February 2007 Archives

You know that funky option in your computer's BIOS, "Network Boot Agent"? Okay, so it goes by a lot of names. "Networking Boot ROM," "Integrated NIC ROM," the list goes on. Maybe you've seen the "Press F12 to network boot option" around. You see this, your curiosity gets the best of you, so you hit F12. Suddenly your computer is scanning the ethernet subnet for a DHCP server and acquiring an IP address!

Only to go away really fast and continue booting up your computer without really telling you much. Awfully anti-climatic, if you ask me. I mean really, you add an option to your boot order, hit the button to make it go, and it starts doing all of these wonderful things only to promptly "stop" and advance in the boot order without telling you a thing.

Let's clear up the mysticism: what you (typically) just activated and attempted to use was this thing called PXE. PXE stands for "Preboot Execution Enviroment." Wikipedia has an awesome article (also available on the German Wikipedia) on the details of PXE, but I may be biased in thinking that because I assisted in it's writing. Admittedly, it has changed a fair amount over time, but the content of the article as a whole is still there. Now, come on, I know you're lazy and didn't read all of that artice. I'd even go as far as to say you didn't read any of it. So, if you're still wondering "What is this PXE thing?" I'll answer that here and now.

PXE is in it's most simple terms, a boot device. At least, that's what it appears to be to your BIOS. However, instead of spinning up your hard drive, it fires up the NIC in your computer and starts probing for DHCP (or BOOTP, but that won't be covered here. It's pretty much obselete). Then, once it has acquired an IP address with the needed DHCP options set, the PXE ROM goes about downloading and executing files off of a TFTP server.

So, what is PXE? A way to boot your computer without the need of a hard drive or any real physical storage medium. It's commonly known as netbooting. The process, as outlined above, is pretty simple. The NIC scans for a DHCP server, and then acquires an IP address. In it's brief exchange with the DHCP server, the client is sent several "DHCP Options" along with the IP address, one of which is commonly known as "filename." If the client does not find this option, it gives up and (typically) advances with the boot order. If it finds this option, however, it tries to download the specified file off of a TFTP server. An additional option which can be given is "next-server" which is the IP address of the TFTP server to contact in order to download "filename." If the "next-server" paramater is omitted, then it defaults to the same IP as the DHCP server, and likewise tries to download "filename" and in turn, execute the file it downloads.

That's it. That right there is the majority of what PXE "is" and how it works. Why did your computer acquire an IP address only to just continue on booting? Because you didn't have the needed DHCP options set. To be fair, the huge majority (99%) of all home routers lack the ability to configure the needed options, so it's likely you've never even heard of "DHCP Options." However, my personal feelings on how retarded home routers are do not belong here.

Let's move on to a "What is/isn't PXE" list real quick.

PXE is:

• A way of booting your computer without a hard drive or CD-ROM (or floppy, for you old people)
• Very useful - does not require physical storage in the computer to work
• Light - DHCP options and a TFTP server are the only requirements
• Powerful - ever wonder what it'd be like to walk into a room of computers, turn them all on, press F12, and come back an hour later to fresh installs of (your OS here)? I've done it with Windows, and I must say, it's management/installation/reinstallation bliss.

PXE isn't:

• A way to "network boot this ISO image I have here" (but it is possible given time)
• ... even related to the boot loader or actual software side of the computer. It downloads a file, it runs a file, that's IT. It's not a kernel, it lacks any real form of hardware support. It exists to run something else, not run your system for you.
• Diskless booting. Sure, it CAN do that, but again, PXE isn't there to run your system for you.
• Thin clients. Refer to above statement. And statement above said above statement. You get the idea.
• Overly detailed. When I started messing with PXE, it made little sense as a whole and felt very hacked together once I got it working. This was largely due to a lack of documentation.

In sum, PXE has a vast number of capabilities, but PXE in and of itself is pretty much worthless. You can't feed it an ISO of a bootable CD and say "Go!," nor can you magically make an entire lab of computers run Firefox without hardrives. I'll admit it in full: PXE does not run your computer for you. You are in charge of that. But, it certaintly can help in installing OSs or running entire diskless labs. If this seems unclear, I'm sure the latter articles will clear it up.

In the next few parts, I'll use the following software: ISC DHCP, tftp-hpa, pxelinux, memtest86+, and maybe a little bit of the debian installer. Who knows, maybe I'll splurge and go overboard with some CentOS installation over PXE, but for the most part, you're safe with the previous list. (Don't go downloading all of the debian CDs though, as we won't be using them.)
It should also be noted that I have written and maintain the only wiki (that I know of anyways) that is dedicated to the topic of PXE booting. For the curious, that wiki is available here.

Microsoft Windows Vista was recently released. To be honest, I'm excited for it. It brings countless good things to the windows world, and to be blunt, XP is beginning to show it's age. (Windows 2000 is timeless though, in my opinion. Maybe I'll post my thoughts of Win2k vs WinXP vs Vista eventually, we'll see.) Let me say that one more time:

I am glad that Vista was released. It is an upgrade. It is worth purchasing. There are too many advantages, both in terms of the technical side of Vista, and user interface side of Vista, to think otherwise. Once again: Vista is good.

