Configuring Committed Access Rate
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Contents
Configuring Committed Access RateLast Updated: April 11, 2012
This module describes the tasks for configuring committed access rate (CAR) and distributed CAR (DCAR).
For complete conceptual information about these features, see the "Classification Overview"module and the "Policing and Shaping Overview" module. For a complete description of the CAR commands in this module, see the Cisco IOS Quality of Service Solutions Command Reference. To locate documentation of other commands that appear in this module, use the command reference master index or search online. Finding Feature InformationYour software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the Feature Information Table at the end of this document. Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required. Committed Access Rate Configuration Task ListThe CAR and DCAR services limit the input or output transmission rate on an interface or subinterface based on a flexible set of criteria. CAR is often configured on interfaces at the edge of a network to limit traffic into or out of the network. CAR can rate limit traffic based on certain matching criteria, such as incoming interface, IP precedence, or IP access list. You configure the actions that CAR will take when traffic conforms to or exceeds the rate limit. You can set CAR rate policies that are associated with one of the following:
Each interface can have multiple CAR policies, corresponding to different types of traffic. For example, low priority traffic may be limited to a lower rate than high-priority traffic. With multiple rate policies, the router examines each policy in the order entered until the packet matches. If a match is not found, the default action is to send. The rate policies can be independent; each rate policy deals with a different type of traffic. Alternatively, rate policies can be cascading; a packet can be compared to multiple different rate policies in succession. You can configure up to 100 rate policies on a subinterface.
Basic CAR and DCAR functionality requires that the following criteria be defined:
IP Precedence or MAC AddressUse the access-list rate-limit command to classify packets using either IP Precedence or MAC addresses. You can then apply CAR policies using the rate-limit command to individual rate-limited access lists. Packets with different IP precedences or MAC addresses are treated differently by the CAR service. See the section Example Rate Limiting in an IXP for an example of how to configure a CAR policy using MAC addresses. IP Access ListUse the access-list command to define CAR policy based on an access list. The acl-index argument is an access list number. Use a number from 1 to 99 to classify packets by precedence or precedence mask. Use a number from 100 to 199 to classify by MAC address.
When you configure DCAR on Cisco 7000 series routers with RSP7000 or Cisco 7500 series routers with a VIP2-40 or greater interface processor, you can classify packets by group, to allow you to partition your network into multiple priority levels or classes of service. This classification is achieved by setting IP precedences based on different criteria for use by other QoS features such as Weighted Random Early Detection (WRED) or weighted fair queueing (WFQ). Configuring CAR and DCAR for All IP TrafficSUMMARY STEPS
DETAILED STEPS
Configuring CAR and DCAR PoliciesSUMMARY STEPS
DETAILED STEPS
Configuring a Class-Based DCAR PolicySUMMARY STEPS
DETAILED STEPS
Monitoring CAR and DCAR
CAR and DCAR Configuration Examples
Example Subrate IP ServicesThe following example illustrates how to configure a basic CAR policy that allows all IP traffic. In the example, the network operator delivers a physical T3 link to the customer, but offers a less expensive 15 Mbps subrate service. The customer pays only for the subrate bandwidth, which can be upgraded with additional access bandwidth based on demand. The CAR policy limits the traffic rate available to the customer and delivered to the network to the agreed upon rate limit, plus the ability to temporarily burst over the limit. interface hssi 0/0/0 rate-limit output 15000000 2812500 5625000 conform-action transmit exceed-action drop ip address 10.1.0.9 255.255.255.0 Example Input and Output Rate Limiting on an InterfaceIn this example, a customer is connected to an Internet service provider (ISP) by a T3 link. The ISP wants to rate limit transmissions from the customer to 15 Mbps of the 45 Mbps. In addition, the customer is allowed to send bursts of 2,812,500 bytes. All packets exceeding this limit are dropped. The following commands are configured on the High-Speed Serial Interface (HSSI) of the ISP connected to the customer: interface Hssi0/0/0 description 45Mbps to R1 rate-limit input 15000000 2812500 2812500 conform-action transmit exceed-action drop ip address 200.200.14.250 255.255.255.252 rate-limit output 15000000 2812500 2812500 conform-action transmit exceed-action drop The following sample output shows how to verify the configuration and monitor CAR statistics using the show interfaces rate-limit command:
