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How to check the integrity of files

Discussion in 'Networking' started by foler59, Apr 16, 2008.

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  1. foler59

    foler59 Thread Starter

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    How can I be sure that the file I just downloaded has not been corrupted? For example I have tried downloading a non-commercial movie from P2P in ISO format and it has some small artifacts at times, and if I try to download it again it might not have those. BTW the subject in question is not P2P networks, just what can guarantee the integrity of a downloaded file either from P2P or a website or from wherever.
     
  2. JohnWill

    JohnWill Retired Moderator

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    Unless the file has been compressed or an MD5 checksum is available, I don't know of a way. However, it's very common to get corrupted files with P2P, so I'm not surprised you get them.
     
  3. foler59

    foler59 Thread Starter

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    Doesn't the protocol provide some kind of guarantee of the integrity? For example I know that utorrent checks to see if a half downloaded file is if fact the one being downloaded (if the download has been interrupted and the system restarted for example), and I suppose it does that using some MD5 checksum technique.

    Hell, I even got a corrupted file from a direct (http) download from a site! Why is this happening?
     
  4. JohnWill

    JohnWill Retired Moderator

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    Probably because you or the ISP are having a problem.

    Register at DSLReports and run their Line Quality Tests. It's best to run this test with a direct wired connection to eliminate any wireless issues from the results. It's useful many times to run this test several times, and we'd like to see each of the results. Post the results link from the top of the test display page for each test run here.

    The link to post is near the top of the page and looks like:

    If you wish to post this result to a forum, please copy/paste this URL
    http://www.dslreports.com/linequality/nil/2357195 <- sample only, yours will obviously be different!
    and your IP will be disguised.

    Copy/paste that link here.

    Note: You will have to enable PING (ICMP) request response either in your router (if you have one), or in your computer's firewall for direct modem connections. This is very important to get the most important part of the test to run.
     
  5. Squashman

    Squashman Trusted Advisor

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    This why many well respected download sites have checksums for you to verify the file Integrity. As file sizes continue to grow, checksums are needed. Even Microsoft does. When I beta tested WHS, I had to verify the checksums on the ISO's I was downloading.
     
  6. foler59

    foler59 Thread Starter

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    So if I get a huge files that has certain bits of it wrong will it still work? And if it works won't its functions be corrupted? That could be a huge disaster! I don't really use checksums, but my programs have worked so far.

    Downloading files for the internet shouldn't be so fragile!
     
  7. JohnWill

    JohnWill Retired Moderator

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    If you get an application that has incorrect bits, there's no telling what it will do, but correct operation is very unlikely! Downloading from legal download sites with a decent ISP isn't that trouble prone, I do it all the time.
     
  8. foler59

    foler59 Thread Starter

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    Don't the protocols used for transfering guarantee the integrity of the downloaded file (if a packet doesn't arrive, it is requested again from the server)?

    If I'm performing HDD or CPU intensive applications while downloading, will my PC throw away the data in the packets that maybe didn't handle due to the overloading of the CPU? Aren't the packets entering a queue where every one is going to get processed at some point?
     
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