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This feature module describes the ATM Cell Loss Priority (CLP) Setting feature. The ATM CLP Setting feature allows users to control the CLP bit setting on routers with the PA-A3 port adapter.
This document includes the following sections:
Before development of the ATM CLP Setting feature, the CLP bit in the ATM header of a cell provided a method of controlling the discarding of cells in a congested ATM environment. A CLP bit contains two settings: 0 or 1. Cells with a CLP bit setting of 1 are discarded before cells with a CLP bit setting of 0. Before the introduction of the ATM CLP Setting feature, the CLP bit was automatically set to 0 when Cisco routers converted packets into ATM cells for ATM networks.
The ATM CLP Setting feature allows users to control the CLP bit setting on routers with the PA-A3 port adapter. The CLP bit is set on each packet individually, and the default CLP bit setting is 0. The application of the ATM CLP Setting feature changes the CLP bit setting to 1. Therefore, users have the option to leave each packet with the default CLP bit setting of 0 or to establish a new CLP bit setting of 1.
The ATM CLP Setting feature allows users to extend their IP QoS policies into an ATM network by setting the ATM Cell Loss Priority (CLP) bit in ATM cells based on the IP precedence value of the packets being transmitted. As congestion occurs in the ATM network, cells with the CLP bit set are more likely to be dropped, resulting in improved network performance for high priority traffic and applications.
The ATM CLP Setting feature works on the PA-A3 port adapter only.
Class maps, policy maps, and service policies are required to enable the ATM CLP Setting feature.
See the following sections for configuration tasks for the ATM CLP Setting feature. Each task in the list indicates if the task is optional or required.
You must perform these tasks before you can enable the ATM CLP Setting feature:
Step 1 Defining a Class Map
Step 2 Configuring a Policy with ATM CLP Setting in the Policy Map
Step 3 Attaching the Service Policy and Enabling the ATM CLP Setting Feature
To create a class map containing match criteria, use the class-map command to specify the class map name, and then use a match command in the class map configuration mode. The "Configuring a Policy with ATM CLP Setting in the Policy Map" section below explains how the ATM CLP Setting feature is applied with this class map.
| Command | Purpose |
|---|---|
Router(config)# class-map class-name | Specifies the user-defined name of class map. |
Router(config-cmap)# match access-group access-group | Specifies the name of the class map to be created and the numbered access list against whose contents packets are checked to determine if they belong to the class. |
Router(config-cmap)# match input-interface interface-name | Specifies the name of the input interface used as a match criterion against which packets are checked to determine if they belong to the class. |
Router(config-cmap)# match protocol protocol | Specifies the name of the protocol used as a match criterion against which packets are checked to determine if they belong to the class. |
Router(config-cmap)# match qos-group number | Specifies the number of the QoS group index used as a match criterion against which packets are checked to determine if they belong to the class. |
Router (config-cmap)# match any | Specifies that all packets will be matched. |
Router (config-cmap)# match ip precedence number | Specifies up to eight IP precedence values used as match criteria. |
Router (config-cmap)# match ip dscp number | Specifies up to 64 differentiated services code point(DSCP) values used as match criteria. |
Before enabling the ATM CLP Setting feature, you must create and configure a policy map.
To configure a policy map, use the policy-map command to specify the policy map name, and then use the following configuration commands to configure the class and the QoS policy. The ATM CLP Setting feature is configured in the policy map with the set atm-clp command. In this example, all output packets with the match criteria specified by the class map are sent with the CLP bit set to 1. If the set atm-clp command was not issued, the default CLP bit setting of 0 would remain.
| Step | Command | Purpose | ||
|---|---|---|---|---|
| Router(config)#policy-map policy-name | Specifies the name of the policy-map to configure. | ||
| Router(config-pmap)#class-map class-name | Specifies the name of a predefined class included in the service policy. | ||
| Router(config-pmap-c)# | Configures the ATM CLP Setting feature. |
To attach a service policy to an interface, use the service-policy output command in configuration mode. Once the service-policy is attached to the interface, the ATM CLP Setting feature is enabled for that interface, provided the set atm-clp command was issued in the policy map configuration,
| Command | Purpose |
|---|---|
Router(config)#service-policy output policy-name | Enables the Set ATM CLP feature by attaching the specified policy map to the interface. |
Step 1 Use the show policy-map command to verify that the ATM CLP Setting feature is enabled. The "set atm-clp" line in the output verifies that the ATM CLP Setting feature is configured on the policy map.
Router#show policy-map Policy Map Montana class Joe set atm-clp
Step 2 Use the show policy-map interface command to verify that the policy map is correctly configured and attached to the interface:
Router#show policy-map interface ATM 10/1/0 service-policy output:x class-map:a (match-all) 20 packets, 2240 bytes 5 minute rate 0 bps match:ip precedence 0
Step 3 Use the show atm pvc command to display statistics regarding the PVCs on the interface. The "Out CLP" line in the display indicates the cell bit setting. When the ATM CLP Setting feature is enabled, the "Out CLP" line is set to 1.
