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# nmap 3.50 scan initiated Wed May 5 09:53:23 2004 as: nmap -sO -v<br />
192.168.124.20<br />
Interesting protocols on domain.com):<br />
PROTOCOL STATE SERVICE<br />
0 open hopopt<br />
1 open icmp<br />
2 open igmp<br />
3 open ggp<br />
4 open ip<br />
5 open st<br />
6 open tcp<br />
7 open cbt<br />
8 open egp<br />
9 open igp<br />
10 open bbn-rcc-mon<br />
11 open nvp-ii<br />
12 open pup<br />
13 open argus<br />
14 open emcon<br />
15 open xnet<br />
16 open chaos<br />
17 open udp<br />
18 open mux<br />
19 open dcn-meas<br />
20 open hmp<br />
21 open prm<br />
22 open xns-idp<br />
...<br />
Filtering by source port<br />
Frequently, filtering rules associated to port sources are found in order to let internal machines<br />
establish a communication on the Internet. For example, to let users surf on the web, answers coming<br />
from port 80 must be accepted. That is also the case for entering DNS answers. So the ports <strong>of</strong>ten<br />
authorised in source are 25/tcp, 53/udp, 80/tcp, 110/tcp. So it is then possible for a hacker to ignore<br />
the access restrictions by establishing connections from the authorised source ports. You can use the<br />
-g option associated to a source port and to a protocol (tcp in standard, -sU for udp) in order to<br />
determine the firewalling rules according to source ports.<br />
The <strong>Hack</strong>ademy DMP -39/209- SYSDREAM
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