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RE: RE: Resolve addresses in web access logs

by zodiac (Beadle)
on May 10, 2000 at 16:27 UTC ( #10941=note: print w/ replies, xml ) Need Help??

in reply to RE: Resolve addresses in web access logs (risk of gethostbyaddr)
in thread Resolve addresses in web access logs

Maybe you are wrong. or may be I am but:
gethostbyaddr returns the names matching the ip. reverse name entries is as secure as dns gets. if the ip has a reverse name, the ip for that name will match the ip.
the discussion in the Cookbook is about looking, whether the ipaddress you got when looking up by name, matches the original name. which it will not, unless you have a reverse entry for the same name.

Comment on RE: RE: Resolve addresses in web access logs
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RE(3): Resolve addresses in web access logs (kudra: gethostbyaddr could give incorrect info)
by kudra (Vicar) on May 22, 2000 at 10:57 UTC
    I don't think there's any looking up by name--in the example the IP was grabbed with getpeername and the name isn't known. If you were to get the ip with gethostbyname and then use gethostbyaddr on the result, you would be verifying it as they suggest, just in reverse.

    Quoting extensively from the Cookbook:
    "...If you want the name of the remote end, call gethostbyaddr to look up the name of the machine in the DNS tables, right?

    "Not really. That's only half the solution. Because a name lookup goes to the name's owner's DNS server and a lookup of an IP addresses goes to the address's owner's DNS server, you have to contend with the possibility that the machine that connecteed to you is giving incorrect names. For instance, the machine could belong to malevolent cyberpirates who tell their DNS server that its IP address ( should be identified as If your program trusts, a connection from will cause getpeername to return the right IP address (, but gethostbyaddr will return the duplicitous name (my italics).

    "To avoid this problem, we take the (possibly deceitful) name returned by gethostbyaddr and look it up again with gethostbyname..."

    I'm just repeating, but it looks to me as if this is talking about gethostbyaddr having the potential to give incorrect information.

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