Cisco Cisco Nexus 5010 Switch Libro bianco

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Latency Monitoring Tool on Cisco Nexus Switches:
Troubleshoot Network Latency

Introduction

Networks often encounter problems related to latency. Troubleshooting such problems can be complicated. End-to-

end system latency that is higher than expected may arise from the servers, applications, network design,

burstiness of traffic to a single port, misconfiguration in the switch, etc.

Latency measurements can be used to identify the flows that are affected by latency. These statistics also allow

administrators to plan network topologies, manage incident responses, and identify root causes of application

problems in the network. The statistics also can be used to provide service-level agreements (SLAs) for

latency-intensive applications.

The Cisco

latency monitoring tool on the Cisco Nexus

5600 platform switches can help you troubleshoot latency

concerns in the network with ease.

Note: All the details presented in this document apply to Cisco Nexus 6000 Series Switches as well.

The latency monitoring tool marks each ingress and egress packet with a time-stamp value. To calculate the

latency for each packet in the system, the switch compares the ingress time stamp with the egress time stamp.

The tool allows you to display historical averages of latency between all pairs of ports as well as real-time latency

data.

By default, Instantaneous mode latency monitoring is enabled between a pair of ports. This mode measures switch

latency for each packet. The switch latency monitoring tool works at line rate; hence, packet sampling is not

required.

This tool is fully implemented in hardware. Hence, it has no effect on the CPU or on data traffic.

Latency monitoring reveals the minimum, average, and maximum latency between a specified port pair and also

maintains a latency histogram (accurate to several nanoseconds [ns]), as shown in Figure 1.