I have a problem with a PC/104 board running QNX 6.6.0 that communicates over an RS232 serial link with a card that 
communicates using Modus RTU over a PPP link. This worked fine until the original PC/104 card became obsolete (Kontron 
MOPSlcdLX) and we had to find a replacement (Diamond Systems Rhodeus). Now every time the software attempts to connect 
to the Modbus link it fails The old hardware still works fine.
I wanted to debug the system over an Ethernet connection so the first thing to do was get the network hardware working 
which I eventually did. The problem is that this seems to have killed off the PPP support.

Here's the problem. After rebooting I can run ifconfig and I see this:

lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 33192
        inet 127.0.0.1 netmask 0xff000000
ppp0: flags=8050<POINTTOPOINT,RUNNING,MULTICAST>mtu 1500

After executing these commands:

io-pkt-v4-hc -ptcpip -drtl &
waitfor /dev/socket 10
ifconfig en0 172.27.12.104 netmask 255.255.255.0 broadcast 172.27.12.255
route add default 172.27.12.253
inetd &

I then do another ifconfig and I get this:

lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 33192
        inet 127.0.0.1 netmask 0xff000000
en0: flags=80008843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST,SHIM> mtu 1500
        address: 00:05:b7:e6:a3:7b
        media: Ethernet 100baseTX full-duplex
        status: active
        inet 172.27.12.104 netmask 0xffffff00 broadcast 172.27.12.255

ppp0 has vanished! Why is this? ppp0 isn't using any network hardware at all, just a serial port, so why does 
configuring the network have any effect on it?

Any help appreciated.