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When I launch an -sA scan of a certain IP address, it shows port "80" as "unfiltered". Code is below.

sudo nmap -sA -vv -p 80 192.168.0.30 -Pn
Host discovery disabled (-Pn). All addresses will be marked 'up' and scan times may be slower.
Starting Nmap 7.92 ( https://nmap.org ) at 2022-03-24 01:09 EDT
Initiating ARP Ping Scan at 01:09
Scanning 192.168.0.30 [1 port]
Completed ARP Ping Scan at 01:09, 1.34s elapsed (1 total hosts)
Initiating Parallel DNS resolution of 1 host. at 01:09
Completed Parallel DNS resolution of 1 host. at 01:09, 0.37s elapsed
Initiating ACK Scan at 01:09
Scanning 192.168.0.30  [1 port]
Completed ACK Scan at 01:09, 0.73s elapsed (1 total ports)
Nmap scan report for 192.168.0.30
Host is up, received arp-response (1.1s latency).
Scanned at 2022-03-24 01:09:50 EDT for 0s

PORT   STATE      SERVICE REASON
80/tcp unfiltered http    reset ttl 64

However, when I launch scan type like -sT, it shows port "80" as "closed". Code is below.

sudo nmap -sT -vv -p 80 192.168.0.30 -Pn
Host discovery disabled (-Pn). All addresses will be marked 'up' and scan times may be slower.
Starting Nmap 7.92 ( https://nmap.org ) at 2022-03-24 01:15 EDT
Initiating Parallel DNS resolution of 1 host. at 01:15
Completed Parallel DNS resolution of 1 host. at 01:15, 0.24s elapsed
Initiating Connect Scan at 01:15
Scanning 192.168.0.30 [1 port]
Completed Connect Scan at 01:15, 0.25s elapsed (1 total ports)
Nmap scan report for 192.168.0.30
Host is up, received user-set (0.25s latency).
Scanned at 2022-03-24 01:15:03 EDT for 0s

PORT   STATE  SERVICE REASON
80/tcp closed http    conn-refused

I would like to know why this occurs and if it is normal. Also, can a port be both closed and unfiltered, like in this case?

1 Answer 1

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The answer to this question is right in the documentation:

-sA (TCP ACK scan)
This scan is different than the others discussed so far in that it never determines open (or even open|filtered) ports. It is used to map out firewall rulesets, determining whether they are stateful or not and which ports are filtered.

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