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LAN & WAN How To

{mospagebreak toctitle= Introduction}

Introduction

If you have an inexpensive IPsec VPN endpoint router and want to connect to the LAN behind it while you're on the road, you'll need to use a VPN client. Microsoft has included an IPsec client in Win 2000 and XP, but it is not the most intuitive thing to configure, and many have given up trying in frustration.

Contrary to what you may read in the forums and newsgroups, Microsoft's IPsec client can be made to work! This article will show you how to get it up and running so you can be tunneling away in no time!

The Setup

Figure 1 shows the network configuration that I'll be using as an example. It uses all private IP addresses, so you should be able to set it up and try it without having to be actually connected to the Internet.

Figure 1: VPN Test setup

This procedure uses a Linksys BEFSX41 as the VPN endpoint router which handles two IPsec tunnels, but should also work with Linksys' BEFVP41, which supports 70 IPsec tunnels. You don't have to use these Linksys routers and could use any other router with built-in VPN endpoint. But many other inexpensive VPN endpoint routers have tunnel throughput in the 400 - 800kbps range vs. the SX41's 2.5Mbps - a limitation you'd definitely notice.


Router Configuration

Figures 2 - 4 show the relevant SX41 admin screens with entries matching the network configuration in Figure 1. You, of course, are welcome to change IP addresses to match your existing LAN scheme, but unless you know what you're doing, you may want to start with the scheme shown, get things working, then make your desired modifications.

There are some important setup points to note:

  • LAN clients should have static IPs assigned

    As you'll see later, you'll need to access computers on the other end of the tunnel by IP address. So using static IPs on the LAN computers that you want to access will make sure that the shortcuts and mapped drives you set up will always work.

    Remember that if you leave the DHCP server on the router active, be sure you assign your static IP addresses outside the range it uses!

  • The two ends of the VPN tunnel must use different subnets

    In our example, the WAN-side client is in the 192.168.3.X subnet and the wired client in 192.168.1.X, which satisfies this requirement.

  • Dynamic IPs won't work
    For reasons given in Microsoft Knowledge Base article 240262, the MS IPsec client supports tunnels between two static IP addresses only. If the mobile client is not located at a known IP address that can be entered into the SX41's VPN setup, you won't be able to use the MS client.

SX41 WAN / LAN Setup

Figure 2: SX41 WAN / LAN Setup
(click on the image for a full-sized view)

Note that the Gateway and DNS information aren't critical to getting the VPN tunnel to work. They can be whatever is required by your ISP. The WAN IP address can also be different, but its value is critical to getting the VPN connection to work and must be used in the IPsec client setup.

SX41 VPN Setup

Figure 3: SX41 VPN Setup
(click on the image for a full-sized view)

SX41 Advanced VPN Setup

Figure 4: SX41 Advanced VPN Setup
(click on the image for a full-sized view)

Although other settings are possible for Encryption and Authentication, I suggest you use the ones shown, which use the best security that the Linksys router can provide. You can, of course, use a different Pre-Shared Key, but again, must substitute the value you choose at the appropriate points in the setup.

Finally, you can try enabling the NetBIOS broadcast option, but I couldn't get network browsing to work (My Network Places), so left it disabled.


IPsec Client Configuration

Now for the hardest part - configuring the Windows IPsec client. These instructions are largely based on the app note on the Linksys website, but aren't as much of a click-by-click procedure. They do contain some critical info that Linksys left out, however, and assume you're running WinXP. You should be able to use the procedure for Win 2000, but some of the windows and default settings may look a little different.

Step 1: Add a Security Policy Snap-In to the MMC

  1. Open a Run window, type "mmc" and click OK.
  2. In the Console1 window choose File > Add/Remove Snap-in
  3. Click the Add button on the window that opens.
  4. Select IP Security Policy Management then click Add
  5. On the Select Computer or Domain window that opens, make sure Local Computer is selected, then click the Finish button.
  6. Close the other windows using their respective Close, Finish, or OK buttons, but leave the Console1 window open.
  7. Close the Console1 window. When prompted to save the settings, click Yes, navigate to your Desktop, enter a file name of "secpol.msc", and click the Save button. You should now have an icon titled secpol.msc on your Desktop.

