Q: Frequent "corrupt" download files

Interesting that your router was the problem. For several months now I have been experiencing corrupt downloads on my home network and not just on the macs, also my windows pc's have the same problem when downloading from the itunes store.

I completely reinstalled my macs but the problem was still there, so I ended up calling the cable company as the problem was likely to be in the network. They have changed over the cable modem (Thomson TWG870U) for a Cisco one but the problem is still remains and the technician believed the cable connection was good.

Interestingly I noticed that the windows pc's also experience corruption on downloads but its not as obvious and they are more likely to succeed in downloading after several attempts than the apple computers. In particular I noticed in the Windows event viewer that large updates from Microsoft regularly fail and take several attempts. I tested this by manually downloading a Microsoft Service pack >400mb and it took seven tries before it succeeded.

This week I have 5 different Pc's all trying to download a movie from the Apple Store but all failing with error -50. Also my macbook air has been trying to download a 10mb update from the App Store for over 10 days but failing with the error (Hash Mismatch).

I have also tried downloading large files for my mac from several sites (e.g. Adobe, Symantec,etc) and the downloads are usually always corrupted (Checksum failed). In one case I downloaded the file 40 times before I had success.

Something is definitely going on as I have never experienced this type of error before and I am using several different varieties of pc/macs to access the internet and they all have similar problems.

Based on my discussions with a Networking expert, corrupted files are sometimes linked to the following problems:

* Faulty RAM

* Failing HD

* Failing NIC (Network Adapters) both local and in your ISP's infrastructure

* possible interference with the file through some points in the internet infrastructure

The problem fluctuates from week to week and most downloads resolve eventually but it is a really frustrating problem. Definitely the Apple computers have a worse time of it than the Windows pc's.

1 X Windows 7x64

2 X Windows Vista 32 laptops

1 Macbook Air (late 2008) 10.7.2

1 Mac Mini (10.7.2)

Cable provider is UPC 120mb downstream/10mb upstream

Following on Tux and Adam's observations, I have also seen people report that restarting the modem/router will somtimes help.

It is now two weeks since I turned off routing of my DSL modem as described above (and attached an own LAN/WLAN router to the modem). I have not experienced one single corrupt download since then, not even over WLAN. Also, the support of the DSL provider confirmed this problem with the modem and told me thomson is working on a firmware update.

@tuxthedownloader, your ISP is UPC?

I can't find option to turn off routing. I see only DHCP. Can u tell me where is this option?

Yes, UPC in Switzerland. See my post from Jan 5, 2011 on the exact type of modem/router and firmware. When logged in to the modem (192.168.100.1) I select 'Gateway' on the top menu bar and 'Switch Mode' on the left side. Set Switch mode to 'Disable Mode'. A connected computer will then directly connect to UPC over the modem and gets IP settings through DHCP from there. The modem is still reachable under the local IP address 192.168.100.1.

I have UPC in Poland.

I don't have "Switch mode": http://i.imgur.com/Jq27w.jpg

I write on facebook in UPC PL profile that I have a problem with link to this topic. One guy form UPC ask me for my client ID. Now I see that I have new firmware

And for now, looks everythink work fine. I have to check Internet Recovery still, but update from 10.7.2 to 10.7.3 goes well so I think they resolve this issue.

I had exactly the same problem (I have UPC in Switzerland with Thomson router), THANK YOU for having found a solution!!!! I was going crazy!!!! Thank you thank you thank you!!!!

Well, it turns out that here in the Netherlands with UPC and a Thomson router I managed to fix the problem doing more or less the same thing.

I accessed to the configuration, I rebooted it from there using the "Initial scan" menu (under Gateway) since I don't have a "Switch" menu. After that, my connection was down for a little bit.

I also had to reboot the Airport Extreme in order to get everything back online.

I then rebooted manually the router and when everything was back online the router firmware had gone from version STBA.01.38 to STBA.01.41.

I tried the download and WOW! Checksum errors no more!

I wonder if this is also behind the problems I have in updating other Apple products I have.

We'll see!

Thanks to everyone for identying and writing about this!

After week with STBA 01.41 i've had it enough. I'm sysadmin. I manage servers thru ssh, directadmin, cpanel etc. All connections on custom port (like 2222, 654, 182, 5353, 2083) all reset by peer. I need to refresh page or try connect via terminal few time before i got connected.

Has anyone had any further insights into this? I am experiencing a similar problem, but it happens in multiple web browsers as well as Apple Software Update. When Software Update downloads the OSX 10.7.3 update, that appears corrupt and won't install.

I have a Verizon Fios Actiontec MI424-WR combo router/modem. I have rebooted that a couple of times without any effect. I suspected the router becuase I am also having problems connecting to my Lacie Network Space 2 NAS, but I can get to websites, Dropbox and other internet resources without any problems.

I have had this same networking setup for about 2 years now, and have been running Lion without any problems for months. I am at a loss as to what has changed that might be causing this.

Any other suggestions?

2007 imac 2.4GHz Intel Core 2 Duo

OSX 10.7.2

I've experienced similar issues with downloads from Apple of software updates, but mostly when I download a combo OS update.

The only workaround I've found is first to restart my Mac Pro then immediately download the Apple software before doing anything else. That usually results in a workable .dmg.

I'm also on UPC in Poland. 50Mbit/s link. Same router - Thomson TWG870U. Previous firmware - *.39

For last month there was constant 'invalid checksum' message for .dmg files downloaded from Apple. Neither Software Update, nor developer downloads worked.

What have worked for me was changing MTU from default (1500) to 1490. Now all downloads work like a charm. UPC has probably changed some parameters of the network, I'm not an expert on networks.

If you're interested I have followed the instructions below on how to optimize MTU.

Quote:

Done everything as above except using Mac OS X syntax - ping -s XXXX bbc.co.uk

For packet size 1500 - all packets were lost

For 1462 all packets went through.

So 1490 is my lucky number.

BTW, I have corrected MTU on my PC, not on the router. Somehow it works. You might do a different variation of a config.

After some experimenting with large downloads of ubuntu distributions (to separate the problem from apple servers) I think I know what works and what doesn't.

What doesn't work

- changing browser doesn't work. Files are corrupted both on Safari and on Firefox

- ftp also gives corrupted files

- fiddling with MTU gives you faster downloads (my downloads improved from 1MB/s to 5MB/s), but still gives you often corrupted files, just faster

What works

- downloading with bittorrent ALWAYS works, whatever happens with the network. Won't help you with apple servers, however

- switching off all other network activity (any video playing in the background, any other downloads, maybe even browsing other sites waiting for download to finish) definitely works

So, after switching off any other network activity I have tried to download 1.5GB file - xcode_431_lion.dmg. It downloaded correctly on the first try. Again, I am not expert on networks, so I'm not able to discuss if my service provider is evil and why.

Exactly the same as @tuxthedownloader:

- Location: Switzerland

- ISP: UPC-Cablecom

- Cable modem: Thomson TWG870UG, Software Version: STBA.01.39 (is there a way to update it?)

- Problem: Large .dmg files (such as the Mac OS 10.7.4 delta update) are corrupted when downloaded with Safari or Software Update

- Solution: Disable routing on the cable modem, enable routing on the Airport Extreme behind the cable modem

Same situation.

To fix: Called Cablecom support. This is a known issue, they replace the box.

Caveat: they initially proposed to replace the Thomson with a modem only box, had to talk them into shipping both modem and router, since I didn't have any other router around.