Network Discovery
	How do we find out what is out there to be managed?
	- Inventory Management
	- Configuration Management
	- Building a Map

1) Personal Knowledge
	- interview people, talk to others who use parts of the network

2) Passive Observation of Traffic
	- watch what happens
	- deduce roles of different hosts based on IP addresses, port numbers,
	  traffic counts, etc
	- local network config, ARP and routing tables 
		ifconfig -a, arp -a and netstat -nr

3) Active Probing - 
	Use what we learned above to bootstrap active discovery, such as what
addresses to start with.
	a) ping - ICMP, Internet Control Message Protocol
                echo request, echo reply
		if success, IP is up and running and a layer 3 path exists
		if no response, it could be anything causing the problem
	b) traceroute - use ICMP TTL expired, gives you the layer 3 (router)
path to the destination but not the return path
	c) port scanning - e.g. Nmap
	d) web crawling - e.g. wget
	e) DNS crawling - e.g. host, dig, nslookup, zone transfers
	f) SNMP queries - MIB-II and beyond
		see demos at simpleweb.org


Remember, there is a fine line between network discovery for good and network
discovery for evil!