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:

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.

Related Documentation

• Creating a Shared IP Interface
• Statically Associating the Shared IP Interface with the Layer 2 Interface
• Dynamically Associating the Shared IP Interface with the Layer 2 Interface
• Example: Configuring Shared IP Interfaces
• Moving IP Shared Interfaces
• Subscriber Interfaces Overview
• interface atm
• ip address
• virtual-router