In a period of one second, a100 Mb/s link can accomodate 100 Mb of traffic across the interface in a neatly-shaped profile with a minimum need to buffer any packet. However, one second is a very large interval when you consider the rate at which buffering and packet switching happens. At the default scale, it appears that there is no bursty traffic.Open the captured file in Wireshark and plot an IO graph like this one.Switch(conf)# monitor session 1 destination interface fa1/2 Switch(conf)# monitor session 1 source interface fa1/1 tx In order to capture this traffic, connect a PC that runs Wireshark and capture packets at the SPAN destination port. Configure SPAN on the switch in order to capture transmitted (TX) traffic.Input queue: 0/75/0/0 (size/max/drops/flushes) Total output drops: 5756ĥ minute input rate 55343353 bits/sec, 9677 packets/secĥ minute output rate 55456293 bits/sec, 9878 packets/sec Switch# show int fa1/1 | i duplex|output drops|rateįull-duplex, 100Mb/s, media type is 10/100BaseTX For example, you notice output drops on a 100Mb link while the average utilization of the link is only 55Mb. Identify an interface that has incremental output drops.In this case, you can use Wireshark in order to capture egress traffic with the Switched Port Analyzer (SPAN), which is analyzed in order to identify the bursts. It is best to average them over 30 seconds. By default, the output rates in the show interface command are averaged over five minutes, which is not adequate to capture any short-lived bursts. Traffic bursts can cause output drops even when the interface output rate is significantly lower than the maximum interface capacity. If your network is live, make sure that you understand the potential impact of any command before executing the command. All of the devices used in this document started with a cleared (default) configuration. The information in this document was created from the devices in a specific lab environment. The information in this document is based on the Cisco Catalyst Switch Series. There are no specific requirements for this document. This document describes how to identify burst traffic on the switchports of Cisco Catalyst switches.
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