Fastest way in perl to reverse dns lookup

Jon- · 02-23-2002, 12:42 PM

Hey all,

I'm trying to write a perl script that can reverse lookup 250K+ IP addresses.

I tried to use Gethostbyname. That seemed to work -- it flew through the entries -- thousands/min. But, as soon as it got stuck on a IP, it would wait an insanely long time before moving onto the next entry.

So, I switched to Net::DNS. (<--not sure how to dump the smiley here...heh... that's a D) This worked -- I set the timeout to 5 seconds. But, it was way slower, by like a factor of 10+. I guess this is because it's opening a seperate socket for each connection? So, it took 12+ hours to lookup about 220K IPs.

Anyone know a better way to do this? I thought I might just modify the Gethostbyname code to allow a timeout (or, probably just change it). But, not sure how Perl is implementing that, and what else it would affect.

Thanks for any feedback :)

Jon

jeremy · 02-23-2002, 01:27 PM

There is a checkbox for disabling smiles for each post. Something like this should work for you:

Code:

use constant TIMEOUT => 2;
$SIG{ALRM} = sub {die "timeout"};

while (<>) { s/^(\S+)/lookup($1)/e; } 
continue { print; }

sub lookup {
    my $ip = shift;
    return $ip unless $ip=~/\d+\.\d+\.\d+\.\d+/;
    unless (exists $CACHE{$ip}) {
        my @h = eval <<'END';
        alarm(TIMEOUT);
        my @i = gethostbyaddr(pack('C4',split('\.',$ip)),2);
        alarm(0);
        @i;
END
    $CACHE{$ip} = $h[0] || undef;
    }
    return $CACHE{$ip} || $ip;
}

Jon- · 02-24-2002, 12:16 AM

Hey Jeremy,

I totally forgot about alarm... that's the ticket... and, caching stuff -- good idea..

I'll give this a shot...thanks again!

Jon

raghupathi · 05-28-2008, 02:37 AM

Whether it shows the reverse lookup for dns with Increment Ipaddress or not.

cnd · 07-20-2016, 06:47 AM

DNS lookups are short UDP packets - the fastest possible way to do those lookups would be to run tcpdump to capture the replies, then write a short perl script to pump every DNS query packet you want out all at once (Net:

NS helps you construct that).
to make it even faster, you could spread the load and use multiple different servers (eg: send some requests to 8.8.8.8 and others to 8.8.4.4 etc).

The entire run should take just 10 or 20 seconds this way (depends a bit on your outgoing traffic bandwidth)

Habitual · 07-20-2016, 08:37 AM

Quote:

Originally Posted by Jon-

So, I switched to Net::DNS. (<--not sure how to dump the smiley here...heh... that's a D)

Code:

[noparse]Net::DNS[/noparse]

Works in quotes too. but usage is a bit tedious after multiple replies.
Or as Jeremy said select "Disable smilies in text" in Additional Options of Reply to Thread Window.

keefaz · 07-20-2016, 10:00 AM

use threads?

jeremy · 07-20-2016, 12:50 PM

Closing this thread, as it's over a decade old.

--jeremy