![]() This means, the SYN-bit (2) needs to be set, the ACK-bit (16) needs to be unset and all other bits in the TCP flags can be set or unset (as they were masked by the AND (&) operator. If the result is exactly 2, then capture the packet. tcp&18 = 2 means: look at offset 0xd (13 in decimal) and then take it's value and then only look at the bits for SYN (2) and ACK (16) by doing a logical AND.This means the SYN-bit (2) and the ACK-bit (16) both needs to be set, but all other TCP flags must be unset tcp=18 means: look at offset 13 in the packet and only capture the packet when its value is 18. ![]() Examples of capture filters include: host IP -address: This filter limits the captured traffic to and from the IP address. If the packets dont match the filter, Wireshark wont save them. protocol names in a BPF filters are case sensitive, so you need to use "udp" instead of "UDP" and "icmp" instead of "UDP" Capture filters limit the captured packets by the chosen filter. ![]()
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