# Configuring IP Tunnels, Shared IP Interfaces, and Subscriber Interfaces

The E Series router supports IP tunnels, shared IP interfaces, and subscriber interfaces.

## Configuring IP Tunnels

IP tunnels provide a way of transporting datagrams between routers separated by networks that do not support all the protocols that those routers support. To configure an IP tunnel, you must first configure a tunnel-service interface. (See Configuring Tunnel Service Interfaces.)

When you have configured a tunnel-service interface, treat it in the same way as any IP interface on the router. For example, you can configure static IP routes or enable routing protocols on the tunnel interface. The IP configurations that you apply to the tunnels control how traffic travels through the network.

## Configuring Shared Interfaces and Subscriber Interfaces

A shared IP interface is one of a group of IP interfaces that use the same layer 2 interface. Shared IP interfaces are unidirectional—they can transmit but not receive traffic. A subscriber interface is an extension of a shared IP interface. Subscriber interfaces are bidirectional—they can both receive and transmit traffic.

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. This capability is useful, for example, when data received in one VRF needs to be forwarded out an interface in another VRF, such as for BGP/MPLS VPNs (see JunosE BGP and MPLS Configuration Guide, for more information). 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 other IP interfaces. Each shared interface has its own statistics.

The E Series router supports subscriber interfaces on a particular type of layer 2 interface, Ethernet. In the absence of VLANS, Ethernet does not have a demultiplexing layer. A subscriber interface adds a demultiplexing layer for an Ethernet interface that is configured without VLANs. Using subscriber interfaces, the router can demultiplex or separate the traffic associated with different subscribers. You can use subscriber interfaces to separate traffic for cable modem subscribers with different levels of service and to separate traffic for VPNs.

For information about configuring shared interfaces and subscriber interfaces, see JunosE IP, IPv6, and IGP Configuration Guide.