Router# show interfaces hssi 0/0/0 rate-limit
Hssi0/0/0 45Mbps to R1
Input
matches: all traffic
params: 15000000 bps, 2812500 limit, 2812500 extended limit
conformed 8 packets, 428 bytes; action: transmit
exceeded 0 packets, 0 bytes; action: drop
last packet: 8680ms ago, current burst: 0 bytes
last cleared 00:03:59 ago, conformed 0 bps, exceeded 0 bps
Output
matches: all traffic
params: 15000000 bps, 2812500 limit, 2812500 extended limit
conformed 0 packets, 0 bytes; action: transmit
exceeded 0 packets, 0 bytes; action: drop
last packet: 8680ms ago, current burst: 0 bytes
last cleared 00:03:59 ago, conformed 0 bps, exceeded 0 bps
Example Rate Limiting in an IXPThe following example uses rate limiting to control traffic in an Internet Exchange Point (IXP). Because an IXP comprises many neighbors around an FDDI ring, MAC address rate-limited access lists are used to control traffic from a particular ISP. Traffic from one ISP (at MAC address 00e0.34b0.7777) is compared to a rate limit of 80 Mbps of the 100 Mbps available on the FDDI connection. Traffic that conforms to this rate is sent. Nonconforming traffic is dropped. interface Fddi2/1/0 rate-limit input access-group rate-limit 100 80000000 15000000 30000000 conform-action transmit exceed-action drop ip address 200.200.6.1 255.255.255.0 ! access-list rate-limit 100 00e0.34b0.7777 The following sample output shows how to verify the configuration and monitor the CAR statistics using the show interfaces rate-limit command:
Router# show interfaces fddi2/1/0 rate-limit
Fddi2/1/0
Input
matches: access-group rate-limit 100
params: 800000000 bps, 15000000 limit, 30000000 extended limit
conformed 0 packets, 0 bytes; action: transmit
exceeded 0 packets, 0 bytes; action: drop
last packet: 4737508ms ago, current burst: 0 bytes
last cleared 01:05:47 ago, conformed 0 bps, exceeded 0 bps
Example Rate Limiting by Access ListThe following example shows how CAR can be used to limit the rate by application to ensure capacity for other traffic including mission-critical applications:
The figure below illustrates the configuration. Notice that two access lists are created to classify the Web and FTP traffic so that they can be handled separately by CAR. Router LEFT Configurationinterface Hssi0/0/0 description 45Mbps to R2 rate-limit output access-group 101 20000000 3750000 7500000 conform-action set-prec- transmit 5 exceed-action set-prec-transmit 0 rate-limit output access-group 102 10000000 1875000 3750000 conform-action set-prec-transmit 5 exceed-action drop rate-limit output 8000000 1500000 3000000 conform-action set-prec-transmit 5 exceed-action drop ip address 10.1.0.9 255.255.255.0 ! access-list 101 permit tcp any any eq www access-list 102 permit tcp any any eq ftp The following sample output shows how to verify the configuration and monitor CAR statistics using the show interfaces rate-limit command:
Router# show interfaces hssi 0/0/0 rate-limit
Hssi0/0/0 45Mbps to R2
Input
matches: access-group 101
params: 20000000 bps, 3750000 limit, 7500000 extended limit
conformed 3 packets, 189 bytes; action: set-prec-transmit 5
exceeded 0 packets, 0 bytes; action: set-prec-transmit 0
last packet: 309100ms ago, current burst: 0 bytes
last cleared 00:08:00 ago, conformed 0 bps, exceeded 0 bps
matches: access-group 102
params: 10000000 bps, 1875000 limit, 3750000 extended limit
conformed 0 packets, 0 bytes; action: set-prec-transmit 5
exceeded 0 packets, 0 bytes; action: drop
last packet: 19522612ms ago, current burst: 0 bytes
last cleared 00:07:18 ago, conformed 0 bps, exceeded 0 bps
matches: all traffic
params: 8000000 bps, 1500000 limit, 3000000 extended limit
conformed 5 packets, 315 bytes; action: set-prec-transmit 5
exceeded 0 packets, 0 bytes; action: drop
last packet: 9632ms ago, current burst: 0 bytes
last cleared 00:05:43 ago, conformed 0 bps, exceeded 0 bps
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