The value 22 (0x16 in hexadecimal) has been defined as being “Handshake” content.Īs a consequence, tcp & 0xf0) > 2)] = 0x16 captures every packet having the first byte after the TCP header set to 0x16. The first byte of a TLS packet define the content type. The offset, once multiplied by 4 gives the byte count of the TCP header, meaning ((tcp & 0xf0) > 2) provides the size of the TCP header. However, this doesnt seem to work for many protocols, including MDNS, which is what Im trying to filter on right now. Tcp means capturing the 13th byte of the tcp packet, corresponding to first half being the offset, second half being reserved. I know that for some protocols, such as http, you can just type 'http' in the filter box and wireshark will filter it.
Tcp & 0xf0) > 2)] = 0x16: a bit more tricky, let’s detail this below Tcp port 443: I suppose this is the port your server is listening on, change it if you need Tcpdump -ni eth0 “tcp port 443 and (tcp & 0xf0) > 2)] = 0x16)”Įth0: is my network interface, change it if you need
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