Earthweb.com Practically Networked Home Earthweb developer.com HardwareCentral earthwebdeveloper CrossNodes Datamation
Welcome to PractiallyNetworked
Product Reviews

 • Routers
 • Hubs/Switches
 • Wireless Gateway
 • Wireless AP
 • Wireless NIC
 • Network Storage
 • Print Servers
 • Bluetooth Adapters
Troubleshooting
& Tutorials

 • Networking
 • Internet Sharing
 • Security
 • Backgrounders
 • Troubleshooting
    Guides

 • PracNet How To's
User Opinions
Practicallynetworked Glossary

 Find a Network Term  
 
Forums
About
Jobs
Home

  Most Popular Tutorials

• Microsoft Vista Home Networking Setup and Options
The most daunting part of upgrading to Windows Vista may be trying to figure out where in the layers of menus the networking and file-sharing options are hidden.

• Do It Yourself: Roll Your Own Network Cables
It may not be something you do everyday, but having the supplies and know-how to whip up a network cable on the spot can be very handy.

• Tips for Securing Your Home Router
Seemingly minor and easily overlooked settings can still have profound security implications. Here are some steps you can take to make sure your wired or wireless home router and by extension, your network is as secure as possible.

  Most Popular Reviews

• Microsoft Windows Home Server
If you have a home network, you'll welcome the easy file sharing, remote access and the image-based backup features of Windows Home Server.

• Iomega StorCenter Network Hard Drive
Iomega's fourth generation StorCenter Network Hard Drive brings many of the features found in higher-end storage devices down to an attractive price.

• MikroTik's The Dude
This free tool delivers many of the same capabilities that you'd find in pricey network monitoring tools. As long as you don't mind tinkering, The Dude is a decent network utility that should be worth the download.


Introduction
Separate Networks  
LAN Wiring
Install TCP/IP
Test TCP/IP
Install Sharing
Configure Clients
Secure LAN
Troubleshoot
Special Applications
Other Info
Summary

Having trouble adding a second NIC? Go here for help!

NOTE! If your PC has a USB connector, you can use it to add a second network!  Go here for more info.


There are two reasons for separating your LAN's network from your ISP's network.  These reasons are detailed below.

1) LAN security 

The only way to keep data that is not intended for the Internet from getting onto your ISP's network, i.e. the Internet, is to have your LAN on a physically separate network from that of your ISP.  Multi-homing or assigning multiple IPs to a single NIC satisfies the need for multiple IPs for Internet connection, but not the need for keeping the data packets local to your LAN.  If your data doesn't get put onto the outside network, it can't be accessed  by people who have no business accessing your data (unless you open a hole into your network by not properly securing your LAN).

 

2) Avoiding problems with your ISP

a) MAC address authentication
Many ISPs use Dynamic Host Configuration Protocol (DHCP) to assign a unique IP address to your computer's NIC or Network Adapter.   They also sometimes bind (or lock) your connection to the MAC address that is hard-coded into the NIC that was present when they installed your service.  Each time you boot your computer or power cycle your cable modem, the modem locks onto the first MAC  it finds.

If you have your cable or DSL modem plugged into a hub along with all your computers, then there is no guarantee of which MAC address will be found  If it's not the one that was present at your sevice install...presto! NO CONNECTION!

Some people go through the trouble of disconnecting everything except the computer that was there during installation, booting, reconnecting everything else, etc...   But do you really want that hassle?

 

b) control of your IP addresses
Most small LANs have a single "Class C" subnet.   By definition, all devices on a subnet must have IP numbers with the same prefix, for example 192.168.0. When you create your own subnet by using a second NIC, then you control the IP numbers that are assigned (as long as you use the non-routable addresses designated for "local" network use, which are

10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255.255
(per RFC 1918
http://info.internet.isi.edu:80/in-notes/rfc/files/rfc1918.txt)

If you have everything plugged into one NIC and don't install proxy, NAT or other routing software, then you'd have to use IP numbers in your cable ISP's subnet.  Those IPs are not yours to assign and "borrowing" them is another way to get on the wrong side of your cable ISP, and again, possibly get you disconnected.

Example:
  Let's say your cable company assigned the IP number 25.122.7.33 to your machine when they installed your modem.  This means that your machine is on the subnet 25.122.7 .  There can be 254 different machines on this subnet, and their full addresses are 25.122.7.1 to 25.122.7.254 (the numbers 0 and 255 are reserved for special purposes). 

Any machines physically connected to the 25.122.7 subnet must have an IP number in this address range.  If you try to assign a number outside this range, your machine won't be able to send or receive Internet data.  If you try to assign a number that is already in use, you'll probably get a message that says that the number is already in use and that your adapter is being disabled or something similar.

 

c) DHCP server conflicts
Most Internet sharing programs include DHCP servers that can be enabled and used to automatically assign the correct IP address information to your Client computers.  However, as described in item a) above, your ISP may also use a DHCP server to assign your IP address to you.  

If you don't separate your LAN from your ISP's, then your DHCP server may try to hand out addresses to other computers on your ISP's subnet.  This is usually a quick way to get "de-provisioned", i.e. shut off, by your ISP.

So make things easy on yourself and keep on friendly terms with your ISP and keep your shared LAN separated from their network.



Earthwebnews.com Earthweb developer.com HardwareCentral earthwebdeveloper CrossNodes Datamation


Home | Networking | Backgrounders | Internet Sharing | Security | HowTo | Troubleshooting | Reviews | News | About | Jobs | Tools | Forums