As an IP datagram contains both a source and a destination address, the expression will evaluate to true whenever at least one of the two addresses differs from 1.2.3.4. The reason for this, is that the expression ip.addr != 1.2.3.4 must be read as “the packet contains a field named ip.addr with a value different from 1.2.3.4”. Instead, that expression will even be true for packets where either source or destination IP address equals 1.2.3.4. Unfortunately, this does not do the expected. Then they use ip.addr != 1.2.3.4 to see all packets not containing the IP address 1.2.3.4 in it. Often people use a filter string to display something like ip.addr = 1.2.3.4 which will display all packets containing the IP address 1.2.3.4. Using the != operator on combined expressions like eth.addr, ip.addr, tcp.port, and udp.port will probably not work as expected. Wireshark allows you to string together single ranges in a comma separated list to form compound ranges as shown above.
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