I run a network for small business. It's a Windows network, through and through. Pair of Win2k3 servers in two locations, a copy of MSSQL, and two point to point T1 lines linking three buildings together. It's all built on Windows Server technology, and I'll be dead honest here: I haven't found a better, easier to use, scalable server system than that of Windows Server. Let's do this in bold too: Windows Server is good. Windows Server makes me happy, and it makes all of the employees happy (even though they could care less, they just want to work.).

So what did I do the day Vista was released to the public?

Blow away my last copy of WinXP. Destroy it. That was also my last copy of anything Microsoft that I use for my own personal computing. Hear that? No more WinXP in my blood. No more XP on anything that I personally use, be it at home or at school. Bye WinXP. Vista is out, and I don't care what the critics and journalists say: Vista is worth purchasing.
So, I replaced my copy of XP with Linux.

And it feels good. So very good.

My number one complaint about Vista is two-fold: versions, and limited features/too many features. I run networks, I build networks. My primary computer has five different NICs in it, three of them are 1000mbit and two of them are 100mbit. Further, I have a PCI wifi card in there, and my router is a soekris box with a hand-rolled distro running on a CompactFlash card. I like my networks, and I like them a lot.

Know what I like MOST about networks? Networking. You know, intra-device communication. The flexibility that networking provides. File is on another computer? So what, just click click, bam, your file is in front of you, even if you're on the opposing side of the globe. Networking is fun.

Networking with Vista is not. Now, don't get me wrong: new TCP/IP stack? Re-worked IPSEC support? Hate to break it to you people, but with about seven clicks (with Vista) I can literally move three buildings from open TCP/IP to straight IPSEC communications between ALL computers, using SSL certificates. Seven clicks, and I have a network that runs IPSEC flawlessly, and effortlessly. And no, the IPSEC implementation isn't broken: it works, and it works well. I'm not trying to say that Vista has horrible networking with that earlier line. The network stack, the possibilities... I love.

What I hate is the arbitrary limitations imposed upon the different versions of Vista. For example, lower end versions of Vista cap the number of connections you can have to any specific computer at five. Let's count.. my desktop, my other desktop, my laptop, my brother's computer, the family computer, my sister's computer, and my xbox. Oops, seven. Vista Home Basic is out of the running.

Also, Remote Desktop (aka 'RDP') has been essentially removed from Vista Home editions. I can't bring up the computer's display at will anymore, I have to install VNC or something similar.
It's these little things that get at me. Want feature X? Gotta spend more money. More connections to a computer than Y? Yeah, spend more money, but note that you're capped at 10 period unless you drop several thousand on a copy of Windows Server, and oh, we don't have Vista Server out yet, it'll be another year or so.

This is the biggest reason I switched to Linux: there are no arbitrary limitations imposed. Anywhere. I can connect thousands of machines to this one, and I can type a single line to bring a window from a desktop to my laptop, in a secure fashion, from anywhere in the world.

Let me give you a scenario here, from my everyday work. At school, I use my laptop for everything. Notes, research, papers, reading, the works. All of my work is kept in a subversion repository. Because of this, I can access my up to date notes from pretty much any computer and any OS anywhere.

I get home, and turn my laptop on. It boots up, and I place it in the dock. The laptop automatically detects that it has been docked, and brings up the wired ethernet interface. As a part of this process, it also registers with my LAN DNS server as it obtains an IP, and then commits my most recent set of school notes to the subversion repository. At this point in time, I can type a line into my desktop, and update my desktop's copy of my notes with the most recent version.

Further, because it has registered with my LAN DNS server, I don't need to worry about assigning static IPs. This can be taken one step further: whenever anyone brings over their laptop, they get the same treatment (I should mention that I run an iTunes server on my desktop also. Not apple software, but linux software providing the same functions).

Because I run linux on my laptop and desktops, I can type one more line and bring up windows from my laptop on to my desktop. If I have a bookmark I want to grab, I just run firefox on my laptop and watch the window appear on my desktop.

Earlier up, I mentioned I have an xbox connected to my network, and counted it as a computer connecting to my other computers. Why? It's a modded xbox, running a copy of XBMC. XBMC uses libsmb from samba to give it networking with other windows computers, in addition to having UPnP support, and the ability to browse for iTunes shares on the network.

You know those mockups that Microsoft and Apple have every so often, where it shows the "house of the future"? Where someone walks in with a laptop and wirelessly collaborates with the people in the home? How the music is there to be listened to, the videos to be watched, and work just "gets done" because of the transparent technology powering it?

Hate to break it to you, Microsoft and Apple, but I've already got all of that and then some. It didn't cost me a dime, it works flawlessly, and I can bring as many networked devices I please into the fold without paying more to get around an arbitrary limitation. I've got an xbox that can play any assortment of video and audio at 1080i resolutions in 5.1 surround, laptops plug in (or wifi in) and mystically "just work," and then "just work" with the desktops in a beautiful unison.
I should also note that the Windows Server network I run has its bits moved around by linux routers. Sure, Windows Server powers the desktops, but the bits don't move from site A to B to C on their own, and quite frankly, I wouldn't want anything Microsoft doing that for me.

I love open networking. As a direct result of networking with open technologies, I already have the home of the future. Plus, all of my private networking is encrypted, transparently. Anything that's "open to the public" is, well, just that: open. It's a beautiful thing.

Sorry Vista, you don't fit that bill at all.