Project Description

Commercial vendors use the term "wireless router"; for a device that connects to the Internet, obtains one globally-valid IP address, and then allows other devices to connect through it. The other devices are given temporary addresses that are not globally-valid, and NAT software translates addresses as packets pass through it. As a result, devices behind the NAT box use standard protocols to obtain an IP address, and they think that they have been assigned a valid address. They can send packets out on the Internet and receive replies.

You will build a NAT box (wireless router) that uses IPv6. For the project, the Xinu lab Ethernet will be our Internet connection. Your NAT box will attach to the lab Ethernet, use standard IPv6 protocols, and obtain a valid IPv6 address. Your NAT box will then allow hosts on two other networks to use standard IPv6 protocols to obtain their own address. For testing, you may also choose to configure a host on the lab network.

               Lab Ethernet -- Internet connection (net 0)

---

                           |                        |
                           |                      ----
                           |                     |    |
                           |                      ----
                     -------------            host on lab Ethernet
                    |             |
                    |   Your NAT  |
                    |     box     |
                    |             |
                     -------------
                       |       |
                       |       |
                       |       |
    Othernet 1 (net 1) |       | Othernet 2 (net 2)
  -----------------------    -----------------------
        |         |                 |         |
      ----      ----              ----      ----
     |    | ...|    |            |    | ...|    |
      ----      ----              ----      ----
    hosts on Othernet 1         hosts on Othernet 1

What you will find in the base code:

In addition to sources for Xinu (Galileo version), there is code that provides three network interfaces. A network is accessed through the if_tab array. Entries in the array are:

0 - The lab Ethernet
1 - An Othernet1 (an emulated network that is Ethernet-like)
2 - An Othernet2 (an emulated network that is Ethernet-like)

The emulated networks are like an Ethernet in the sense that the frame format, maximum payload (1500 octets) and header fields are exactly the same as Ethernet. Some of the MAC addressing differs. Each interface has a unique 48-bit MAC address as usual. In place of the all-1s broadcast address, however, Othernet hardware uses a special broadcast address. When your code starts running, the interface table will already be initialized. You will find a 48-bit MAC address for each network interface in the if_tab entry for the interface.

The computer's MAC address on the lab Ethernet is in

if_tab[0].if_macucast

the Othernet 1 interface MAC address is in:

field if_tab[1].if_macucast

and the Othernet 2 interface MAC address is in:

if_tab[2].if_macucast

Similarly, the MAC broadcast address for interface X is in

if_tab[X].if_macbcast

For the lab Ethernet, the MAC broadcast address is all 1's, but for the Othernets, it is no. So, instead of filling in all 1's, always obtain the broadcast address from the interface table.

One Code Base To Rule Them All

Because many pieces of code are used for both host protocols and NAT protocols, there is only one code base. It can run as a host or as a NAT box. When you build your code, you will build it all in one code base, and then have a few run-time checks to see how to process packets.

You are given initialization code that configures the interface table at startup. When the system boots, the user is prompted for a Bind ID (the ID you were assigned in class), and then asked whether the system should be configured to be a host or a router. If a host, the user must specify the interface (a host on the lab Ethernet, a host or Othernet 1, or a host of Othernet 2). You can create multiple instances of hosts on the three networks (just use cs-console to grab a new Xinu backend, and download the image into to. The initialization code does not handle IPv6 for you -- you have to write that code. You will need to use IPv6 protocols to obtain an IPv6 address for each network, and put each IPv6 address in the interface table. The only thing the initialization code does for you is generate the necessary MAC addresses and set field if_state in each interface to indicate whether that interface is "up" or "down". For a host, only one interface will be "up"; for a wireless router, all interfaces will be "up". The initialization code also sets global variable ifprime to the index of the primary interface (0 for a wireless router and 0, 1 or 2 for a host).