This is how to configure a Netopia Internet Router to accept a connection from a dial-in TA.

Problem:

The Netopia Router is not only an excellent choice for connecting a local LAN to the Internet, it can be used to accept dial-in connections from other ISDN routers or Terminal Adapters (TA) as well. With a basic understanding of IP addressing, host/network routes, and routing tables, you can simply configure the Netopia Router to accept a dial-in connection from a TA, which is the focus of this Technical Note.

Parameters:

Below is a list of hardware and firmware loads that this Technical Note is based upon:

Network Configuration:

Below is a diagram of the network configuration that will be referenced in this Technical Note.

Background:

A Terminal Adapter (TA), commonly called an ISDN Modem, is an external device that connects to the serial port of a workstation. This workstation can be virtually anything with a serial port, but usually is a Macintosh, PC, UNIX Workstation, or Terminal Server.

There are two main ways a Netopia Router can be configured to accept a connection from a dial-in TA. The first way is to assign a Static IP address and the second is to assign a Dynamic IP address. If the router assigns a static IP address, then the dial-in TA will be assigned an IP address derived from the LAN at Customer Site A. The remote user can then access services on the LAN at Customer Site A as well as the Internet.

In order to assign a Dynamic IP address to the dial-in TA, the address server within the Netopia Router must be configured. The IP address server can be configured to distribute IP addresses to hosts on the local LAN as well as to dial-in TAs through an option called 'WanIP'. With WanIP enabled, a pool of IP addresses can be allocated for dial-in TAs.

Configuration:

Here are the corresponding Netopia configuration screens:

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Enter an IP address in decimal and dot form (xxx.xxx.xxx.xxx).
Set up the basic IP attributes of your Netopia in this screen.
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The Netopia Router must first be configured to communicate with the local IP network attached to its Ethernet interface. The Netopia Router is assigned the Ethernet IP Address of 192.168.1.2 with a Default IP Gateway of 192.168.1.1.

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Enter the maximum number of dynamic IP clients to support.
Configure Address Serving (DHCP, BOOTP, etc.) here.
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In this case, the Netopia Router is set to distribute two IP addresses starting at 192.168.1.6. These addresses must not overlap any IP addresses that are currently assigned on the local LAN. After the addresses are allocated, WanIP must be turned on. This allows the Netopia Router to give an IP address to a dial-in TA that requests an address. If the address server has been configured for the first time or has been re-configured, the Netopia Router must be reset before the changes take effect.

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Return/Enter accepts * Tab toggles * ESC Cancels
Configure values which may be used when receiving a call in this screen.
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This is the Default Answer Profile for the Netopia Router. This is used to answer incoming calls, and redirect a call to a defined Connection Profile if necessary. Since the dial-in TA will be requesting a dynamic IP address from the Netopia Router as well as having a username and password, the Default Answer Profile should have Must Match A Defined Profile set to YES and PPP Authentication set to PAP. This matches the incoming call to a defined Connection Profile within the Netopia Router and uses PAP authentication by default.

DYNAMIC CONFIGURATION

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A Connection Profile must be created in order to answer and assign a dynamic IP address. This profile is for Customer Site B, which is receiving a dynamic IP address.

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This is the IP Profile Parameters in the Connection Profile for Customer Site B. NAT is OFF and the Remote IP Address and Subnet Mask are all zeros. By leaving the Remote IP Address and Subnet Mask as all zeros, this tells the Netopia Router to pull an IP address from the pool of addresses [set up in the IP Address Serving screen via WanIP] and assign it to the incoming caller. In this case the caller is the Dial-in TA.

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In this Screen you will configure the PPP/MP specific connection params.
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This is the PPP/MP Options in the Connection Profile for Customer Site B. STAC Standard compression can be used when connecting to compatible TAs. Authentication must be used in order to assign a dynamic IP address through WanIP. Specifically, the Receive User Name and Password must be filled out, since this Connection Profile is going to be used to receive calls. Note that if there are multiple Connection Profiles in the same Netopia Router, the Receive Password must be unique.

STATIC CONFIGURATION

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A Connection Profile must be created in order to assign a static IP address. This profile is for Customer Site C, which is receiving a static IP address.

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This is the IP Profile Parameters in the Connection Profile for Customer Site C. NAT is OFF and the Remote IP Address is 192.168.1.133 and the Subnet Mask is 255.255.255.255. This is the IP address that will be assigned to the Dial-in TA every time, thus this will be a statically assigned IP address.

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In this Screen you will configure the PPP/MP specific connection params.
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This is the PPP/MP Options in the Connection Profile for Customer Site C. STAC Standard compression can be used when connecting to compatible TAs. Authentication must be used in order to match the correct Connection Profile and assign the static IP address. Specifically, the Receive User Name and Password must be filled out, since this Connection Profile is going to be used to receive calls. Note that if there are multiple Connection Profiles in the same Netopia Router, the Receive Password must be unique.

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EN = Ethernet Address; AT = AppleTalk Address; CP = Profile Name; HX = Hex
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This is the Served IP Addresses screen found under Statistics, Tests, and Utilities. From this screen you can see what IP addresses have been allocated to dial-in clients.

Once the Connection Profiles have been defined and added, the Netopia Router automatically enters the IP information contained in these profiles into its IP routing table. An example of the IP routing table is as follows:

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Here you can see all the individual routes contained within the Netopia Router at Customer Site A. The first line is the default route, which in this case points to the downstream router on the Netopia Router's local Ethernet port. The second line is an internal loopback address, and the third line is the route to the Netopia Router's local Ethernet. Finally, the fourth line is a host route pointing to a single address derived from the Connection Profile for Customer Site C.

As you can see, there is no route for the Connection Profile defined for Customer Site B. This is because the Connection Profile defined for Customer Site B does not contain any IP address or subnet information. Once an incoming call has been matched against the Connection Profile defined for Customer Site B and an IP address is assigned from the IP Address Server pool via WanIP, then a route will appear in the IP Routing Table.

Note that even though the profiles for Customer Site B and Customer Site C overlap the address space of the Netopia Internet Router's Ethernet LAN at Customer Site A, the routes are still entered. This is because the Netopia Internet Router is employing ProxyARP so the hosts on the LAN at Customer Site A think that the workstations on Customer Site B and Customer Site C are part of the same network, even though they are separated by an IP router.

After the respective connection profiles for Customer Site B and Customer Site C have been entered, the IP addresses contained within these profiles must be entered in the PPP stack of the workstation connected to the dial-in TA. For example, the address of 192.168.1.133 will be manually entered into the PPP stack of the workstation at Customer Site C, as this is a statically defined IP address. A workstation at Customer Site B on the other hand does not need to enter any IP addresses as this IP address information will be acquired from and assigned by the Netopia Router. Any authentication that has been defined must be entered into the PPP stack at this point as well.

The IP address configured in the PPP stack of the workstation connected to the dial-in TA will be negotiated with the Netopia Router when the dial-in TA calls the Netopia Router. This will allow the Netopia Router to match the correct profile as well as set up IP routing. Once done, the dial-in TA will be able to access services on the LAN at Customer Site A and also the Internet through Router A.

Summary:

Setting up a Netopia Router for a dial-in TA is quite simple. First, create a profile in the Netopia Router with either a host route, network route or use WanIP, then use some type of authentication, and finally enter the IP address from the profile in the Netopia Router into the PPP stack of the workstation connected to the dial-in TA. After these steps have been followed, the dial-in TA can access services on the LAN at Customer Site A as well as the Internet.