Can anyone tell me how exactly a firewall works and can User data protocol services work under a firewall?
My doubt comes from the fact that UDP bypasses the initial ' handshaking' and perhaps a firewall will not allow communication under these circumstances.
A firewall acts as an intermediary between the protected network and the unsecure network (usually the internet). It takes requests from the computers on the protected side, remembers which computer asked for what, then moves those requests to the 'net. When the replies come form the 'net, the firewall redirects those to the requesting computers.
While doing this, it can scan the data for malware, filter out undesirable content, and even regulate bandwidth, depending on the software used and options set.
Firewalls can handle UDP.
I use Smoothwall Express 3.0 running on a P4 with 768MB RAM, running CLAMAV and Dansguardian content filtering.
UDP The way I understand it, the requesting computer tells the target computer (via IPort) that it wants data and then waits for the reply. If the reply takes too long, it may make the request again, usually by addressing a different port.
You might have to program the firewall to accept specific UDP queries from outside; this would fall the category of tunneling. I am not well-versed with tunneling, though I have set up tunneling from my less-secure wireless network to my secure wired network so that I can synchronize my PDA wirelessly.
Allowing a computer on the internet to tunnel a UDP request through your firewall is very risky, though.