How to configure a cisco router as a frame relay switch?

1. How to Configure a Cisco Router as a Frame Relay Switch?
A Cisco router now has the capability to simulate a Frame Relay switch. Although this
appendix will not show you how configure all of the features that a true Frame Relay
switch will have, it will show you how to configure a Cisco router to propagate DLCIs
and match them to the appropriate outgoing interfaces to make the router act as a
Frame Relay switch.
The most important thing to remember about a Frame Relay switch in the lab is that
the DLCI is sent through LMI out a particular interface, and then that DLCI and
interface are mapped to an outgoing DLCI and interface.
Physical Connections to the Frame Relay Switch (Cisco 2523)
Before you start configuring the Frame Relay switch, take a look at how the lab
routers are connected to the Cisco 2523 acting as the Frame Relay switch. Figure
B-7 illustrates the physical connections.
Figure B-7 Frame Relay Physical Connections
As you can see from Figure B-7, R3 will be the "hub" site and requires two PVCs and
DLCIs to be configured on interface S0 of the Cisco 2523. R2 and R4 need only one
PVC and one DLCI. Begin by configuring the router as a Frame Relay switch.
Steps for Configuring a Cisco Router as a Frame Relay Switch
Table B-1 defines the steps to configuring a Cisco router as a Frame Relay switch.
Table B-1. Configuring a Cisco Router as a Frame Relay Switch
Step Description Command
Step Enable Frame Relay switching. frame-relay switching
1
Step Configure Frame Relay encapsulation
2 encapsulation, Frame Relay LMI frame-relay frame-relaylmi-type
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2. Step Description Command
type, Frame Relay DCE interface ansi frame-relay intf-type dce clock rate
mode, and clock rate on 64000
individual interfaces.
Step Configure DLCI to interface frame-relay
3 mappings on individual route {local-dlci} interface {outgoing
interfaces. interface and number} {outgoing-dlci}
The first thing is to connect to the Cisco 2523's console port. There is no
configuration on the router at this point. You should be in setup mode or at
the Router> prompt. If you are in setup mode, just exit this mode (Ctrl-c).
When you are into the router, give it a host name of Frame-Switch.
Router>en
Router#config t
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#hostname Frame-Switch
Do not worry about passwords and Telnet connectivity. This router will be a
standalone Frame Relay switch. If you need to access it, you will connect to the
console port.
Begin with the first step documented in Table B-1, and enable Frame Relay switching
on the router. Example B-1 illustrates this configuration step.
Example B-1. Enable Frame Relay Switching
Frame-Switch(config)#frame-relay switching
Frame-Switch(config)#
After the Frame Relay switching process has been started, configure the individual
interfaces for the Frame Relay switch. This includes changing the encapsulation type
to frame-relay and changing the LMI type to ANSI. Because all interfaces on the
Frame Relay switch are DCEs (refer to the Figure B-7), they will need to be changed
to the Frame
Relay type DCE and must have the clock rate command issued as well. Example B-2
demonstrates these commands for interface Serial0.
Example B-2. Frame-Relay Commands for Serial0
Frame-Switch(config)#int serial0
Frame-Switch(config-if)#encapsulation frame-relay
Frame-Switch(config-if)#frame-relay lmi-type ansi
Frame-Switch(config-if)#frame-relay intf-type dce
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3. Frame-Switch(config-if)#clock rate 64000
Now that all the Frame Relay commands have been set, you need to map the local
DLCI of this interface to the outgoing DLCI and port. Because the Serial0 interface has
two PVCs, it needs two mappings. Example B-3 shows the commands.
Example B-3. DLCI-to-Interface Mappings for Serial0
Frame-Switch(config-if)#frame-relay route 100 interface serial 2
101
Frame-Switch(config-if)#frame-relay route 200 interface serial 1
201
Frame-Switch(config-if)#no shutdown
From Figure B-7, you know that Serial 0 has two PVCs, one to R2 and one to R4. The
first highlighted portion of lines 1 and 2 in Example B-3 point out the local DLCI that
will be advertised out Serial 0. Therefore, R3 will see DLCI 100 and DLCI 200 because
R3 is connected to the Frame Relay switch on Serial0. The second portion of
highlighting in lines 1 and 2 marks the outgoing interface to which each DLCI is
mapped. Therefore, anything coming from R3 on DLCI 100 will be sent to Serial2, and
anything coming from R3 on DLCI 200 will be sent to Serial1. The last portion of
highlighting in lines 1 and 2 indicates the DLCI assigned to the outgoing port. So,
anything coming from R3 on DLCI 100 will go out Serial2 to DLCI 101, and anything
coming from R3 on DLCI 200 will go out Serial1 to DLCI 201. Don't forget to remove
the interfaces from shutdown mode.
