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Handle TCP protocol on your own
Dec 10, 2019 at 2:59pm
Is it possible to somehow dive deeper, and handle the initial TCP handshake(SYN/ACK) on your own? At the moment winsock is doing this for me.
Dec 10, 2019 at 3:38pm
Yes, if you open a raw socket you can send packets at layers 2 (Ethernet) and 3 (IP).
https://docs.microsoft.com/en-us/windows/win32/winsock/tcp-ip-raw-sockets-2
https://docs.microsoft.com/en-us/windows/win32/winsock/tcp-ip-raw-sockets-2
Dec 10, 2019 at 4:23pmThanks Helios, you've been golden as usual.
So when I use raw sockets will I see all messages going back and forth between the machines? Or is there still a lower protocol that handles messages before it reaches me (my raw socket)? Based on your reply there might be something happening at layer 1?
Last edited on Dec 10, 2019 at 4:25pm
Dec 10, 2019 at 4:38pm
If you open at layer 2 you'll see all traffic on the network segment, some of which will be addressed to your NIC. You won't see the traffic being generated by other processes on your host.
If you open at layer 3 you'll see all traffic addressed to your NIC and you'll have to filter based on IP (like how you pass an address to bind()).
If you open at layer 3 you'll see all traffic addressed to your NIC and you'll have to filter based on IP (like how you pass an address to bind()).
Dec 10, 2019 at 4:47pm
How can I skip all layers/protocols, and see what's really going on?
Last edited on Dec 10, 2019 at 4:51pm
Dec 10, 2019 at 4:51pm
You can't go lower than Ethernet from software, since layer 1 is the physical protocol. You would need to build your own NIC and measure the electrical signals passing through the cable.
Dec 10, 2019 at 5:08pm
Okey. If I understood you correctly. When I've set up the raw socket, and sent a http request to my self from a client... I'll first have to handle the TCP/IP protocol, before I see the http request?
Dec 10, 2019 at 5:24pm
Yes, obviously. If you're at layer 3 you'll have to handle everything yourself: IP, TCP, and HTTP.
Dec 10, 2019 at 5:49pm
If you want to watch the wire.
One of these (or the pre-assembled one if you can't solder).
https://www.amazon.co.uk/d/Computer-Accessories/Great-Scott-Gadgets-Throwing-Star/B01COWCXF6
Also at https://greatscottgadgets.com/throwingstar/
One of these (or two singles if you have plenty of spare USB ports).
https://www.amazon.co.uk/StarTech-com-Dual-Gigabit-Ethernet-Adapter-Black/dp/B00D8XTOD0
Three LAN patch cables.
Two patch cables to between the Tap ports and the USB dongle.
The third patch cable continues the connection from the Tap to the equipment under test.
Then use https://www.wireshark.org/ to watch the two ends of the tap and you'll see everything.
One of these (or the pre-assembled one if you can't solder).
https://www.amazon.co.uk/d/Computer-Accessories/Great-Scott-Gadgets-Throwing-Star/B01COWCXF6
Also at https://greatscottgadgets.com/throwingstar/
One of these (or two singles if you have plenty of spare USB ports).
https://www.amazon.co.uk/StarTech-com-Dual-Gigabit-Ethernet-Adapter-Black/dp/B00D8XTOD0
Three LAN patch cables.
Two patch cables to between the Tap ports and the USB dongle.
The third patch cable continues the connection from the Tap to the equipment under test.
Then use https://www.wireshark.org/ to watch the two ends of the tap and you'll see everything.
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