I would never try restoring a config file to a different firmware version, ever. Even if ASUS or whoever claims its OK.
If I was going to do that, I'd probably try an NVRAM scripting backup/restore utility. There's threads here on one that used to be great but it hasn't been maintained therefore is no longer recommended. Basically it uses nvram commands to save and restore text files and had a 'migrate' function that was for taking you from one version to another but that was based on somebody doing some detailed work on which parms were safe to restore and which were not and which things changed between which versions etc.
There's a school around here and in the general open (lowercase) wrt world, of "you must ALWAYS ALWAYS ALWAYS reconfig from scratch every single time, always stone-cold-clear NVRAM and start over". There's all these little acronyms for - "M&M" or "30/30/30" or "peacock" whatever.
Before I say the next thing that makes the religious extremists heads explode, I completely recognize the value there absolutely.
There's huge truth in that and reasons why that is the recommended way to go.
However, I've upgraded x_wrt routers probably 100 times without resetting to factory defaults again with no problems.
Have probably had less than a dozen times something got borked after an upgrade.
I've probably saved weeks of man-time not full-factory-resetting every time I upgrade. I think its foolish to tell everyone to always always stone-cold reconfig, unless your config is super simple vanilla and really close to the factory setup. My main site routers are not and have loads of stuff to have to re-do - manual IP's, multiple networks, custom scripting, SSL keys, etc. etc. etc. Reset? Ugggh.
My routine is basically what L&LD says - try it first and then reconfig if you need to - but with the following options
- Backup old config, flash new firmware, do not reset
- If problems occur, make a judgement call on one of the following options
- Investigate/diag in-situ without reset to see if problem is an easy "sysadmin-able" fix, or,
- Restore prior firmware, reset to factory, then restore the backup, and leave the upgrade for another time, or,
- Stone cold reset and reconfig routine
The factors that go into choosing a path there are:
- Nature/severity of issue
- Time available to diag/futz around
- Site-related urgency (will users set the house on fire if service is out for 5 minutes)
- Urgency of the upgrade (is there security related patch or is this 'general currency' upgrade)
- Complexity of the router/site in question
While the reset-jihadiis talk incessantly about NVRAM corruption and the like, my strong experience with x_wrt is that a firmware upgrade hiccup
these days is as likely to be some other file-format or config-file related change that was made as anything else, therefore maybe its just some minor tweak you need to make to a /jffs script or a permission or whatever, and very likely a stone-cold reset and reconfig is a complete and massive waste of time.
To be fair, I think this maybe was different years ago when the factory firmwares were far less reliable and more likely that some NVRAM parm changed but wasn't migrated properly or whatever (or on the older routers with tiny memory that the NVRAM space would over-run).
So - to answer your last post - I would:
- Reload prior firmware (that matches your config backup) and select reset factory defaults
- Perhaps do a 2nd 'reset defaults' for good measure when it comes back up
- Restore your jffs
- Restore the config backup file