Exam: 640-802
Exam Objective: Configure and verify Frame Relay on Cisco routers
Contents
- Introduction
- Technology Background
- Lab Scenario
- Lab Objectives
- Lab Solution
Introduction
Frame Relay is a high-performance WAN protocol that operates at the physical and data link layers of the OSI reference model. Frame Relay originally was designed for use across Integrated Services Digital Network (ISDN) interfaces. Today, it is used over a variety of other network interfaces as well. This chapter focuses on Frame Relay's specifications and applications in the context of WAN services.Frame Relay is an example of a packet-switched technology. Packet-switched networks enable end stations to dynamically share the network medium and the available bandwidth. Frame Relay often is described as a streamlined version of X.25, offering fewer of the robust capabilities, such as windowing and retransmission of last data that are offered in X.25. Frame Relay is a layer 2 technology.
Technology Background
The default encapsulation on a Cisco Router's serial interface is HDLC. To use Frame-Relay on them, the encapsulation needs to be changed using the "encapsulation frame-relay" command. With Frame Relay, there are further two encapsulation types - Cisco and IETF. Cisco is the default type and you will need to manually change it to IETF if you are connecting to a non-Cisco device. The command to do this is:Router(config)#interface s0/0
Router(config-if)#encapsulation frame-relay ietf
Frame Relay operates using virtual circuits. These virtual circuits are what link together the devices connected to the provider's network. Frame Relay provides a virtual circuit between your two DTE devices, making them appear to be connected via a circuit when they are actually sending devices through a shared medium. There are two types of Virtual Circuits - Permanent virtual circuit (PVC) and Switched Virtual Circuit (SVCs). PVCs will always remain in place but SVCs are setup and torn down as and when data needs to be sent.
Frame Relay PVCs use Data Link Connection Identifiers (DLCIs). A Frame Relay service provider assigns DLCI values, which are used on Frame Relay interfaces to distinguish between different virtual circuits.
A DLCI can be assigned to an interface using the following command
Router(config)#interface s0/0
Router(config-if)#frame-relay interface-dlci <dlci>
The DLCI value can be anything between 16 and 1007.
Local Management Interface (LMI) is a signaling standard used between your router and the first Frame Relay switch it's connected to. It allows for sharing information about the operation and status of the virtual circuit between the provider's network and your router. The following information is shared using LMI:
Keepalives: These verify that data is flowing.
Global addressing: This provides global significance to DLCIs, allowing the Frame Relay
cloud to work exactly like a LAN.
Status of virtual circuits: This provides DLCI status. The status inquiries and messages are
used as keepalives when there is no regular LMI traffic to send.
There are three different types of LMI message formats: Cisco, ANSI, and Q.933A. The different
kinds in use depend on both the type and configuration of the telco's switching gear, so it's important the router is configured to use the LMI type configured at the telco's end. Cisco is default LMI type.
LMI type can be configured using the following command:
Router(config-if)#frame-relay lmi-type <cisco|ansi|q933a>
LMI is autosensed in routers running IOS version 11.2 and above.
Let's see the configuration of a PVC on a Serial Interface:
Router(config)#interface s0/0
Router(config-if)#encapsulation frame-relay ietf
Router(config-if)#ip address 192.168.1.1 255.255.255.0
Router(config-if)#frame-relay interface-dlci 101
The above example will configure a serial interface to use frame relay IETF encapsulation and DLCI 101. The router at the other end can use a DLCI provided by the ISP and 192.168.1.1 IP Address to reach us.
We can have multiple virtual circuits on a single Physical interface and each circuit can be treated as a different network/interface. This can be achieved using sub-interfaces. Frame Relay sub-interfaces can be point-to-point or multipoint. Point-to-Point sub-interfaces treat each DLCI as a different network. Multipoint interfaces will treat a group of DLCI as single network. Frame relay can be configured on sub-interfaces using the following commands:
Router(config)#interface s0/0
Router(config-if)#encapsulation frame-relay ietf
Router(config-if)#exit
Router(config)#interface s0/0.1 point-to-point
Router(config-subif)#ip address 192.168.1.1 255.255.255.0
Router(config-subif)#frame-relay interface-dlci 101
The following commands can be used to verify frame relay configuration:
- show frame-relay pvc
- show frame-relay lmi
- show interfaces
Lab Scenario
We have purchased Frame Relay links between our Head Office and Branch Offices. Your task is to configure the Routers as shown in Figure 1. Ensure that IETF frame-relay encapsulation is used.