Router#show atm pvc 120 ATM10/1/0:VCD:120, VPI:0, VCI:120 PeakRate:44209, Average Rate:0, Burst Cells:0 AAL5-LLC/SNAP, etype:0x0, Flags:0xC20, VCmode:0x0 OAM frequency:0 second(s), OAM retry frequency:0 second(s) OAM up retry count:0, OAM down retry count:0 OAM Loopback status:OAM Disabled OAM VC state:Not Managed ILMI VC state:Not Managed InARP DISABLED Transmit priority 4 InPkts:0, OutPkts:24, InBytes:0, OutBytes:4608 InPRoc:0, OutPRoc:0, Broadcasts:4 InFast:0, OutFast:0, InAS:0, OutAS:20 InPktDrops:0, OutPktDrops:0 CrcErrors:0, SarTimeOuts:0, OverSizedSDUs:0 Out CLP=1 Pkts:20 OAM cells received:0 F5 InEndloop:0, F5 InSegloop:0, F5 InAIS:0, F5 InRDI:0 F4 InEndloop:0, F4 InSegloop:0, F4 InAIS:0, F4 InRDI:0 OAM cells sent:0 F5 OutEndloop:0, F5 OutSegloop:0, F5 OutRDI:0 F4 OutEndloop:0, F4 OutSegloop:0, F4 OutRDI:0 OAM cell drops:0
To monitor and maintain the ATM CLP Setting feature, use the following commands:
| Command | Purpose |
|---|---|
Router#show policy-map | Shows the contents of a policy map. |
Router#show policy-map interface | Shows the contents of a policy map, including the attached interface. |
Router#show atm pvc | Shows general ATM PVC statistics of the PVCs on the interface. |
Router#show atm pvc pvc-name | Shows more in-depth ATM PVC statistics of a particular interface. |
In this example, all output packets with IP precedence values of 0 or 1 are sent with the CLP bit set to 1:
Router(config)#class-map Joe Router(config-cmap)#match ip precedence 0 1 Router(config-cmap)#exit Router(config)#policy-map Montana Router(config-pmap)#class Joe Router(config-pmap-c)#set atm-clp Router(config-pmap-c)#exit Router(config-pmap)#exit Router(config)#interface atm 1/0/0 Router(config-if)#service-policy output Montana
In this example, Joe is the name of the class map and Montana is the name of the policy map. The match ip precedence 0 1 command in the class map specifies the IP precedence values of 0 or 1 as the match criteria. The set atm-clp command in the policy map enables the ATM CLP Setting feature, which will change the CLP bit from the default value of 0 to 1 when the service policy is attached to the interface. The interface atm 1/0/0 command specifies the ATM interface to attach this service policy to, and the service-policy output Montana command is used to place the policy-map Montana onto this interface.
This section documents new or modified commands. All other commands used with this feature are documented in the Cisco IOS Release 12.0 command reference publications.
In Cisco IOS Release 12.0(1)T or later, you can search and filter the output for show and more commands. This functionality is useful when you need to sort through large amounts of output, or if you want to exclude output that you do not need to see.
To use this functionality, enter a show or more command followed by the "pipe" character (|), one of the keywords begin, include, or exclude, and an expression that you want to search or filter on:
command | {begin | include | exclude} regular-expressionFollowing is an example of the show atm vc command in which you want the command output to begin with the first line where the expression "PeakRate" appears:
show atm vc | begin PeakRateFor more information on the search and filter functionality, refer to the Cisco IOS Release 12.0(1)T feature module titled CLI String Search.
To control the cell loss priority (CLP) bit setting on Cisco routers, use the set atm-clp command when configuring a policy map.
set atm-clpThis command has no arguments or keywords.
The CLP bit is automatically set to 0 when Cisco routers convert packets into ATM cells for ATM networks.
Privileged EXEC. This command can only be issued while configuring a policy map.
| Release | Modification |
|---|---|
12.0(7)S | This command was introduced. |
This command can only be issued while configuring a policy map.
To disable this command, remove the service policy from the interface.
The following example illustrates a CLP bit set using the set atm-clp command in the policy map:
Router(config)#class-map grizzly Router(config-cmap)#match ip precedence 0 1 Router(config-cmap)#exit Router(config)#policy-map bear Router(config-pmap)#class grizzly Router(config-pmap-c)#set atm-clp Router(config-pmap-c)#exit Router(config-pmap)#exit Router(config)#interface atm 1/0/0 Router(config)#service-policy output bear
| Command | Description |
|---|---|
policy-map | Specifies the policy map to which the class belongs. |
show policy-map | Displays information about the policy-map for an interface. |
show atm pvc | Displays information about the PVCs on an interface. |
CLP---Cell Loss Priority. Field in the ATM cell header that determines the probability of a cell being dropped if the network becomes congested. Cells with CLP = 0 are insured traffic, which is unlikely to be dropped. Cells with CLP = 1 are best-effort traffic, which might be dropped in congested conditions in order to free up resources to handle insured traffic.
PVC---Permanent Virtual Connection or Circuit. Virtual circuit that is permanently established. PVCs save bandwidth associated with circuit establishment and tear down in situations where certain virtual circuits must exist all the time. In ATM terminology, called a permanent virtual connection.
QoS---Quality of Service. QoS refers to the capability of a network to provide better service to selected network traffic over various technologies, including Frame Relay, Asynchronous Transfer Mode (ATM), Ethernet and 802.1 networks, SONET, and IP-routed networks that may use any or all of these underlying technologies.
Posted: Thu Oct 28 12:54:04 PDT 1999
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