Contents

Configuring data buffers· 1

About data buffers· 1

Data buffer types· 1

Cell resources and packet resources· 1

Fixed area and shared area· 1

Restrictions and guidelines: Data buffer configuration· 2

Enabling the Burst feature· 2

Configuring data buffer alarms· 3

About data buffer alarms· 3

Restrictions and guidelines for data buffer alarm configuration· 3

Configuring queue-level alarm thresholds for the ingress or egress buffer 3

Configuring queue-level alarm thresholds for the Headroom buffer 4

Configuring packet-drop alarms· 5

Displaying and maintaining data buffers· 5

 

Configuring data buffers

About data buffers

Data buffer types

Data buffers temporarily store packets to avoid packet loss.

The following data buffers are available:

·     Ingress buffer—Stores incoming packets when the CPU is busy.

·     Egress buffer—Stores outgoing packets when network congestion occurs.

·     Headroom buffer—Stores packets when the ingress buffer or egress buffer is used up.

Figure 1 shows the structure of ingress and egress buffers.

Figure 1 Data buffer structure

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Cell resources and packet resources

A buffer uses the following types of resources:

·     Cell resources—Store packets. The buffer uses cell resources based on packet sizes. Suppose a cell resource provides 208 bytes. The buffer allocates one cell resource to a 128-byte packet and two cell resources to a 300-byte packet.

·     Packet resources—Store packet pointers. A packet pointer indicates where the packet is located in cell resources. The buffer uses one packet resource for each incoming or outgoing packet. Packet resources are not supported in the current software version.

Fixed area and shared area

Each type of resources has a fixed area and a shared area.

·     Fixed area—Partitioned into queues, each of which is equally divided by all the interfaces on a card, as shown in Figure 2. When congestion occurs or the CPU is busy, the following rules apply:

a.     An interface first uses the relevant queues of the fixed area to store packets.

b.     When a queue is full, the interface uses the corresponding queue of the shared area.

c.     When the queue in the shared area is also full, the interface discards subsequent packets.

The system allocates the fixed area among queues as specified by the user. Even if a queue is not full, other queues cannot preempt its space. Similarly, the share of a queue for an interface cannot be preempted by other interfaces even if it is not full.

·     Shared area—Partitioned into queues, each of which is not equally divided by the interfaces, as shown in Figure 2. The system determines the actual shared-area space for each queue according to user configuration and the number of packets actually received and sent. If a queue is not full, other queues can preempt its space.

The system puts packets received or sent on all interfaces into a queue in the order they arrive. When the queue is full, subsequent packets are dropped.

Figure 2 Fixed area and shared area

 

Restrictions and guidelines: Data buffer configuration

Inappropriate data buffer changes can cause system problems. Before enabling the Burst feature, make sure you understand its impact on your device. As a best practice, use the burst-mode enable command only if the system requires large buffer spaces.

Enabling the Burst feature

The Burst feature enables the device to automatically allocate buffer resources. It is well suited to the following scenarios:

·     Broadcast or multicast traffic is intensive, resulting in bursts of traffic.

·     Traffic comes in and goes out in one of the following ways:

¡     Enters a device from a high-speed interface and goes out of a low-speed interface.

¡     Enters from multiple same-rate interfaces at the same time and goes out of an interface with the same rate.

Before enabling the Burst feature, make sure all interfaces on cards that support this feature use SP queuing.

A card enabled with the Burst feature supports only WRR queuing. To use other queuing methods, first disable the Burst feature.

SF and LSQM1TGS16GPSA0 interface modules do not support the Burst feature.

To enable the Burst feature:

 

Step	Command	Remarks
1.     Enter system view.	system-view	N/A
2.     Enable the Burst feature.	In standalone mode: burst-mode enable slot slot-number In IRF mode: burst-mode enable chassis chassis-number slot slot-number	By default, the Burst feature is disabled.

 

Configuring data buffer alarms

About data buffer alarms

This feature works with a network management system (such as IMC). Data buffer alarms include threshold-crossing alarms and packet drop alarms. The device reports these alarms to the network management system for displaying the data buffer usage. Threshold-crossing alarms are generated when the usage of a data buffer type exceeds the specified alarm thresholds.

