OpenShift Packet Capture Helper

FAQ

  • Q: How does one execute the tcpdump command on an RHCOS node?

    A: The tcpdump command is available within the toolbox or debug container image.

  • Q: How can multiple packet capture commands be executed simultaneously in toolbox?

    A: You can utilize the & symbol at the end of each packet capture command. This will execute each tcpdump command concurrently in the background. To halt each process, you can bring it to the foreground using the fg command and terminate it by pressing Ctrl+c. 

    $ tcpdump -i br-ex -w br-ex.pcap &
[1] 207592
$ tcpdump -i ovn-k8s-mp0 -w ovn-k8s-mp0.pcap &
[2] 207003
$ fg 1 <-- Run and press Ctrl+c
$ fg 2 <-- Run and press Ctrl+c

  • Q: Is there an essential article available for convenient packet collection from Pods or nodes on OpenShift?

    A: Yes, there are must-have articles (KCS4569211 and KCS5074041) that serve as a handy guide for efficiently collecting packets from both Pods and nodes within an OpenShift environment.

  • Q: What are the additional information required for packet analysis?

    A: When preparing to analyze packets, certain supplementary details are essential. These include:

    • Timestamp in date +%d-%m-%Y-%H-%M-%S-%Z format (applicable for timestamping events): This ensures accurate time representation during analysis.
    • Source and destination of the connection: Knowing the origin and destination of the connection aids in understanding the network flow.
    • tcpdump command utilized: Providing the specific tcpdump command used for packet capture helps in understanding the different options used.
    • Location of packet capture (if hostname in the pcap name is ambiguous): Clarifying the location of packet capture is crucial, especially if the hostname in the pcap name lacks clarity.
    • Network topology of connectivity (if available, utilize asciiflow.com): Sharing the network topology, preferably visualized using tools like asciiflow.com, offers valuable insights into the network's architecture and connectivity patterns.

  • Q: How can one reduce the size of the pcap file while conducting an iperf test?

    A: To minimize the size of the pcap file generated by the tcpdump command, you can utilize the -s 200 option. This option sets the snapshot length to 200 bytes, meaning tcpdump will only capture the first 200 bytes of each packet. This reduces the amount of data captured and subsequently the size of the resulting pcap file.

  • Q: What are the potential disadvantages of using -i any?

    A: Using -i any with tcpdump is not inherently wrong, but it has potential downsides and should be used judiciously. Analyzing a large volume of traffic from multiple interfaces can be challenging.