[Pacabel]

I don't think it's anywhere near "close to 100%", like you're claiming.

IIS is still quite widely used for many web sites. Netcraft's latest survey results suggest just slightly under 30% of all web sites are served by it. So that's some closed-source software powering a significant portion of the web, at least.

And it's quite safe to say that those IIS installations are running on some variant of Windows, which is yet another generally closed-source software system. Then there are other non-web services (DNS, FTP, and so on) handled by such Windows systems.

There are still a surprising number of proprietary UNIX systems out there in production, on the public Internet. We're talking HP-UX, AIX, UnixWare, and even BSD/OS in some cases. There are many behind the scenes, indirectly supporting web sites and other publically-accessible services.

There is a lot of other networking gear that runs proprietary software, too.

Is open source software important to the Internet? Absolutely. Is it the "100%" you're claiming? Absolutely not.

[moreentropy]

Yes, you're right if you take it that way. I didn't mean the internet is built exclusively with open source software, but the majority of developed applications contain at least a bit of open source software, like a library, curl, Apache, PHP etc. That's much closer to 100% I think. Something where you can say "we took something for free, we give something back". Not that that's required in any way.

There's some high profile exceptions like the infrastructure parts you mentioned, but noone expects you to open source your router and unix config, there's nothing worth contributing and collaborating on here.

[cstejerean]

The one exception I've seen though is Microsoft stack applications. For whatever reason open source libraries aren't as widespread there. Sure, there are some and with things like NuGet it's getting easier to use them, but a lot of developers don't seem to bother going outside of what Microsoft offers out of the box.