To configure Frame Relay traffic shaping, you must first enter the map class configuration mode
so you can define a map class. You enter the map class with the global configuration command
map-class frame-relay name. The name parameter is the name you use to apply the map class
to the VC where you want traffic shaping performed. The command looks like the following:
RouterA#config t
RouterA(config)#map-class frame-relay scott
RouterA(config-map-class)#
Notice that the map-class frame-relay scott command changes the prompt to
config-map-class. This enables you to configure the parameters for your map class.
The map class is used to define the average and peak rates allowed in each VC associated
with the map class. The map class mechanism enables you to specify that the router can dynamically
fluctuate the rate at which it sends traffic, depending on the BECNs received. It also
enables you to configure queuing on a per-VC basis.
To define the average and peak rate for links that are faster than the receiving link can handle,
use the following command:
RouterA(config-map-class)#frame-relay traffic-rate average [peak]
The average parameter sets the average rate in bits per second, which is your CIR. Now, how
do you calculate the peak value? First, start with the EIR. The EIR is the average rate over which
bits will be marked with DE and is given by the formula EIR = Be/Tc, with Be being excessive
burst and Tc representing the committed rate measurement interval. The peak value is then calculated
by taking the CIR plus EIR, or peak = CIR + EIR.
The peak parameter is optional. An example of a line is as follows:
RouterA(config-map-class)#frame-relay traffic-rate 9600 18000
To specify that the router should dynamically fluctuate the rate at which it is sending traffic
depending on the number of BECNs received, use the following command:
RouterA(config-map-class)#frame-relay adaptive-shaping becn
To set bandwidth usage for protocols, you can configure traffic shaping to use queuing on
a per-VC basis. To perform this function, use the following commands:
RouterA(config-map-class)#frame-relay custom-queue-list number
RouterA(config-map-class)#frame-relay priority-group number
You can use either command, depending on the type of queuing you are using. The number
parameter at the end of the command is the queue list number. A detailed discussion of queuing
is presented in the next chapter.
After the map class parameters are completed, you then need to configure the traffic shaping
on the interface you want. The following commands are used to perform traffic shaping on an
interface and to apply the map class and its parameters to a subinterface and, by association, its
corresponding VC:
RouterA#config t
RouterA(config)#interface serial0
RouterA(config-if)#frame-relay traffic-shaping
RouterA(config-if)#interface serial0.16 point-to-point
RouterA(config-subif#frame-relay class scott
RouterA(config-subif)#frame-relay interface-dlci 16
You first must enable traffic shaping and per-VC queuing on the interface with the
frame-relay traffic-shaping command. You can then go to the interface or subinterface
and assign the map class by using the frame-relay class name command. The example
just shown uses the name scott because that is the name of the map class defined in the
earlier example.
After you have completed the configuration, use the show running-config and the show
frame-relay pvc commands to verify the configuration.
IT Certification CCIE,CCNP,CCIP,CCNA,CCSP,Cisco Network Optimization and Security Tips
Using Traffic-Shaping Techniques
The following list outlines the traffic-shaping techniques used with Frame Relay:
To control the access rate transmitted on a Cisco router, you can configure a peak rate to
limit outbound traffic to either the CIR or excess information rate (EIR).
You can configure BECN support on a per-VC basis, which will enable the router to then
monitor BECNs and throttle traffic based on BECN-designated packets.
Queuing can be used for support at the VC level. Priority, custom, and weighted fair queuing
(WFQ) can be used. This gives you more control over traffic flow on individual VCs.
It’s also important to understand when you would use traffic shaping with Frame Relay. The
following list explains this:
Use traffic shaping when one site, such as the corporate office, has a higher speed line (for
example, a T1), and the remote branches have slower lines (for example, 56Kbps). This
connection would cause bottlenecks on each VC and would result in poor response times
for time-sensitive traffic such as SNA and Telnet. This can cause packets to be dropped. By
using traffic shaping at the corporate office, you can improve response on each VC.
Traffic shaping is also helpful on a router with many subinterfaces. Because these subinterfaces
will use traffic as fast as the physical link allows, you can use rate enforcement on the subinterface
to match the CIR of the VC. This means you can preallocate bandwidth to each VC.
Traffic shaping can be used to throttle back transmission on a Frame Relay network that
is constantly congested. This can help prevent packet loss and is done on a per-VC basis.
Traffic shaping is used effectively if you have multiple Network layer protocols and want
to queue each protocol to allocate bandwidth effectively. Since IOS version 11.2, queuing
can be performed at the VC level.
To control the access rate transmitted on a Cisco router, you can configure a peak rate to
limit outbound traffic to either the CIR or excess information rate (EIR).
You can configure BECN support on a per-VC basis, which will enable the router to then
monitor BECNs and throttle traffic based on BECN-designated packets.
Queuing can be used for support at the VC level. Priority, custom, and weighted fair queuing
(WFQ) can be used. This gives you more control over traffic flow on individual VCs.
