Example: Using a Destination Address to Demultiplex Traffic

This example shows how you can use static subscriber interfaces to direct traffic toward special local content on the network, based on the traffic’s destination address.

Requirements

This example uses the following software and hardware components:

Overview

The example in Figure 7 shows how you can use static subscriber interfaces to direct traffic toward special local content on the network, based on the traffic’s destination address. In this application, a local VoIP service is on network 10.11.0.0./16, and a local gaming service is on network 10.12.0.0/16.

Figure 7: Subscriber Interfaces Using a Destination Address to Demultiplex Traffic

Subscriber Interfaces Using a Destination
Address to Demultiplex Traffic

Using a Destination Address to Demultiplex Traffic

To configure the static subscriber interfaces shown in Figure 7, perform the following steps:

  1. Configure a primary IP interface on a supported layer 2 interface.
    1. Create a layer 2 interface.
      host1(config)#interface fastEthernet 3/1
    2. Create a primary IP interface.
      host1(config-if)#ip address 10.1.1.1 255.0.0.0
    3. Configure the primary interface to use a destination address to demultiplex traffic for the subscriber interface. (By default, a source address is used to demultiplex traffic.)
      host1(config-if)#ip demux-type da-prefix

      Use the no version to restore the default situation in which the router uses a source address to demultiplex traffic.

    4. Exit Interface Configuration mode.
      host1(config-if)#exit
  2. Configure subscriber interface IP1.
    1. Create the shared IP interface.
      host1(config)#interface ip ip1

      Use the specified name to refer to the shared IP interface; you cannot use the layer 2 interface to refer to the shared IP interface, because the shared interface can be moved.

      Use the no version to delete the IP interface.

    2. Associate the shared IP interface with the layer 2 interface by using one of the following methods:
      • Static
        host1(config-if)#ip share-interface fastEthernet 3/1

        If you issue this command on a shared IP interface, you cannot issue the ip share-nexthop command for the 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 and IP is properly configured. You can create operational shared IP interfaces in the absence of a primary IP interface.

        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.

      • Dynamic
        host1:vr-a:vrf-1(config-if)#ip share-nexthop 10.1.1.2

        You can use this command to specify that the shared IP interface dynamically tracks a next hop. 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.

        If you issue this command on a shared IP interface, you cannot issue the ip share-interface command for the interface. If you issue this 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.

        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 associated with the specified next hop is operationally up and IP is properly configured.

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

    3. To fully configure the shared interface, assign an address or make it unnumbered.
      host1(config-if)#ip unnumbered loopback 0
    4. Specify the destination addresses for the subscriber interface to use to demultiplex traffic.
      host1(config-if)#ip destination-prefix 10.11.0.0 255.255.0.0

      On the ERX1440 Broadband Services Router or the E320 router, you can configure up to 1024 subnets for static subscriber interfaces per primary IP interface when each subnet has a variable network mask that is less than /32. The number of subnets identifying a single route (/32) is still limited by the global maximum of 16,000 hosts per line module.

      Use the no version to remove the association between the interface and the specified IP destination address and mask.

    5. Exit Interface Configuration mode.
      host1(config-if)#exit
  3. Repeat Step 2 to configure subscriber interface IP2.
    host1(config)#interface ip ip2 host1(config-if)#ip share-interface fastEthernet 3/1 host1(config-if)#ip unnumbered loopback 0 host1(config-if)#ip destination-prefix 10.12.0.0 255.255.0.0

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