The next thing you need to do is perform a similar mapping statement on interfaces
Serial1 and Serial2, except that the numbers will be reversed. See Example B-4.
Example B-4. Frame Relay Commands and DLCI-to-Interface Mappings for Serial1
Frame-Switch(config)#interface serial1
Frame-Switch(config-if)#encapsulation frame-relay
Frame-Switch(config-if)#frame-relay lmi-type ansi
Frame-Switch(config-if)#frame-relay intf-type dce
Frame-Switch(config-if)#clock rate 64000
Frame-Switch(config-if)#frame-relay route 201 interface serial 0
200
Frame-Switch(config-if)#no shutdown
The highlighted portion of the configuration shows the local DLCI (201), the outgoing
interface (Serial0), and the outgoing DLCI (200). Next, do the same for interface
Serial2. See Example B-5.
Example B-5. Frame-Relay Commands and DLCI-to-Interface Mappings on Serial2
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4. Frame-Switch(config)#interface serial2
Frame-Switch(config-if)#encapsulation frame-relay
Frame-Switch(config-if)#frame-relay lmi-type ansi
Frame-Switch(config-if)#frame intf-type dce
Frame-Switch(config-if)#clock rate 64000
Frame-Switch(config-if)#frame-relay route 101 interface serial 0
100
Frame-Switch(config-if)#no shut
Frame-Switch(config-if)#
The highlighted portion of the configuration shows the local DLCI (101), the outgoing
interface (Serial0), and the outgoing DLCI (100). At this point, you have a functional
Frame Relay switch. You will be able to verify the connections in Chapter 7, "Router
Interface Configuration," but for now, take a look at the configuration and do a show
frame-relay route to verify that the configuration matches the lab diagram. Example
B-6 shows the running-config file. Notice where the commands are located in the
configuration file.
Example B-6. Output from show running-config
Frame-Switch#show running-config
Building configuration...
Current configuration:
!
version 11.2
no service password-encryption
no service udp-small-servers
no service tcp-small-servers
!
hostname Frame-Switch
!
!
frame-relay switching
!
interface Serial0
noip address
encapsulation frame-relay
clockrate 64000
frame-relaylmi-type ansi
frame-relayintf-type dce
frame-relay route 100 interface serial2 101
frame-relay route 200 interface Serial1 201
!
http://www.router-switch.com/

5. interface Serial1
noip address
encapsulation frame-relay
clockrate 64000
frame-relaylmi-type ansi
frame-relayintf-type dce
frame-relay route 201 interface Serial0 200
!
interface Serial2
noip address
encapsulation frame-relay
clockrate 64000
frame-relaylmi-type ansi
frame-relayintf-type dce
frame-relay route 101 interface Serial0 100
!
interface Serial3
noip address
shutdown
!
interface Serial4
noip address
shutdown
!
interface Serial5
noip address
shutdown
!
interface Serial6
noip address
shutdown
!
interface Serial7
noip address
shutdown
!
interface Serial8
noip address
shutdown
!
interface Serial9
noip address
shutdown
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6. !
interface TokenRing0
noip address
shutdown
!
interface BRI0
noip address
shutdown
!
noip classless
!
!
line con 0
exec-timeout 0 0
line aux 0
linevty 0 4
login
!
end
Frame-Switch#
The highlighted portions illustrate all the Frame Relay configuration tasks that you
completed. Notice that none of the interfaces has IP addresses, nor do any of the
interfaces need them. You are only mapping DLCIs to interfaces. This is a Layer 2
function, not a Layer 3 function, therefore, no IP address are needed.
The show frame-relay route command is a useful command in determining that your
configuration is correct. Example B-7 shows the output from this command.
Example B-7. Output from show frame-relay route Command
Frame-Switch#show frame-relay route
Input Intf Input Dlci Output Intf Output Dlci Status
Serial0 100 Serial2 101 inactive
Serial0 200 Serial1 201 inactive
Serial1 201 Serial0 200 inactive
Serial2 101 Serial0 100 inactive
Frame-Switch#
From this output, you can see that the Input Dlci matches the correct interfaces from
the lab diagram in Figure B-7. You also can see that Output Intf and Output
Dlci match to the correct interfaces and DLCIs as well. From here, you can assume
that everything is configured correctly. The status will be inactive until you configure
the Frame Relay interfaces on R2, R3, and R4 and remove them from shutdown
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7. mode.
More Related Cisco Network Tips:
How to Configure Cisco Routers as Frame Relay Switch (FRS)?
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