It’s also important to understand when you would use traffic shaping with Frame Relay. The
following list explains this:
Use traffic shaping when one site, such as the corporate office, has a higher speed line (for
example, a T1), and the remote branches have slower lines (for example, 56Kbps). This
connection would cause bottlenecks on each VC and would result in poor response times
for time-sensitive traffic such as SNA and Telnet. This can cause packets to be dropped. By
using traffic shaping at the corporate office, you can improve response on each VC.
Traffic shaping is also helpful on a router with many subinterfaces. Because these subinterfaces
will use traffic as fast as the physical link allows, you can use rate enforcement on the subinterface
to match the CIR of the VC. This means you can preallocate bandwidth to each VC.
Traffic shaping can be used to throttle back transmission on a Frame Relay network that
is constantly congested. This can help prevent packet loss and is done on a per-VC basis.
Traffic shaping is used effectively if you have multiple Network layer protocols and want
to queue each protocol to allocate bandwidth effectively. Since IOS version 11.2, queuing
can be performed at the VC level.
Frame Relay Traffic Shaping
Traffic shaping on Frame Relay provides different capabilities, and because this information
might be covered on the exam, it is important that you can describe each one. On production
networks, this information can help you understand whether switch problems are occurring.
In this section, you will learn about traffic-shaping techniques and when to use them. You’ll
then learn how to configure traffic shaping.
might be covered on the exam, it is important that you can describe each one. On production
networks, this information can help you understand whether switch problems are occurring.
In this section, you will learn about traffic-shaping techniques and when to use them. You’ll
then learn how to configure traffic shaping.
Frame Relay Switching Commands
The command used to enable Frame Relay switching on a Cisco router is as follows:
Router_A#config t
Router_A(config)#frame-relay switching
This command must come before any of the other Frame Relay switching–related commands
can be executed, or these commands won’t be allowed. When Frame Relay encapsulation is
enabled on an interface, it defaults to DTE, so you will need to change it to DCE for Frame
Relay switching. For a Frame Relay serial connection to function, you must have a DTE at one
end and a DCE at the other. You first configure the router with the following command:
Router_A(config)#interface serial0
Router_A(config-if)#frame-relay intf-type dce
The clocking on a serial link is provided by the DCE device, which is determined
by the type of cable connected to the serial interface. For a Frame Relay connection,
the DCE status is configured, whereas serial DCE status is cabled. For
Frame Relay, the DCE device is the one that provides LMI.
Because this interface is now functioning as the Frame Relay DCE device, you can change the
LMI type from the default of Cisco with the following command:
Router_A(config-if)#frame-relay lmi-type ?
cisco
ansi
q933a
Router_A(config-if)#frame-relay lmi-type
The next step in the configuration process is to create the proper DLCI forwarding rules.
These rules dictate that when a frame enters a particular interface on a certain DLCI, it will be
forwarded to another interface and DLCI. Let’s look at such an example on interface serial 1:
Router_A#config t
Router_A(config)#interface serial 1
Router_A(config-if)#frame-relay route 100 interface Serial2 101
This command states that any frame received on interface serial 1, with DLCI 100, shall be
forwarded to interface serial 2, with DLCI 101. You can view all the frame routing information
with the show frame-relay route command. The following router output shows the settings
of Router A:
Router_A#show frame-relay route
Input Intf Input Dlci Output Intf Output Dlci Status
Serial0 300 Serial1 200 active
Serial1 100 Serial2 101 active
Serial1 200 Serial0 300 active
Serial2 101 Serial1 100 active
Router_A#
The configuration of a router as a Frame Relay switch can be useful for a lab environment
or even as part of a production network.
Now, let’s look at the configuration of the Frame Relay switch:
Router_A#show running-config
Building configuration...
Current configuration:
!
version 11.2
!
hostname Router_A
!
frame-relay switching
!
interface Serial0
no ip address
encapsulation frame-relay
clockrate 56000
frame-relay intf-type dce
frame-relay route 300 interface Serial1 200
!
interface Serial1
no ip address
encapsulation frame-relay
clockrate 56000
frame-relay intf-type dce
frame-relay route 100 interface Serial2 101
frame-relay route 200 interface Serial0 300
!
interface Serial2
no ip address
encapsulation frame-relay
clockrate 56000
frame-relay intf-type dce
frame-relay route 101 interface Serial1 100
!
end
Router_A#
Notice the global command frame-relay switching is at the top of the configuration.
Also notice that both interfaces are configured with frame-relay intf-type dce commands.
On the serial interfaces, you’ll also see that the clock rate command is used to provide clocking
for the line because the router serving as the Frame Relay switch is a DCE device on the
physical interface.
Router_A#config t
Router_A(config)#frame-relay switching
This command must come before any of the other Frame Relay switching–related commands
can be executed, or these commands won’t be allowed. When Frame Relay encapsulation is
enabled on an interface, it defaults to DTE, so you will need to change it to DCE for Frame
Relay switching. For a Frame Relay serial connection to function, you must have a DTE at one
end and a DCE at the other. You first configure the router with the following command:
Router_A(config)#interface serial0
Router_A(config-if)#frame-relay intf-type dce
The clocking on a serial link is provided by the DCE device, which is determined
by the type of cable connected to the serial interface. For a Frame Relay connection,
the DCE status is configured, whereas serial DCE status is cabled. For
Frame Relay, the DCE device is the one that provides LMI.
