Scenario: Connecting your corporate and remote networks with a modem

A modem enables two remote locations (such as a central office and a branch office) to exchange data between them. Point-to-Point Protocol (PPP) can connect two LANs together by establishing a connection between a system in the central office and another one in the branch office.

Situation

Suppose that you have a branch and corporate networks in two different locations. Every day the branch office needs to connect with the corporate office to exchange database information for their data entry applications. The amount of data exchanged does not constitute the purchase of a physical network connection, so you decide to use modems to connect the two networks as required.

Figure 1. Connecting your corporate and remote networks with a modem
Connect your corporate and remote networks with a modem

Solution

PPP can connect two LANs together by establishing a connection between the systems as shown in the figure. In this case, assume that the remote office initiates the connection to the central office. You configure an originator profile on the remote system and a receiver profile on the central office system.

If the remote office PCs need access to the corporate LAN (192.168.1.0), the central office receiver profile will need IP forwarding turned on and IP address routing should be enabled for the PCs (192.168.2, 192.168.3, 192.168.1.6, and 192.168.1.5 in this example). Also, IP forwarding for the TCP/IP stack must be activated. This configuration enables basic TCP/IP communication between the LANs. You should consider security factors and DNS to resolve host names between the LANs.

You can also configure IPv6 access for the remote office PCs by enabling IP forwarding in the TCP/IP IPv6 Settings section of the connection profiles. IP forwarding for the TCP/IP stack must also be activated. However, even though IP forwarding is enabled, the Router Advertisement messages on the PPP link cannot be used to provide an address prefix to the PCs on either of the LANs. The reason is because the Router Advertisement messages are local to the PPP link. Therefore, IPv6 address assignment for the PCs is not affected by configuration in the PPP connection profiles.

Sample configuration

To set up a sample configuration from IBM® Navigator for i, follow these steps:

  1. Configure an originator connection profile on the remote office system.

    Ensure that you select the following information:

    • Protocol type: PPP
    • Connection type: Switched-line
    • Operating mode: Dial
    • Link configuration: This might be single line, or line pool, depending on your environment.
  2. On the General page of the New Point-to-Point Profile Properties, enter a name and description for the originator profile.
  3. Click Connection to open the Connection page. Choose the appropriate Line name or create a new one by typing a new name and clicking Open.
    1. On the General page of the new line properties, select an existing hardware resource and set the Framing to Asynchronous.
    2. Click Modem to open the Modem page. From the Name select list, choose the modem that you are using.
    3. Click OK to return to New Point-to-Point Profile Properties page.
  4. Click Add and type the telephone number to reach the central office system. Ensure that you include any required prefixes.
  5. Click Authentication to open the Authentication page, and select Allow the remote system to verify the identity of this system. Select Require encrypted password (CHAP-MD5), and enter the required user name and password information.
  6. Click TCP/IP IPv4 Settings to open the TCP/IP IPv4 Settings page.
    1. Select Enable IPv4.
    2. For Local IP address, select the IP address of the remote office LAN interface (192.168.2.1) from the Use fixed IP address select box.
    3. For the remote IP address, choose Assigned by remote system.
    4. In the routing section, select Add remote system as the default route.
  7. Click TCP/IP IPv6 Settings to open the TCP/IP IPv6 Settings page.
    1. Select Enable IPv6.
    2. Select Generate for Interface identifier.
    3. Select Yes for Allow remote system to access other networks (IP forwarding).
    4. Select *None for Address prefix.
    5. Do not select Advertise IPv6 default route or Advertise DHCPv6.
    6. Add the appropriate IPv6 routes.
  8. Click DNS to open the DNS settings page.
    1. Enter one of the following options:
      • The IP address or host name for a DNS server on the corporate LAN.
      • Select None if you do not want to add any DNS servers when the connection is established.
  9. Click OK to complete the originator profile.
  10. Configure a receiver connection profile on the central office system.
    Ensure that you select the following information:
    • Protocol type: PPP
    • Connection type: Switched-line
    • Operating mode: Answer
    • Link configuration: This might be single line, or line pool, depending on your environment.
  11. On the General page of the New Point-to-Point Profile Properties, enter a name and description for the receiver profile.
  12. Click Connection to open the Connection page. Choose the appropriate Line name or create a new one by typing a new name and clicking Open.
    1. On the General page, select an existing hardware resource and set the Framing to Asynchronous.
    2. Click Modem to open the Modem page. From the Name select list, choose the modem that you are using.
    3. Click OK to return to New Point-to-Point Profile Properties page.
  13. Click Authentication to open the Authentication page.
    1. Check Require this systemto verify the identity of the remote system.
    2. Add a new remote user to the validation list.
    3. Check the CHAP-MD5 authentication.
  14. Click TCP/IP IPv4 Settings to open the TCP/IP IPv4 Settings page.
    1. Select Enable IPv4.
    2. For the local IP address, select the IP address of the central office interface (192.168.1.1) from the select box.
    3. For the remote IP address, select Based on remote system's user ID. The IP Addresses Defined By User Name dialog will appear. Click Add. Fill in the fields for Caller user name, IP address, and Subnet mask. In our scenario, the following will be appropriate:
      • Caller user name: Remote_site
      • IP address: 192.168.2.1
      • Subnet mask: 255.255.255.0
      Click OK, and click OK again to return to the TCP/IP Settings page.
    4. Select IP forwarding to enable other systems in the network to use this system as a gateway.
  15. Click TCP/IP IPv6 Settings to open the TCP/IP IPv6 Settings page.
    1. Select Enable IPv6.
    2. Select Generate for Interface identifier.
    3. Select Yes for Allow remote system to access other networks (IP forwarding).
    4. Select None for Address prefix.
    5. Do not select Advertise IPv6 default route or Advertise DHCPv6.
    6. Add the appropriate IPv6 routes.
  16. Click OK to complete the receiver profile.