Lab 5-3 – Configuring Point-to-Point Frame Relay Sub-Interfaces

In this lab you’ll learn how to configure a Cisco Router to simulate multiple Point-to-Point Frame Relay links using a single physical interface by configuring sub-interfaces.

Real World Application & Core Knowledge

Now that you’re familiar with Point-to-Point Frame Relay links lets take a step further and demonstrate how you can have multiple frame relay links on a single router using a single physical interface but multiple sub-interfaces to represent the multiple PVC’s (Permanent Virtual Circuits)

By Creating a Point-to-Point Sub-interface which will have an interface-dlci assigned to it you’ll have the ability for R1 to communicate to R2 and R3 as if R1 has two completely separate point-to-point links using only a single physical link to the Frame Relay cloud.

When creating a Sub-interface for interface-dlci’s it is a fairly common practice to use the DLCI number as the sub-interface number for documentation purposes however this is not a requirement.

In this lab you’ll familiarize yourself with the following new commands;

interface Serial#/#.### point-to-point – This command when in global configuration creates a new point-to-point sub-interface that can be used to configure interface dlci’s.

Lab Prerequisites

• If you are using GNS3 than load the Stub Area Networking GNS3 topology than start devices; R1, R2 and R3.
• Establish a console session with devices R1, R2 and R3 than configure the devices respected hostname(s).
• Configure R1, R2 and R3′s Serial0/0 interface encapsulation to frame relay and enable the interfaces using the no shut command.

Lab Objectives

• On R1, create the sub-interface Serial0/0.122 and assign it the interface DLCI of 122 and the IP Address of 172.18.12.1/30 then create interface Serial0/0.123 and assign it the IP Address 172.18.13.1/30
• On R2, create the sub-interface Serial0/0.221 and assign it the interface DLCI of 221 and the IP Address of 172.18.12.2/30
• On R3, create the sub-interface Serial0/0.321 and assign it the interface DLCI of 321 and the IP Address of 172.18.13.2/30
• Verify connectivity using the show frame-relay pvc and ping commands on R1.

Lab Instruction

Objective 1. – On R1, create the sub-interface Serial0/0.122 and assign it the interface DLCI of 122 and the IP Address of 172.18.12.1/30 then create interface Serial0/0.123 and assign it the ip address 172.18.13.1/30

R1 con0 is now available

Press RETURN to get started.

R1>enable
R1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
R1(config)#interface Serial0/0.122 point-to-point
R1(config-subif)#ip address 172.18.12.1 255.255.255.252
R1(config-subif)#frame-relay interface-dlci 122
R1(config-fr-dlci)#exit
R1(config-subif)#interface Serial0/0.123 point-to-point
R1(config-subif)#ip address 172.18.13.1 255.255.255.252
R1(config-subif)#frame-relay interface-dlci 123
R1(config-subif)#end
R1#
%SYS-5-CONFIG_I: Configured from console by console
R1#

Objective 2. – On R2, create the sub-interface Serial0/0.221 and assign it the interface DLCI of 221 and the IP Address of 172.18.12.2/30

R2 con0 is now available

Press RETURN to get started.

R2>enable
R2#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
R2(config)#interface Serial0/0.221 point-to-point
R2(config-subif)#ip add 172.18.12.2 255.255.255.252
R2(config-subif)#frame-relay interface-dlci 221
R2(config-fr-dlci)#end
R2#
%SYS-5-CONFIG_I: Configured from console by console
R2#

Objective 3. – On R3, create the sub-interface Serial0/0.321 and assign it the interface DLCI of 321 and the IP Address of 172.18.13.2/30

R3 con0 is now available

Press RETURN to get started.

R3>enable
R3#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
R3(config)#interface Serial0/0.321 point-to-point
R3(config-subif)#ip add 172.18.13.2 255.255.255.252
R3(config-subif)#frame-relay interface-dlci 321
R3(config-fr-dlci)#end
R3#
%SYS-5-CONFIG_I: Configured from console by console
R3#

Objective 4. – Verify connectivity using the show frame-relay pvc and ping commands on R1.

R1#show frame-relay pvc

PVC Statistics for interface Serial0/0 (Frame Relay DTE)

              Active     Inactive      Deleted       Static
  Local          2            0            0            0
  Switched       0            0            0            0
  Unused         2            0            0            0

DLCI = 122, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0/0.122

  input pkts 20            output pkts 19           in bytes 5395
  out bytes 5187           dropped pkts 0           in pkts dropped 0
  out pkts dropped 0                out bytes dropped 0
  in FECN pkts 0           in BECN pkts 0           out FECN pkts 0
  out BECN pkts 0          in DE pkts 0             out DE pkts 0
  out bcast pkts 14        out bcast bytes 4667
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
  pvc create time 00:14:33, last time pvc status changed 00:14:33

DLCI = 123, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0/0.123

  input pkts 22            output pkts 20           in bytes 6045
  out bytes 4380           dropped pkts 0           in pkts dropped 0
  out pkts dropped 0                out bytes dropped 0
  in FECN pkts 0           in BECN pkts 0           out FECN pkts 0
  out BECN pkts 0          in DE pkts 0             out DE pkts 0
  out bcast pkts 10        out bcast bytes 3340
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
  pvc create time 00:17:27, last time pvc status changed 00:17:27

R1#ping 172.18.12.2

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.18.12.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/82/188 ms
R1#ping 172.18.13.2

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.18.13.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 28/96/168 ms
R1#