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Testing and Troubleshooting

Once the first system was built, we tested the PPP connection locally by connecting a DOS-based PC to it, with FTP Software’s PC/TCP PPP stack. Everything looked fine; a ping from the PC to the Linux box worked, which meant that PPP was happening. Then we pinged the Internet router successfully, which meant that the IP forwarding also worked.

At this point, it was time to "clone" the first machine to create the remote router. A quick modification of the Slackware root diskette was in order. We deleted tar and replaced it with cpio, so that we could restore a backup of the entire filesystem, including device files. We backed up the first system over the network to the unixhost:

cd / ; find . -print | cpio -ocv | rsh unixhost -l username
dd of=/dev/rmt1

Then, we booted the second machine, a Dell 486/33SL with 8Mb and a 250Mb hard drive. We started with the Slackware boot diskette, and inserted the modified root diskette when prompted for the root diskette.

We used the convenient Slackware setup program to format and setup the root and swap partitions identically to the first machine. Specifically, we made the root partition and the swap partition the same partition letter as the first machine, /dev/hda3 and /dev/hda2 respectively. This ensured that the root filesystem and swap partition would be the "cloned" kernel expected them to be. Then we exited setup, started the network, mounted the new root filesystem, and restored the filesystem from the unixhost tape drive.

#ifconfig tr0 netmask broadcast add -net 167.195.160 netmask
#mount /dev/hda3 /mnt
#cd /mnt ; rsh unixhost -l username "dd if=/dev/rmt1" | cpio -icv

We shut down the clone, removed it from the LAN, and rebooted. We then changed the IP number and network on the clone machine as shown in Figure 1 (full startup files for both machines are detailed in Figure 4).

We set the clone up three feet away from the first machine, using a directly connected null-modem cable, in order to test the PPP without the complications of ISDN or geographic distance. We connected a hub and a PC to the cloned machine to simulate conditions at the remote site. This was where routed caused everything to fall apart. As soon as we replaced routed with gated, all was well.

We moved the clone to the remote site, connected the ISDN terminal adaptors, auto-dialed between them, then plugged them into both of our new Linux routers. Of course, one of the ISDN modems turned out to be configured for the wrong type of channel. As soon as that was corrected, everything worked perfectly.