MMC Snap-In list

Figure 5: MMC Snap-In list
(click on the image for a full-sized view)

Step 2: Create an IPsec Policy

  1. Double click the secpol.msc icon you just created on your Desktop
  2. Right-click IP Security Policies on Local Computer in the left hand window pane, and click Create IP Security Policy. The IP Security Policy Wizard window will open.
  3. Click the Next button, type a name for your policy (the example uses "wirelessvpn"). Click Next.
  4. Deselect the Activate the default response rule check box, then click the Next button.
  5. Click the Finish button, making sure the Edit properties check box is checked. A Properties window titled with the name of the security policy you just created (wirelessvpn) will open.

Security Policy Editor

Figure 6: Security Policy Editor
(click on the image for a full-sized view)

IPsec Client Configuration, continued

Step 3: Create the "To LAN" Security Rule

  1. In the wirelessvpn Properties window, deselect the Use Add Wizard check box then click the Add button to create a new rule.
  2. In the New Rule Properties window that opens, select the IP Filter List tab then click the Add button.
  3. In the IP Filter List window that opens, Type "To LAN" into the Name box, deselect the Use Add Wizard check box then click the Add button.
  4. In the Filter Properties window that opens, make the entries shown in Figure 7, making sure the Mirrored check box is checked.
  5. Click OK to close all the windows until you get back to the wirelessvpn Properties window.

"To LAN" IP Filter Properties

Figure 7: "To LAN" IP Filter Properties
(click on the image for a full-sized view)

Step 4: Create the "From LAN" Security Rule

  1. Starting at the wirelessvpn Properties window, repeat Step 3, but enter "From LAN" in the IP Filter List window and enter the info shown in Figure 8 in the IP Filter Properties window.

"From LAN" IP Filter Properties

Figure 8: "From LAN" IP Filter Properties
(click on the image for a full-sized view)

IPsec Client Configuration, continued

Step 5: Configure the "To LAN" Filter Action

  1. Starting at the wirelessvpn Properties window, select the "To LAN" rule, making sure its check box is checked, then click the Edit button
  2. The Edit Rule Properties window shown in Figure 9 should open. Check that the "To LAN" radio button is selected.

"To LAN" Security Rule Properties

Figure 9: "To LAN" Security Rule Properties
(click on the image for a full-sized view)
  1. Select the Filter Action tab, then click the Require Security radio button to select it as shown in Figure 10, then click the Edit button.

"To LAN" IP Filter Action

Figure 10: "To LAN" IP Filter Action
(click on the image for a full-sized view)
  1. Verify that the Require Security Properties window looks the same as shown in Figure 11. It's most important that the item at the top of the list have the following entries:
    - Type = Custom
    - AH Integrity = <None>
    - ESP Confidentiality = 3DES
    - ESP Integrity = MD5

    The Key Lifetimes column defaults should be 100000 / 900, but any values should work.

    Change the order of list items by selecting the item and using the Move up and Move down buttons

Require Security Filter Action Properties

Figure 11: Require Security Filter Action Properties
(click on the image for a full-sized view)
  1. If you need to change a Security method, select it and click the Edit button to open the Modify Security Method window, click the Custom radio button, then click the Settings button to open Custom Security Method Settings window shown in Figure 12.
  2. When you're done, click the OK button to close the window(s) and get back to the Edit Rule Properties window.

Custom Security Method Settings

Figure 12: Custom Security Method Settings
(click on the image for a full-sized view)

IPsec Client Configuration, continued

Step 6: Configure the "To LAN" Authentication Method

  1. Select the Authentication Methods tab, then click the Add button. The Edit Authentication Method Properties window shown in Figure 13 will open.
  2. Select the Use this string (preshared key) radio button, then enter your alpha-numeric string into the text box (the example uses "7n7eq8*").
  3. Click OK to close the window and your Authentication Methods tab should look like Figure 14.

Authentication Method Properties

Figure 13: Authentication Method Properties
(click on the image for a full-sized view)

Authentication Methods

Figure 14: Authentication Methods
(click on the image for a full-sized view)

Step 7: Configure the "To LAN" Tunnel setting.

