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Internet Connection Sharing in Windows XP

How to use Internet Connection Sharing

To use Internet Connection Sharing to share your Internet connection, the host computer must have one network adapter that is configured to connect to the internal network, and one network adapter or modem that is configured to connect to the Internet.

On the host computer

On the host computer, follow these steps to share the Internet connection:

1.	Log on to the host computer as Administrator or as Owner.
2.	Click Start, and then click Control Panel.
3.	Click Network and Internet Connections.
4.	Click Network Connections.
5.	Right-click the connection that you use to connect to the Internet. For example, if you connect to the Internet by using a modem, right-click the connection that you want under Dial-up.
6.	Click Properties.
7.	Click the Advanced tab.
8.	Under Internet Connection Sharing, select the Allow other network users to connect through this computer's Internet connection check box.
9.	If you are sharing a dial-up Internet connection, select the Establish a dial-up connection whenever a computer on my network attempts to access the Internet check box if you want to permit your computer to automatically connect to the Internet.
10.	Click OK. You receive the following message: When Internet Connection Sharing is enabled, your LAN adapter will be set to use IP address 192.168.0.1. Your computer may lose connectivity with other computers on your network. If these other computers have static IP addresses, it is a good idea to set them to obtain their IP addresses automatically. Are you sure you want to enable Internet Connection Sharing?
11.	Click Yes.

The connection to the Internet is shared to other computers on the local area network (LAN). The network adapter that is connected to the LAN is configured with a static IP address of 192.168.0.1 and a subnet mask of 255.255.255.0

To view a video about how to configure the host computer for Internet Connection Sharing, click the Play button () on the following Windows Media Player viewer:

http://support.microsoft.com/servicedesks/ShowMeHow/3061261.asx

Note To view this video, you must use Windows Media Player 7.0 or later.

For additional information about how to obtain Windows Media Player version 7.1, click the following article number to view the article in the Microsoft Knowledge Base:

299321 (http://support.microsoft.com/kb/299321/) Description and availability of Windows Media Player 7.1

On the client computer

To connect to the Internet by using the shared connection, you must confirm the LAN adapter IP configuration, and then configure the client computer. To confirm the LAN adapter IP configuration, follow these steps:

1.	Log on to the client computer as Administrator or as Owner.
2.	Click Start, and then click Control Panel.
3.	Click Network and Internet Connections.
4.	Click Network Connections.
5.	Right-click Local Area Connection, and then click Properties.
6.	Click the General tab, click Internet Protocol (TCP/IP) in the This connection uses the following items list, and then click Properties.
7.	In the Internet Protocol (TCP/IP) Properties dialog box, click Obtain an IP address automatically (if it is not already selected), and then click OK. Note You can also assign a unique static IP address in the range of 192.168.0.2 to 192.168.0.254. For example, you can assign the following static IP address, subnet mask, and default gateway: IP Address 192.168.0.2 Subnet mask 255.255.255.0 Default gateway 192.168.0.1
8.	In the Local Area Connection Properties dialog box, click OK.
9.	Quit Control Panel.

To view a video about how to confirm the LAN adapter IP configuration, click the Play button () on the following Windows Media Player viewer:

http://support.microsoft.com/servicedesks/ShowMeHow/3061262.asx

Note To view this video, you must use Windows Media Player 7.0 or later.

For additional information about how to obtain Windows Media Player version 7.1, click the following article number to view the article in the Microsoft Knowledge Base:

299321 (http://support.microsoft.com/kb/299321/) Description and availability of Windows Media Player 7.1

To configure the client computer to use the shared Internet connection, follow these steps:

1.	Click Start, and then click Control Panel.
2.	Click Network and Internet Connections.
3.	Click Internet Options.
4.	In the Internet Properties dialog box, click the Connections tab.
5.	Click the Setup button. The New Connection Wizard starts.
6.	On the Welcome to the New Connection Wizard page, click Next.
7.	Click Connect to the Internet, and then click Next.
8.	Click Set up my connection manually, and then click Next.
9.	Click Connect using a broadband connection that is always on, and then click Next.
10.	On the Completing the New Connection Wizard page, click Finish.
11.	Quit Control Panel.

When you now start Microsoft Internet Explorer, the client computer will try to connect to the Internet by using the host computer's shared Internet connection.

To view a video of how to configure the client computer to use the shared Internet connection, click the Play button () on the following Windows Media Player viewer:

http://support.microsoft.com/servicedesks/ShowMeHow/3061263.asx

Note To view this video, you must use Windows Media Player 7.0 or later.

For additional information about how to obtain Windows Media Player version 7.1, click the following article number to view the article in the Microsoft Knowledge Base:

299321 (http://support.microsoft.com/kb/299321/) Description and availability of Windows Media Player 7.1

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Troubleshooting

When you turn on Internet Connection Sharing on the host computer, the host computer's LAN adapter is automatically assigned the IP address of 192.168.0.1. Therefore, one of the following situations may occur:

•	IP address conflict Each computer on the LAN must have a unique IP address. If more than one computer has the same IP address, an IP conflict occurs, and one of the network adapters turns off until the conflict is resolved. To resolve this conflict, configure the client computer to automatically obtain an IP address, or assign it a unique IP address.
•	Loss of network connectivity If your network is configured with a different IP address range than Internet Connection Sharing uses, you will lose network connectivity with the host computer. To resolve this issue, configure the client computers to automatically obtain an IP address, or assign each client computer a unique IP address in the range of 192.168.0.2 to 192.168.0.254.

