[PROBLEM] No Receivers Discovered

[Tim Curtis]

The raw commands allow you to see exactly what is being used to perform the "Discover receivers" function.

I would start by entering the http URL in your Browser to see if you can contact one of the Receivers via HTTP. If that works then try running the nmap command. If it returns nothing then it would suggest one of the following:

- Port scans are being blocked on your network
- Network is not using typical 255.255.255.0 subnet mask

Note that nmap defaults to using a TCP SYN scan technique.

Code:

-sS (TCP SYN scan)
SYN scan is the default and most popular scan option for good reasons. It can be performed quickly, scanning thousands of ports per
second on a fast network not hampered by restrictive firewalls. It is also relatively unobtrusive and stealthy since it never completes
TCP connections. SYN scan works against any compliant TCP stack rather than depending on idiosyncrasies of specific platforms as Nmap's
FIN/NULL/Xmas, Maimon and idle scans do. It also allows clear, reliable differentiation between the open, closed, and filtered states.

This technique is often referred to as half-open scanning, because you don't open a full TCP connection. You send a SYN packet, as if you
are going to open a real connection and then wait for a response. A SYN/ACK indicates the port is listening (open), while a RST (reset)
is indicative of a non-listener. If no response is received after several retransmissions, the port is marked as filtered. The port is
also marked filtered if an ICMP unreachable error (type 3, code 0, 1, 2, 3, 9, 10, or 13) is received. The port is also considered open
if a SYN packet (without the ACK flag) is received in response. This can be due to an extremely rare TCP feature known as a simultaneous
open or split handshake connection (see https://nmap.org/misc/split-handshake.pdf).

Enter nmap --help to see the various options. For more details enter man nmap.