  1. Select the Tunnel Setting tab and enter the WAN IP address of the remote VPN endpoint router. (In this example, the SX41's WAN IP is set to 192.168.3.254 as shown in Figure 15).

 

Step 8: Verify the "To LAN" Connection Type.

  1. Select the Connection Type tab and check that the All network connections radio button is selected.

"To LAN" Tunnel Setting

Figure 15: "To LAN" Tunnel Setting
(click on the image for a full-sized view)

Step 9: Save the "To LAN" rule.

  1. This completes the "To LAN" Rule configuration. Click the Close button to return to the wirelessvpn Properties window shown in Figure 16.

IP Security Policy Properties

Figure 16: IP Security Policy Properties
with completed rules

(click on the image for a full-sized view)

IPsec Client Configuration, continued

Step 10: Verify the "From LAN" Rule Properties

  1. Starting at the wirelessvpn Properties window, select the "From LAN" security rule and click the Edit button.
  2. Verify that the IP Filter List tab has the "From LAN" radio button selected (Figure 17). You can use the Edit buttons and verify that the settings are the ones programmed in Step 4.
  3. Select the Filter Action tab and verify that the settings are the ones programmed in Step 5.
  4. Select the Authentication Methods tab and verify that the settings are the ones programmed in Step 6.

"From LAN" Security Rule Properties

Figure 17: "From LAN" Security Rule Properties
(click on the image for a full-sized view)

Step 11: Configure the "From LAN" Tunnel setting.

  1. Select the Tunnel Setting tab and enter the IP address of the computer that you are configuring the IPsec policy on. (In this example, the computer's IP address is 192.168.3.149). Figure 18 shows the completed tab.

Step 12: Verify the "From LAN" Connection Type.

  1. Select the Connection Type tab and check that the All network connections radio button is selected.

"From LAN" Tunnel Setting

Figure 18: "From LAN" Tunnel Setting
(click on the image for a full-sized view)

Step 13: Save the "From LAN" rule.

  1. This completes the "From LAN" Rule configuration. Click the Close button to return to the wirelessvpn Properties window shown in Figure 16.

Step 14: Save and Assign the policy

  1. Click the OK button in the wirelessvpn Properties window to save the policy and return to the secpol window.
  2. Right-click on the wirelessvpn policy and choose Assign. Verify that there is a Yes in the Policy Assigned column for the wirelessvpn policy as shown in Figure 19.

This completes the IP policy configuration. You can either leave the Security Policy console open or close it. The assigned policy will be automatically started each time you boot your system.

Security Policy Editor

Figure 19: Security Policy Editor
(click on the image for a full-sized view)

Fix the IPsec client routing

Since a VPN tunnel is a routed connection, i.e. it connects different subnets, clients on each end of the VPN tunnel must send their packets to a router that knows where to send packets destined for clients at the opposite end. If your IPsec client and VPN router's WAN side both have public, i.e. routable IP address, you'll probably have no problem communicating once your IPsec tunnel is established.

If either or both of the IP addresses is private, however, you could be in for trouble if either the LAN or WAN-side clients have incorrect Gateways specified.

Clients on the LAN side of the VPN router will have the correct Gateway info as long as they use the router's IP address as their IP address Gateway - 192.168.1.1 in the example setup - because the router handles both Internet and VPN tunnel routing.

PN router LAN client routing

Figure 20: VPN router LAN side client routing

Figure 20 shows the output of the route print command (entered in a Command prompt or MS-DOS window) for our example LAN client. You can see that the default route - where data is sent if it doesn't match any other routes and indicated by 0.0.0.0 - is 192.168.1.1.

Gateway information for clients on the WAN side of the router may not be correct and need to be modified. In our example, the WAN-side client's IP address is 192.168.3.149, so its expected that its Gateway IP would be something in the 192.168.3.X subnet. Figure 21 shows the output of the route print command for our example WAN client.

WAN LAN client routing

Figure 21: WAN-side VPN client routing

You can see that the default route is 192.168.3.1, which happens to be the IP address of my LAN's main Internet-connected router. Although that router may know how to get our computer's data to and from the Internet, it doesn't know anything about the 192.168.1.X subnet at the other end of the test VPN tunnel. So if we fire up the tunnel that we just configured, we'll connect, then be very frustrated when nothing on the other end of the tunnel responds to a ping!


