Reverse DNS entries

As promised, the next step would be reverse resolve scanning some nets. By doing this we could possibly see interesting reverse DNS names that might give away information about the host. We proceed to reverse scan all the mentioned blocks, as well as the corresponding class C block of the IPs that does not fall in above mentioned blocks (the ISP-like blocks). Extracts of the reverse scan looks like this:
- 17 - Breaking into computer networks from the Internet [Roelof Temmingh & SensePost]
1.195.193.192.IN-ADDR.ARPA domain name pointer global1.citicorp.com
2.195.193.192.IN-ADDR.ARPA domain name pointer global2.citicorp.com
3.195.193.192.IN-ADDR.ARPA domain name pointer global3.citicorp.com
4.195.193.192.IN-ADDR.ARPA domain name pointer global4.citicorp.com
119.195.193.192.IN-ADDR.ARPA domain name pointer arrow1.citicorp.com
119.195.193.192.IN-ADDR.ARPA domain name pointer arrow1-a.citicorp.com
120.195.193.192.IN-ADDR.ARPA domain name pointer global120.citicorp.com
150.195.193.192.IN-ADDR.ARPA domain name pointer fw-a-pri.ems.citicorp.com
151.195.193.192.IN-ADDR.ARPA domain name pointer fw-b-pri.ems.citicorp.com
192.195.193.192.IN-ADDR.ARPA domain name pointer egate3.citicorp.com
194.195.193.192.IN-ADDR.ARPA domain name pointer egate.citicorp.com
232.195.193.192.IN-ADDR.ARPA domain name pointer iss-pix11.citicorp.com
233.195.193.192.IN-ADDR.ARPA domain name pointer iss-pix12.citicorp.com
234.195.193.192.IN-ADDR.ARPA domain name pointer nr1.citicorp.com
121.196.193.192.IN-ADDR.ARPA domain name pointer qapbgweb1.pbg.citicorp.com
122.196.193.192.IN-ADDR.ARPA domain name pointer qapbgweb1b.pbg.citicorp.com
123.196.193.192.IN-ADDR.ARPA domain name pointer qapbgweb3a.pbg.citicorp.com
231.196.193.192.IN-ADDR.ARPA domain name pointer iss2.citicorp.com
232.196.193.192.IN-ADDR.ARPA domain name pointer iss-pix21.citicorp.com
233.196.193.192.IN-ADDR.ARPA domain name pointer iss-pix22.citicorp.com
190.74.128.210.IN-ADDR.ARPA domain name pointer telto-gw.dentsu.co.jp
190.74.128.210.IN-ADDR.ARPA domain name pointer citibank-gw.dentsu.co.jp
192.74.128.210.IN-ADDR.ARPA domain name pointer webby-gcom-net.dentsu.co.jp
10.38.193.192.IN-ADDR.ARPA domain name pointer pbgproxy1a.pbg.citicorp.com
11.38.193.192.IN-ADDR.ARPA domain name pointer pbgproxy1b.pbg.citicorp.com
12.38.193.192.IN-ADDR.ARPA domain name pointer pbggd1a.pbg.citicorp.com
53.73.193.192.IN-ADDR.ARPA domain name pointer www.citicommerce.com
Most of the non-192.193 block does not resolve to anything. Some of the 192.193 reverse DNS names tells us about the technology used. There are PIX firewalls (nr-pix21.citicorp.com_), possible ISS scanners or IDS systems (iss2.citicorp.com) and proxy servers (cd-proxy.citicorp.com). We also see that there are other Citibank-related domains - citicorp.com, citicorpmortgage.com, citimarkets.com, citiaccess.com and citicommerce.com. It can clearly be seen that most of the IP numbers reverse resolves to the citicorp.com domain. There are sub-domains within the Citicorp domain - ems.citicorp.com, pki.citicorp.com, pbg.citicorp.com and edc.citicorp.com.
How do we get reverse entries for hosts? Well – there is two ways. Just as you can do a Zone Transfer for a domain, you can do a Zone transfer for a netblock. Really. Check this out:
#host -l 74.128.210.in-addr.arpa
74.128.210.in-addr.arpa name server www.inter.co.jp
74.128.210.in-addr.arpa name server ns1.iij.ad.jp
126.74.128.210.in-addr.arpa domain name pointer cabinet-gw.dentsu.co.jp
128.74.128.210.in-addr.arpa domain name pointer telto-net.dentsu.co.jp
etc. etc.
And just as some Zone Transferes are denied on some domains, some ZTs are also denied on netblocks. This does not keep us from getting the actual reverse DNS entry. If we start at getting the reverse DNS entry for 210.128.74.1 and end at 210.128.74.255 (one IP at a time), we still have the complete block. See the script reversescan.pl at the end of the chapter for how to do it nicely.