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For 2 PC's to access the same ISP, is a hub *and* a router necessary or just the hub?

Mar 29th, 2002 09:44
Lars Gaarden, Anthony Boyd, raad sneder,


The short answer is that you need a router with NAT/masquerade 
capability, and that the router and PCs are connected through a 
hub/switch.
The long answer:
Every computer connected to the Internet has a unique IP address.
When you connect to an ISP, you usually only get a single address.
Thus, to share a single internet connection all your local PCs
must look like a single address to the rest of the net. This
is often called 'Network Address Translation' or 'IP masquerading'.
In other words, you need something that supports NAT on the
border between your internal network and the connection to your
ISP. In addition, all PCs on your internal network must be
connected through a hub or switch.
A typical shared internet connection will look like this:
            ---------     ------------
ISP -------| NAT Box |---| Hub/Switch |-- Internal network
            ---------     ------------
The 'NAT Box' can be a stand-alone router with NAT functionality,
a Linux PC with IP masquerade, a Win98SE+ PC with Internet Connection
Sharing (ICS) enabled. There are even some ADSL and Cable modems
with integrated NAT functionality.
Hubs, switches and routers:
A hub/switch is the glue that holds your local network together, a
router is a bridge between your network and other networks.
Hubs and switches are essentially the same - they connect PCs and
other network devices on the same network (LAN). Switches are more
intelligent than hubs and are better at handling large amounts of
traffic (many devices talking at the same time). The performance
between a hub and a switch is in most situations negligable on a
home network.
There is one special case that is worth mentioning.
If you only have 2 PCs, you don't need a hub. Instead you can use a
cross over cable to connect them directly. If you also have a computer
with Win98SE or later, you can use ICS. Then we get a 'budget' internet
sharing solution without a stand-alone router or hub:
        -----   cross-over  -----
ISP ---| PC1 | ------------| PC2 |
        -----     cable     -----
      ICS enabled