# Configuring Data Link-Layer Interfaces

You can configure the following data link-layer interfaces:

- IP/Frame Relay or multilink Frame Relay
- IP/ATM
- IP/PPP or multilink PPP
- IP/Cisco HDLC
- IP/Ethernet

## Configuring IP/Frame Relay

The router supports IP over Frame Relay PVCs on the CT3 12-F0 and OCx/STMx POS modules. The interface presented to the incoming traffic is an IP/Frame Relay router. In addition, IP/PPP/Frame Relay is supported on the T3 and E3 modules. With this interface, the service provider can:

- Receive traffic from subscribers that have CPE equipment, such as routers with Frame Relay interfaces
- Take in traffic from other network devices that use Frame Relay, such as DSLAMs and Frame Relay switches
- Use Frame Relay as an uplink technology on an unchannelized T3 or E3 link

Figure 9 shows the structure of the Frame Relay interface. Each Frame Relay major interface sits on top of an HDLC interface. The Frame Relay implementation is divided into two levels: a major interface and one or more subinterfaces. This division allows a single physical interface to support multiple logical interfaces. Multiple IP interfaces can also be assigned to each Frame Relay major interface through the subinterfaces.

Figure 9: Frame Relay Interface Design

Figure 10 shows the structure of the Frame Relay protocols with the physical layer as the foundation. For Frame Relay, the physical layer can be channelized E1, E3, channelized T1, T3, or a fractional service, as supported by the different line module ports. The HDLC layer is on top of the physical layer and can support flexible assignment of physical resources.

For example, an HDLC channel can support one DS0, a fractional T1, or an entire T1. The major Frame Relay interface sits on top of the HDLC resource, and the subinterfaces sit on top of the major interface. The Frame Relay subinterfaces connect to the IP interface layer.

Figure 10: Structure of Frame Relay Protocols

The router supports Frame Relay LMI (local management interface) to provide the operator with configuration and status information relating to the Frame Relay VCs in operation. LMI specifies a polling mechanism to receive incremental and full-status updates from the network. The router can represent either side of the User-to-Network Interface (UNI) and supports unidirectional LMI. Bidirectional support for the Network-to-Network Interface (NNI) is also supported.

Figure 11 shows sample configuration parameters for Frame Relay on a serial interface.

Figure 11: Serial Interface Configuration Parameters for a Frame Relay Connection

The following sample command sequence configures a serial interface for Frame Relay. See JunosE Link Layer Configuration Guide, for information.

host1(config)#interface serial 0/1:1/5 host1(config-if)#encapsulation frame-relay ietf host1(config-if)#frame-relay intf-type dte host1(config-if)#frame-relay lmi-type ansi host1(config-if)#interface serial 0/1:1/5.1 host1(config-subif)#frame-relay interface-dlci 17 ietf host1(config-subif)#ip address 192.32.10.2 255.255.255.0

## Configuring IP/ATM

The router supports IP over ATM PVCs on ATM line modules. This support allows service providers to receive traffic from subscribers who have CPE equipment, such as routers with ATM interfaces, to take in traffic from other network devices that use ATM, such as DSLAMs, and to connect to service providers with ATM backbone structures.

Figure 12 shows an IP/ATM access connection.

Figure 12: E Series Router IP/ATM Access Connection

Figure 13 shows the structure of the ATM interface. For ATM, this can be SONET, DS3, or E3 as supported by the different line modules. The major ATM interface sits on top of the SONET/DS3/E3 resource, and the subinterfaces sit on top of the major interface. The ATM subinterfaces connect to the IP interface layer.

Figure 13: Structure of the ATM Interface Design

Figure 14 shows the structure of the ATM protocols. The physical layer (SONET and/or DSx/Ex) is the foundation and provider of layer 1 framing service. The ATM layer is on top and provides cell, circuit, and OAM services. The AAL5 layer provides a frame-oriented interface to the ATM layer. The integrated local management interface (ILMI) provides local management across the UNI.

Figure 14: Structure of ATM Protocol

Figure 15 shows sample configuration parameters for a typical ATM interface configuration.

Figure 15: ATM Interface Configuration Parameters

The following sample command sequence configures an ATM interface on port 0 of the line module in slot 1. See JunosE Link Layer Configuration Guide, for information about how to configure an ATM interface.

host1(config)#interface atm 0/1 host1(config-if)#interface atm 0/1.22 host1(config-if)#atm pvc 22 100 10 aal5snap host1(config-subif)#ip address 192.32.10.20 255.255.255.0

## Configuring IP/PPP

The router supports IP/PPP on the channelized T3, E1, and T3/E3 interfaces and IP/PPP/SONET on the OC3/STM1 and OC12/STM4 interfaces. This support allows service providers to accept traffic from subscribers who have CPE equipment, such as routers with PPP interfaces, and to transmit traffic in PPP format to other network devices.

Figure 16 shows that the router supports the incoming IP/PPP traffic from the CPE. This traffic can then be routed to the uplink(s) attached to the router or to other CPEs that are attached to the router.

Figure 16: IP/PPP Connections from the CPE on an E Series Router

As shown in Figure 17, the PPP protocol can exist directly on top of the HDLC layer or on top of a layer 2 Frame Relay or ATM interface. In either case, IP rides on top of PPP, providing support for IP/PPP/ATM, IP/PPP/HDLC, and IP/PPP/Frame Relay. Both SONET and DSx/Ex interfaces are supported at the physical layer.

Figure 17: Structure of PPP

Figure 18 shows sample configuration parameters for PPP on a serial interface.

Figure 18: PPP Interface Configuration Parameters

The following sample command sequence configures PPP on a serial interface. See JunosE Link Layer Configuration Guide, for details.

host1(config)#interface serial 3/0:2/5 host1(config-if)#encapsulation ppp host1(config-if)#ip address 192.32.22.10 255.255.255.0

## Configuring IP/HDLC

The E Series router supports IP over Cisco HDLC on many types of serial interfaces. Cisco HDLC monitors line status on a serial interface by exchanging keepalive request messages with peer network devices. It also allows routers to discover IP addresses of neighbors by exchanging Serial Link Address Resolution Protocol (SLARP) address request and address response messages with peer network devices.

The E Series router Cisco HDLC is compatible with the Cisco Systems Cisco-HDLC protocol, the default protocol for all Cisco serial interfaces.

The router supports the following framing features:

- HDLC for data-link framing
- 18,000-byte information field size

  Figure 19: Structure of Cisco HDLC Protocol

As shown in Figure 19, the Cisco HDLC protocol can exist directly on top of the HDLC layer or ATM or SONET interface. Both SONET and DSx/Ex interfaces are supported at the physical layer.

The following example configures HDLC on a serial interface. See JunosE Link Layer Configuration Guide , for details.

host1(config)#interface serial 3/1:2/1 host1(config-if)#encapsulation hdlc host1(config-if)#ip address 192.32.10.2 255.255.255.0

## Configuring IP/Ethernet

The E Series router supports IP/Ethernet. When you select an Ethernet interface, you can assign an IP address to it, as the following example shows:

host1(config)#interface fastethernet 4/1 host1(config-if)#ip address 192.5.127.8 255.255.255.0

Figure 20 shows an IP/Ethernet interface stack.

Figure 20: Example of IP over Ethernet Stacking Configuration Steps