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I've been using the nmap tool on my Windows machine to ping my Uni house home network range using the following command:

nmap -sn 

I had no problems with this and it was only taking 5-10 seconds to complete. Since I've returned home for Easter (different home/network) I've tried to use the command again (albeit this time with a different subnet address

nmap -sn

and it is taking around 50 seconds+ to do the same.

I just checked a simple nmap -sn and that is taking around 12 seconds...

Does anyone know why this could be? Some bad network setup or something? I'm pretty baffled at the moment but maybe i've missed something simple..

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closed as off topic by mfinni, Shane Madden, rnxrx, sysadmin1138 Sep 29 '12 at 18:38

Questions on Server Fault are expected to relate to server, networking, or related infrastructure administration within the scope defined by the community. Consider editing the question or leaving comments for improvement if you believe the question can be reworded to fit within the scope. Read more about reopening questions here.If this question can be reworded to fit the rules in the help center, please edit the question.

As a new user, you should read the FAQ. Questions pertaining to home users and home networks, particularly for enthusiasts, should be posted to SuperUser, not ServerFault. SF is meant for people who work in IT professionally. This question will be migrated automatically when it's gathered enough close-votes. – mfinni Apr 3 '12 at 14:58
Do you administer this network ? – mfinni Apr 3 '12 at 19:33
Yeah, they are both my home networks (& apologies for posting on wrong site) – Bernard Apr 4 '12 at 13:59

nmap tries to scan your network for live IPs addresses and ports. If there are more live IPs in your subnet, nmap will finish sooner. This is because it is faster to say there is a live host with IP than to say there is no live host with the IP

So, it should be normal to get different times for different subnets.

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