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REFERENCES

For additional information about Internet Connection Sharing, click the following article numbers to view the articles in the Microsoft Knowledge Base:

234815 (http://support.microsoft.com/kb/234815/) Description of Internet Connection Sharing

308552 (http://support.microsoft.com/kb/308552/) Description of the Network Setup Wizard in Windows

308021 (http://support.microsoft.com/kb/308021/) Resources for troubleshooting Internet Connection Sharing in Windows XP

308006 (http://support.microsoft.com/kb/308006/) Troubleshooting Internet Connection Sharing in Windows XP

310563 (http://support.microsoft.com/kb/310563/) Description of Internet Connection Sharing in Windows XP

What I did for internet connection sharing from my Kubuntu PC to a Windows XP PC

In my case I did the following

• I created a file named connection, made it executable and copied the following contents into it
• ifconfig eth0 192.168.0.1
• iptables -A FORWARD -i eth1 -o eth0 -s 192.168.0.0/24 -m state --state NEW -j ACCEPT
• iptables -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT
• iptables -A POSTROUTING -t nat -j MASQUERADE
• sh -c "echo 1 > /proc/sys/net/ipv4/ip_forward"
  

• In the windows computer I set the following configurations
• IP 192.168.0.30
• Subnet mask 255.255.255.0
• Default Gateway 192.168.0.1
• DNS 192.168.0.1

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The following was in the Official Ubuntu Documentation at
https://help.ubuntu.com/community/InternetConnectionSharing

InternetConnectionSharing

• On Server:

  • You will need one or two network cards in the server, or a network card and a PPP interface. One network card connects to your internal network, we will call this card eth1. The other, or your PPP interface, connects to the internet, we will call this eth0 or ppp0. If you are running both networks off of the same card, then use eth0:0 for the internal network and eth0 for the internet.

  • First, configure the interface of your network card, for example using eth0 or eth0:0 like so:

    $sudo ifconfig eth0 192.168.0.1

  • then configure NAT on iptables:

    $sudo iptables -A FORWARD -i eth1 -o eth0 -s 192.168.0.0/24 -m state --state NEW -j ACCEPT
    $sudo iptables -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT
    $sudo iptables -A POSTROUTING -t nat -j MASQUERADE 

(rule1 allows forwarded packets (initial ones), rule2 allows forwarding of established connection packets (and those related to ones that started), rule3 does the NAT.):

$sudo sh -c "echo 1 > /proc/sys/net/ipv4/ip_forward"

(in case of ADSL, you sometimes need to use ppp1)

FYI: There is a "Bug" in Gutsy (Ubuntu 7.10) and you will need to make a small edit in /etc/sysctl.conf

Add these lines :

net.ipv4.conf.default.forwarding=1
net.ipv4.conf.all.forwarding=1

Launchpad Bug Report

• Then move on to the clients:

  • Unconfigure all network cards:

    $sudo /etc/init.d/networking stop

  • Set the new IP address with the same network range as the server (for example 192.168.0.xxx)

    $sudo ifconfig eth 

    , where eth is the network card and is the IP for the client.

  • Configure routing:

    $sudo route add default gw 

    , where is the server IP (in this example 192.168.0.1).

  • Add gateways, ask the server maintainer for the DNS and include then on /etc/resolv.conf such as:

And you are all set, any questions/comments, mail me =)

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A beginner's working example of a Ubuntu Desktop with 2 nic cards, sharing internet connection http://ubuntuforums.org/showthread.php?p=3713684

Other approaches

Internet connection sharing is called masquerading or Network Address Translation.

To serve dynamic addresses, you need to be a DHCP server. You also need to do IP and DNS masquerading. Easy:

Install dnsmasq (a DNS masquerade as well as a DHCP server) and ipmasq (IP masquerading).

Configure dnsmasq by editing the config file and making it go: (basically, two things)

sudo /etc/init.d/dnsmasq restart

configure ipmasq to allow dhcp requests, otherwise you need to stop ipmasq to make a connection. You need to copy a .rul from the documentation directory into the /etc config and edit the interface name. Then reconfigure ipmasq to start after networking has been started

sudo dpkg-reconfigure ipmasq.

Another approach --- set up Firestarter, to run connection sharing, set up dhcp3-server, and set its configuration to listen to the correct eth*. To change this later, run sudo dpkg-reconfigure dhcp3-server.

Basically, you need to have Firestarter active/turned on/protecting, to have the connection shared.

When you install dhcp3-server, it will place a sample config file in your /etc/dhcp3 folder, called dhcpd.conf. I suggest you install dhcp3-server first, and then firestarter, cause if you are lucky, firestarter will set up a new config file for dhcp3 for you.

If you are less lucky, well, this file works, and I got it from another person, so it seems generic enough: http://www.mts.net/~danb/sampledhcpd.conf . Remember to change the DNS server if using that file, cause you don't want name resolution to be done by my ISP, it will be slow. To find what DNS server your Ubuntu is using: System>Admin>Network>DNS tab.

At any time that changes are made to your dhcpd.conf file, restart the server - sudo /etc/init.d/dhcp3-server restart will do it. Alternatively, every time you run the sudo dpkg-reconfigure dhcp3-server, at the end, your server will restart.

There are several issues that I had...first of all, the Firestarter firewall won't even start if you don't have it configured to listen to the right interface...You can change which one it listens to in Preferences --> Network Settings. The Local network connected device must be the same as you have dhcp3-server listening to, of course, both checkboxes under that need to be checked. The Internet connected network device will be the one that is configured for Internet. Now, I have two NICs, but I have pppoe configured on eth0, and I have Internet connection sharing configured on the same one, cause eth0 is also configured for a static 192.168 internal IP for my internal network.

Internet Connection Sharing Documentation thread http://ubuntuforums.org/showthread.php?s=88b74f79f0ab07638e6b361c09040b45&t=503287

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