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.

A timestamp will be added to the filename as a suffix. On the Output tab, perform the following: Browse capture file location and provide a filename. 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. From toolbar, select Capture -> Options On the Input tab, select input adapter. Query For Available Interfaces In the first step the extcap is queried for its interfaces. All the steps performed are done for every extcap. Tcp means capturing the 13th byte of the tcp packet, corresponding to first half being the offset, second half being reserved. The actual capture is run after a setup process that can be done manually by the user or automatically by the GUI. 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 There's still TLSv1.2 packets being captured.Tcpdump -ni eth0 “tcp port 443 and (tcp & 0xf0) > 2)] = 0x16)”Įth0: is my network interface, change it if you need There's a breakdown on the page)īut it doesn't seem to give the expected results. (I'm not going to pretend I understand all of it. So I want to filter out everything we're not interested in, only capturing the deprecated protocols. I know, the display filter for showing SSL 3.0, TLS 1.0 & TLS 1.1 packets is pretty simple: = 0x0300 or = 0x0301 or = 0x0302īut I want to avoid capturing everything, as these are very active servers. I imagine that's not that uncommon to be curious about, but to my surprise I couldn't find much on how to build a proper capture filter for this. We're trying to identify applications which are still connecting to our shared SQL servers with deprecated SSL/TLS protocols, so anything older than TLS 1.2.

Https wireshark capture