Posts

Showing posts with the label router

Bit errors still not a myth

I had this post in draft for a long time now, however it is evergreen. Just consider the recent exploits  focused on RAM leakage. Although, do note that ECC by itself can't give 100% protection against row hammer, so it is only loosely related. An excellent empirical work has been published in 2009 regarding DRAM Errors in the Wild: A Large Scale Field Study . " About a third of machines and over 8% of DIMMs in our fleet saw at least one correctable error per year. " - analysis by  James Hamilton " Besides error rates much higher than expected - which is plenty bad - the study found that error rates were motherboard, not DIMM type or vendor, dependent. This means that some popular mobos have poor EMI hygiene. " - analysis by ZDnet Note that such an event plainly translates to faults on non-ECC machines. So despite the fact that human error is much more probable, it is not unlikely at all that you encounter bit errors in everyday life. Consider the foll...

Vista DHCP bug - WiFi connect failed

Vista refuses to connect to certain wifi routers. I worked around the wide spread issue by forcing a static IP to the client. Is this the proper solution? http://support.microsoft.com/kb/928233 I guess we will never know. Thankfully the now vintage laptop is well supported by Ubuntu 14.04 LTS, so the problem is solved for good.

Hidden TFTP of TP-Link routers

I did some more investigation after the positive results with the TL-WR740Nv4  (click the link to get introduced to the way of recovery). Most users report that devices and firmware updates released after a point in time usually have this mode enabled. If a firmware update is available from the vendor for your device, it's a good idea to apply that update before installing OpenWRT or dd-wrt UNLESS you own something for which upgrading will ensure incompatible with OpenWrt, like a TL-WR730N , and possible some other models (please report). Note that some old models have newer updates in different languages, those may also be worth a try ( TODO : compatibility?). Also remember that later on, tftp recovery will need a type of firmware image without a boot loader, so strip it with dd if yours has it ( grep U-Boot , or check the filename). Positive reported claims so far (personal results highlighted): TL-WDR4300 router 192.168.0.86 server 192.168.0.66 query wdr4300v1_tp_...

Tftp secret of TL-WR740N uncovered

I've found out that even this particular entry level router supports anti-bricking, so there's no need for soldering, unless of course you are modding. The method I used is the following: Set up a tftp server  on your PC and verify if it works correctly (configuration, permissions, firewalls, etc.) Rename your target firmware to wr740v4_tp_recovery.bin and copy it to your base folder (by default /tftpboot). I tested with openwrt-ar71xx-generic-tl-wr740n-v4-squashfs-factory.bin r43602. Set up the following static IP for your PC: 192.168.0.66 /255.255.255.0. If you're not sure about the firmware name on a different model, start a packet sniffer on your PC ( tcpdump -i eth0 -n -l ) and look for the name in the RRQ message. Preferably disconnect WAN from the router Connect the PC to a LAN port Power off the router Press and hold the reset button Power on the router After the leftmost (power) LED and the rightmost (padlock) LED turn on alone in a few seconds, release...

Xperia on certain wifi routers connection problem

Image
Works perfectly with two smarter routers using default settings, but does the well known Android Ice Cream Sandwich dance on a legacy one. It sometimes connects on first attempt, other times after a dozen loops, in the rest of the cases not at all. A loop consists of saved, connecting, authenticating, obtaining IP and scanning. The signal strength goes very low in the authenticating and obtaining IP phases. It spends most of the time displaying obtaining IP address, which takes a few seconds. Lowering the beacon interval does help a bit. Altering channel selection, RTS, TKIP, MAC filtering, preamble type, IAPP, data rate or G-only vs. B/G doesn't make much of a difference. A timing issue related bug in the wireless driver is probable, as loading the router CPU sometimes helps. The router log is filled with the following actions 3 second apart: "syslog: wlan0: WPA2-AES PSK authentication in progress.." Sprinkled with authentication failed and "udhcpd Received a ...