TCP/IP Development Kit
Getting Started
PREV NEXT INDEX


4. Using the TCP/IP Features

Chapter 4 provides an introduction to using the TCP/IP features on your TCP/IP Development Board.

4.1 TCP/IP Connections

Before proceeding you will need to have the following items.

The Ethernet cables and Ethernet hub are available from Rabbit Semiconductor in a TCP/IP tool kit. More information is available at www.rabbitsemiconductor.com.

  1. Connect the AC adapter and the programming cable as shown in Section 2.2, "Connections."

  2. Ethernet Connections

If you do not have access to an Ethernet network, use a crossover Ethernet cable to connect the TCP/IP Development Board to a PC that at least has a 10Base-T Ethernet card.

If you have access to an Ethernet network, use a straight through Ethernet cable to establish an Ethernet connection to the TCP/IP Development Board from an Ethernet hub or switch. These connections are shown in Figure 6.

The PC running Dynamic C through the serial programming port on the TCP/IP Development Board does not need to be the PC with the Ethernet card.

  1. Apply Power

Plug in the AC adapter. The TCP/IP Development Board is now ready to be used.

NOTE A hardware RESET is accomplished by unplugging the AC adapter, then plugging it back in.

When working with the TCP/IP Development Board, the green LNK light is on when a program is running and the board is properly connected either to an Ethernet hub or to an active Ethernet card. The red ACT light flashes each time a packet is received.


Figure 6. Ethernet Connections

4.2 Running TCP/IP Sample Programs

We have provided a number of sample programs demonstrating various uses of TCP/IP for networking embedded systems. These programs require that the user connect his PC and the TCP/IP Development Board together on the same network. This network can be a local private network (preferred for initial experimentation and debugging), or a connection via the Internet.

Obtaining IP addresses to interact over an existing, operating, network can involve a number of complications, and must usually be done with cooperation from your ISP and/or network systems administrator (if your company has one). For this reason, it is suggested that the user begin instead by using a direct connection between a PC and the TCP/IP Development Board using an Ethernet crossover cable or a simple arrangement with a hub. (A crossover cable should not be confused with regular straight through cables.) The hub and a wide variety of cables can also be purchased from a local computer store.

In order to set up this direct connection, the user will have to use a new PC (right out of the box), or disconnect a PC from the corporate network, or as yet another approach install a second Ethernet adapter and set up a separate private network attached to the second Ethernet adapter. Disconnecting your PC from the corporate network may be easy or nearly impossible, depending on how it is set up. Mobile PCs, such as laptops, are designed to be connected and disconnected, and will present the least problem. If your PC boots from the network or is dependent on the network for some or all of its disks, then it probably should not be disconnected. If a second Ethernet adapter is used, be aware that Windows TCP/IP will send messages to one adapter or the other, depending on the IP address and the binding order in Microsoft products. Thus you should have different ranges of IP addresses on your private network from those used on the corporate network. If both networks service the same IP address, then Windows may send a packet intended for your private network to the corporate network. A similar situation will take place if you use a dial-up line to send a packet to the Internet. Windows may try to send it via the local Ethernet network if it is also valid for that network.

The following IP addresses are set aside for local networks, and are not allowed on the Internet: 10.0.0.0 to 10.255.255.255, 172.16.0.0 to 172.31.255.255, and 192.168.0.0 to 192.168.255.255.

The TCP/IP Development Board uses a 10Base-T type of Ethernet connection, which is the most common scheme. The RJ-45 connectors are similar to U.S. style telephone connectors, are larger and have 8 contacts.

An alternative to the direct connection using a crossover cable is a direct connection using a hub. The hub relays packets received on any port to all of the ports on the hub. Hubs are low in cost and are readily available. The TCP/IP Development Board uses 10 Mbps Ethernet, so the hub or Ethernet adapter must be either a 10 Mbps unit or a 10/100 Mbps unit.