The alarm thresholds are configured on a per-queue basis.

Restrictions and guidelines for data buffer alarm configuration

Only the following modules support this feature:

·     FD interface modules.

·     FE interface modules.

·     SG interface modules: LSQM1CQGS12SG0, LSQM1QGS24RSG0, LSQM1TGS48RSG0, LSQM2TGS48SG0.

If an interface is not configured with generic flow control or PFC in the inbound direction, alarms for Headroom buffer will not occur. For information about generic flow control or PFC, see Ethernet interface configuration in Interface Configuration Guide.

If you have configured the burst-mode enable, flow-control, or priority-flow-control command before configuring alarm thresholds, you must reconfigure the alarm thresholds. For more information about the flow-control and priority-flow-control commands, see Ethernet interface commands in Interface Command Reference.

Configuring queue-level alarm thresholds for the ingress or egress buffer

Step	Command	Remarks
1.     Enter system view.	system-view	N/A
2.     Configure the alarm thresholds.	Configure the global alarm threshold for a queue. In standalone mode: buffer { egress | ingress } usage threshold slot slot-number queue queue-id ratio ratio In IRF mode: buffer { egress | ingress } usage threshold chassis chassis-number slot slot-number queue queue-id ratio ratio	The default setting is 100%.
	Execute the following commands in sequence to configure the alarm threshold for a queue on an interface: ·     interface interface-type interface-number ·     buffer { egress | ingress } usage threshold queue queue-id ratio ratio	By default, an interface uses the global alarm threshold. In this case, the display this [ all ] command does not display the global alarm threshold that the interface uses when it is executed in interface view. For this command to display the alarm threshold that the interface uses, configure the alarm threshold as the default value and or a non-default value in interface view.
3.     Enable threshold-crossing alarms.	buffer threshold alarm { egress | ingress } enable	By default, threshold-crossing alarms are disabled.
4.     (Optional.) Set the interval for sending threshold-crossing alarms.	buffer threshold alarm { egress | ingress } interval interval	The default setting is 5 seconds.

 

Configuring queue-level alarm thresholds for the Headroom buffer

Step	Command	Remarks
1.     Enter system view.	system-view	N/A
2.     Configure the alarm thresholds.	Configure the global per-queue alarm threshold. In standalone mode: buffer usage threshold headroom slot slot-number ratio ratio In IRF mode: buffer usage threshold headroom chassis chassis-number slot slot-number ratio ratio	The default setting is 100%.
	Execute the following commands in sequence to configure the alarm threshold for a queue on an interface: ·     interface interface-type interface-number ·     buffer usage threshold headroom queue queue-id ratio ratio	By default, an interface uses the global per-queue alarm threshold. In this case, the display this [ all ] command does not display the global per-queue alarm threshold that the interface uses when it is executed in interface view. For this command to display the per-queue alarm threshold that the interface uses, configure the per-queue alarm threshold as the default value and or a non-default value in interface view.
3.     Enable threshold-crossing alarms.	buffer threshold alarm headroom enable	By default, threshold-crossing alarms are disabled.
4.     (Optional.) Set the interval for sending threshold-crossing alarms.	buffer threshold alarm headroom interval interval	The default setting is 5 seconds.

 

Configuring packet-drop alarms

This feature allows the device to periodically send packet-drop information to the NMS.

This feature does not take effect on the Headroom buffer.

To configure packet-drop alarms:

 

Step	Command	Remarks
1.     Enter system view.	system-view	N/A
2.     Enable packet-drop alarms.	buffer packet-drop alarm enable	By default, packet-drop alarms are disabled.
3.     (Optional.) Set the interval for sending packet-drop alarms.	buffer packet-drop alarm interval interval	The default setting is 5 seconds.

 

Displaying and maintaining data buffers

Execute display commands in any view.

 

Task	Command
(In standalone mode). Display data buffer usage.	display buffer usage [ slot slot-number ]
(In IRF mode.) Display data buffer usage.	display buffer usage [ chassis chassis-number slot slot-number ]