(config)#service dhcp-local standalone
- Use the no version to disable the DHCP local server.
- See service dhcp-local

set dhcp relay giaddr-selects-interface

- Use to configure DHCP relay to use information in the giaddr in DHCP server-destined packets to identify the primary interface on which dynamic subscriber interfaces are built. See Using the Giaddr to Identify the Primary Interface for Dynamic Subscriber Interfaces for additional information about this feature.
- Example
  host1(config)#set dhcp relay giaddr-selects-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.
- See set dhcp relay giaddr-selects-interface

vlan id

- Use to configure a VLAN ID for a VLAN subinterface.
- Specify a VLAN ID number that is in the range 0–4095 and is unique within the Ethernet interface.
- Issue the vlan id command before you configure any upper-layer interfaces, such as IP.
- Example
  host1(config-if)#vlan id 400
- There is no no version.
- See vlan id