The main idea here is how an ACK scan works and what it can reveal about a firewall. The -sA option performs a TCP ACK scan, sending ACK packets to each port. Because ACKs aren’t used to open a connection, the target’s responses (or lack thereof) depend on the firewall’s rules rather than on whether a port is actually open. If a firewall is stateful, it tends to filter unsolicited ACKs and may drop them, producing no response for filtered ports; if a firewall is stateless, you’ll see different, predictable responses for allowed versus blocked paths. By observing which ports elicit a RST or no response, you can map the firewall’s rule set and determine whether filtering is stateful or stateless. This doesn’t indicate open ports, which is why this scan is specifically about firewall behavior rather than port openness.

The option is about showing why Nmap classified a port in a particular state. Enabling it adds a reason for each port’s state, so you can see the underlying cause—like a firewall filter or a specific type of response—that led to labels such as open, closed, or open|filtered. This makes results much easier to interpret, especially when the state is ambiguous or influenced by intermediate devices. It’s not about kinematics, filtering by reason codes, or simply increasing verbosity, which is why those other ideas don’t fit.

Idle scans rely on a zombie host and IPID timing to infer the target’s port state, offering a covert probing method rather than directly from the scanner. The zombie is used to generate traffic toward the target, with the scan manipulating IP spoofing so the target’s responses appear to come from the zombie. By watching how the zombie’s IPID—the identification value in IP headers—changes between probes, Nmap can deduce whether the target port is open or closed based on the observed timing patterns. This approach is appealing for stealth, since the true source appears to be the zombie, but it’s often less reliable because it hinges on the zombie’s IPID behavior being predictable. Some operating systems randomize IPID or behave inconsistently under load, and network factors like NAT, firewalls, packet loss, or traffic elsewhere on the path can disrupt the timing measurements, leading to unclear results or failures to detect states accurately.

In Nmap, the -p option controls which ports are scanned. You can mix individual ports with port ranges by listing them separated with commas. For your target of ports 80, 443, and the range 1024-1050, the correct syntax is -p 80,443,1024-1050. This exactly specifies the two single ports plus the block from 1024 through 1050. This works because -p accepts a comma-separated list of ports and ranges, and the range 1024-1050 includes every port from 1024 to 1050 inclusive. Using a range like 80-443 would scan every port between 80 and 443, which isn’t the same as scanning only 80 and 443. And using spaces or a non-existent flag like -ports would not be parsed correctly by Nmap.