Asumming I've understood your question correctly, something like the following?

#!/usr/bin/perl -w 
 
use strict; 
 
my $data = join '', <DATA>; 

$data =~ s|(?=^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\nOS Type: unknown$)|
+\n|gm; 
 
print $data; 
 
exit(1); 
 
__DATA__
10.1.1.1
bogus info
10.1.1.2
this could be anything
10.1.1.3
OS Type: unknown
10.1.1.4
filler information
10.1.1.5
OS Type: unknown
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