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10

fedora seems to have the following package in the repos "dhcp_probe" Description : dhcp_probe attempts to discover DHCP and BootP servers on a directly-attached Ethernet network. A network administrator can use this tool to locate unauthorized DHCP and BootP servers. Looks like the man dhcp_probe has some good pointers for DHCP discovery strategy ...


10

I doubt that a setup that large has ever been attempted before, so you likely will be pushing limits when trying. I could find an article on a VPN deployment for 400 clients but judging from the text, the author just relied on rough estimates about how many clients could be run per CPU and lacked some understanding about how his setup would perform. You ...


7

I have actually done this, albeit with "only" a few hundred remote connections similarly behind DSL routers. I can't comment too much about the rekeying issues, but a few practical things I learned along the way: 1) When deploying clients, make sure you specify multiple VPN servers in the client conf, vpn1.example.com, vpn2.example.com, vpn3..... Even if ...


7

You could use the block2mtd driver to use the transactional jffs2 or yaffs(2) filesystems you seem to be employing elsewhere for your SD card, which would solve your problem of data loss or filesystem corruption at poweroff. Doing so might incur other problems, though. As the SD card is likely to have own mechanisms for wear levelling and sector remapping ...


6

Avoid any fixed address. Even if you try to avoid addresses commonly found for other kinds of devices (like routers), you still should ask yourself: what if the user has two or more of this device? As many people stated, you should try to automatically configure the device using DHCP. In this way, the network administrator can easily control the address of ...


5

DHCP and DNS might be a good solution if it wasn't for the fact that plenty of networks out there still have no server present and use fixed IP addresses. If you don't want to lock those people out from using your device then you at least need to fall back to some other system. ZeroConf was invented to deal with just this situation: no DHCP or DNS server. ...


5

The problem is that your client is not talking DHCP but bootp. Not all dhcp servers handle bootp as well due to design limitations or configuration settings.


5

Check whether the kernel you use supports flush and/or sync flag for vfat (it seems some versions ignore it, be careful!). Or just do away with the filesystem altogether if everything can go into one file (as would be the case with a raw log stream!) or into a few fixed size files (use partitions ;)


4

If you have "dhcpcd" installed, you can use the "-T" flag, to get the "test" mode, which just echoes the settings, but does not actually set the IP address and the gateway. dhcpcd -T and the output: emily ~ # dhcpcd -T wlan0 dhcpcd[6205]: version 5.2.12 starting dhcpcd[6205]: wlan0: broadcasting for a lease dhcpcd[6205]: wlan0: offered 192.168.2.194 from ...


4

I've done a reasonable amount of hobbyist embedded hacking, and I've got two suggestions: Linksys WRT600N (which has usb) or Linksys WRT54GL with dd-wrt or some other custom firmware. Get the cross-compiling setup on your desktop and start porting some open-source software that you might want to run on them. Once you're comfortable with the build ...


3

Here are some interesting cards Atmel NGW100 - http://www.atmel.com/dyn/products/tools_card.asp?tool_id=4102 BeagleBoard - http://beagleboard.org/ LinuxStamp - http://www.opencircuits.com/Linuxstamp Gumstick - http://www.gumstix.com/ Maybe you can have some fun with one of those?


3

If it's limited budget you want, you want the Sheevaplug. Mine has just been delivered a few hours ago and I can't wait to get home and start checking it out. Basically, it's an ARM processor with 512MB of RAM, some flash memory, a USB port, a NIC. All built into a powerplug(!). Hence the name. A very cool device, low power, low cost (less than $100). ...


3

Solved by following the excellent How To: Build A Read-Only Linux System. From one of the two little scripts making the magic (uses an aufs union): ro_mount_point="${rootmnt%/}.ro" rw_mount_point="${rootmnt%/}.rw" # Create mount points for the read-only and read/write layers: mkdir "${ro_mount_point}" "${rw_mount_point}" # Move the already-mounted root ...


