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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

Image g013670.gif

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

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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

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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

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