Provide more accurate reverse DNS results

What DNS server does onionoo use for reverse DNS lookups to generate the host_name entries?

https://onionoo.torproject.org/details?search=SGGS

example, of onionoo's reverse lookup results for SG.GS relays, all IPs:

+----------+--------------+
| nickname | host_name    |
+----------+--------------+
| SGGSUK4  | 124.6.36.196 |
| SGGSHK0  | 124.6.32.230 |
| SGGSUK6  | 124.6.36.198 |
| SGGSUK0  | 124.6.36.230 |
| SGGSUK3  | 124.6.36.195 |
| SGGSUK7  | 124.6.36.199 |
| SGGSUK1  | 124.6.36.193 |
| SGGSUK8  | 124.6.36.200 |
| SGGSUK5  | 124.6.36.197 |
| SGGSUK2  | 124.6.36.194 |
| SGGSLAX0 | 124.6.40.230 |
| SGGSNYC0 | 124.6.44.230 |
| SGGSUK9  | 124.6.36.201 |
+----------+--------------+

compare that with http://torstatus.blutmagie.de/index.php