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Julian Nguyen
Julian Nguyen

Capture Nexum For Mac


Ethanalyzer is a Cisco NX-OS protocol analyzer tool based on the Wireshark (formerly Ethereal) open source code. Ethanalyzer is a command-line version of Wireshark that captures and decodes packets. You can use Ethanalyzer to troubleshoot your network and analyze the control-plane traffic. This document covers configuration of Ethanalyzer, examples of its implementation and Ethanalyzer usage together with ACLs "log" option to sniff data plane traffic.




Capture Nexum For Mac



Nexus switches are among the most powerful data center switches in the industry. This is partly because of the CPU and memory available in the switch, but also because of the wide range of integrated tools that the NX-OS offers. These tools provide the capability to capture packets at different ASIC levels within the switch and help verify both hardware programming and the action taken by the hardware or the software on the packet under investigation. Some of these tools include the following:


These tools are capable of performing packet capture for the traffic destined for the CPU or transit hardware-switched traffic. They are helpful in understanding the stages the packet goes through in a switch, which helps narrow down the issue very quickly. The main benefit of these features is that they do not require time to set up an external sniffing device.


The ELAM capture is supported on all Nexus switches, but because it requires deeper understanding of the ASICs and the configuration differs among Nexus platforms, it is outside the scope of this book. Additionally, ELAM is best performed under the supervision of a Cisco Technical Assistance Center (TAC) engineer. ELAM also is not supported on N5000 or N5500 switches.


Ethanalyzer is an NX-OS implementation of TShark, a terminal version of Wireshark. TShark uses the libpcap library, which gives Ethanalyzer the capability to capture and decode packets. It can capture inband and management traffic on all Nexus platforms. Ethanalyzer provides the users with the following capabilities:


Ethanalyzer does not allow hardware-switched traffic to be captured between data ports of the switch. For this type of packet capture, SPAN or ELAM is used. When the interfaces are configured with ACLs with ACEs configured with the log option, the hardware-switched flows gets punted to the CPU and thus are captured using Ethanalyzer. However, this should not be tried in production because the packets could get dropped as a result of CoPP policies or the excessive traffic punted to the CPU could impact other services on the device.


The next step is to set the filters. With a working knowledge of Wireshark, configuring filters for Ethanalyzer is fairly simple. Two kinds of filters can be set up for configuring Ethanalyzer: capture filter and display filter. As the name suggests, when a capture filter is set, only frames that match the filter are captured. The display filter is used to display the packets that match the filter from the captured set of packets. That means Ethanalyzer captures other frames that do not match the display filter but are not displayed in the output. By default, Ethanalyzer supports capturing up to 10 frames and then stops automatically. This value is changed by setting the limit-captured-frames option, where 0 means no limit.


All in-band Ethernet ports that send or receive data to the switch supervisor are captured with the inbound-hi or inbound-low option. However, display or capture filtering can be applied.


To start a packet capture with Ethanalyzer, use the command ethanalyzer local interface [inbound-hi inbound-lo mgmt] options, with the following options:


While using Ethanalyzer, specifying the filters is easier for someone who is familiar with Wireshark filters. The syntax for both the capture filter and the display filter is different. Table 2-1 lists some of the common filters and their syntax with the capture-filter and display-filter options.


Example 2-9 illustrates the use of Ethanalyzer to capture all packets hitting the inbound-low as well as inbound-hi queue on Nexus 6000. From the following outputs, notice that the TCP SYN/SYN ACK packets even for a BGP peering are part of the inbound-low queue, but the regular BGP updates and keepalives (such as the TCP packets after the BGP peering is established) and the acknowledgements are part of the inband-hi queue.


As stated earlier, optimal practice is to write the captured frames in a file and then read it after the frames are captured. The saved file in a local bootflash is read using the command ethanalyzer local read location [detail].


Nexus 7000 offers no option for inbound-hi or inbound-low. The CLI supports captures on the mgmt interface or the inband interface. The inband interface captures both high- and low-priority packets. Example 2-10 illustrates how to write and read the saved packet capture data. In this example, Ethanalyzer is run with a capture-filter on STP packets.


Capture executable (presentation) files should also receive these network levels. Note that you may need to install the Capture application in order to use its network adaptor selection tools. Capture is available for download from the Capture website, www.capturesweden.com.


It only runs in the default VDC. If you do not have access to the admin or default VDC you cannot use this command. You can still capture from another VDC by setting an interface ACL and log the traffic you want in the VDC you want. Then you can go to the default VDC and run ethanalyzer to see your traffic.


The PAUSE frames are an indication that the device sending the PAUSE frames is experiencing issues. If the calculations confirm that the maximum amount of time a port might have been paused is a significant portion of the time over which the data was captured, then consider investigating why the device sending the PAUSE frames is experiencing difficulty.


If the maximum amount of time that the PAUSE frames might have stopped traffic flow is a small portion of the time during which the data was captured, the presence of the PAUSE frames should not be of much concern. However, the presence of PAUSE frames will still indicate, some level of difficulty being experienced by the device that is sending the PAUSE frames.


Before we get started, we need to define exactly the type of traffic we wish to capture. Here is some sample configuration for capturing IPv4 traffic on a specific Port in both directions.


CircuitLab provides online, in-browser tools for schematic capture and circuit simulation. These tools allow students, hobbyists, and professional engineers to design and analyze analog and digital systems before ever building a prototype. Online schematic capture lets hobbyists easily share and discuss their designs, while online circuit simulation allows for quick design iteration and accelerated learning about electronics.


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