Fix the IPsec client routing (cont'd)

More sophisticated VPN gateways and IPsec client applications handle this problem by assigning virtual IP addresses to VPN clients during the authentication process. These virtual IPs are in the same subnet as clients on the gateway's LAN side, so for all intents and purposes, the client on the remote end of the tunnel looks like a full-fledged member of the local LAN.

Unfortunately, we're running a low-budget operation and neither the SX41 nor Microsoft's IPsec client can handle virtual IPs. So we have to solve the problem by fixing the Gateway IP address so that it properly points to the VPN router's WAN side IP address, i.e. 192.168.3.254.

If for some reason we need to use one router to get to the Internet and another for our VPN tunnel, adding a static route on the WAN client will make everything work. To do this for our example, just open up a Command prompt (MS-DOS) window and type:

route add 192.168.1.0 mask 255.255.255.0 192.168.3.254

This says to your client, "take all the data intended for any IP address between 192.168.1.1 and 192.168.1.254 and send it to 192.168.3.254".

WAN LAN client routing with 192.168.1.0 static route added

Figure 22: WAN LAN client routing with 192.168.1.0 static route added

Figure 22 shows the output of a route print run after the route is added. Since 192.168.3.254 is the WAN IP address of the SX41, and the remote end of our VPN tunnel, our data will now properly find its way and your ping (and everything else) should work. Note that the default gateway for all other traffic (including Internet) remains 192.168.3.1.

Tip! TIP: If you're running Win2000 or XP, you can use the "-p" option of the router add command, i.e. route add -p 198.168.1.0 ... to create a persistent static route that will be there next time you boot.

If you're running earlier Windows OSes, just open Notepad, type in the desired "route add ..." command, save as routeadd.bat and put a copy in your Startup folder. This will run the batch command every time you boot and add the desired route.


Testing the Connection

We're finally ready to test the connection. You can bring up the VPN tunnel either by clicking the Connect button on the SX41's VPN page, or trying to make a connection to a computer on the SX41's LAN side from the WAN-side client. Easiest way to do that is with a ping.

First ping from IPsec to LAN-side client

Figure 23: First ping from IPsec to LAN-side client

The Negotiating IP Security message in Figure 23 indicates that the IPsec policy is up and running and trying to establish a tunnel. But since it takes time to set things up, the ping completes before the tunnel is established, so we need to try a second ping.

Second ping from IPsec to LAN-side client

Figure 24: Second ping from IPsec to LAN-side client

The successful replies in Figure 24 show that the tunnel is up and running. Alternatively, we could use the "-n" option in the ping command to run a longer ping and see the setup in one try. Figure 25 shows what that looks like.

Long ping from IPsec to LAN-side client

Figure 25: Long ping from IPsec to LAN-side client

At any rate, once you get a successful ping you should be up and running - at least when working from the WAN-side IPsec client. As I said earlier, I could not share files on the WAN-side IPsec client from the LAN-side computer, even though I could ping it and even access a test FTP server that I set up on it.

But File and Printer sharing worked fine when going from WAN to LAN, as long as I opened the connection by opening the Windows Run box and entering the desired folder in UNC format as shown in Figure 26.

Accessing the LAN computer

Figure 26: Accessing the LAN computer

Once you have confidence in the tunnel setup process, you can skip the ping and just go right to opening the desired share. Just be patient and allow time for the tunnel to be opened!


Troubleshooting

If you're having trouble, try these troubleshooting tips:

  • Double check your settings

    I wasted a good amount of time trying to get a connection running that had the wrong IP address or setting in the maze of configuration windows used by the Windows IPsec client. So check and double-check the settings carefully!

  • Try again

    It sometimes takes two tries to get a successful tunnel setup. Don't ask me why...

  • Reboot the client

    I found that I had to sometimes reboot the IPsec client machine in order to get it to connect. First try unassigning and re-assigning the security policy via the secpol console, though.

  • Re-apply the router settings or reboot
    On the router side, I sometimes got a balky connection running by clicking the Apply buttons on the Main and Advanced VPN admin screens. Sometimes a reboot of the router did the trick.

Happy VPNing!

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