In a corporate setting where the Internet is brought in via a high-speed line, there are typically machines between the outside Internet and the internal network. These machines include a combination of proxy servers and firewalls that filter and multiplex Internet traffic. In the configuration below, the TCP/IP Development Board could be given a fixed address so any of the computers on the local network would be able to contact it. It may be possible to configure the firewall or proxy server to allow hosts on the Internet to contact the TCP/IP Development Board directly, but it would probably be easier to place the TCP/IP Development Board directly on the external network outside the firewall. This avoids some of the configuration complications by sacrificing some security.


If your system administrator can give you an Ethernet cable along with its IP address, the netmask and the gateway address, then you may be able to run the sample programs without having to setup a direct connection between your computer and the TCP/IP Development Board. You will also need the IP address of the nameserver, the name or IP address of your mail server, and your domain name for some of the sample programs.

4.3 IP Addresses Explained

IP (Internet Protocol) addresses are expressed as 4 decimal numbers separated by periods, for example:

216.103.126.155

10.1.1.6

Each decimal number must be between 0 and 255. The total IP address is a 32-bit number consisting of the 4 bytes expressed as shown above. A local network uses a group of adjacent IP addresses. There are always 2N IP addresses in a local network. The netmask (also called subnet mask) determines how many IP addresses belong to the local network. The netmask is also a 32-bit address expressed in the same form as the IP address. An example netmask is

255.255.255.0

This netmask has 8 zero bits in the least significant portion, and this means that 28 addresses are a part of the local network. Applied to the IP address above (216.103.126.155), this netmask would indicate that the following IP addresses belong to the local network:

216.103.126.0

216.103.126.1

216.103.126.2

etc.

216.103.126.254

216.103.126.255

The lowest and highest address are reserved for special purposes. The lowest address (216.102.126.0) is used to identify the local network. The highest address (216.102.126.255) is used as a broadcast address. Usually one other address is used for the address of the gateway out of the network. This leaves 256 - 3 = 253 available IP addresses for the example given.

4.4 How IP Addresses are Used

The actual hardware connection via an Ethernet uses Ethernet adapter addresses (also called MAC addresses). These are 48-bit addresses and are unique for every Ethernet adapter manufactured. In order to send a packet to another computer, given the IP address of the other computer, it is first determined if the packet needs to be sent directly to the other computer or to the gateway. In either case, there is an IP address on the local network to which the packet must be sent. A table is maintained to allow the protocol driver to determine the MAC address corresponding to a particular IP address. If the table is empty, the MAC address is determined by sending an Ethernet broadcast packet to all devices on the local network asking the device with the desired IP address to answer with its MAC address. In this way, the table entry can be filled in. If no device answers, then the device is nonexistent or inoperative, and the packet cannot be sent.

Private IP addresses are arbitrary and can be allocated as desired, provided that they don't conflict with other IP addresses. However, if IP addresses are to be used with the Internet, then the IP addresses must be assigned to your connection by the proper authorities, generally by delegation via your service provider.

4.5 Dynamically Assigned Internet Addresses

In many instances, IP addresses are assigned temporarily. This is the normal procedure when you use a dial-up Internet service provider (ISP). Your system will be provided with an IP address that it can use to send and receive packets. This IP address will only be valid for the duration of the call, and may not actually be a real IP address. Such an address works for browsing the Web, but cannot be used for transactions originating elsewhere since no other system has any way to know the Internet address except by first receiving a packet from you. (If you want to find the IP address assigned by a dial-up ISP, run the program winipcfg while connected and look at the address for the ppp adapter under Windows 98.)

In a typical corporate network that is isolated from the Internet by a firewall and/or proxy server using address translation, the IP addresses are not usually actual Internet addresses, and may be assigned statically or dynamically.

  1. An external IP address may be assigned statically. All you need to do is get an unused IP address and assign it to the TCP/IP Development Board.

  2. An external IP address may be assigned dynamically. You will have to get an IP address that is valid, but is outside the range of IP addresses that are assigned dynamically.

  3. A combination of the external address and port number can be translated to the combination of IP address and port number being used by your TCP/IP Development Board.

