#!/usr/bin/perl
#
use strict;
use warnings;

# open file for reading
open ( XML, "/path/to/file" ) || die "Can't open file $!"

while ( <XML> ) {   # go through line by line
     $_ =~ ( /<IP-(ADDRESS|NEIGHBOUR)>(.+?)<\/IP.+?/ )
     my $ip = $2;  # IP is the value in 2nd parenthesis
}