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Author Topic: DIR-615 config_checksum  (Read 3588 times)

sega01

  • Level 1 Member
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  • Posts: 2
DIR-615 config_checksum
« on: October 15, 2010, 09:52:18 AM »

Hi,

In reference to my previous post, I'm trying to disable stateless IPv6 advertisements on my 615 revision E1, as it's running as simply an AP with IPv6 configured on my router. On occasion, the advertisements conflict, and partially break my external v6 connectivity in strange ways.

I've taken a peek in the the exported config files that can be uploaded/restored off of. They are simple text files, that look like this:

hostname=DIR-615
admin_password=********
user_username=user
user_password=*********
default_html=index.asp
lingual=EN

This makes it look quite simple for me to modify it and reupload it with modified IPv6 portions, but alas, there is a problem. At the end of these files, there is a checksum. I imagine it's of the prior file until the checksum, or the rest of the file without that whole line (meaning the config_checksum= text, too). Either way, it appears to be up to 2^16 in length, and is obviously numeric. It looks like this and is always at the end of a file:

config_checksum=35814

Or,

config_checksum=27622

Removing it or keeping it the same won't help. Any minor change in the config (as changed through the web interface) drastically changes it. My guess is that it's CRC-16, but my understanding of CRC-16 is that it varies drastically with whatever polynomial you use.

I'd really appreciate it if someone could tell me the algorithm used or if there's a bypass, especially with any suggested utilities so I don't have to code my own to regenerate the checksum so that I can use my own config.

Thanks so much,
Teran (sega01)

PS: I've grepped fairly heavily through the source code and not found any mention of this. Then again, it appears that source tarballs are downloaded separately for everything but the kernel, and I have not tried to do that, yet.
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Trikein

  • Guest
Re: DIR-615 config_checksum
« Reply #1 on: October 15, 2010, 07:56:29 PM »

::gets popcorn:: I would love to see someone respond to this. Beyond my pay grade. Very interesting though. Anyone going to take a stab?
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