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    Shared IP Interfaces

    You can create multiple shared IP interfaces over the same layer 2 logical interface.

    Shared IP Interfaces Overview

    You can create multiple shared IP interfaces over the same layer 2 logical interface—for example, atm 5/3.101—enabling more than one IP interface to share the same logical resources. You can configure one or more shared IP interfaces. Data sent over shared interfaces uses the same layer 2 interface. You can configure shared interfaces as you would unshared IP interfaces. Each shared interface has its own statistics.

    Some layer 2 interfaces require a primary IP interface to negotiate certain IP parameters—for example, Internet Protocol Control Protocol (IPCP) for Point-to-Point Protocol (PPP), Address Resolution Protocol (ARP) for Ethernet, and Inverse ARP for Frame Relay. If you do not configure a primary IP interface in such cases, the layer 2 interface cannot become operationally up.

    A primary IP interface is the default interface for receiving data that arrives on the layer 2 interface. If you configure shared IP interfaces for the same layer 2 interface as your primary IP interface, by default data received on the layer 2 interface is received on the virtual router corresponding to the primary IP interface. A primary IP interface and all of its shared IP interfaces have the same interface location. You can configure a shared IP interface to receive data on the same layer 2 interface as a primary IP interface. You can delete primary and shared IP interfaces independently of each other.

    You can create a primary IP interface as you do any other IP interface, as shown in the following example:

    host1(config)#virtual-router vr-a:vrf-2 host1:vr-a:vrf-2:(config)#interface atm 5/3.101 host1:vr-a:vrf-2:(config-if)#ip address 10.1.1.1 255.255.255.255 host1:vr-a:vrf-2:(config-if)#exit

    You do not have to configure a primary IP interface if you do not need one as described above. In the absence of a primary interface, you can still configure shared IP interfaces; however, in this scenario, data received on the layer 2 interface is discarded.

    You cannot create shared IP interfaces for the following kinds of interface:

    • IP floating interfaces (IP interfaces that stack over MPLS stacked tunnels)
    • Loopback interfaces
    • Null interfaces

    For information about configuring shared IP interfaces to receive data on the same layer 2 interface as a primary IP interface, see JunosE Broadband Access Configuration Guide.

    Creating a Shared IP Interface

    You can create an IP interface for interface sharing using the interface ip command. You can use the specified name to refer to the shared IP interface; you cannot use the layer 2 interface to refer to them, because the shared interface can be moved.

    To create an IP interface for interface sharing:

    • Issue the interface ip command in Global Configuration mode.
      host1(config)#interface ip si0

      Use the no version to delete the IP interface.

    Statically Associating the Shared IP Interface with the Layer 2 Interface

    You can specify the layer 2 interface used by a shared IP interface using the ip share-interface command. The command fails if the layer 2 interface does not yet exist. The command is not supported (that is, it fails) if you use an RSVP tunnel (for example, tunnel mpls:1) to identify the layer 2 interface.

    After creating the shared IP interface, you can configure it as you do any other IP interface.

    The shared interface is operationally up when the layer 2 interface is operationally up.

    You can create operational shared IP interfaces in the absence of a primary IP interface.

    Note:

    • All IP configurations will be removed from the interface when you issue the no ip interface command in Interface Configuration mode.
    • You cannot issue the ip share-nexthop command for the IP shared interface if the ip share-interface command is issued on the IP shared interface.

    To specify the layer 2 interface to be used by a shared IP interface:

    • Issue the ip share-interface command in Interface Configuration mode.
      host1(config-if)#ip share-interface atm 5/3.101

      Use the no version to remove the association between the layer 2 interface and the shared IP interface. You can delete shared and primary IP interfaces independently.

    Dynamically Associating the Shared IP Interface with the Layer 2 Interface

    You can specify that the shared IP interface dynamically tracks a next hop using the ip share-nexthop command. If the next hop changes, the shared IP interface moves to the new layer 2 interface associated with the IP interface toward the new next hop.

