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.
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 1
|
Enable Frame Relay switching.
|
frame-relay switching
|
|
Step 2
|
Configure Frame Relay encapsulation,
Frame Relay LMI type, Frame Relay DCE interface mode, and clock rate on
individual interfaces.
|
encapsulation frame-relay frame-relay lmi-type ansi frame-relay
intf-type dce clock rate 64000
|
|
Step 3
|
Configure DLCI to interface mappings on
individual interfaces.
|
frame-relay route {local-dlci} interface {outgoing
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
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
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
no ip address
encapsulation frame-relay
clockrate 64000
frame-relay lmi-type ansi
frame-relay intf-type dce
frame-relay route 100 interface
serial2 101
frame-relay route 200 interface Serial1
201
!
interface Serial1
no ip address
encapsulation frame-relay
clockrate 64000
frame-relay lmi-type ansi
frame-relay intf-type dce
frame-relay route 201 interface
Serial0 200
!
interface Serial2
no ip address
encapsulation frame-relay
clockrate 64000
frame-relay lmi-type ansi
frame-relay intf-type dce
frame-relay route 101 interface
Serial0 100
!
interface
Serial3
no ip address
shutdown
!
interface
Serial4
no ip address
shutdown
!
interface
Serial5
no ip address
shutdown
!
interface
Serial6
no ip address
shutdown
!
interface
Serial7
no ip address
shutdown
!
interface
Serial8
no ip address
shutdown
!
interface
Serial9
no ip address
shutdown
!
interface
TokenRing0
no ip address
shutdown
!
interface
BRI0
no ip address
shutdown
!
no
ip classless
!
!
line
con 0
exec-timeout 0 0
line
aux 0
line
vty 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 mode.
---Original reading from informit.com
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