IP Network Scanning - Identifying Subnet Network and Broadcast Addresses

Nmap identifies subnet network and broadcast addresses by counting the number of ICMP echo replies for each IP address during an ICMP ping sweep. Such addresses respond with multiple replies, providing insight into the target network and its segmentation. In Example 4-3 we use Nmap to enumerate subnet network and broadcast addresses in use for a given network (154.14.224.0/26).

Example 4-3. Enumerating subnet network and broadcast addresses with Nmap

$ nmap -sP 154.14.224.0/26

Starting Nmap 4.10 ( http://www.insecure.org/nmap/ ) at 2007-04-01 20:39 UTC
Host 154.14.224.16 seems to be a subnet broadcast address (returned 1 extra pings). Host pipex-gw.abc.co.uk (154.14.224.17) appears to be up.
Host mail.abc.co.uk (154.14.224.18) appears to be up.
Host 154.14.224.25 appears to be up.
Host intranet.abc.co.uk (154.14.224.26) appears to be up.
Host 154.14.224.27 appears to be up.
Host 154.14.224.30 appears to be up.
Host 154.14.224.31 seems to be a subnet broadcast address (returned 1 extra pings). Host 154.14.224.32 seems to be a subnet broadcast address (returned 1 extra pings). Host pipex-gw.smallco.net (154.14.224.33) appears to be up.
Host mail.smallco.net (154.14.224.34) appears to be up.
Host 154.14.224.35 seems to be a subnet broadcast address (returned 1 extra pings). Host 154.14.224.40 seems to be a subnet broadcast address (returned 1 extra pings). Host pipex-gw.example.org (154.14.224.41) appears to be up.
Host gatekeeper.example.org (154.14.224.42) appears to be up.
Host 154.14.224.43 appears to be up.
Host 154.14.224.47 seems to be a subnet broadcast address (returned 1 extra pings).

This scan has identified six subnets within the154.14.224.0/26network, as follows:

• An unused or filtered block from154.14.224.0to154.14.224.15(14 usable addresses)
  
• Theabc.co.ukblock from154.14.224.16to154.14.224.31(14 usable addresses) 
  
• Thesmallco.netblock from154.14.224.32to154.14.224.35(2 usable addresses) 
  
• An unused or filtered block from154.14.224.36to154.14.224.39(2 usable addresses) 
  
• Theexample.orgblock from154.14.224.40to154.14.224.47(6 usable addresses) 
  
• An unused or filtered block from154.14.224.48to154.14.224.63(14 usable addresses)

Useful details about subnet network and broadcast addresses and CIDR slash notation can be found at http://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing. An online IP calculator is also available at http://jodies.de/ipcalc.

Next: Gleaning Internal IP Addresses >>
 

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