HOST DISCOVERY WITHOUT NMAP OR SCRIPT FILES
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Useful when no scanning tools are installed, or you can't write a script
file (e.g. no write permissions). Set the network prefix once at the start
of each command (n= / net=) instead of editing the IP in several places.
Key idea: a ping sweep finds hosts that answer ICMP. Many hosts block ICMP
(Windows Firewall does by default), but every host on your local subnet
must still answer ARP. So run the sweep first, then read the ARP cache:
that catches the hosts ping alone misses. ARP results only cover your own
local subnet; hosts beyond a router only show up via ping.
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WINDOWS (cmd)
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1) Ping sweep, IP addresses only, saved to IPs.txt:
for /L %i in (1,1,254) do @for /f "tokens=3 delims=: " %a in ('ping -n 1 -w 300 192.168.1.%i ^| find "TTL="') do @echo %a>>IPs.txt
Notes:
- -w is in milliseconds (-w 1 = 1 ms, far too short). 200-500 ms suits a LAN.
- Filtering on "TTL=" instead of "Reply" avoids false positives such as
"Reply from 192.168.1.1: Destination host unreachable", and also works
on non-English Windows.
- In a .bat file, write %%i and %%a instead of %i and %a.
- The loop is sequential, so a full /24 can take about a minute.
2) Then add hosts that blocked ping but answered ARP:
arp -a | findstr /i "dynamic"
3) findstr and regular expressions:
findstr has no "print only the match" option (no equivalent of grep -o);
it always returns the whole line. It also doesn't support {n} quantifiers.
It is still useful for matching lines, e.g.:
ipconfig | findstr /r "[0-9][0-9]*\.[0-9][0-9]*\.[0-9][0-9]*\.[0-9][0-9]*"
To extract only the IP, use "for /f" tokenizing (as in #1) or PowerShell.
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WINDOWS (PowerShell 5.1+, parallel, finishes in seconds)
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1) Ping sweep, IP addresses only:
$n='192.168.1'; $t=1..254|%{(New-Object Net.NetworkInformation.Ping).SendPingAsync("$n.$_",500)}; [Threading.Tasks.Task]::WaitAll($t); $t.Result|?{$_.Status -eq 'Success'}|%{$_.Address.IPAddressToString}
2) ARP cache afterwards (IP + MAC):
Get-NetNeighbor -AddressFamily IPv4 -State Reachable,Stale,Delay,Probe | ? IPAddress -like "$n.*" | select IPAddress,LinkLayerAddress
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LINUX (bash)
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1) Parallel ping sweep, IP addresses only, sorted:
net=192.168.1; for i in {1..254}; do (ping -c1 -W1 $net.$i &>/dev/null && echo $net.$i) & done | sort -t. -k4n; wait
Notes:
- -W is the reply timeout in seconds. (-i is the interval between pings,
which does nothing with -c 1.)
- "wait" stops results printing after the prompt returns, and stops
redirected/piped output from being cut off.
2) Sweep + ARP cache (recommended; also catches ICMP-blocking hosts):
net=192.168.1; for i in {1..254}; do ping -c1 -W1 $net.$i &>/dev/null & done; wait; ip -4 neigh show to $net.0/24 | awk '!/FAILED|INCOMPLETE/{print $1}' | sort -t. -k4n
To include MAC addresses, replace {print $1} with {print $1, $5}.
Notes on ARP:
- arp / ip neigh send nothing; they only read the local cache of hosts
your machine has recently talked to. That's why they are run after a
sweep, not instead of one.
- The extra column is the MAC (hardware) address, not an IPv6 address.
- "arp" (net-tools) is deprecated on modern Linux; use "ip neigh".
- Dump the table once instead of calling arp 254 times.
3) Bonus: IPv6 discovery in one packet (replace eth0 with your interface):
ping -6 -c2 ff02::1%eth0 >/dev/null; ip -6 neigh show dev eth0
This pings the link-local all-nodes multicast address, then lists the
IPv6 neighbors that answered.
Portability:
- {1..254} and &> are bash-specific. Under plain sh, use $(seq 1 254)
and >/dev/null 2>&1.
