My top 2 articles on the internals of broadcom-based routers

Embedded devices are energy efficient, and their limited memory and storage present some satisfying challenges. How have I missed this for all these years, I don't know, but it is time to play catch up. For a few weeks, I've been spending some of my free time reading on Openwrt and the WRT54GL and other devices of similar design.

Of course, flashing a custom firmware can be daunting enough for an average user, but an average geek like myself will want to know how exactly these devices work. There is a published book on the subject but upon reading the table of contents, I decided against buying it as I deemed it not technical enough.

So, I assumed there was information somewhere for people like me, info that didn't require me to read source code. And there is, but you have to search for it.

And what are the top two articles I found on the subject? Here they are.

1. First of all, there is a three year-old post entitled "Everything you need to know about Broadcom hardware" here in the Openwrt forums: https://forum.openwrt.org/viewtopic.php?id=11304

It is extremely informative on the boot process of these devices and it finally clarified for me how the CFE bootloader works. I didn't understand the SquashFS + JFFS2 combination details, thanks to this post now I do. You also should read about union mounts if you're not familiar with the topic (I wasn't, HP-UX does not support this!).

2. Then you should read about how VLANs and network interfaces work on the Broadcom platform -- this article is from the old OpenWRT wiki but well done, too. It is specifically for the Asus WL-500g but being a Broadcom design I can only suspect other routers are very similar, if not identical:

http://wiki.openwrt.org/oldwiki/openwrtdocs/networkinterfaces

This article explains why you have a bridge interface on your router. It especially shines in explaining how these routers isolate the interfaces cheaply using VLANs. In fact, there is only one twisted pair interface (eth0), the other one being the wireless antenna (eth2). I was under the impression that firewalls needed different and isolated interfaces, but the VLAN trick lets you do something similar on cheaper designs. And I guess it is good enough!

I might replace my m0n0wall PC soon in order to reclaim real estate in my utility room and save a few bucks on electricity. I just need a router, and disable the wireless radio. But I will NOT be purchasing a WRT54GL. Why? I'll tell you in a future post!

O.

Ah, Mom, I bricked my router!

Remember I was running OpenWRT on a Bufallo WLI-TX4-G54HP ? After playing with OpenWrt a bit I spent some time setting up a Ubuntu-based build environment to be able to build my own custom firmware.

There's no particular reason for building a custom firmware since the package I want to ultimately run fits on the JFFS2 partition. I just wanted to get my hands dirty. But gasp... the documentation for OpenWRT is sparse and disseminated in four areas: an unfinished HTML manual, an old Wiki, a new Wiki being slowly migrated from the old one, and the OpenWRT forums. One really has to spend some time reading through all of them to understand how everything works, and I've covered maybe 10% of that. And that's okay. I don't pay a cent for OpenWRT and it's a distribution targeted to power-users... If I wasn't looking for a challenge, I'd be running Tomato instead.

Anyway. It turns out that I bricked my device yesterday after flashing that darn custom firmware. I didn't solder a serial or JTAG port, wasn't really looking into doing this, so I couldn't do much to troubleshoot. One thing that no longer worked, and this was supposed to be my planned way out, was the 2-3 seconds it pings on 192.168.1.1 when it's at the CFE bootloader so that I can TFTP a correct firmware. Since it no longer did this, I couldn't do that to unbrick it.

I was about to throw it in the garbage but found somewhere in the DD-WRT forums that some Buffalo routers listen to 192.168.11.1. I tried this address and it worked! Now as to why it decided to listen to 192.168.11.1 while the first time it was 192.168.1.1, I don't know. I must have pressed the reset button 50 times on this thing so who knows what it ended up doing.

Back to square one, I have a router that works, but no custom firmware.

O.

VMware player... what have I been missing?

Up until now, after all these years, I never considered using VMware Player because as its name implies, it used to be be a player for virtual appliances. That's what it was initially designed to do, but it looks like it can do much more than I thought.

Since I used to be an ESX admin, I don't feel the need to learn to use something else and the only solution I knew to virtualize random stuff for free on my low-end laptop, if I stuck with VMware's offering, was to use VMware Server. I tried Server a few times over the years, but must admit that it isn't really interesting when compared to ESX. The web interface is clunky, and it does not integrate well on a "home" PC.

Little did I know that versions 3 and up of VMware Player now let you create virtual machines at your liking, without needing to use pre-made appliances. I've tried it and it works well, and it is much easier to use than Server's web interface.

I've been "converted".

O.