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Thread: Linux TTL values.

  1. August 17th, 2004, 03:40 AM #1
    hobbdebub
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    Linux TTL values.

    I have been studying up on OS fingerprinting and I have hit a part where I scratch my head, and need some outside advice. From all of the stuff I have read it says that most *nix based OS's will return a TTL value of 255 in an ICMP echo reply. This is fine but for one thing, I am running slack 9.1 and it returns 64. Which Kernel did they change it back to 64? Or did theynot and I am an idiot. I am just wondering. Thanks for the help.
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  2. August 17th, 2004, 04:33 AM #2
    chsh
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    Genetic unixes may in fact be 255, but to my recollection linux has always been 64. All my slack boxes (dating back to slack 7) here return 64.
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  3. August 17th, 2004, 04:39 AM #3
    hobbdebub
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    Thank you very much chsh. I was a bit confused because something I read stated that 2.4.x kernels returned 255. Anyways thanks again for the answer.
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  4. August 17th, 2004, 11:29 AM #4
    thehorse13
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    RedHat 6.2 - 9.0, Fedora and Enterprise Linux all return 64. You must be an idiot.
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  5. August 17th, 2004, 11:38 AM #5
    SirDice
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    FreeBSD also uses a default TTL of 64. This can easily be changed:
    Code:
    sysctl net.inet.ip.ttl=128
    Just beware the TTL on the echo-reply is the one used by the remote host.
    If you receive TTLs back of say 126 you're probably pinging a windows host.
    AFAIK most windows versions use a default TTL of 128.
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