Configuring Static Subscriber Interfaces

You can configure static subscriber interfaces on ATM, Fast Ethernet, Gigabit Ethernet, 10-Gigabit Ethernet, or POS layer 2 interfaces.

The examples in this section show how to configure static subscriber interfaces on a Fast Ethernet interface, but the steps for configuring static subscriber interfaces over other supported layer 2 interface types are similar.

Using a Destination Address to Demultiplex Traffic

The example in Figure 20 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 20: Subscriber Interfaces Using a Destination Address to Demultiplex Traffic

To configure the static subscriber interfaces shown in Figure 20, 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. (By default, a source address is used to demultiplex traffic.)

      host1(config-if)#ip demux-type da-prefix

   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

   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

      • Dynamic

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

   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

   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

Using a Source Address to Demultiplex Traffic

Figure 21 shows how you can use static subscriber interfaces to differentiate traffic for VPN access, based on the traffic’s source address.

Figure 21: Subscriber Interfaces Using a Source Address to Demultiplex Traffic

To configure the static subscriber interfaces shown in Figure 21, 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 4/1

   2. Create a primary IP interface.

      host1(config-if)#ip address 10.1.1.1 255.255.255.0

   3. Exit Interface Configuration mode.

      host1(config-if)#exit

2. Configure subscriber interface IP1.
   1. Create the shared IP interface.

      host1(config)#virtual-router vra
      Proceed with new virtual-router creation? [confirm] yes
      host1:vra(config)#interface ip ip1

   2. Associate the shared IP interface with the layer 2 interface by using one of the following methods:
      • Static

        host1:vra(config-if)#ip share-interface fastEthernet 4/1

      • Dynamic

        host1:vra(config-if)#ip share-nexthop 10.1.1.2

   3. To fully configure the shared interface, assign an address or make it unnumbered.

      host1:vra(config-if)#ip unnumbered loopback 0

   4. Specify the source addresses for the subscriber interface to use to demultiplex traffic, then exit Interface Configuration mode.

      host1:vra(config-if)#ip source-prefix 10.10.3.0 255.255.255.0

      host1:vra(config-if)#exit

3. Create a static route that sends traffic for destination address 10.10.3.0 to subscriber interface IP1.

   host1:vra(config)#ip route 10.10.3.0 255.255.255.0 ip ip1

4. Repeat Step 2 to configure subscriber interface IP2.

   host1(config)#virtual-router vrb
   Proceed with new virtual-router creation? [confirm] yes
   host1:vrb(config)#interface ip ip2
   host1:vrb(config-if)#ip share-interface fastEthernet 4/1
   host1:vrb(config-if)#ip unnumbered loopback 0
   host1:vrb(config-if)#ip source-prefix 10.10.4.0 255.255.255.0
   host1:vrb(config-if)#exit

5. Create a static route that sends traffic for destination address 10.10.4.0 to subscriber interface IP2.

   host1:vrb(config)#ip route 10.10.4.0 255.255.255.0 ip ip2

6. Specify that DHCP relay does not install host routes—this avoids a conflict that can causes undesirable ARP behavior.

   host1(config)#set dhcp relay inhibit-access-route-creation

   For details about the cause of this conflict and the use of the set dhcp relay inhibit-access-route-creation command to avoid the conflict, see “Configuring DHCP Relay”.

interface ip

• Use to create an IP interface to share a layer 2 interface.
• 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.
• Example

  host1(config)#interface ip si0

• Use the no version to delete the IP interface.
• See interface ip

ip demux-type da-prefix

• Use to specify that the router use a destination address to demultiplex traffic for the subscriber interface.
• Example

  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.
• See ip demux-type da-prefix

ip destination-prefix

• Use to specify a destination address for a subscriber interface or for a primary IP interface.
• On the ERX-1440 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.
• Example

  host1(config-if)#ip destination-prefix 196.168.2.2 255.0.0.0

• Use the no version to remove the association between the interface and the specified IP destination address and mask.
• See ip destination-prefix

ip share-interface

• Use to specify the layer 2 interface for this IP interface to share. The command fails if the layer 2 interface does not yet exist.
• 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.
• Example

  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.
• See ip share-interface

ip share-nexthop

• Use 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.
• Example

  host1(config-if)#ip share-nexthop 192.168.10.16

• Use the no version to halt tracking of the next hop.
• See ip share-nexthop

ip source-prefix

• Use to specify a source address for a subscriber interface.
• On the ERX-1440 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.
• Example

  host1(config-if)#ip source-prefix 192.168.0.0 255.0.0.0

• Use the no version to remove the association between the interface and the specified IP source address and mask.
• See ip source-prefix

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