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These expressions consist of one or several primitives, and primitives consist of an identifier (values or names that you’re trying to find within different packets), followed by one or several qualifiers. The Berkley Packet Filter syntax captures filters based on different filtering expressions. Since this is the syntax that is most commonly used in packet analysis, it’s important to understand how it works. Within Wireshark, a syntax called Berkley Packet Filter (BPF) syntax is used for creating different capture filters. How do they work? By setting a specific filter, you immediately remove the traffic that does not meet the given criteria. These filters are used before the process of packet capturing. Knowing how to use different filters is extremely important for capturing the intended packets.
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Different ports are used for different protocols. And public ports are ports from 49152-65535, they can be used by any service.
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Then, from 1024 to 49151 are registered ports – they are assigned by ICANN to a specific service. They can be divided into three different categories: ports from 0 – 1023 are well-known ports, and they are assigned to common services and protocols.
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