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).