Are router firmware based on linux?

Question

I was reading this book "the linux command line" and in the introduction it states that linux is internet backbone starting from servers to router infrastructure.

That got me thinking to what extent this would be true.

Yes I do have dd-wrt installed on my home router. But what about stock firmware of my belkin router? Is it linux based?

I saw a list of distributions for routers: http://en.wikipedia.org/wiki/List_of_router_and_firewall_distributions

Incredibly long one!

I know cisco develops IOS, and some of their low end routers are linux, but what about IOS? is it unix derivative? or written from scratch?

Solution

Linux is most common at the low end, where its strong built-in networking gives it a leg up over less capable embedded OSes that used to be used for tasks like this. Basically, using Linux saves companies considerable money vs. licensing an OS capable enough to match it for the purpose.

Cisco IOS is not based on Linux, or on any other common OS, that I know of. It may well be entirely custom. Cisco is certainly large enough to have accomplished that. It can't be Linux-based, since they'd have to be giving away the GPL'd parts at least, and they aren't doing that.

Cisco's largest competitor in the router arena, Juniper Networks, uses Junos on most of their equipment. It is based on FreeBSD.

As for your Belkin router, the F5D8235-4, it is indeed based on Linux. That link takes you to a page linking to tarballs containing the GPL source code each of their products uses, as is required under the GPL. I had a peek inside the F5D8235-4 tarball and found a copy of the Linux kernel sources inside.

To answer this question for other routers, you can do what I did: look for a place to download GPL'd sources for the router, or look for copies of the GPL license in the product manuals or downloads. The GPL also requires that they tell recipients of products containing GPL-licensed software about the license. The fact that you got a copy of the GPL doesn't mean you have a product based on Linux, but it does mean you should be able to download the source code from the company somehow, and thus answer the question by examination.

Another method is to try telnetting to the device. Many Linux-based home gateway routers will respond to Telnet. If it lets you in, some elementary exploration can answer the question; a uname -a command, for instance.

Another big clue is discovering that it runs BusyBox. BusyBox runs on other OSes besides Linux, but it's very commonly used on embedded Linuxes, whereas the more minimal stock BSD toolset means embedded BSDs tend to go with the standard, rather than the even more stripped-down BusyBox tools.

Comments

[ChrisR.]

Isn't IOS (Internetwork Operating System) closed source?

[Admin]

@ChrisR. Yes it is.

[Rafael Ortega]

@salivan ... "what is difference between bsd license and gpl?" ... talks.dixongroup.net/nycbsdcon2008 ... a starting point about BSD license vs GPL. I bet this is the most entertaining explanation... :-)

[Warren Young]

@salivan: You still haven't told us the model number. You aren't under the impression that all Belkin routers have to be based on Linux or none of them, are you? It could easily be a mix, especially now that Belkin owns Linksys.

[Rafael Ortega]

@WarrenYoung Yes, I was under impression that business/development/cost wise it would be profitable to develop 1 system and stick to it, instead of writing 4 different OSs that essentially do the same thing. Belkin F5D8235-4

[Warren Young]

@salivan: Engineers are a fractious lot and arm-twist business types to let them use the tools they prefer. No two engineers agree on the same set of preferred tools, so a company of any size has a mish-mash of technologies in use at any one time. The spread grows over time. Anyway, yes, the F5D8235-4 is based on Linux. See edit above.