S3300 Bricked Firmware Recovery Howto

Good day all,

I just spent the better part of 8 hours recovering a bricked S3300 switch (GS728TXP) where the web-interfaced crashed mid-firmware-update. Backup firmware was also broken.

Couldn't get official support because the unit was a 2nd-hand import and our single local  Netgear distributor in South Africa refuse to touch anything they didn't sell. We also couldn't replace the unit as they had no stock of a similar unit for over 6 months now.

Just posting this here, maybe someone can save themselves some money and time as it doesn't look like we will get official support for this sort of problem. I will summarise it here, if you need more direct instructions or assistance, just ask.

This is what I did:

1. You need a TTL RS232 UART adapter/cable/interface. I used a Raspberry Pi unit available from RS Components (TTL-232R-Rpi | FTDI Chip 1m USB to UART Cable in Black | RS (rs-online.com))

2. At the back of the switch there is a port labelled "Debug". Complete undocumented with 4 pins. Connect the TTL RS232 UART interface with the following pins: 1: empty. 2: TX/Output. 3: RX/Input. 4. GND/Ground.

3. Open up a serial console on the interface (I used putty) with the settings printed next to the DEBUG port. 115200-N-8-1.

4. With my situation, image-1 failed to boot because of a checksum error (corrupted image) and image-2 just continously rebooted the unit for no reason at all.

5. Pull the power, hold in the factory defaults button and keep holding it in until you get a prompt BCM.0>

6. Run 'sh' for a workable shell, and then 'su -' to elevate permissions. Once you are there, you need to run /etc/profile (/bin/sh /etc/profile) and "mount -a" to have block devices assigned and tmpfs on /media to download the iamge.

7. Put the firmware image somewhere on a TFTP server on your network reachable locally.

8. Navigate to /mnt/media (cd /mnt/media) and use tftp to download the image (tftp -g -r s3300v6.6.4.28.stk 192.168.0.10).

9. Write this image into the block device for the active image (cat s3300v6.6.4.28.stk > /dev/mtdblock4). If you're using firmware-slot-2 this will be /dev/mtdblock5. You can double check by catting /proc/mtd

10. Reboot, it will finish the firmware configuration work and you'll be sorted out.

Hope someone else finds this useful.