TCPDUMP - Packet size limited during capture HTTP truncated

In Linux environment, if you want to use command base to capture network packets, you can use the following command with TCPDUMP

tcpdump -i eth0 -w out.pcap

The above command will dump network packet for network interface eth0 to a file call out.pcap. This file is a pcap format which you can open by Wireshark.

The above command will use a default capture size of 96 bytes and the benefit of this is to create a small output file. However, the downside is that certain large packet information will be lost and you may not see a complete picture of network communication. Especially in Wireshark, such situation will display with a message "Packet size limited during capture HTTP truncated" for large packet

To solve this issue, use the following command

tcpdump -i eth0 -w out.pcap -s 0

-s 0 flag tell tcpdump to capture packet at original size (65535 bytes). And, this will create much larger output file.

Comments

  1. Thanks for the information, it was very useful.

    ReplyDelete
  2. Thank you so much for the clear explanation.

    ReplyDelete

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