I've just done a simple nmap scan of my network with nmap: nmap -sP

networkserver@networkServer:~$ sudo nmap -sP

Starting Nmap 5.00 ( http://nmap.org ) at 2010-08-26 17:46 NZST
Host RTA1320.home ( is up (0.00060s latency).
MAC Address: 00:26:B6:C9:E7:48 (Unknown)
Host is up (0.00057s latency).
MAC Address: 00:23:69:16:85:D7 (Cisco-Linksys)
Host is up (0.00015s latency).
MAC Address: 02:27:19:B4:61:DB (Unknown)
Host networkServer ( is up.
Host is up (0.0012s latency).
MAC Address: 00:1A:4D:9C:70:0E (Giga-byte Technology Co.)
Host is up (0.0076s latency).
MAC Address: 78:E4:00:8E:FE:63 (Unknown)
Nmap done: 255 IP addresses (6 hosts up) scanned in 28.74 seconds

That seemed to take a rather long time, so I check with a friend on his network and it only took 2.74 secconds!

My network layout is:


I figure something is wrong with the routing settings on my network but I'm not sure how to check it? Any ideas?

  • Which machine are you scanning from? What OS/Version etc? – Grizly Aug 26 '10 at 6:23
  • I am scanning from "server", OS=Ubuntu 10.4 – glisignoli Aug 26 '10 at 6:31
  • Ok I tried this: nmap -sP (modem) ... Nmap done: 1 IP address (1 host up) scanned in 0.72 seconds nmap -sP (LAPTOP) ... Nmap done: 1 IP address (1 host up) scanned in 13.68 seconds So the problem is the wifi router, I just tried plugging in a device into the router and the same problem happens. So it's not just over wifi connections but also wired ones! ARGH! – glisignoli Aug 26 '10 at 6:50

The network you checked was the same ? Machines / Os / topology. Also, do you (or he) have/has QOS enabled on your / his switch ?

Also it would be helpful it you give the Ip's of every machine. (to know what is what). Just to mention that it seems that your bottleneck is located on (Giga-byte Technology Co.). What is it ?

  • was it! – glisignoli Dec 26 '10 at 8:27

Could you give the output of command (on the server): # route -n ?

  • Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface U 0 0 0 eth0 UG 100 0 0 eth0 – glisignoli Aug 26 '10 at 6:55

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