Regulating Packet Flow on a Per-Interface Basis Using Generic Traffic Shaping

GTS is a traffic shaping mechanism (also known as a "traffic shaper"). A traffic shaper typically delays excess traffic using a buffer, or queueing mechanism, to hold packets and shape the flow when the data rate of the source is higher than expected. It holds and shapes traffic to a particular bit rate by using the token bucket mechanism. See the "Regulating Packet Flow Using Traffic Shaping" module.

Note	GTS is similar to Class-Based Traffic Shaping. Although Class-Based Traffic Shaping is the Cisco-recommended mechanism, GTS is still supported.

GTS supports traffic shaping on most media and encapsulation types on the router.

GTS works with a variety of Layer 2 technologies, including Frame Relay, ATM, Switched Multimegabit Data Service (SMDS), and Ethernet.

GTS performs the following tasks:

• Applies traffic shaping on a per-interface basis and uses access control lists (ACLs) to select the traffic to shape.
• On a Frame Relay subinterface, dynamically adapts to available bandwidth by integrating backward explicit congestion notification (BECN) signals, or shapes to a specified rate. This is known as adaptive GTS.
• On an ATM/ATM Interface Processor (AIP) interface, responds to the Resource Reservation Protocol (RSVP) feature signalled over statically configured ATM permanent virtual circuits (PVCs).

If adaptive GTS is configured on a Frame Relay network using the traffic-shape rate command, you can also use the traffic-shape adaptive command to specify the minimum bit rate to which the traffic is shaped.

With adaptive GTS, the router uses backward explicit congestion notifications (BECNs) to estimate the available bandwidth and adjust the transmission rate accordingly. The actual maximum transmission rate will be between the rate specified in the traffic-shape adaptive command and the rate specified in the traffic-shape rate command.

Configure these two commands on both ends of the network link, enabling the router at the high-speed end to detect and adapt to congestion even when traffic is flowing primarily in one direction.

For more information about configuring adaptive GTS, see the Configuring Adaptive Generic Traffic Shaping for Frame Relay Networks.

Access control lists filter network traffic by controlling whether routed packets are forwarded or blocked at the router interface. When configured with GTS, the router examines each packet to determine how to shape the traffic on the basis of the criteria you specified for the access control list.

Access control list criteria could be the source address of the traffic, the destination address of the traffic, the upper-layer protocol, or other information. Note that sophisticated users can sometimes successfully evade or fool basic access control lists because no authentication is required.

All of the benefits associated with traffic shaping also apply to GTS. For information about the benefits of traffic shaping, see the "Regulating Packet Flow Using Traffic Shaping" module.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    interface type number

4.    traffic-shape rate bit-rate [burst-size] [excess-burst-size] [buffer-limit]

5.    end

6.    show traffic-shape [interface-type interface-number]

7.    show traffic-shape statistics [interface-type interface-number]

8.    exit

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	interface type number Example: Router(config)# interface s4/0	Configures an interface (or subinterface) type and enters interface configuration mode. Enter the interface type number.
Step 4	traffic-shape rate bit-rate [burst-size] [excess-burst-size] [buffer-limit] Example: Router(config-if)# traffic-shape rate 128000	Enables traffic shaping for outbound traffic on an interface based on the bit rate specified. Enter the bit rate.
Step 5	end Example: Router(config-if)# end	Returns to privileged EXEC mode.
Step 6	show traffic-shape [interface-type interface-number] Example: Router# show traffic-shape serial4/0	(Optional) Displays the current traffic-shaping configuration.
Step 7	show traffic-shape statistics [interface-type interface-number] Example: Router# show traffic-shape statistics serial4/0	(Optional) Displays the current traffic-shaping statistics.
Step 8	exit Example: Router# exit	(Optional) Exits privileged EXEC mode.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    access-list access-list-number {deny | permit} source [source-wildcard]

4.    interface type number

5.    traffic-shape group access-list bit-rate [burst-size [excess-burst-size]]

6.    end

7.    show traffic-shape [interface-type interface-number]

8.    show traffic-shape statistics [interface-type interface-number]

9.    exit

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	access-list access-list-number {deny | permit} source [source-wildcard] Example: Router(config)# access-list 1 permit 192.5.34.0 0.0.0.255	Shapes traffic according to specified access list. Enter the access list number, one of the required keywords, and the source information.
Step 4	interface type number Example: Router(config)# interface s4/0	Configures an interface (or subinterface) type and enters interface configuration mode. Enter the interface type number.
Step 5	traffic-shape group access-list bit-rate [burst-size [excess-burst-size]] Example: Router(config-if)# traffic-shape group 101 128000	Enables traffic shaping based on a specific access list for outbound traffic on an interface. Enter the access list number and the bit rate.
Step 6	end Example: Router(config-if)# end	Returns to privileged EXEC mode.
Step 7	show traffic-shape [interface-type interface-number] Example: Router# show traffic-shape serial4/0	(Optional) Displays the current traffic-shaping configuration.
Step 8	show traffic-shape statistics [interface-type interface-number] Example: Router# show traffic-shape statistics serial4/0	(Optional) Displays the current traffic-shaping statistics.
Step 9	exit Example: Router# exit	(Optional) Exits privileged EXEC mode.

What to Do Next

Note	Repeat the above procedure for each additional type of traffic you want to shape.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    interface type number

4.    traffic-shape rate bit-rate [burst-size] [excess-burst-size] [buffer-limit]

5.    traffic-shape adaptive bit-rate

6.    traffic-shape fecn-adapt

7.    end

8.    show traffic-shape [interface-type interface-number]

9.    show traffic-shape statistics [interface-type interface-number]

10.    exit

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	interface type number Example: Router(config)# interface s4/0	Configures an interface (or subinterface) type and enters interface configuration mode. Enter the interface type number.
Step 4	traffic-shape rate bit-rate [burst-size] [excess-burst-size] [buffer-limit] Example: Router(config-if)# traffic-shape rate 128000	Enables traffic shaping for outbound traffic on an interface based on the bit rate specified. Enter the bit rate.
Step 5	traffic-shape adaptive bit-rate Example: Router(config-if)# traffic-shape adaptive 64000	Configures a Frame Relay subinterface to estimate the available bandwidth when BECNs are received. Enter the bit rate.
Step 6	traffic-shape fecn-adapt Example: Router(config-if)# traffic-shape fecn-adapt	Configures reflection of forward explicit congestion notifications (FECNs) as BECNs.
Step 7	end Example: Router(config-if)# end	Returns to privileged EXEC mode.
Step 8	show traffic-shape [interface-type interface-number] Example: Router# show traffic-shape serial4/0	(Optional) Displays the current traffic-shaping configuration.
Step 9	show traffic-shape statistics [interface-type interface-number] Example: Router# show traffic-shape statistics serial4/0	(Optional) Displays the current traffic-shaping statistics.
Step 10	exit Example: Router# exit	(Optional) Exits privileged EXEC mode.