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SCANNING MORE THAN ONE /24 (RANGES THAT CROSS OCTETS)
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Two cases to keep separate:
A) Whole subnets, e.g. 192.168.2.0 through 192.168.5.255
-> just nest a loop over the third octet.
B) A precise range, e.g. 192.168.2.3 through 192.168.5.67
-> convert start/end to integers, loop over the integers, convert
each back to a dotted IP. This is the only clean way to start and
stop partway through a subnet.
A full multi-subnet sweep launches hundreds or thousands of pings. Throttle
the parallelism (xargs -P on Linux, the async batch on Windows), and expect
it to take longer and put noticeable traffic on the wire.
--- Linux (bash) ---
A) Whole subnets 192.168.2-5.x, sweep + ARP cache:
net=192.168; for o3 in {2..5}; do for o4 in {1..254}; do ping -c1 -W1 $net.$o3.$o4 &>/dev/null & done; done; wait; ip -4 neigh show | awk '!/FAILED|INCOMPLETE/{print $1}' | sort -t. -k1,1n -k2,2n -k3,3n -k4,4n
B) Precise range 192.168.2.3 - 192.168.5.67, throttled with xargs:
s=$(( (192<<24)+(168<<16)+(2<<8)+3 )); e=$(( (192<<24)+(168<<16)+(5<<8)+67 )); for ((i=s;i<=e;i++)); do printf '%d.%d.%d.%d\n' $((i>>24&255)) $((i>>16&255)) $((i>>8&255)) $((i&255)); done | xargs -P256 -I{} sh -c 'ping -c1 -W1 {} >/dev/null 2>&1 && echo {}' | sort -t. -k1,1n -k2,2n -k3,3n -k4,4n
Change the four numbers in s=(...) and e=(...) to set the start and end IP.
After it finishes, read the ARP cache to add ICMP-blocking hosts:
ip -4 neigh show | awk '!/FAILED|INCOMPLETE/{print $1}' | sort -t. -k1,1n -k2,2n -k3,3n -k4,4n
--- Windows (PowerShell 5.1+) ---
Paste these two helpers into the session once:
function ip2int($ip){ $b=$ip -split '\.'; [uint32]$b[0]*16777216 + [uint32]$b[1]*65536 + [uint32]$b[2]*256 + [uint32]$b[3] }
function int2ip([uint32]$i){ '{0}.{1}.{2}.{3}' -f (($i -shr 24) -band 255),(($i -shr 16) -band 255),(($i -shr 8) -band 255),($i -band 255) }
Precise range 192.168.2.3 - 192.168.5.67, parallel:
$s=ip2int '192.168.2.3'; $e=ip2int '192.168.5.67'; $ips=for($i=$s;$i -le $e;$i++){int2ip $i}; $t=$ips|%{(New-Object Net.NetworkInformation.Ping).SendPingAsync($_,500)}; [Threading.Tasks.Task]::WaitAll($t); 0..($t.Count-1)|?{$t[$_].Result.Status -eq 'Success'}|%{$ips[$_]}
For whole subnets just pass '192.168.2.0' and '192.168.5.255' as start/end.
A for-loop counter is used instead of the .. range operator on purpose:
these IPs exceed int32, which .. can't handle in PowerShell 5.1.
--- Windows (cmd) ---
Whole subnets 192.168.2-5.x, IPs to IPs.txt (nested for /L):
for /L %j in (2,1,5) do @for /L %i in (1,1,254) do @for /f "tokens=3 delims=: " %a in ('ping -n 1 -w 300 192.168.%j.%i ^| find "TTL="') do @echo %a>>IPs.txt
In a .bat file use %%j, %%i and %%a. For a precise start/end that isn't a
whole subnet (starting at .3, ending at .67), use the PowerShell version
above - integer math is far cleaner there than in cmd.
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macOS / BSD
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- ping -W is in milliseconds on macOS, so use -W 1000.
- ARP cache, IP addresses only:
arp -an | grep -v incomplete | grep -Eo '([0-9]{1,3}\.){3}[0-9]{1,3}'
(The original "grep on" filter matches this BSD/macOS output format,
e.g. "? (192.168.1.1) at aa:bb:cc:dd:ee:ff on en0", but not Linux output.)
