8.4 Sharing a Network Connection over IrDA

If you want to accept PPP connections from other IrDA-enabled devices, start pppd listening on the ircomm device that corresponds to your IrDA adapter (these devices are numbered ircomm N , where N is a number from 0 to one less than the number of IrDA adapters on your system). See Chapter 7.

In most cases, you'll want more than just a PPP connection. If you want to connect to the Internet from the other device, you'll need your Linux box to act as a NAT router, and you'll also need to tell the PPP client device where it can find its name server. We've found that the following script works well (you may need to customize $LOCAL , $REMOTE , $DNS , $INTERFACE , and $IRDEV ):

 #!/bin/sh     LOCAL=192.168.2.1   # IP address for the server running pppd REMOTE=192.168.2.2  # IP address for the device DNS=192.168.254.1   # A DNS server INTERFACE=wlan0     # Interface that connects to the network IRDEV=/dev/ircomm0  # Infrared device     # Set up forwarding. # echo 1 > /proc/sys/net/ipv4/ip_forward /usr/sbin/iptables -t nat --flush /usr/sbin/iptables -t nat -A POSTROUTING -o "$INTERFACE" -j MASQUERADE     # Start the PPP link. # /usr/sbin/pppd $IRDEV 115200 local \      $LOCAL:$REMOTE ms-dns $DNS \      silent noauth persist nodetach \ 

8.4.1 Connecting from Linux

To connect from another IrDA-enabled Linux device, align the infrared ports and then issue the following command:

 #  pppd /dev/ircomm0 115200 usepeerdns local nodetach defaultroute  

You may need to bring down any existing network interfaces, because the defaultroute option generally does not override existing default routes. Some versions of Linux ship with a modified pppd that lets you use the replacedefaultroute option to replace any existing default route.

8.4.2 Connecting from Palm OS

To set up the connection to the Linux system:

1. Select Prefs Communication Network (Figure 8-5)

2. Give the new service a name and select IR to a PC/Handheld under Connection as shown in Figure 8-6.

Figure 8-5. Opening Network Preferences on the Palm

Figure 8-6. Setting up a new network connection on the Palm

To connect, align the infrared ports of your Linux system and the Palm. Return to Network preferences, select the service you created in Step 3, and click Connect. When you are done with the network connection, return to the Network preferences and click Disconnect.

To test out your connection, ping a remote host. To do this, stay in the Network preferences after the connection is made and select Menu Options View Log. Scroll to the bottom of the log, use Graffiti to write ping hostname and then use the Graffiti stroke for a carriage return (a diagonal stroke in the ABC region from upper right to lower left). If you've made the network connection successfully, you'll be able to ping a remote host, as shown in Figure 8-7. (Be sure that the remote host accepts pings and that your network does not block them).

Figure 8-7. Pinging a remote host from the Palm

8.4.3 Connecting from Pocket PC

Making a simple PPP connection is more complicated under the Pocket PC than under Palm OS. To set up the connection to the Linux system with Windows Mobile 2003.

1. Click the Start menu, and choose Settings Connections. The Connections settings will appear, as shown in Figure 8-8. Click Add a New Modem Connection.

Figure 8-8. Connection settings on the Pocket PC

2. You'll be prompted to choose a name for the connection and to select a modem. Select Generic IrDA and click Next .

3. You'll be prompted to type in a phone number. Pick anything you want ”it's just a placeholder ”and then click Next.

4. On the next screen, you'll be asked to supply a username, password, and domain. Leave these all blank and click Advanced.

5. On the General tab of the advanced settings, set the Baud rate to 115200 and uncheck Wait for Dial Tone before Dialing, as shown in Figure 8-9.

Figure 8-9. Specifying general settings on the Pocket PC

6. Click the Port Settings tab and check the box labeled Enter Dialing Commands Manually, as shown in Figure 8-10. Click OK.

7. You'll be back at the dialog (username, password, and domain) that you originally saw in Step 4. Click Finish to return to the Connections settings.

Figure 8-10. Specifying port settings on the Pocket PC

To connect to the Linux system, align your infrared ports, and then:

1. Click the Start menu and choose Settings Connections. Click Manage Existing Connections under the same section where you created the connection originally.

2. A list of connections appears, showing the connection that you created. Tap and hold on it to bring up a context menu and select Connect, as shown in Figure 8-11.

Figure 8-11. Making the connection on the Pocket PC

3. You'll be prompted for a username, password, and domain. Leave these blank and click Save Password to have this (hopefully) never bother you again, and then click OK.

4. After a few seconds, the Manual Dial Terminal should appear full of PPP gibberish, as shown in Figure 8-12. Click OK, and you should get confirmation of your connection, as shown in Figure 8-13.

Figure 8-12. The Manual Dial Terminal on the Pocket PC

Figure 8-13. Confirming the connection on the Pocket PC

You can hide this notification and make it reappear by clicking its icon at the top of the screen. Use the Disconnect button to disconnect when you are finished. Test your connection by visiting a web site with Pocket Internet Explorer.