Белая книга для Cisco Cisco Nexus 5010 Switch

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What You Will Learn

This white paper describes how to configure the Buffer Utilization Histogram feature on Cisco Nexus

5600 and

Nexus 6000 Switch Families, and explains the benefits that this feature offers. Traffic drops happen in every

network, and it can be difficult to discover the cause of the drops. Sometimes the buffer overflow is the cause of the

traffic drop. After a drop occurs it can be difficult to see the buffer state before and during traffic overflow.

Nexus 5600 and Nexus 6000 Switch Families introduced the Buffer Utilization Histogram feature. It provides a way

to look in the past and see the state of buffer. The feature can show buffer state with time granularity for up to 250

milliseconds.

Introduction

A micro-burst of traffic is an example where buffer plays a role of preserving traffic not to be dropped. Buffer should

not be shallow because it can easily overflow in the event of traffic microbursts. Furthermore, buffer that is too

deep can affect traffic latency. This is not a desirable behavior in a network. Before a network administrator

connects a new device to a switch, the admin should first gain data of buffer usage on the particular device. To do

so, the admin needs to see how buffer has been used in the past.

With common tools on the switch, it is hard to see how buffer is used. Unfortunately, many of the regular tools in

the network do not provide a history of usage. As a result, a user must connect a device to the switch (without

previous knowledge about buffer usage) and wait to see how that new device will affect the traffic. The same
situation may occur simply by installing a new server with a “bursty” application.

The Buffer Utilization Histogram feature on Cisco Nexus 5600 and Nexus 6000 switches provides per-port,

instantaneous, and histogram buffer utilization. Buffer Utilization Histogram provides data of buffer utilization in

both ingress and egress directions. For the egress direction, data is separated on multicast and unicast traffic. The

results can be extracted into an XML file to help network administrators analyze and compare data with other

processes in the network on the remote system.

Buffer Utilization Histogram Concept

The Buffer Utilization Histogram feature gives admins the ability to analyze the maximum queue depth and buffer

utilization on Cisco Nexus 5600 and Nexus 6000 switches in real time. Every three ports of 40 Gigabit Ethernet or

every 12 ports of 10 Gigabit Ethernet share a 25 MB buffer space. The devices maintain separate buffer on the

ingress and egress directions. 15.6 MB are reserved for ingress and 8.6 MB are reserved for egress. The

remaining space is used for switched port analyzer (SPAN) and control packets buffer. Egress buffer is divided into

unicast and multicast buffer pools.

The Buffer Utilization Histogram feature brings instantaneous and histogram statistics on a per-port basis. The

instantaneous mode gives current buffer states. To obtain the histogram of buffer utilization, software pools usage

values from the hardware. Hardware pooling happens every 1 second for slow pooling mode and every 250

milliseconds for fast pooling. After execution show command, switch uses software pooling to make and display a

histogram (Figure 1).