Nmap unable to perform full host discovery

[Sahib Jakhar <sahib.jakhar () gmail com>]

Hi,

Sorry if I am missing something obvious. I am trying to find all the
hosts that are up on local intranet using nmap -sP 192.168.1.0/24.
I expect around 10 hosts to be reported but I get anywhere between
4 to 6 hosts (this number varies with each run). I can ping 9 hosts
using ping command but nmap still reports 4 to 6 hosts. What's more,
if I do nmap -sP <ip-address> to individual host, nmap is able to
detect it as up. The problem only comes when I use CIDR notation.

Please see the following sequence of commands and their corresponding
output which were executed in (immediate) succession:

# nmap -sP 192.168.1.22

Starting Nmap 7.01 ( https://nmap.org ) at 2016-02-07 11:59 IST
Nmap scan report for 192.168.1.22
Host is up (0.089s latency).
MAC Address: E0:DB:10:--:--:-- (Samsung Electronics)
Nmap done: 1 IP address (1 host up) scanned in 0.38 seconds

# nmap -sP 192.168.1.0/24

Starting Nmap 7.01 ( https://nmap.org ) at 2016-02-07 11:59 IST
Nmap scan report for 192.168.1.1
Host is up (0.00035s latency).
MAC Address: 0C:D2:B5:--:--:-- (Binatone Telecommunication Pvt.)
Nmap scan report for 192.168.1.16
Host is up (0.00019s latency).
MAC Address: 00:1B:24:--:--:-- (Quanta Computer)
Nmap scan report for 192.168.1.27
Host is up (0.071s latency).
MAC Address: 60:A4:4C:--:--:-- (Asustek Computer)
Nmap scan report for 192.168.1.11
Host is up.
Nmap done: 256 IP addresses (4 hosts up) scanned in 1.94 seconds

# nmap -sP 192.168.1.22

Starting Nmap 7.01 ( https://nmap.org ) at 2016-02-07 11:59 IST
Nmap scan report for 192.168.1.22
Host is up (0.096s latency).
MAC Address: E0:DB:10:--:--:-- (Samsung Electronics)
Nmap done: 1 IP address (1 host up) scanned in 0.39 seconds


As can be seen both before and after running nmap for all targets,
nmap is able to identify this host as up. Am I doing something wrong, or
is it some defect?

BTW I understand document mentions equivalent -sn instead of -sP, but
I get identical results with -sn as well.


Thanks for any help,
Sahib
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