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This chapter describes the tasks for configuring QoS Generic Traffic Shaping (GTS) on a router.
For complete conceptual information, see the section "Traffic Shaping" in the chapter "Policing and Shaping Overview" in this book.
For a complete description of the GTS commands mentioned in this chapter, refer to the Cisco IOS Quality of Service Solutions Command Reference. To locate documentation of other commands that appear in this chapter, use the command reference master index, or search online.
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Note GTS is not supported on ISDN and dialup interfaces. It is only supported on generic routing encapsulation (GRE) tunnel interfaces. Traffic shaping is not supported with flow switching. |
See the end of this chapter for the section "GTS Configuration Examples."
To configure GTS for outbound traffic on an interface or subinterface, use the following command in interface configuration mode:
Command | Purpose |
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traffic-shape rate bit-rate [burst-size [excess-burst-size]] |
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To configure GTS for outbound traffic on an access list, use the following commands beginning in global configuration mode:
| Command | Purpose | |
|---|---|---|
Step 1 | access-list access-list-number | Assigns traffic to an access list. |
Step 2 | interface interface-type interface-number | Enters interface configuration mode. |
Step 3 | traffic-shape group access-list-number bit-rate [burst-size [excess-burst-size]] | Configures traffic shaping for outbound traffic on an interface for the specified access list. |
Repeat the steps for each type of traffic you want to rate limit.
If traffic shaping is performed on a Frame Relay network with 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.
To configure adaptive GTS for outbound traffic on an interface or subinterface, use the following commands in interface configuration mode:
| Command | Purpose | |
|---|---|---|
Step 1 | traffic-shape rate bit-rate [burst-size [excess-burst-size]] | Enables traffic shaping for outbound traffic on an interface. |
Step 2 | traffic-shape adaptive [bit-rate] | Configures minimum bit rate that traffic is shaped to when BECNs are received on an interface. |
Step 3 | traffic-shape fecn-adapt | Configures reflection of BECN signals as FECNs. |
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 commands on both ends of the link, enabling the router at the high-speed end to detect and adapt to congestion even when traffic is flowing primarily in one direction.
To monitor the current traffic shaping configuration and statistics, use one or more of the following commands in EXEC mode:
Command | Purpose |
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show traffic-shape [interface-name] |
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show traffic-shape statistics [interface-name] |
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The following sections provide GTS configuration examples:
This example shows the configuration of two traffic-shaped interfaces on a router. Ethernet 0 is configured to limit User Datagram Protocol (UDP) traffic to 1 Mbps. Ethernet 1 is configured to limit all output to 5 Mbps.
access-list 101 permit udp any any interface Ethernet0 traffic-shape group 101 1000000 125000 125000 ! interface Ethernet1 traffic-shape rate 5000000 625000 625000
The following is sample output for the show traffic-shape command for this example:
Router# show traffic-shape
access Target Byte Sustain Excess Interval Increment Adapt
I/F list Rate Limit bits/int bits/int (ms) (bytes) Active
Et0 101 1000000 23437 125000 125000 63 7813 -
Et1 5000000 87889 625000 625000 16 9766 -
The following is sample output for the show traffic-shape statistics command for this example:
Router# show traffic-shape statistics
Access Queue Packets Bytes Packets Bytes Shaping
I/F List Depth Delayed Delayed Active
Et0 101 0 2 180 0 0 no
Et1 0 0 0 0 0 no
In this example, a T1 line may be used for 100 milliseconds in a burst, but the long-term average is limited to 64 kbps. This configuration example restricts the amount of load the system can induce on the outbound network interface.
interface serial 4/1:0 traffic-shape rate 64000 6400 6400
If you need to restrict the amount of load the system can induce outbound, and therefore the total load it can impose on the Internet service provider (ISP), configure traffic shaping on the outbound interfaces.
Perhaps you need to restrict the flow of NNTP to each of some set of sites across an intervening backbone out an interface to 64 kbps. This example shows how to configure that control and provide one site with 256 kbps:
access-list 101 permit 10.10.10.10 access-list 102 permit 10.10.10.20 access-list 103 permit 10.10.10.30 ! interface serial 0 traffic-shape group 101 64000 traffic-shape group 102 64000 traffic-shape group 103 256000
Separate token buckets are maintained for each access list, and traffic not matching any access list is not shaped at all.
This example does not restrict flow across a Frame Relay subinterface that has been layered onto a single DLC. However, in the presence of BECN bits from the network, the flow is throttled back to the committed information rate (CIR). The access rate of the interface is assumed to be 1544 kbps, and the CIR is 64 kbps.
interface serial 2 traffic-shape rate 1544000 traffic-shape adaptive 64000 traffic-shape fecn-adapt
If the traffic-shape fecn-adapt command is configured at both ends of the link, the far end will reflect received forward explicit congestion notifications (FECNs) as BECNs in a Q.922 TEST RESPONSE messages.
Frame Relay networks are often asymmetrical, that is, the access rate at one site may differ from the access rate at another. In such cases, it may be worthwhile to configure the faster rate to shape to the access rate of the slower rate, as well as to respond to BECNs. Using the previous example as a starting point, in which the access rate is 1544 kbps and the CIR is 64 kbps, and the access rate at the far end is 128 kbps, the configuration of the subinterfaces would be as follows:
interface serial 3 traffic-shape rate 128000 traffic-shape adaptive 64000
Posted: Mon Aug 21 21:27:48 PDT 2000
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