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This chapter describes how to configure committed access rate (CAR) and Distributed CAR (DCAR). For a complete description of the commands in this chapter, refer to the Quality of Service Solutions Command Reference; the commands are arranged alphabetically in that guide. To locate documentation of specific commands, use the command reference, master index, or search online.
CAR is supported on these platforms:
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 transmit.
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 20 rate policies on a subinterface.
To configure CAR, perform the tasks in the following sections:
See the section "CAR and DCAR Configuration Examples" later in this chapter for ideas of how to configure CAR and DCAR on your network.
To configure CAR (or DCAR on Cisco 7000 series with RSP7000 or Cisco 7500 series routers with a VIP2-40 or greater interface processor) for all IP traffic, use the following commands beginning in global configuration mode:
| Step | Command | Purpose |
|---|---|---|
1 | interface interface-type interface-number | Specify the interface or subinterface. This command puts the router in interface configuration mode. |
2 | rate-limit {input | output} bps burst-normal burst-max | Specify a basic CAR policy for all IP traffic. See Table 4 for a description of conform and exceed action keywords. |
3 | end | Exit interface configuration mode. |
Basic CAR and DCAR functionality requires the following criteria to be defined:
Conform and exceed actions are described in Table 4.
| Keyword | Description |
|---|---|
continue | Evaluate the next rate-limit command. |
drop | Drop the packet. |
set-prec-continue new-prec | Set the IP Precedence and evaluate the next rate-limit command. |
set-prec-transmit new-prec | Set the IP Precedence and transmit the packet. |
transmit | Transmit the packet. |
See the sections "Configure CAR and DCAR Policies" and "Configure a Class-Based DCAR Policy" to understand how to configure other CAR and DCAR policy options. See the sections "Subrate IP Services Example" and "Input and Output Rate Limiting on an Interface Example" for examples of how to configure CAR for all IP traffic.
To configure CAR (or DCAR on Cisco 7000 series with the RSP7000 or Cisco 7500 series routers with a VIP2-40 or greater interface processor), use the following commands beginning in interface configuration mode (only the first two commands are required):
| Step | Command | Purpose |
|---|---|---|
1 | interface interface-type interface-number | Specify the interface or subinterface. This command puts the router in interface configuration mode. |
2 | rate-limit {input | output} [access-group [rate-limit] | Specify the rate policy for each particular class of traffic. See Table 4 for a description of conform and exceed action keywords. Repeat this command for each different class of traffic. |
3 | access-list rate-limit acl-index {precedence | mac-address | | (Optional) Specify a rate-limited access list. Repeat this command if you wish to specify a new access list. |
4 | access-list acl-index {deny | permit} source or access-list acl-index {deny | permit} protocol source | (Optional) Specify a standard or extended access list. Repeat this command to further configure the access list or specify a new access list. |
5 | end | Exit interface configuration mode. |
The following sections describe requirements for specific policies.
Use 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 "Rate Limiting in an IXP Example" for an example of how to configure a CAR policy using MAC addresses.
Use the access-list command to define CAR policy based on 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.
See the section "Rate Limiting by Access List Example" for an example of how to configure a CAR policy using IP access lists.
When you configure DCAR on Cisco 7000 series 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 done 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).
To configure a class-based DCAR policy, use the following commands beginning in interface configuration mode (the access-list command is optional):
| Step | Command | Purpose |
|---|---|---|
1 | interface interface-type interface-number | Specify the interface or subinterface. This command puts the router in interface configuration mode. |
2 | rate-limit {input | output} [access-group [rate-limit] | Specify the rate policy for each particular class of traffic. Repeat this command for each different class of traffic. See Table 4 for policy conform and exceed action keywords. |
3 | random-detect precedence precedence min-threshold | Configure WRED and specify parameters for packets with specific IP Precedence. |
4 | access-list acl-index {deny | permit} source or access-list acl-index {deny | permit} protocol source | (Optional) Specify a standard or extended access list. Repeat this command to further configure the access list or specify a new access list. |
5 | end | Exit interface configuration mode. |
To monitor CAR and DCAR services in your network, use any the following commands in EXEC mode:
| Command | Purpose |
|---|---|
Show the contents of current IP and rate-limited access lists. | |
Show information about rate-limited access lists. | |
show interfaces [interface-type interface-number] | Show information about an interface configured for CAR. |
The following sections provide examples of ways you might use CAR and DCAR to control traffic into and out of your network:
The 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 20 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 20000000 24000 32000 conform-action transmit exceed-action drop ip address 10.1.0.9 255.255.255.0
In this example, a customer is connected to an Internet service provider (ISP) by a T3 link. The ISP wants to rate limit the customer's transmissions to 20 Mbps of the 45 Mbps. In addition, the customer is allowed to transmit bursts of 24000 bytes. All exceeding packets are dropped. The following commands are configured on the ISP's High-Speed Serial Interface (HSSI) connected to the customer:
interface Hssi0/0/0 description 45Mbps to R1 rate-limit input 20000000 24000 24000 conform-action transmit exceed-action drop ip address 200.200.14.250 255.255.255.252 rate-limit output 20000000 24000 24000 conform-action transmit exceed-action drop
To verify the configuration and monitor CAR statistics, use 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: 20000000 bps, 24000 limit, 24000 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: 20000000 bps, 24000 limit, 24000 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
interface Fddi2/1/0 rate-limit input access-group rate-limit 100 800000000 64000 80000 conform-action transmit exceed-action drop ip address 200.200.6.1 255.255.255.0 ! access-list rate-limit 100 00e0.34b0.7777
To verify the configuration and monitor the CAR statistics, use 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, 64000 limit, 80000 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
The following example shows how CAR can be used to limit the rate by application to ensure capacity for other traffic including mission-critical applications. In the example:
Figure 4 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.
interface Hssi0/0/0 description 45Mbps to R2 rate-limit output access-group 101 20000000 24000 32000 conform-action set-prec- transmit 5 exceed-action set-prec-transmit 0 rate-limit output access-group 102 10000000 24000 32000 conform-action set-prec-transmit 5 exceed-action drop rate-limit output 8000000 16000 24000 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
To verify the configuration and monitor CAR statistics, use 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, 24000 limit, 32000 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, 24000 limit, 32000 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, 16000 limit, 24000 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
Posted: Thu Jun 3 14:23:10 PDT 1999
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