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Nmap will list all IP's in the target specified, can specify subnet or range of IP addresses. It will attempt to resolve all IP's listed. No packets sent to target only generates DNS queries.
Check to see if a port is open or closed on a given host.
TCP Connect scanning for localhost and network 192.168.0.0/24
Change the IP address from 127.0.0.1 to the target machines ip address. Even if the target has ICMP (ping) blocked, it will show you what ports are open on the target. Very handy for situations where you know the target is up and online but wont respond to pings.
Using NMAP to check to see if port 22(SSH) is open on servers and network devices.
nmap for windows and other platforms is available on developer's site: http://nmap.org/download.html
nmap is robust tool with many options and has various output modes - is the best (imho) tool out there..
from nmap 5.21 man page:
-oN/-oX/-oS/-oG : Output scan in normal, XML, s|
Shows how many Windows and Linux devices are on your network.
May add support for others, but that's all that are on my network right now.
This command uses nmap to perform reverse DNS lookups on a subnet. It produces a list of IP addresses with the corresponding PTR record for a given subnet. You can enter the subnet in CDIR notation (i.e. /24 for a Class C)). You could add "--dns-servers x.x.x.x" after the "-sL" if you need the lookups to be performed on a specific DNS server.
On some installations nmap needs sudo I believe. Also I hope awk is standard on most distros.
the command for the impatient sysadmin: simply checks every five secs, if a host or a specific service running on it is up. ideal for hosts that are configured not to respond on pings.
populate the auth.hosts file with a list of IP addresses that are authorized to be in use and when you run this command it will return the addresses that are pingable and not in the authorized list.
Can be combined with the "Command line Twitter" command to tweet unauthorized access.