    The shared interface is operationally up when the layer 2 interface associated with the specified next hop is operationally up. However, if the layer 2 interfaced associated with the specified next hop is an MPLS next hop (for example, an RSVP or LDP tunnel), the shared interface remains operationally down.

    If you issue the ip share-nexthop command on a shared IP interface, the shared interface cannot dynamically track the next hop for the specified destination if the next-hop IP address is resolvable over MPLS.

    If you specify a virtual router, the command fails if the VR does not already exist. If you do not specify a VR, the current VR is assumed.

    Note:

    • All IP configurations will be removed from the interface when you issue the no ip interface command in Interface Configuration mode.
    • You cannot issue the ip share-interface command for the IP shared interface if the ip share-nexthop command is issued on the IP shared interface.

    To specify that the shared IP interface dynamically tracks a next hop:

    • Issue the ip share-nexthop command in Interface Configuration mode.
      host1:vr-a:vrf-1(config-if)#ip share-nexthop 10.0.0.1

      Use the no version to halt tracking of the next hop.

    Example: Configuring Shared IP Interfaces

    This example shows you how to create and configure shared IP interfaces.

    Requirements

    This example uses the following software and hardware components:

    • JunosE Release 7.1.0 or higher-numbered releases
    • E Series router (ERX7xx models, ERX14xx models, the ERX310 router, the E120 router, or the E320 router)
    • ASIC-based line modules that support Fast Ethernet or Gigabit Ethernet

    Overview

    You can create multiple shared IP interfaces over the same layer 2 logical interface—for example, atm 5/3.101—enabling more than one IP interface to share the same logical resources.

    Configuring Shared IP Interfaces

    To configure shared IP interfaces:

    1. Create a layer 2 interface.
      host1(config)#interface atm 5/3 host1(config-if)#interface atm 5/3.101
    2. (Optional) Create a primary IP interface.
      host1(config-if)#ip address 10.1.1.1 255.255.255.255 host1(config-if)#exit
    3. Create the shared IP interface.
      host1(config)#interface ip si0
    4. Associate the shared IP interface with the layer 2 interface by one of the following methods:
      • Statically
        host1(config-if)#ip share-interface atm 5/3.101
      • Dynamically
        host1:vr-a:vrf-1(config-if)#ip share-nexthop 10.0.0.1
    5. To fully configure the shared interface, assign an address (or make the interface unnumbered).
      host1(config-if)#ip address 2.2.2.2 255.0.0.0

    Moving IP Shared Interfaces

    You can move an IP shared interface from one layer 2 interface to another by issuing the ip share-interface command to specify a different layer 2 interface. Moving an IP interface does not affect interface statistics, packets forwarded through the interface, or policies attached to the IP interface.

    Note: All IP configurations will be removed from the interface when you issue the no ip interface command in Interface Configuration mode.

    To move an IP shared interface from one layer 2 interface to another:

    1. Create a shared interface and assign it to one layer 2 interface.
      host1(config)#virtual-router vr-a:vrf-1 host1:vr-a:vrf-1(config)#interface ip si0 host1:vr-a:vrf-1(config-if)#ip share-interface atm 5/3.101 host1:vr-a:vrf-1(config-if)#exit
    2. Move the shared interface to another layer 2 interface.
      host1:vr-a:vrf-1(config)#interface ip si0 host1:vr-a:vrf-1(config-if)#ip share-interface atm 5/3.201

    IP Shared Interface Statistics Overview

    Each shared interface has its own statistics. Packets transmitted on a shared IP interface are always counted only in the shared IP interface.

    Subscriber Interfaces Overview

    A subscriber interface is an extension of a shared IP interface. Shared IP interfaces are unidirectional—they can transmit but not receive traffic. In contrast, subscriber interfaces are bidirectional—they can both receive and transmit traffic.

    For details about configuring and using subscriber interfaces, see JunosE Broadband Access Configuration Guide.

    Published: 2014-08-13