Page 237 - Hacking Roomba

218 Part III — More Complex Interfacing

Debugging Network Devices Continued

Host gw.home (192.168.0.1) appears to be up.
MAC Address: 00:06:29:15:F3:13 (IBM)
Host openwrt.home (192.168.0.8) appears to be up.
MAC Address: 00:16:B6:DA:91:2F (Cisco-Linksys)
Host nasty.home (192.168.0.9) appears to be up.
MAC Address: 00:0D:A2:01:04:70 (Infrant Technologies)
Host minimi.home (192.168.0.25) appears to be up.
MAC Address: 00:11:24:77:84:FA (Apple Computer)
Host 192.168.0.134 appears to be up.
Host 192.168.0.136 appears to be up.
MAC Address: 00:11:24:3F:3A:50 (Apple Computer)
Host 192.168.0.144 appears to be up.
MAC Address: 00:13:10:3A:16:17 (Cisco-Linksys)
Host 192.168.0.148 appears to be up.
MAC Address: 00:30:65:06:63:67 (Apple Computer)
Host 192.168.0.149 appears to be up.
MAC Address: 00:04:20:03:00:34 (Slim Devices)
Nmap finished: 256 IP addresses (9 hosts up) scanned in 7.459
seconds

To find errant network devices, first do a scan with the device disconnected; then do a sec-
ond scan with it plugged into your network. There should be an extra host in the nmap list
that will be your gadget.
nmap is capable of much more than simple ping scanning. It’s an awesomely powerful net-
work scanning tool that happens to be free, open-source, and available for Mac OS X,
Linux, and Windows. It was also featured briefly in the second Matrix movie when Trinity
used it to learn about an enemy computer system.

Debugging MAC Addresses

The most poorly understood of the three address layers are MAC addresses. It’s not under-
stood mainly because it works so well no one has to think much about it. The Ethernet
hubs, switches, and routers used by everyone do the MAC routing for us. (The MAC
acronym has nothing to do with Macintosh computers.) For a computer connected to the
same hub as a networked gadget in question, that computer will store the gadget’s MAC
address in its ARP cache as soon as either of them try to talk to one another. The way you
inspect this mapping of IP address to MAC address is with the arp command:
% arp -a
gw (192.168.0.1) at 0:6:29:15:f3:13 on en1 [ethernet]
nas (192.168.0.9) at 0:d:a2:1:4:70 on en1 [ethernet]
minimi (192.168.0.25) at 0:11:24:77:84:fa on en1 [ethernet]
? (192.168.0.131) at 0:2:2d:c:11:1 on en1 [ethernet]
? (192.168.0.139) at 0:4:20:5:2:d1 on en1 [ethernet]