Because this interface is now functioning as the Frame Relay DCE device, you can change the
LMI type from the default of Cisco with the following command:
Router_A(config-if)#frame-relay lmi-type ?
cisco
ansi
q933a
Router_A(config-if)#frame-relay lmi-type
The next step in the configuration process is to create the proper DLCI forwarding rules.
These rules dictate that when a frame enters a particular interface on a certain DLCI, it will be
forwarded to another interface and DLCI. Let’s look at such an example on interface serial 1:
Router_A#config t
Router_A(config)#interface serial 1
Router_A(config-if)#frame-relay route 100 interface Serial2 101
This command states that any frame received on interface serial 1, with DLCI 100, shall be
forwarded to interface serial 2, with DLCI 101. You can view all the frame routing information
with the show frame-relay route command. The following router output shows the settings
of Router A:
Router_A#show frame-relay route
Input Intf Input Dlci Output Intf Output Dlci Status
Serial0 300 Serial1 200 active
Serial1 100 Serial2 101 active
Serial1 200 Serial0 300 active
Serial2 101 Serial1 100 active
Router_A#
The configuration of a router as a Frame Relay switch can be useful for a lab environment
or even as part of a production network.
Now, let’s look at the configuration of the Frame Relay switch:
Router_A#show running-config
Building configuration...
Current configuration:
!
version 11.2
!
hostname Router_A
!
frame-relay switching
!
interface Serial0
no ip address
encapsulation frame-relay
clockrate 56000
frame-relay intf-type dce
frame-relay route 300 interface Serial1 200
!
interface Serial1
no ip address
encapsulation frame-relay
clockrate 56000
frame-relay intf-type dce
frame-relay route 100 interface Serial2 101
frame-relay route 200 interface Serial0 300
!
interface Serial2
no ip address
encapsulation frame-relay
clockrate 56000
frame-relay intf-type dce
frame-relay route 101 interface Serial1 100
!
end
Router_A#
Notice the global command frame-relay switching is at the top of the configuration.
Also notice that both interfaces are configured with frame-relay intf-type dce commands.
On the serial interfaces, you’ll also see that the clock rate command is used to provide clocking
for the line because the router serving as the Frame Relay switch is a DCE device on the
physical interface.
Frame Relay Switching Network
Routers are typically edge devices that connect your LANs to the Frame Relay network. However,
you can use a router as part of the Frame Relay cloud or you can use it to create your own Frame
Relay network. Frame Relay switching is the forwarding of Frame Relay frames based upon their
DLCI assignments. You have seen how to configure a Frame Relay DTE device; now, let’s look
at how to configure a Frame Relay DCE switch. Routers are DTE devices by default; however, by
changing the Frame Relay interface type to a DCE, you can provide switching of frames.
Compare Figure 29.8 to Figure 29.9. Both of these diagrams represent the same network. In
Figure 29.8, you see the Frame Relay cloud without any detail. Each router on the right side will
send traffic to the router on the left by using DLCI 100. Keep in mind that the DLCI is an identifier
and that the DLCIs in this diagram could be the same or different and still communicate.
The router on the left will use DLCIs 101 and 300 to reach each router on the right. This is the
normal way that you should think about the frame cloud. It is typically not your concern what
happens within the Frame Relay network. Figure 29.9 shows that this particular Frame Relay
cloud is a single router configured as a switch.
FIGURE 2 9 . 8 Logical Frame Relay network
DLCI 300
DLCI 100 DLCI 101
DLCI 100
Frame Relay cloud
Physical Frame Relay network
DLCI 101
DLCI 100
Frame Relay cloud
Serial 1
Serial 0
Serial 2
you can use a router as part of the Frame Relay cloud or you can use it to create your own Frame
Relay network. Frame Relay switching is the forwarding of Frame Relay frames based upon their
DLCI assignments. You have seen how to configure a Frame Relay DTE device; now, let’s look
at how to configure a Frame Relay DCE switch. Routers are DTE devices by default; however, by
changing the Frame Relay interface type to a DCE, you can provide switching of frames.
Compare Figure 29.8 to Figure 29.9. Both of these diagrams represent the same network. In
Figure 29.8, you see the Frame Relay cloud without any detail. Each router on the right side will
send traffic to the router on the left by using DLCI 100. Keep in mind that the DLCI is an identifier
and that the DLCIs in this diagram could be the same or different and still communicate.
The router on the left will use DLCIs 101 and 300 to reach each router on the right. This is the
normal way that you should think about the frame cloud. It is typically not your concern what
happens within the Frame Relay network. Figure 29.9 shows that this particular Frame Relay
cloud is a single router configured as a switch.
FIGURE 2 9 . 8 Logical Frame Relay network
DLCI 300
DLCI 100 DLCI 101
DLCI 100
Frame Relay cloud
Physical Frame Relay network
DLCI 101
DLCI 100
Frame Relay cloud
Serial 1
Serial 0
Serial 2
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