Configuring Frame Relay on a T1 Interface

Problem

You have a router that provides Frame Relay circuits to your customers. You want to set up a back-to-back connection between your router and that of a customer.

Solution

Use the following commands to configure Frame Relay:

[edit interfaces t1-0/0/3] aviva@RouterF# set description "J2300 T1 line in local office" aviva@RouterF# set encapsulation frame-relay aviva@RouterF# set dce aviva@RouterF# set unit 0 description "Customer A" aviva@RouterF# set unit 0 dlci 100 aviva@RouterF# set unit 0 family inet address 10.0.13.2/24

Discussion

Frame Relay is a point-to-point technology that switches packets through a network instead of routing them. The paths through the network are called virtual circuits (VCs). Each VC is identified by a Data Link Connection Identifier (DLCI), which is a number from 0 to 1023. In the JUNOS software, DLCIs 0 through 15 are reserved, so you can use 16 through 1023 to carry traffic. Generally, you might want to configure Frame Relay on slower interfaces, such as T1, serial, or ISDN.

You configure each VC on a separate logical interface, setting a DLCI number and IP address. You also set the encapsulation to frame-relay on the physical interface itself. On the remote side of the VC, you configure a DLCI that has the same number. Because the two router interfaces are in a back-to-back configuration, include the set dce command on one end of the link to have the router look like a Frame Relay switch.

Use the show interfaces command to verify that the DLCI is up and running:

aviva@RouterF> show interfaces t1-0/0/3 Physical interface: t1-0/0/3, Enabled, Physical link is Up Interface index: 140, SNMP ifIndex: 38 Description: J2300 T1 line in local office Link-level type: Frame-Relay, MTU: 1504, Clocking: Internal, Speed: T1, Loopback: None, FCS: 16, Framing: ESF Device flags : Present Running Interface flags: Point-To-Point SNMP-Traps 16384 Link flags : No-Keepalives DCE ANSI LMI settings: n392dce 3, n393dce 4, t392dce 15 seconds LMI: Input: 0 (never), Output: 0 (never) CoS queues : 8 supported Last flapped : 2005-05-26 05:50:29 PDT (03:45:59 ago) Input rate : 0 bps (0 pps) Output rate : 0 bps (0 pps) DS1 alarms : None DS1 defects : None Logical interface t1-0/0/3.0 (Index 71) (SNMP ifIndex 40) Description: Customer A Flags: Point-To-Point SNMP-Traps Encapsulation: FR-NLPID Input packets : 0 Output packets: 0 Protocol inet, MTU: 1500 Flags: None Addresses, Flags: Is-Preferred Is-Primary Destination: 10.0.13/24, Local: 10.0.13.2, Broadcast: 10.0.13.255 DLCI 100 Flags: Active Total down time: 0 sec, Last down: Never Input packets : 0 Output packets: 0

The physical interface properties show the Frame Relay encapsulation on the link layer (Link-level type: Frame-Relay). Under logical interfaces, the logical interface is up (no flags are set; if it were down, you would see Device-Down) and the DLCI is operational (Flags: Active).