Most ISPs provide you with 1 IP address when you connect.
The setup:
BB Modem --- hub or switch --- PCs
is possible - if your ISP only allocates you one IP address, you can only connect 1 PC, 2 IPs = 2 PCs, etc.
The hub/switch doesn't get an IP address, the connected PCs use the public IP(s) provided by the ISP.
Most ISPs only provide 1 IP address as standard.
As most ISPs charge extra for providing extra IP addresses, the following setup is more common:
BB Modem --- ROUTER --- PCs
In this case, the router has 2 sides: the WAN side and the LAN side.
The WAN side is given the IP provided by the ISP, the LAN side is given an IP by you.
All the PCs in the LAN share the same IP policy - normally 192.168.x.x and subnet mask 255.255.255.0, which allows connection of (up to) 253 PCs. The PCs are then given a default gateway - this is the (LAN) IP address of the router - normally 192.168.x.1
Basically, the PCs connect to the router, which then forwards the request to the internet.
2 advantages:
firstly - you can connect loads of PCs but only need 1 WAN IP
secondly - you're behind a NAT firewall: much more secure
disadvantages:
-if you run a server (web/ftp/gaming), you need a more complex router setup
-some other programs also require a more complex router setup (e.g. Voice over MSN Messenger, Remote assistance...)
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