Understanding NAT, Firewalls, TCP/IP
- From: Roedy Green <my_email_is_posted_on_my_website@xxxxxxxxxxxxxx>
- Date: Wed, 11 Jan 2006 04:09:26 GMT
I am asking this for two reasons:
1. I want to know if I am in any danger of BitTorrent like need for
firewall configuring if I write a Java app that uses pure sockets
talking to a server. The clients always initiate conversations. Do I
have to use HTTP to be safe from firewalls blocking outgoing calls?
2. I thought this be interesting to write up for the Java glossary.
Is this correct?
Lets say I have two computers A and B on a LAN with IP 192.168.0.2 and
192.168.0.3.
Lets say I have a router/firewall on the LAN internally addressable as
192.168.0.1 and with a face IP to the world of 4.69.120.20.
Lets say I want to talk to a server with IP 65.110.20.44.
Lets say that both A and B want to look at web page on the server.
They each send a request containing their own IP, a random spare port
for the return packets to come to, the IP of the server, and 80 the
port of the server, to the router's internal IXP.
To the outside world, router looks like a single computer. So it has
to fake the two requests from A and B as if they both came from
itself. So it sends on request two packets with the routers face IXP,
a spare port on the router, the IP of the server and port 80.
When the server responds, it has to look up which spare port is
associates with spare port on which computer and forward the response.
--
Canadian Mind Products, Roedy Green.
http://mindprod.com Java custom programming, consulting and coaching.
.
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