This post explains you to capture the network traces of ESXi host using tcpdump utility.In most case during network issues or troubleshooting purposes, It might be useful to perform a tcpdump on the ESXi host. tcpdump-uw command is based on standard tcpdump utility. tcpdump command captures the network traces from the network interface perspective.
You may need decide first in which network interface you need to capture the network traces of ESXi host. Identify the list of VMkernel network adapters using the below command
Capture default first 68 bytes using tcpdump
tcpdump-uw command with -i option can be used to display the packets on the VMkernel interface. Let’s choose vmk1 for our example.
tcpdump-uw -i vmk1
Capture entire packet using tcpdump
tcpdump and tcpdump-uw command capture only the first 68 bytes of data from a packet by default. To capture the entire packet, tcpdump-uw need to be used with -s option.
Value of 1514 for normal traffic
tcpdump-uw -i vmk1 -s 1514
Value of 9014 if jumbo frames are enabled.
tcpdump-uw -i vmk1 -s 9014 -B 9
Capture packets with filters using tcpdump
TCP switch with tcpdump-uw command can be used to display only the TCP packtes on VMk1
tcpdump-uw -i vmk1 -s 1514 tcp
Host option can be used with tcpdump-uw command to see traffic to/from only a single IP address
tcpdump-uw -i vmk1 -s 1514 host 192.168.0.20
Capture packets with verbose option
-vvv option can be used with tcpdump-uw command to display all packets on the vmk1 with verbose detail
tcpdump-uw -i vmk1 -s 1514 -vvv
Save the tcpdump inpcap format for later analysis
Output of the tcpdump command can be saved in Pcap format and it can be used later with wireshark to analyse. Save the output with filename.pcap
tcpdump-uw -i vmk1 -s 1514 -w esxihost1.pcap
Limiting the log files using tcpdump
You can limit the log files to a specific number during the tcpdump capture using -W option.
tcpdump-uw -i vmk1 -s 1514 -C 50M -W 5 -w /var/esxihost1-capture.pcap
Above command creates 5 trace files of size 5MB each. This settings helps you to avoid run out of space on ESXi host due to packet capture.
I believe this is informative for you. Thanks for reading!!!