FreeBSD上でnslookupを実行すると、 *** Can't find server name for address 203.139.160.75: Timed out *** Default servers are not available というエラーが返ってきまして、tcpdumpの出力が 61.214.128.214.1039 > 203.139.160.75.domain: 41935+ PTR? 75.160.139.203.in-addr.arpa. ×5 61.214.128.214.1045 > 203.139.160.75.domain: 47631+ PTR? 214.128.214.61.in-addr.arpa. ×3