Figure 1
Lab Objectives
- Configure Frame Relay using sub-interfaces on RouterA using DLCI 102 and 103
- Configure Frame Relay using the physical interface of Router B and DLCI 201
- Configure Frame Relay using the physical interface of Router C and DLCI 301
Lab Solution
Before we configure Frame-relay, it should be noted that a Frame Relay switch is required between the devices for the link to work. A Cisco router can be configured as a Frame Relay Switch. See the References section for the URL to the document explaining the Frame Relay switch configuration:Let's configure RouterA first:
RouterA(config)#interface s0/0
RouterA(config-if)#encapsulation frame-relay ietf
RouterA(config-if)#no shut
RouterA(config-if)#exit
RouterA(config)#interface s0/0.1 point-to-point
RouterA(config-subif)#frame-relay interface-dlci 102
RouterA(config-fr-dlci)#exit
RouterA(config-subif)#ip address 192.168.1.1 255.255.255.0
RouterA(config-subif)#exit
RouterA(config)#interface s0/0.2 point-to-point
RouterA(config-subif)#frame-relay interface-dlci 103
RouterA(config-fr-dlci)#exit
RouterA(config-subif)#ip address 192.168.2.1 255.255.255.0
Configuration on RouterB:
RouterB(config)#interface s0/0
RouterB(config-if)#encapsulation frame-relay ietf
RouterB(config-if)#frame-relay interface-dlci 201
RouterB(config-fr-dlci)#exit
RouterB(config-if)#ip address 192.168.1.2 255.255.255.0
RouterB(config-if)#no shut
Configuration on RouterC:
RouterC(config)#interface s0/0
RouterC(config-if)#encapsulation frame-relay ietf
RouterC(config-if)#frame-relay interface-dlci 301
RouterC(config-fr-dlci)#exit
RouterC(config-if)#ip address 192.168.2.2 255.255.255.0
RouterC(config-if)#no shut
Let's verify connectivity from RouterA:
RouterA#ping 192.168.1.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/22/32 ms
RouterA#ping 192.168.2.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.2.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/17/64 ms
PVC status on RouterA:
RouterA#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 0 0 0 0
DLCI = 102, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0/0.1
input pkts 7 output pkts 18 in bytes 610
out bytes 3502 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 7 out bcast bytes 2358
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
pvc create time 00:04:33, last time pvc status changed 00:04:13
DLCI = 103, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0/0.2
input pkts 8 output pkts 16 in bytes 758
out bytes 2378 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 3 out bcast bytes 1026
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
pvc create time 00:04:34, last time pvc status changed 00:04:14
PVC status on RouterB:
RouterB#show frame-relay pvc
PVC Statistics for interface Serial0/0 (Frame Relay DTE)
Active Inactive Deleted Static
Local 1 0 0 0
Switched 0 0 0 0
Unused 0 0 0 0
DLCI = 201, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0/0
input pkts 16 output pkts 7 in bytes 2542
out bytes 610 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 1 out bcast bytes 30
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
pvc create time 00:03:34, last time pvc status changed 00:02:23
PVC status on RouterC
RouterC#show frame-relay pvc
PVC Statistics for interface Serial0/0 (Frame Relay DTE)
Active Inactive Deleted Static
Local 1 0 0 0
Switched 0 0 0 0
Unused 0 0 0 0
DLCI = 301, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0/0
input pkts 18 output pkts 8 in bytes 2750
out bytes 758 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 1 out bcast bytes 30
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
pvc create time 00:03:53, last time pvc status changed 00:02:39
References:
Configuring Frame Relay Switching
http://www.cisco.com/en/US/tech/tk713/tk237/technologies_tech_note09186a008014f8a7.shtml#topic7
Frame Relay
http://www.cisco.com/en/US/docs/internetworking/technology/handbook/Frame-Relay.html
Comprehensive Guide to Configuring and Troubleshooting Frame Relay
http://www.cisco.com/en/US/tech/tk713/tk237/technologies_tech_note09186a008014f8a7.shtml
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