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I am working on a school task, where I have to use Nmap in order to scan for open port on another device on the same network. However, when I use Nmap my network suddenly gets limited. I have tried Nmap GUI on Windows where I write the target IP-address. I am doing this at home with my own laptop.

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  • Are you on windows, bsd or linux?
    – aurelien
    Nov 27, 2016 at 14:28
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    So you are scanning another device on your home network and your home network kicks you off? We might need to explore what is actually happening when you say "kicks me out".
    – schroeder
    Nov 27, 2016 at 15:53
  • You might also help us out if you list here what nmap command you are running.
    – schroeder
    Nov 27, 2016 at 15:53
  • Are you running any kind of Virus/Security software on you laptop? Does the rest of the network go down or just your laptop, can you still use another computer/phone on the same network? Nov 27, 2016 at 20:21

3 Answers 3

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I'm not sure how stable your network is, but maybe you are creating too much traffic for it to handle. I would start by doing a simple scan on the one up address with a slower speed to verify. Example:

nmap -sS -T2 -p 0-1000 192.168.1.25

Please note to change the IP address to the one you know is alive.

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If you check the man pages of nmap (if you are on Linux):

FIREWALL/IDS EVASION AND SPOOFING:
         -f; --mtu <val>: fragment packets (optionally w/given MTU)
         -D <decoy1,decoy2[,ME],...>: Cloak a scan with decoys
         -S <IP_Address>: Spoof source address
         -e <iface>: Use specified interface
         -g/--source-port <portnum>: Use given port number
         --proxies <url1,[url2],...>: Relay connections through HTTP/SOCKS4 proxies
         --data <hex string>: Append a custom payload to sent packets
         --data-string <string>: Append a custom ASCII string to sent packets
         --data-length <num>: Append random data to sent packets
         --ip-options <options>: Send packets with specified ip options
         --ttl <val>: Set IP time-to-live field
         --spoof-mac <mac address/prefix/vendor name>: Spoof your MAC address
         --badsum: Send packets with a bogus TCP/UDP/SCTP checksum

Try -f, most Intrusions Detection Systems dont defragment packet, because that is resource intensive.

Be careful with portscans, I've heard stories about ISP's blocking internet after portscans. Consider using a VPN or VPS, or just check out previous findings on services like shodan/netcraft

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  • The OP is on their own home network, it seems.
    – schroeder
    Nov 27, 2016 at 21:49
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If you are using Nmap 7.30 or 7.31 on Windows, you have most likely installed Npcap to handle the packet capture that Nmap requires. Unfortunately, there have been a few bugs in Npcap that have been discovered since that release. One of those involves WiFi adapters becoming unresponsive after an Nmap scan.

Download the latest Npcap release which has a fix for this issue. Once it is installed, you may have to reboot your computer or restart networking to clear the error, but you shouldn't have the problem again.

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