3

The write cache has usually nothing to do with the BIOS, mostly there is no option for switching disk cache settings in there. With linux, using hdparm -W 0 should help. The setting is persistent, so if you don't have hdparm to play around with in your production systems, you should be able to disable the disk write cache on a different system and replug ...


3

The write cache suggestion is a good start but this sounds like an architectural design flaw. On an embedded system the internal flash should probably NOT be mounted R/W except in rare circumstances. You should really be doing most of the work in a memory filesystem and syncing changes back to the RW flash upon some user command or regular interval. It is ...


3

Three possibilities that I see: VPN. Yes, you could rig some kind of VPN connection between each device and a concentrator. That would be expensive monetarily if you didn't use open source tools. That would be a bit of a pest to manage since each meter would then have an IP on the endpoint. Sure, you could manage it with subnetting and/or IP schemes and ...


3

Your idea of a Linux configuration seems good. A small Linux distro such as Arch or LFS (BSD works too) with all services except X11 and DHCP ripped out. X11 can be configured to start anything - so make it launch a web browser and a very minimal window manager (such as dwm).


3

On SSDs you could try using the ext4 filesystem, then mount it using the discard option. In fstab: UUID=XXXXXXXXXXXX / ext4 discard 0 1 Add whatever other options you want, such as noatime or errors=remount-ro. The discard option potentially enables TRIM in the SSD which may increases its lifetime, ...


2

It sounds as though the device tried to chat with the OS on first boot and since the stack wasn't ready at that time, it "logged out" from the hub. Consider adding a section to the end of boot process to drop the driver and to force a reload. (modprobe -vr ehci_hcd; modprobe -v ehci_hcd if USB2.0, uhci_hcd if USB1.x) Another possibility is that when the ...


2

Here is what I finally found: To enable the MC31XX device to associate to the AP, go into the Fusion tool and select Options. From the list of available options, select Regulatory from the dropdown. Then uncheck the option Enable 802.11d.


2

Something like ajaxterm ? You could also create a SSH tunnel over HTTP but your network admin probably doesn't want you to do that and it's overkill.


2

One way to make embedded filesystems reliable is to make the entire filesystem read-only. If you really need to write things you can use tmpfs and lose them at reboot, or have a separate filesystem for that data that isn't necessary for successful boot (i.e. boot scripts fsck or rebuild that fs if it's damaged.)


2

The 8051 is a very old and small microcontroller. You may have difficulty implementing an IP stack on it depending ont he features required. I would also imagine it is underpowered unless of course you are implementing it at a higher clock rate in an fpga. That being said using IP is pretty much a foregone conclusion because of the router and switch elements ...


2

When in doubt, over Ethernet, use IP. If you want to use UDP or TCP is another issue entirely. Both have advantages, but honestly I would consider this. How stable is the RF part? How often do the devices reassociate? If not often, you could quite easily implement a lazy learning system where the device associates, and the AP sends a single UDP frame ...


2

I'm afraid it's too vague a question, the range of embedded devices is huge, and the hardware that makes sense depends on the application. I'd look at some of the magazine websites to get started: Embedded Systems Design, EDN, EETimes And google embedded systems design to get pages like this one: Embedded System Design (a textbook)


2

The world of embedded systems covers so much territory that you can't possibly create a single comparison chart. Give some clues as to what you are doing and what sort of processing power you need, and perhaps a narrow range can be compared. Embedded systems covers everything from tiny little 8 bit micros in the PIC and 8051 families all the way up to ...


2

The WRT54G has already been mentioned, but I'm a big fan of the NSLU2. It's an very inexpensive NAS device. 266 MHz 32 MB of SDRAM 8 MB Flash 100 Mbit Ethernet 2 USB. The NSLU2 is fanless, which is a big plus for me. There are several alternative firmwares and it can run debian: see NSLU2-Linux.



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