So, this is the topic of this blog post: how to go about programmatically processing packet capture (pcap) files. It is important to realize that we are not precluding the use of Wireshark for example, after your program locates the proverbial needle(s) in the haystack, you can use that information (say a packet number or a timestamp) in Wireshark to look at a specific point inside the pcap and gain more insight. In all these cases, it is immensely helpful to write a custom program to parse the pcaps and yield the data points you are looking for. Repeat the above exercises several times a week (or several times a day) with different sets of packet captures Prove that it is (or is not) because of the network. At some point the application server sporadically becomes slow (retransmits on both sides, TCP windows shrinking etc.). You are given two pcaps, one gathered on a SPAN port on an access switch, and another on an application server a few 元 hops away. In a pcap that captures thousands of TCP connections between a client and several servers, find the connections that were prematurely terminated because of a RST sent by the client at that point in time, determine how many other connections were in progress between that client and other servers

Given a pcap that contains hundreds of thousands of packets, find the first connection to a particular server/service where the TCP SYN-ACK took more than 300ms to appear after the initial SYN

There are situations, however, where the ability to process a pcap programmatically becomes extremely useful. And for good reason too - Wireshark provides an excellent GUI that not only displays the contents of individual packets, but also analysis and statistics tools that allow you to, for example, track individual TCP conversations within a pcap, and pull up related metrics.

For most situations involving analysis of packet captures, Wireshark is the tool of choice.

Wireshark pcap analysis