These steps will enable you to communicate from a PC on the network to the TCP/IP Development Board. If you want to communicate to the TCP/IP Development Board from the external Internet, then an actual IP address must be assigned to the TCP/IP Development Board. It may be possible to set up the firewall to pass a real IP address, or it may be necessary to connect the TCP/IP Development Board in front of the firewall to accomplish this.

4.6 How to Set IP Addresses in the Sample Programs

Most of the sample programs use macros to define the IP address assigned to the board and the IP address of the gateway, if there is a gateway.

In order to do a direct connection, the following IP addresses can be used for the BL2000:

In this case, the gateway is not used and is commented out. The IP address of the board is defined to be 10.1.1.2. The IP address of your PC can be defined as 10.1.1.1.

4.7 How to Set Up your Computer's IP Address for a Direct Connection

When your computer is connected directly to the BL2000 via an Ethernet connection, you need to assign an IP address to your computer. To assign the PC the address 10.1.1.1 with the subnetmask 255.255.255.248 under Windows 98, do the following.

Click on Start > Settings > Control Panel to bring up the Control Panel, and then double-click the Network icon. In the window find the line of the form TCP/IP > Ethernet adapter name. Double-click on this line to bring up the TCP/IP properties dialog box. You can edit the IP address directly and the subnet mask. (Disable "obtain an IP address automatically.") You may want to write down the existing values in case you have to restore them later. It is not necessary to edit the gateway address since the gateway is not used with direct connect.

The method of setting the IP address may differ for different versions of Windows, such as 95, NT or 2000.

4.8 Run the PINGME.C Demo

In order to run this program, edit the IP address and netmask in the PINGME.C program (SAMPLES\TCPIP\ICMP) to the values given above (10.1.1.2 and 255.255.255.248). Compile the program and start it running under Dynamic C. The crossover cable is connected from your computer's Ethernet adapter to the TCP/IP Development Board's RJ-45 Ethernet connector. When the program starts running, the green LNK light on the TCP/IP Development Board should be on to indicate an Ethernet connection is made. (Note: If the LNK light does not light, you may not have a crossover cable, or if you are using a hub perhaps the power is off on the hub.)

The next step is to ping the board from your PC. This can be done by bringing up the MS-DOS window and running the ping program:

or by Start > Run

and typing the command

Notice that the red ACT light flashes on the TCP/IP Development Board while the ping is taking place indicating the transfer of data. The ping routine will ping the board four times and write a summary message on the screen describing the operation.

4.9 Running More Demo Programs With a Direct Connection

The programs STATIC.C and SSI.C (SAMPLES\TCPIP\HTTP\) demonstrate how to make the TCP/IP Development Board a Web server. This program allows you to turn the LEDs on an attached Demonstration Board from the Tool Kit on and off from a remote Web browser. In order to run these sample programs, edit the IP address as for the pingme program, compile the program and start it executing. Then bring up your Web browser and enter the following server address: http://10.1.1.2.

This should bring up the Web page served by the sample program. The demo program STATIC.C is a static Web page. The sample program SSI.C allows you to control the TCP/IP Development Board from the Web browser, turning the LED indicators on and off on the Demo Board attached to the main TCP/IP Development Board.

The sample program RXSAMPLE.C (SAMPLES\TELNET\) allows you to communicate with the TCP/IP Development Board using the Telnet protocol. To run this program, edit the IP address and compile it and start it running. Run the telnet program on your PC (Start > Run telnet 10.1.1.2). Each character you type will be printed in Dynamic C's STDIO window, indicating that the board is receiving the characters typed via TCP/IP.

4.10 Where Do I Go From Here?

NOTE If you purchased your TCP/IP Development Board through a distributor or through a Z-World or Rabbit Semiconductor partner, contact the distributor or Z-World partner first for technical support.

If there are any problems at this point:

If the sample programs ran fine, you are now ready to go on.

Refer to the Dynamic C TCP/IP User's Manual to develop your own applications. An Introduction to TCP/IP provides background information on TCP/IP, and is included on the CD.

Rabbit Semiconductor
http://www.rabbitsemiconductor.com
Voice: (530) 757-8400
FAX: (530) 757-8402
sales@rabbitsemiconductor.com
PREV NEXT INDEX