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Comment by cperciva | Hacker News Reader

I must admit, some secret part of me always hopes I'll be in a situation on an airplane where they need an emergency perl script written

On a flight from Sydney to Vancouver earlier this year, the in-flight entertainment system on my plane was broken. I spoke up: "Hi, I have a doctorate in computer science and I know a bit about these systems... want me to take a look?"

I was surprised when they agreed, brought me up to the front galley, and showed me their interface to the entertainment system (alas, the server itself was in the ceiling and not accessible). I ended up pulling out my laptop, borrowing a cat5 cable from one of the flight attendants (all of mine were in my checked suitcase) and running tcpdump on the plane's network. Alas, while that allowed me to diagnose the problem, I lacked the serial cable needed to connect to the server's console and wasn't able to fix it.

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Don't leave us hanging :) What was the problem?

The AV server had been replaced after there were problems with it on the previous Vancouver-Sydney flight (the cabin crew told me this) but it looked like the DHCP server had not been updated with the new MAC address (or the replacement server hadn't been programmed to use the same MAC address as the one it replaced).

I considered sending DHCP responses to the server myself, but decided that injecting traffic would be too risky during flight... especially since I was flying back from a conference where one of the speakers had been talking about inadequate firewalling between IFE systems and aeronautical control systems.

> inadequate firewalling between IFE systems and aeronautical control systems

How is this possible? Why do they even need to be on the same network?

I didn't work on that particular system, but I can say from experience that systems on an airplane are a lot more interconnected than you might expect, just from seeing them as a passenger. There probably is a sequence diagram somewhere that says, "Inform pilot of movie progress, reduce intercom volume, dim cabin lights, reset passenger overhead lights, consult schedule to determine selected movie, lower projector screen, play movie." And there are probably similar diagrams for landing, maintenance, encountering problems, and so forth.

Furthermore, the IFE might not need to talk to critical control systems, but they both might need to talk to some of the same other systems. Cabin lights seem like a likely candidate. Displays for the pilot, too. And maybe maintenance fault logs.

It can be a real hassle to have totally isolated systems on different networks. You can do it, but you need a Good Reason. The easy thing, from an engineering perspective, is to make it so everything can talk to everything.

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