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I can't update or downgrade my iPhone 3GS, Firmware 4.3.5 tethered with redsn0w.

Whenever I try to update it, I get a "device isn't eligible" error. I researched on how to do that, like changing host files, but none of them worked for me. I use OS X Snow Leopard.

# Host Database
# localhost is used to configure the loopback interface
# when the system is booting.  Do not change this entry.
##   localhost broadcasthost
::1             localhost 
fe80::1%lo0 localhost

This is my host file – not sure if it's the orginal one or not.

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migrated from Apr 16 '12 at 4:23

This question came from our site for computer enthusiasts and power users.

The host file is not the original. That

resolves to ( and not the real server by Apple, so that the SHSH trick works. Probably you have added it at some point. If you remove that you should be able to upgrade to iOS 5.1 using Apple's update. However, depending on the bootrom that you phone has, you may or may not be able to do a untethered jailbreak with Redsn0w, so be very careful before deciding whether you want to upgrade (although you say you have tethered jailbreak so probably you can live with tethered).

As for downgrading, I am not sure why you can't do this, chances are that you don't have SHSH for lower versions in Cydia.

Edit: for downgrading you may have to use another IP address in the hosts file. I've seen used recently (check the recent tutorials for saving SHSH blobs, the IP address may have changed)

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@lupincho is correct that you should remove the line if you want to be able to upgrade to the latest version of iOS (5.1) using iTunes.

If you want to upgrade or downgrade to any iOS version other than the latest version, you'll need to have already saved SHSH blobs for that version. And more specifically, if you want to upgrade to iOS 5.x using SHSH blobs (such as to iOS 5.0.1), you need to stitch the SHSH blobs into custom firmware instead of using the host file trick due to changes in how Apple does the SHSH blob verification process. See here for a detailed guide to using SHSH blobs to restore to iOS 5.x.

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