router doubt...

Hi,
i have a question mark in my head about router...

i am planning to build a network in my house. Using a broadband router...to connect to my 2 pc...based on what i know...the ISP will assign the router an IP and the router would run a DHCP to assign my 2 PCs in the LAN...

1. In the case above, is my router in a firewall position?If yes then how how does a hacker hack to my PC behind the router?

2. I have been doing a chatting program for fun using Java, how to i experiment it with my friend in the net with the router?

Your router most likely has a firewall built-in. Most do. You need to specify the settings, never pays to leave security settings at default. Always nice to tweak them and see what works well for you.
Java should go through fine, is this in a web browser or outside of one? If it is within a browser, there shouldn't be a problem, if it is without, you need to set your router up to accept traffic for the ports your chat program uses.

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1. In the case above, is my router in a firewall position?If yes then how how does a hacker hack to my PC behind the router?

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Yes, the router will provide firewalling. The router will presumably use dynamic NAT to make outgoing connections. Because of this it is difficult for an attacker to initiate a connection to an internal machine, because he cannot route packets to it (it has a private non-routable address)

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2. I have been doing a chatting program for fun using Java, how to i experiment it with my friend in the net with the router?

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I am assuming you have a chat server written in Java?

Anyway, this will prove problematic because of course your internal IP address is not routeable from the outside. The solution is to use a static NAT rule, and NAT a port on the external interface of the router into the port your Java app is listening on

This is possible (and indeed fairly easy) on most routers these days.

Having done that, any connection from the outside into your router's port will be nat'd into your local machine's port.

Depending on the protocol your chat server uses, this may not work. If you use a single TCP connection, it should be ok. If you use UDP and always respond to the address that sent the packets, that's ok too. Try to avoid sending IP addresses inside the data, as those will NOT be NAT'd, and hence may confuse things (because the packets src/dest addresses will be NAT'd, they won't match up)

If you didn't understand that paragraph, don't worry - just another rant :)

what is NAT and how do i configure it...i mean in a generic way that most router have it...

yah it is a program that runs outside broswer...however i am using TCP/IP on this program...

btw if i setup a port for outside IP to access my internal network then am i creating a hole for ppl to access too?

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what is NAT and how do i configure it...i mean in a generic way that most router have it...

yah it is a program that runs outside broswer...however i am using TCP/IP on this program...

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NAT stands for network address translation and is more a protocol then a program. It is designed to work with tcp/ip (you can correct me here). There's nothing to configure for it to work on these routers (well on the ones i've worked on) .

Here is some info on NAT.


Hope that helps